Drive Line: Differentials

Topics covered:


From: Jamie Austin[]
Sent: Wednesday, July 05, 2000 10:11 AM
Subject: Re: [D90] Diff Bowl Casing

Sounds like you need some Southdown guards!! (BTW, the southdown rear guard bolts on under the diff, where the 2 threaded holes are, so that WON'T fall off!!)

on the rear of my new 90, i got a friend to weld on some 8mm plate sll around the lower portion of the pumpkin bit, and he scalloped it all in so neat, that at a quick glance, you can't even notice that it's there...and boy is it strong.

On the question of replacement bowls, Steve Parker in the UK does them, quite expensive (79.50 UKP....$120 ish)

No affiliation to either company etc etc blah blah.....

'96 Tdi D110
'92 V8i D90
'85 Tdi D90


User Experience and Recommendations

From: Easton Trevor A[]
Sent: Friday, August 25, 2000 10:05 AM
Subject: TrueTrac and etc

There is a good explanation of TrueTrac operation and other LSDs at

From: Jamie Austin[]
Sent: Sunday, August 27, 2000 3:21 PM
Subject: [D90] ARB application list

found this link... it's got all the ARB lockers and what ones fit different vehicles.

(As if we'd be interested in OTHER VEHICLES!!!)
heh heh!

Sent: Friday, August 11, 2000 1:10 AM
Subject: Re: [D90] Hypoid diffs [was: Earless rear links]

Reverse rotation hypoid diffs are primarily used for improving driveshaft angle on extremely short wheel base rigs and they are usually used in the front. If you have an 80" wheel base Jeep CJ 5 with a non-stock engine and transmission, you would be amazed at how short driveshafts can get. I have one laying around the shop that was in a pile of parts I purchased, that is a grand total of 8 or 9 inches long! I think it is mainly a slip joint with flanges on the ends!

As you pointed out another advantage of using a reverse rotation gear set in the front is that it is stronger . The front diff runs in reverse so that with a standard rotation gear set you are running on the coast side of the gears. You lose approximately 20 to 30% of the potential strength because of this. This is also why until recently you didn't see reverse rotation gear sets in the rear - you lose 20 to 30% of the strength because in the rear with a reverse rotation gear set you are also running on the coast side of the gear. You also wear out your pinion bearings faster when you run on the coast side of diff gears, because the gears are trying to push themselves apart.This loads the pinion bearings much more causing them to wear out at a faster rate. On a standard rotation gear set in the rear or a reverse rotation in the front, where you are running on the drive side of the gear, the gears are pulling themselves together and hence not loading the bearings as much. This is why if you do differential repair work in a 4 wheel drive business you work on front diffs about three times as often as rear diffs.

You might ask the question - if a reverse rotation diff in the rear is weaker, why would you want one? I personally think it is a bit of a fad but there are two technical reasons in my opinion that you could possibly justify it.

1) its a tradeoff between driveshaft u-joint strength vs ring and pinion gear strength. As the angle of the u-joint increases it loses strength so if you can raise the pinion and hence reduce the angle of the u-joints, they become much more durable. Personally I would rather replace u-joints than diff gears and you can also deal with u-joint angle with double carden driveshafts or even double double carden driveshafts so you can have both a strong diff gear set and durable u-joints, which is why I think the engineering argument in favor of reverse rotation rear diff gears is weak.

The second reason reverse rotation rear gear sets are used, is driveshaft ground clearance. Since it is higher up it is harder to damage it by it coming in contact with some hard immovable object. In my opinion this is a limited benefit because the most vulnerable part of an axle assembly is the bulge where the ring gear protrudes on either the inspection cover or the axle case depending upon the type of diff you have. This bulge does not change with the use of reverse rotation gear sets. The second most vulnerable part of the axle assembly is the u-joint but this can be easily protected as can the ring gear bulge.

I have considered manufacturing a reverse rotation hypoid differential for Land Rover front axles but have put the project on hold due to a lack of confidence in its economic viability. One of the difficulties with a hypoid diff if you are designing a front reverse rotation, is that the front diff housing is completely different from the rear housing necessitating a duplication of most of the costs - engineering, casting, machining etc. On a related point,as you recall most Land Rover differentials are a non-hypoid design, meaning - a center pinion. This means that one can design a reverse rotation gear set and use the existing housing. I have made several improvements in the design of my next batch of differential gear sets, one of which is a reverse rotation front gear set. They are currently in production and will be available in a few months.

Hope this answers your questions and adds to the collective knowledge base.

Great Basin Rovers

Date: Tue, 1 Jun 1999 09:05:32 +0100
From: "Matthew Reeve & Mel Mauger"
Subject: Re: [D90] Center Diff lock: A cautionary tale!

> I didn't miss your original point. The Detroit True track combo is a
> permanent set up always on, and from day one after the install of it I
> had much more control of the D90.
> Chris "V"

Does anyone else get loads of torque steer with the trutrac? I've got the truetrac in the front, and the locker in the back, and I find that the front end steers dramatically with the loud pedal, and the back end is constantly clonking away, and also affects the steering by pushing straight on at corners until it releases sometimes, not for more than a split second, but it's enough to be annoying.

The front is a real pain though, the more power, the more it fights to go straight, so if you're going around a roundabout, you have your foot down to accelerate out of the junction, and you're putting a fair amount of power in to hold the curve, but when you stop accelerating when you reach the natural speed for the roundabout, the steering stops fighting you, and because you're pushing into the curve, you end up over turning. I'm gradually getting used to it, and it doesn't make much of a problem now as it's a reflex, but it doesn't strike me as being right.

If I can't get a fix to this, then I'm considering putting the trutrac in the rear, getting an ARB for the front, and selling the locker.

UK, nr Heathrow

Date: Tue, 01 Jun 1999 12:46:22 -0500
From: (Douglas Aitken)
Subject: Re: [D90] Center Diff lock: A cautionary tale!

as an open diff guy (and therefore not really qualified to comment!) I have to say that your proposal looks like the worst possible solution to your problem.

First a preamble:
I originally started the thread with a comment on a locked center giving a tendancy to fishtail. Chris raised the point that a detroit at the rear helps fight that tendency. I at first thought he missed my original point, but after his clarification and reflecting on comments from Bill Richie (who has the same combo) it seems logical that a Detroit (or locked ARB) at rear would help fight the fishtail tendency.

Now your problem:
A limited slip should only cause any strange torque transfer/steer if you are starting to lose traction on one tire. In normal circumstance, the diff will be effectively open. A detroit at rear will tend to stay locked if you are powering it. so I believe that you have to go through (paved) corners with a light foot to allow it to release. But you should not be having a problem with the limited slip at front, unless it is defective.

If you put a limited slip in rear, you lose the ability to lock it, so are not really gaining much from an ultimate traction point of view. If you do not like the cornering behavour with your current setup and want to change, better swap out the rear Detroit for an ARB, which will give you a fully open (fully locked on demand) rear, and a limited slip at front.

At least, this (IMHO) seems to be the logical step. But would love to hear opinions from Locker users!

Doug (who can't help jumping in!)

Date: Tue, 01 Jun 1999 16:54:46 -0500
From: Chris Velardi
Subject: Re: [D90] Center Diff lock: A cautionary tale!

The True Trac is an active driving and steering device , not passive like open set ups . And there is a learning curve to it like any new or different acting device. My first report on it's use was based on it's point and go feel. There is no laying back take you hands off the wheel and serving cocktails around the cabin during it's use. It is similar to adding power steering to a old heavy truck. On a side note to the perfect system. I just got back from Extreme Challenge '99 in Haliburton Highlands Ontario Canada. We did some nice long trails with some very set up rigs that ranged from 36" tires to ARB lockers front and rear; 110 " ; 100" and 90" wheel based Rovers; the only rig to challenge every obstacle and remain unstuck was mine. (I also drove the rig comfortably 13 hours to the site and 11 hours back) The Detroit /True Trac combo has treated me well and left some our Canadian friends scratching their heads.

Chris "V"

Date: Tue, 01 Jun 1999 20:49:23 -0500
From: Bill Ritchie
Subject: [D90] Detroit Locker and TrueTrac Legends, Myths, and Facts

I just thought I would add some personal experience to this discussion about the Detroit Locker and TrueTrac combination in the D90.

First of all to respond to the post from Matthew - Your D90's driving characteristics may be due to an older version of the Rear locker, I am assuming it is a Detroit. Before the "new" Detroit "softer" Locker was introduced the older lockers were more likely to be harsh when cornering and affected steering more than the new one. If you have a solid locker in the rear of your D90 (Detroit or otherwise) it is unwise to accelerate while turning during anything but a gentle curve. You risk breaking a rear axle (although some joker on the list seems to think that spinning the tires around a curve is cool). If you accelerate around corners enough you will eventually break a halfshaft, not to mention potentially loosing control of the vehicle. This is especially true when driving in slick conditions - rain and snow. Changing your driving style to coast through curves and corner while coasting is no big deal - I do it now without a second thought (although I still remind my wife to do it).

This combination does (as previously posted by Chris V. and myself) introduce some interesting changes to the steering effort and required input. My D90 wants to drive straight all the time now - after a turn it centers itself with more force than before. I find that highway driving is more pleasant now and less prone to wander (with the 35" and no swaybars) than before I installed this combo. Actual turning force required to turn the steering wheel is only slightly increased. I think that "torque steer" will be a problem only for those with aggressive driving styles that accel. around corners.

As far as additives go - as prev. posted the installation instructions that came with my TT explicitly state no special diff additives were needed (in fact it was written boldly - almost as an advertisement). I haven't used additives, although I do use synthetic diff. oil (per several diff shop's advice).

On performance I can confidently say (as Chris has said by example in Moab and otherwise) that I have not yet been outperformed by similarly equipped D90's with ARB's in front and back. This includes all terrains - extreme slick rock (Moab), sand, mud, hillclimbing, rockcrawling, or any of the above plus a lifted wheel (although rare with a long travel suspension). In fact this combo has certain advantages over ARB's like turning during hillclimbing etc.

I don't have experience in snow and ice like Chris so I will defer to him. I have not encountered a lifted wheel or "poor traction with one tire situation" in which the single wheelspin was not controlled with light brake input (easy on our auto D90's). Several obsticles at Moab (like Suzuki Slide) are supposed to be 2 solid locker only but were no problem for my D90.

From: "Ben and Pat"
Subject: [D90] ARB Lockers - Noise? ...NOT
Date: Sun, Dec 26, 1999, 3:20 PM

Continuing saga of the "noisy" lockers......

Land Rover Austin was unable to fix the noises. They determined that the rear locker was bad and had us order another one. Mark Bowers at Air Locker promptly sent a new RD56. Of course, the locker wasn't bad, but LRA replaced it and returned the vehicle and extra locker to us. The noises are EXACTLY the same as when we brought it to them.

We thought we recognized two noises: 1) gear backlash, and 2) torsional vibration at neutral throttle.

We agreed with some on the list, that a drive shaft with a CV joint may quiet the torsional vibration. BTW, we removed the rear drive shaft, locked the center diff, and our front wheel drive D90 was quiet, smooth and gear noise free.

We ordered and received a rear Drive Shaft with CV joint and 3/4" adapter from Six States. After installation, while it changed the noises slightly, it is arguable whether the noise improved, which pretty much says that the noise problems are ALL in the differential. However, there is now a new vibration. We figured that we didn't have the drive shaft centered well, since we noticed some slop in the adaptor mounting holes when we installed it. So we gauged the shaft (rear wheels on jacks and turning) expecting to find excessive wobble on one end of the shaft or the other, most likely the end that attaches to the diff. Much to our surprise, there is a mere 15 mil wobble at either end, and a 35 mill wobble in the center of the shaft. This tells us that the shaft is not straight. Are we having fun yet???

Has anyone ever heard of a problem like this from Six States? Are we missing something?

Ben and Pat
'97 White D90 SW #428
'99 White Disco Series II


From: Mike Ladden[]
Sent: Monday, December 27, 1999 8:41 AM
Subject: Re: [D90] ARB Lockers - Noise? ...NOT

> From: "Chris Velardi"
> You may want to have a discussion with Mile Ladden . His 97 D90 has had this
> same problem.......

Unfortunately, I do not have the solution. I did do numerous modifications to try to correct the excessive noise and vibration problems but so far nothing has worked. In fact my truck is so bad at this point that it is sitting and is not driving and may never return to the road again. I shortened the trailing arms to get a better angle from diff to t box. I also went with a custom drive shaft w/cv joint on t-box side (in fact I am on the 3rd drive shaft) Visually eying the angle everything looks good. I am not sure of the exact angle however. The spacer plate on the t-box must be tightened carefully- I did notice that it will loosen up easily if not loc tited. After having my arb unit out once already. I do not think the problem originates from the diff. I am pretty sure it has something to do with the drive shaft or output shaft of the t box. When I remove the rear shaft the vibration goes away in front wheel drive. The question is: Is the problem related to something that is only occurs under load? I would love to hear some ideas on this situation..

- Mike

Date: Mon, 19 Apr 1999 23:12:19 -0500
From: Bill Ritchie
Subject: Re: [D90] lockers again

>does anyone out
>there have the detroit rear/truetrac front combo,

Yup, have a Detroit in the rear and a TT up front as well as Ashcroft 4.1 ring and pinions. Everyday driving is pretty normal. You hear a slight click in the rear when cornering, and the steering wants to stay straighter (recenters after a turn quicker and with more force). I have no experience in the snow, but rain driving is relatively normal - just don't accel around corners hard.

Offroad the combo is great. I haven't been shown up by a fully locked D90 yet, at least on 21 Road, Moab, and Ft. Hood. On slickrock the TT locks up almost 100%. Some turns under power are slowed by the locked up Detroit, but it generally handles great.

Saved a bundle installing just Detroit and TT as well.
Detroit + TT was about $750
ARB's - 2 for $1050, plus compressor, plus much more labor for compressor, lines, switch install.

Date: Sat, 10 Jul 1999 21:05:05 -0500
From: Bill Ritchie
Subject: RE: [D90] Detroit install

The part number straight from Tractech for the Lockers are:

Detroit Locker "No Spin"

Detroit TrueTrac

Both the diffs came with Timkin bearings from the factory, cool stickers, and good instruction manuals (that the installation dudes promptly lost).

Can't find the install articles tonight and I am on call tomorrow so I will look for them on Monday.

Talk to you later,
Bill Ritchie

Date: Thu, 6 May 1999 11:25:15 -0600
Subject: Re: [D90] RE: lurker looking for a Defender

I ran a tru-trac on my 95 for a while. It worked really well off road, but it's on road manners left something to be desired. Tight corners (aka parking lot stuff) would cause a lot of jerking around, and I had to develop a clutch-it-around-the-corner driving style to get around it. This was exacerbated by the drive train slop which made the lurching noisy as well as entertaining for bystanders. I switched to air lockers.


Doug Boehme added:
Believe it or not, synthetic gear oil (Amsoil) fixed this "jerking" problem for me. I'm running a Detroit Locker in the rear, not a true-trac.

and Alan countered:
I tried a bunch of different oils in the rear. I am a fan of Red Line and I got the best results with shockproof gear oil from same. Best results were VERY MINOR and never did cure the lurching and jerking. The only way I could get rid of it was the corner-clutch-coast routine.

Date: Thu, 1 Jun 2000 13:01:08 -0500
From: "Bill Ritchie"
Subject: Re: Truetrac affecting steering

Will Ferguson wrote:
> So I finally had my Detroit Truetracs installed in both the front and rear
> axles, along with 4.10 gears. I had it done by a very conscientious localshop
> that works mostly on local Rovers, Jags, etc. and the guy that actually did the
> work owns a 95 D90 that he just put ARBs in a couple of months ago. He asked me
> if I had any pull in the steering before he did the work, because he hadn't
> driven it before he did it and I said no. So he said well, it pulls some now,
> and he isn't sure why. He admits to not knowing very much about the Truetrac,
> and I knew that before I had him do the work. He and I are wondering what to do
> about the pull. I have to hold the steering wheel about 30-40 degrees to the
> right, as it is pulling to the left. It is the same at any speed, and whether
> it is in gear or not.
> Other than the pull, the Truetracs feel fine on the road after a little getting
> used to, and the 4.10s make the gearing a lot more sensible (particularly with
> the 33 inch tires). A much more confident ride off road.
> I am going to have the alignment checked. Any other suggestions?

Several points to check here.

1) Check your tierod - they prolly took it off when the installed the front diff and may have changed your toe in.

2) Make sure they put the correct True Trac in the front (different part numbers for front and back) I am not sure it would cause the problems you are talking about, but it may affect performance.

3) Maybe they buggered the reinstallation of one of the hubs and the brake is binding, or the outerhub has too much preload on the bearings on one side.

4) Did you by chance put on a gas charged steering stabilizer? or maybe they buggered the reinstallation (its on the tierod on a Disco? vs the draglink on a D90).

My front TrueTrac worked very well. It did not pull in either direction when driving straight. In fact it wanted to drive straight all the time, and self-centered after a turn with much "gusto". It actually tracked down the highway very straight after the install, much "tighter" than before or after (now have an ARB front).

Hope some of this helps,
Bill R.
'97 AA Yellow D90 ST #2078

Date: Fri, 2 Jun 2000 10:13:45 EDT
Subject: Re: Truetrac affecting steering

Will Assuming that there isn't some other reason such as noted by Bill Ritchie, the cause is proably lack of break in time on the diffs. Truetracs have preload washers in them that assist the torque transfering effect. When a unit is brand new the washers have more friction due to their machined surfaces. They will polish up within a few hundred miles and should moderate the effect to the extent that the diffs will become invisible in everyday driving. Your situation may be more pronounced because you have Truetracs both front and rear.

Great Basin Rovers


From: Bill Ritchie[]
Sent: Tuesday, February 15, 2000 6:41 PM
Subject: [D90] ARB diff install and assorted other thoughts

This past weekend was a fun filled event that included 2 long days of tearing down 2 complete front axle assemblies and installing a front ARB in my D90.

The install was completed with the help of Alan Dobbs, Doug Aitken and Antonio Manega, with Mimi Dobbs as the ever present support person.

The ARB install page on was very helpful during the install. The page is very picture rich and was very well done. The takedown of the front hubs and removal of both front axles went very smoothly (we had already taken down and rebuilt Alan's front end). The bearings and seals were all in very good condition (they will all be replaced when I get some new front axles in the near future) so they were cleaned, repacked and left in place.

The 3rd member was dropped and the old diff (TrueTrac) was unbolted and removed. The ring gear slid off with no effort. Meanwhile we had "frozen" the ARB diff in dry ice (no liquid nitrogen avail. on the weekend). With the frost wiped off the ring gear (Ashcroft 4.1) slid on the new diff easily, however the ring gear bolts would not go through the ARB diff holes. Fortunately before we tried to drill the holes out bigger it was noted that the ARB case (which is 2 big pieces) had twisted on itself and made the holes uneven. Once this was corrected the bolts went in very easily and were torqued to spec.

The 3rd member case was prepared by drilling a hole in the casing and taping for the supplied air-line hardware. We "adjusted" the position of the hole in the casing to make it easier to fit a wrench in and tighten the fitting, but in doing so inadvertently came very close to crowding one of the 3rd member mounting bolt holes. Once the air-line hole was finished, we moved on to drilling out and taping the 2 holes in the flat portion underneath the pinion to fascilitate installation of the 3 link SG stuff later.

After installing the ARB in the 3rd member and checking ring gear run out and installing the copper air line fitting we moved on to the backlash adjustment. The ring and pinion had originally been set up by a local 4x4 shop (at considerable expense) and we had run a pattern on the gears before removing the TrueTrac. The pattern looked good, but was a little close to the inner edge of the ring gear. The backlash before we touched anything was 4.5 thousanths. The ring and pinion were free of any visible wear (had about 10,000 miles on them), and the setup was free of significant gear noise.

Upon installation of the new diff with the old gears the first backlash we checked was about 5 thousanths. Great we thought, this was really easy to set up. However, once everthing was tight and torqued to spec the backlash was rechecked and found to be about 2 thousanths (too tight). After much adjusting and fiddling (during which time we probably were seating the bearing races into the proper position) we finally got a decent setting with everything torqued to spec. (about 5 thousanths). The pattern looked about the same, so we installed the diff.

To those with the ARB installed already, it appears that they are shipping with a new switch (conventional rocker with "Front ARB Airlocker, or Rear ARB Airlocker" written on it).

The air-line install on my setup is somewhat different in that it involves nothing electric. It is powered by my CO2 tank connected to a 3 way pneumatic switch (with a toggle very similar to an electric switch - thanks Alan!) that is connected directly to the ARB air-line. Very simple (KISS principle) and works very well.

A quick test drive after the install revealed no gear noise and returned the steering effort to stock (it had increased steering effort because of the TT diff).

If anyone is interested in the install particulars or need some photo's let me know.

Bill Ritchie '97 D90 ST AA Yellow

Sent: Wednesday, February 23, 2000 8:05 AM
Subject: Diff "cross shaft" replaced - AND a question!

I should have written this on Monday, but have been too busy... Well, I replaced the broken cross shaft in the rear differential of my Rangie. After emailing "Powertrax" (Lock Right manufacturer) and them telling me that the Lock Right locker "eats cross shafts" I ordered one from British Pacific at about $12 less than the dealer price. The replacement went very smoothly, except I ruined the differential gasket which I wanted to try to re-use. Oh well... I used "ultra copper RTV" in place of the diff gasket and the axle seals. Works great! No leaks!

The cross shaft had snapped in two pieces, with a very small amount of metallic slivers in the gear lube. I cleaned out the diff housing as best I could, and wiped off the gears and locker. Lock Right sells hardened cross shafts for SOME applications, but you guessed it, not for Land Rovers.

I guess my point in "reporting" this to y'all is this: Don't use a Lock Right locker in the Land Rover. Spend the extra $100 to $150 and get a Detroit, or go for the ultimate $ and get an ARB. (I have no personal experience with Detroit or ARB lockers, but they have an excellent reputation.) I found Detroit lockers for as little as $412 by calling all the "800" numbers in the "4-Wheeler" magazine. I think I paid near $300 for the Lock Right several years ago. BTW the Lock Right showed no signs of wear at all. Looked new after 2 years of use! Don't get me wrong, the Lock Right works as advertised, and if you see me selling it in another year or two from now, forget what I just said and don't hesitate to buy it from me. ;-)

(extraneous mat'l deleted - ed.)

Thanks, Dave Brown - '87 Rangie

Bill Davis [] added:
You don't need to worry about anyone using Lock-Rites in Rovers. They were pulled off the market very shortly after they were introduced. This was for two reasons. 1) there was too much backlash in a Rover drivetrain (especially 10 spline) that it caused some problems in the operation of the unit. 2) They rely on the strength of the stock 2 pinion carrier, which isn't up to the additional strain a traction device puts on it, and as a result they had a 100% failure rate in heavy duty testing in Australia. A Detroit is a much better value since it is a 4 pinion style diff and hence much stronger.

From: Clarke Williams[]
Sent: Thursday, March 09, 2000 8:07 AM
Subject: Re: [D90] Strengthened Axles

>Please elaborate on the difference the Quaife diff, and center (?) diff

Quaife's are a torque sensing differential similar in design and operation to the Torsen and (somewhat less similar) a TrueTrac. Most people seem fairly familiar with the effects of TrueTrac differentials in the axles compared with open and locked differentials so I'll be brief.

A Quaife or similar differential in an axle increases the proportional bias in the amount of torque being delivered to the tires from left to right. An open axle is zero bias (lift one wheel, the other gets no torque). A locked differential (e.g. spool or ARB) is 100% (lift one wheel, the other gets all available torque). A Quaife seems to be (I cannot get "real" numbers so this is an estimate) about the same torque bias as a Torsen, ~~4-5:1. One wheel has limited torque before slipping of say 50 lb-ft, the other wheel will get 4 to 5 times the 50 lb-ft or 200-250 lb-ft before the diff slips. Alberto designed a very fine Excel spreadsheet that calculates the available torque for each wheel in a single axle, including nice 3D graphs, that shows very dramatically the improvement in traction available from limited-slip and locking differentials in the axle.

When I discovered a few months ago that Quaife was making a center differential for the LT-230, I asked Alberto to design a similar spreadsheet to calculate available traction when both axles *AND* the center differential were taken into account. I was frankly amazed at the results. With limited slip diff in all 3 locations the available torque is around 97% of that available with all three differentials LOCKED. The big advantages, to my mind at least, of going limited slip as opposed to lockers are:

1. less complex mechanism (less likely to fail in field)
2. reduced driver workload (automatic action w/o driver intervention)
3. less drivetrain stress - no binding of axles or driveshafts
4. usable under ALL conditions, including pavement driving
5. improved handling compared to a locked diff (axles)
Disadvantage? Cost. The Quaife differentials are not inexpensive.

And that is the nutshell ;-)
Clarke Williams

Sent: Tuesday, March 14, 2000 9:43 AM
Subject: Re: [D90] Diff selection [was Strengthened Axles]

You are on the right track in my opinion, there is no such thing as one particular type of traction diff being better than all others in all conditions. This also applies to most other components suspensions, tires etc. All traction diffs have plusses and minuses. The questions I ask when someone calls me about diffs are:
1) intended use of the vehicle
2) personal driving style
3) budget

The most important question to honestly answer to yourself, is the first one. Frequently we let our macho egos (or feminine egos for that matter, although they seem to under better control at least in the 4X4 toy dept.) guide the decision. I frequently talk folks out of buying any upgraded product because in the coarse of the discussion it becomes obvious a stock vehicle is actually the best choice (and cheaper too!). Another frequent senario is the "I know I don't need it - I want it, This is my hobby and it gives me pleasure to spend money on it!!". I personally understand this, being the owner of numerous Land Rovers, most of which are in no danger of running anytime soon. But it does give me pleasure to know I own them - honest! In reference to the terminology "traction enhancing diffs", I personally think it is correct and it is the term I use, actually traction diffs for short. This is because LSD's, automatic or selectable locking diffs are all types of traction diffs. To describe them as "lockers" is incorrect because not all traction diffs are lockers. An example would be a TrueTrac, which is a gear driven limited slip.

Great Basin Rovers


Set-Up and Installation

Date: Wed, 12 May 1999 18:34:27 -0500
From: (Douglas Aitken)
Subject: [D90] The Mysteries of Differentials

While looking for some info on the Web, I surfed across the following two sites, which may be useful to some!:
(1) Clarify understanding of what a Differential is and how it works:
(2) Some useful stuff on troubleshooting funny noises and vibrations......


From: Alan Dobbs[]
Sent: Tuesday, April 11, 2000 9:36 AM
Subject: RE: [D90] Shims

(3.215 in O.D. x 2.632 in I.D.)

PART No. mm

549230 0.97
549232 1.02
549234 1.07
549236 1.12
549238 1.17
549240 1.22
549242 1.27
549244 1.32
549246 1.37
549248 1.42
549250 1.47
549252 1.52
576236 1.57
576237 1.60
576238 1.63
576239 1.65
(1.620 in O.D. x 1.265 in I.D.)

PART No. mm

FRC1193 1.52
FRC 195 1.57
FRC1197 1.63
FRC1199 1.68
FRC1201 1.73
FRC1203 1.78
539718 1.83
539720 1.88
53979P 1.93
539724 2.03

>Do they go on different parts of the pinion shaft?
Yes they do.

The shop manual isn't very clear on this. If you are close to a Land Rover dealer talk to the service manager and ask to see the book on differentials. It is a more detailed book than the standard shop manual.

I have started a How to page on the diff's though incomplete here is the URL:

Alan Dobbs

From: Alan Dobbs[]
Sent: Tuesday, April 11, 2000 11:17 AM
Subject: RE: [D90] Shims

Yes and no David
This was my first actual diff rebuild and in comparison to rebuilding a CNC machine tools (my true career) the mechanics of the diff are not complicated it is just time consuming to get a good pattern and bearing pre load. If you change the pinion height it will change the preload height theoretically by that amount.

In short this is the procedure I was given by Ian Ashcroft.
1. Clean &pattern check before disassembly.
2. Remove pinion cup carefully & add or subtract height shims in 0.010 increments.
3. Install pinion and flange and hand tighten the pinion nut (with no preload shim)
4. Pattern check again.
5. Do steps #2 and #4 until the pattern looks like it is on the center of the tooth.
6. Install pinion then add some preload shims then install the flange and torque to 80 foot pounds.
7. The pinion should then turn freely with 2 to 3 foot-pounds of force to turn while having the nut at 80 Ft/Lb.
8. Add or subtract pinion shims until 2 to 3 FT/Lb is achieved (there will be a point where 0.001 of difference in preload shims will make it tight to loose in my findings)
9. Remove pinion nut and Flange then install oil seal
10. Mount ring gear and adjust backlash & double check the pattern then check for radial run-out on the ring gear.

Hope this helps

From: Alan Dobbs[]
Sent: Tuesday, April 11, 2000 11:34 AM
Subject: RE: [D90] Shims

>So the preload shims must go on the tail end
>of the shaft as opposed to the top (bearing end) (?).

First off have you removed the cup/race from the housing? This is where the pinion height shim is.
The preload shim is on the pinion first then the bearing then spacer, flange, nut and washer.
This pic may help


From: Jamie Austin[]
Sent: Wednesday, April 12, 2000 1:54 AM
Subject: [D90] Shims?


he Salisbury axles on 109" and 110's have a 'collapsible sleeve' behind the drive have to do the drive flange nut up to an amazing torque of about 400 ft/lb to 'collapse' the sleeve. This then 'sets' the preload on the flange.

Jamie Austin
'96 D110 Tdi
'92 D90 Tdi
'85 D90 V8i


Ring and Pinion Ratios

Date: Fri, 4 Jun 1999 04:07:48 EDT
Subject: Re: [D90] Running 4.1 Gears

I'm going to write a small novel as the topics in question (axles, diffs, gears) are my specialty. In my opinion 4.1's are just about ideal for most late model V8 Land Rovers even with stock tires. They lower your overall gearing between 12 and 13 percent. Most people who do gearing changes uaually already have larger tires and are unsatisfied with the resulting loss of performance, ( Yes larger tires alone will affect on road performance negatively), or are eventually planning on installing them at a later date. Increasing your tire size results in raising your gearing, hence you are giving back some of what you got with the gearing. Depending on what size tire you install you will end up with somewhere between a 5 to 9 percent gearing reduction. I would be more exact but I am at home and can't reference my charts. With 4.1 gears and 33" tires you are in the range of 8/9% reduction. This change may sound small but by gearing standards is a significant jump and is actually quite noticeable. The reason is that your engine for the same road speed is actually operating further up the power curve, which is quite steep at lower engine speeds. A 9% reduction in gearing actually feels much greater than 9%! This results in the benefit that at low speeds, particularly starting from a standing start, your Rover will have much better acceleration and overall will feel much peppier, and thats a good thing - lets face it nobody has ever accused a Rover of being a drag racer!

There are even more advantages of lower gearing off road - compression braking, low speed control, again increased power and accelaration. The disadvantage of lower gearing, particularly at higher road speeds, is that your engine is running faster resulting in more engine/drivetrain noise, wear and tear. 4.1 gears are a modest enough change that the the disadvantages at higher speeds are for the most part not noticeable. The same can't be said for 4.7 gears, obviously you can over do anything and most people find 4.7's to be too low, resulting in a vehicle that is noticeably over reving at highway speeds. This is not to say 4.7's can't be a viable alternative - 35' tires, operating at a higher altitude (6000'+), heavily laden, towing, large % of use off road etc, but I highly recommend realisticly looking at the projected use of your Rover before selecting ultra low R&P gearing - it is very expensive to change your mind after the fact! If you are considering changing to traction diffs, of whatever brand (ARB'S, Detroits etc), you definitely want to do gears at the same time. Approximately 80% of the work is overlapping, someone mentioned that it is 100% duplicated but that is not true. When you change gear sets you need to remove the pinion gear and reset the pinion height. This usually requires setting up the diff, checking your contact pattern, disassembling it again, banging out your inner bearing cup, adding or subtracting shims as required, reassembling it and checking the contact pattern again etc. If the pattern is good then you have to set the outer pinion bearing preload. If you don't change gears you don't even have to remove the pinion gear.

Doug - excellent explanation of ring & pinion gears vs diffs and I generally agree with your opinion of the order of upgrades (tires, suspension, gears/diffs) with one exception. I think that the last two items can be substituted back and forth equaly depending on the type of conditions you are off roading in. Traction diffs compensate for a lack of suspension travel and suspension travel compensates for the short comings of an open diff. There are situations of limited traction such as snow/ice, mud and loose surfaces where all four tires are on the ground and suspension travel is not the issue, in these situations traction diffs will give you much more utility. This along with the on road benefits of gearing as detailed in paragraph one in my opinion make it a toss up, although idealy its nice to do all of the upgrades - if you can afford it! Your comment about being at the Twist Off and doing just fine without most of the fancy equipment reminds me that the most valuable piece of equipment you can own is good driving skills and common sense. Speaking of the Twist Off, one of the most surprising results in my opinion was the performance of the Old Man Emu package so I would add it to your list of suspension upgrades. You also mentioned that Ashcroft 4.1 gears as being stronger than stock 3.54 gears, this is not true actually the stock 3.54's are stronger. This is because as with any gear set as the the numeric ratio gets larger the pinion gear gets smaller and hence the gear set becomes weaker. This is why with my GBR 4.1 gears I specify a higher grade material, shot peen and radius the teeth to stress relieve them . All of these extra steps are only found in professional racing applications and are designed to build strength back into the gear set. GBR gear sets don't require new pinion flanges or the addition of spacer rings. Contrary to a previous comment spacer rings for the ring gear don't necessarily weaken a gear set, they only add expense, also Land Rover never made a 4.1 ratio so any comparisons to stock 4.1 ratio's are not valid.

Hopefully I haven't bored everone to sleep
Great Basin Rovers

Sent: Monday, May 22, 2000 11:55 PM
Subject: Re: [D90] 4.7:1 Gears

There are 2 ultra low ratios for the Rover differential, 4.7 and 4.75. There is no such thing as a 4.77 - I'm not sure how that one got started. To get the ratio, you divide the tooth count of the pinion gear into the tooth count of the ring gear. The major difference between the two real ratios is the tooth count. A 4.7 is a 10 X 47, the 4.75 is 8 X 38. The advantage of of the 4.75 ratio is since it has fewer teeth, they are thicker and hence stronger. Its actually not quite that simple since other factors such as face ratio, contact ratio are factors also but in a nutshell that is the story.

If you are going to use Series 4.7 gears make sure you use genuine gears. Some of the aftermarket ones are junk (an example is whoever makes Bearmach R & P gears). Another critical factor is the carrier you are installing the gears in. Any of the 4 pinion style carriers (ex: Detroits, ARBs, Maxi-Drives, McNamaras) will double the strength of a gear set. The 2 pinion style carrier is not up to very heavy duty usage. The most common failures are the cross shaft, either the circlip or the shaft itself breaking, followed by the carrier developing stress cracks, which eventually develop into big cracks. If you use Series gears and hence a spacer ring, use the thinest one possible. You want the maximum amount of the gear on the carrier pilot and spacer rings move the gear away from the carrier. As a result you start putting more stress on the ring gear bolts. I can't remember how close the Series 4.7's are to the end of the pilot because my gears have the correct offset and hence don't require a spacer ring.

KAM gears are not "anything to write home to mother about" as they do not use OEM quality material.

The deciding factor as to what set to use is whether the vehicle is for show or go. The 4.75s are more expensive but all you have to do is grenade one set of Series gears and the difference in price is a moot point after you consider the cost of new gears, bearings, setup and very likely a new carrier.

Great Basin Rovers


Break-in and Work Hardening

From: Doug Marbourg[]
Sent: Tuesday, April 18, 2000 4:18 PM
Subject: Re: [D90] Work Hardened R&P

>myth or reality?
>Should modern day R&P's be work hardened? The old tale of short drives
>with cool
>down periods for a new set of R&P's is still out there. Is it true?
>Any opinions from the pro's on this one?

Yes they should. Check out Randy's Ring and Pinion sight...He DEFINITELY recommends a break-in period. In a nutshell:
1) Keep it below 60mph for 100miles,
2) Take a break to let'um cool after 15-20miles for a 100 miles,
3) Change the diff fluid at 100miles and at 500.
4) Replace fluids w/synthetics on very low ratio's,
5) Don't use for towing for (i think) 500miles.

He get's into all the basic questions on his site you might have about R&P's, such as why doesn't the factory (new) car require a break-in, ect... Good info.


Sent: Sunday, April 23, 2000 11:49 PM
Subject: Re: [D90] Work Hardened R&P

Land Rover diffs, with the exception of the Salisbury diffs found on 110's and 101's, are a spiral bevel gear (non-hypoid) design. One of the few advantages of a spiral bevel gear set is that they run much cooler because the teeth do not slide against each other like a hypoid set does. They mesh more like helical gears found in transmissions. As a result they require little if any break in although it is probably a good idea to take it easy with any new part for a while.
I talked with Randy Lyman of Randys Ring and Pinion in Moab at the EJS this past week and asked his opinion and he concurred.

Great Basin Rovers


Best Practices for Use (Lockers, LS, Center Diff Lock)

Date: Thu, 27 May 1999 00:48:09 EDT
Subject: Re: [D90] When to switch on the ARB lockers!

It appears that others have answered your specific question as to when to engage your diff locks, I would like to add another reason. ARB's need to be engaged to be properly lubricated, failure to do so can damage them. I know some people who have the idea that when they go off roading they will not engage their diff locks until they are either stuck or cannot negotiate a specific obstacle after several trys unlocked. If you are doing very challenging off roading with lots of side to side tire spinning, these are the situations that can damage an unengaged ARB. As to exactly when to engage a diff lock is at your discretion, but from a lubrication stand point, it is important to engage them!

Great Basin Rovers

Bill later added:
I decided to check with ARB because I was sure someone was going to ask for specifics (no one has yet it appears) and lo and behold the info I got was different than the first time I asked. It appears that what is bad for them is non-use of the locking mechanism, not heavy usage un-locked. The U ring can lose its flexibility and stick with non-use. This actually makes more sense to me, when I asked the first time I just filed the info away in the mental hard drive and would occasionally ponder it, trying to understand why without ever coming up with an answer. Sorry about sending along some incorrect info even if it was only for a couple of days.