Overdrive for 110 with 2.8 TGV - Defender Source
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  #1  
Old May 7th, 2008, 11:13 PM
Santiago
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Overdrive for 110 with 2.8 TGV

Hi,

Currenlty thinking about installing an overdrive on my 110 with 2.8 TGV engine.
Reasons:

a) to reduce rpm while travelling long distances along flat country. I usually travel at 115kms/hour and that implies aproximately 2,800rpm (more or less). I would like to reduce these RPM's so that the engine is less stressed and I am less stressed too. My journeys along flat country are usually around 1,000kms long (have to make'em in 1 day).

b) as important as reducing the rpm's is reducing the engine noise accordingly.

c) my engines is powerful and capable of achievening >140kms/hour but the rpm's are too high to travel all day at 115/120 kms/hour. I know that by travelling at 100 kms/hour in 5th gear the problem is solved but I need to travel at 115/120kms per hour.

My specific questions are as follows:
1) should an Overdrive work adequately with the engine and vehicle I have (standard 2000 Defender 110 Td5 except for the Brazilian engine and running BFG MT 265/75/16 rubber)?

2) I understand GKN is not selling any more and had some problems, is this correct?

3) I am thinking about the RoverDrive overdrive being built in the US and sold for aprox. 1,350 U$.
Is it good? Anybody has it?
I understand it has the advantage that there is no electronic activation (?) as the GKN, is this correct?

Finally, I am a bit worried about the cost/benefit ecuation since, as you know, overdrives are not cheap. On the other hand I often do these long trips along flat country and it seems to me that an overdrive could eventually make my trips in my Defender much more pleasent and relaxed.
I keep on thinking about it but I've reached a point where I need advice from people with experience.

Any comments wil be very much appreciated.

Thank you
Santiago
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  #2  
Old May 7th, 2008, 11:28 PM
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First of all, what ratio transfer case do you have? A 1.4? With your amount of power and torque a 1.2 would still work nicely and get you some of the result you're looking for. I'm not really sure what sort of noticable result you'd get, but of course on paper its different.
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  #3  
Old May 8th, 2008, 12:15 AM
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Good advice from JimC
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  #4  
Old May 8th, 2008, 05:05 AM
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110 will have the 1.4 T-case gearing.

GKN has stopped manufacture of its Overdrive because of the number of problems it had with the unit. You'll probably be able to pick one up from somewhere, but these will still suffer the traditional GKN failings. Speed sensor failure, oil seal failure and oil transfer when hot. There are users of the GKN device that have had no problems, but there are plenty more who have. For the asking price, the GKN unit is an expensive gamble. For that sort of money I'd expect a quality piece of kit. The GKN unit isn't! The basic design is something like 40 years old!

The Roverdrive is fully mechanical. Never seen one in the UK so no idea whether it's any good or not. The guys here will probably have a better knowledge of the unit.

Pal of mine had two GKN's fail. He now runs a 1.2 Discovery transfer box in his 110. Since then he's never looked back. Crucially for you, the one thing the GKN doesn't like is being run for long period of time where it can get hot. My friends GKN always failed on long runs from the UK to Africa.

The Discovery gearing is cheaper, more reliable and the 2.8 will pull the gearing all day long without any problem. For your intended use, forget the Overdrive and go with the Discovery transfer box gearing.
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  #5  
Old May 8th, 2008, 07:27 AM
Santiago
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My transfer is the original for my 2000 defender 110 Td5: ratio=1.4?
Anybody knows if "on paper" the 1.2:1 transfer will imply similar gearing as the Roverdrive overdrive?
I am trying to compare driving on 5th gear and 1.2:1 transfer vs 5th gear and Roverdrive overdirve with 1.4:1 transfer

Kevin, thanks for answering in both forums!

Thanks for your comments
Regards,
SG
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  #6  
Old May 8th, 2008, 03:11 PM
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Kamdiffs may have gears for your front and rear differentials that will give you what you want, 2.83's I think.
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  #7  
Old May 8th, 2008, 06:06 PM
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Ashcroft sells the set for the transfer mod; from 1.410 ratio transfer box to 1.222 ...
http://www.ashcroft-transmissions.co.uk/part_34.html
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  #8  
Old May 8th, 2008, 10:05 PM
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Anybody knows if there is a place to buy the Ashcroft Discovery transfer gear set in Canada (preferably) or the States?

Thanks
Santiago
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  #9  
Old May 9th, 2008, 11:12 PM
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Santiago - All of the overdrives (GKN, Roverdrive, Paynes) will reduce the gear ratio by 26-28%. Going from a 1.41 transfer case to a 1.22 is a 13% reduction. So there is a big difference between the two options. I agree with everyone else that the better option is going with the 1.22 transfer case. I have the 2.8 in my 110 with a 1.41 transfer case, and I believe the OD reduction will be way too much (unless you only drive downhill). I've contemplated going to the 1.22 myself, but I drive in the hills a lot so even that 13% reduction might be too much. Good luck.
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  #10  
Old May 10th, 2008, 09:15 AM
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I was looking into this at one time as well but have a 300tdi w/ 4.11 gears and a 1.4 t-case... I like my gearing in gereral but need one more top gear. I would like to eventually get a roverdrive if that is a good Idea. What about the new Rover 6 speeds? are they an option?
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  #11  
Old May 10th, 2008, 07:46 PM
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Ryan,

Very interesting comment, thanks.
Makes me wonder what is the correct thing to do.

I was a bit afraid that the Roverdrive overdrive would be too much for my engine but a guy on the LR 4x4 forum told me he has achieved speeds of 90mph on his 2.8 powered Defender 110 with the Roverdrive Overdrive engaged so.....I donīt know (he did not mention if it was down hill or with strong wind from behind so I imagined it was on flat land and with no wind...)

I have 265/75/16 (32 inch) rubber in my 2.8 Defender now and it happily climbs up to 90mph (way too high rpm's though).
In the past I've used 285/75/16 (33 inch) and the final speed was lower and the reaction (acceleration) of the vehicle was less impressive.

I like the geraing of my vehicle as it is but would just love to have another gear so I was mainly considering the overdrive option. As I said, now, I donīt know.

Cheers,
Santiago
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  #12  
Old May 11th, 2008, 03:44 AM
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Santiago - I'm running 285/75 (33") with 3.54 axles and ZF trans, and I can do 90 mph on perfectly flat roads. But the slightest incline will slow me down. I sometimes have to downshift on small hills just to maintain 65 mph, and then the engine's really revving (which is where a 1.22 transfer case would help me). I wish someone would make a 15% overdrive. Then you could effectively use it as an overdrive and a gear splitter.

It's definitely a difficult decision, but probably the most economical approach is to swap in a used 1.22 transfer case. If you don't like it, swap back in the 1.41 and sell the 1.22. I should probably still do this myself since I have a 1.22 sitting here. But I'm in the midst of a lot of other work on the truck so it won't be for a while.

Just noticed that you're from Mendoza. I was there many years ago to climb Aconcagua. I can't remember how flat the roads were there, just the long walk to the mountain
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  #13  
Old May 11th, 2008, 10:52 AM
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Ryan,

Not many flat roads around Aconcagua but many east of the Andes, all the way to the Atlantic coast.
Never went to Aconcagua but I understad that IT IS a very long walk to the base of the mountain.

Your comments about how your Defender performs with the 33 inch tires are very similar to what I experienced. I am happier with the 32 inch tires since I can stay in 5th gear longer when finding gentle slopes, better acceleration, etc. but I just need to lower the revs while cruising at 115/120km/h. I have ruled out the possibility of overdrive AND 33 inch tires. Maybe 32 inches and overdrive will just make it with the 2.8 as it is (I guess that if you tune the 2.8 engine with another intercooler and tuning the fuel pump it would be another story but I undertsand that is too risky).

On the other hand I've read many comments from Td5 users (and one 2.8 Defender 110 owner) in the UK who seem to be happy with their GKN overdrive performance so I guess that if the Td5 can push the overdrive then the 2.8 should be able to do it as well since it has more torque and power (than the satndard, non chipped Td5).

I still feel the overdrive might be a better option in my case because I do not want to change the general gearing of the vehicle, I just want 1 more option beyond 5th gear in order to use it on flat roads, I know it won't work uphill or with strong headwind. That's what I like about this possibility, you just disengage overdrive and you still have the same overall gearing.

Having said this the cheapest option (at least down here) seems to be buying the 1.22gear set from Ashcroft so I may end up doing that and, as you suggest, eventually going back later and selling the gear kit in case I do not like the result.

When (and if) I take the decision and implement it I will let you know about the results.


Cheers,
Santiago

Follow-up Post:

Ryan,

Where is Escondido (hidden), California?
Been to Sacramento, LA, San Francisco, Santa Barbara once but never heard of Escondido.

Cheers,
Santiago
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  #14  
Old May 12th, 2008, 12:54 AM
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Santiago - I'll be very interested to hear about whatever you end up doing. For what you want, an overdrive is exactly what you need. But I'm just afraid that the 28% taller gearing will be too much. To put it in perspective, it would be like running 41" tires! Yes, you can switch it On and Off. But I wonder if you'll be On enough to justify the price?

Do you know what's involved in changing out the LT230 gearset? I've never done more than remove the input gear so I don't know how involved that swap is. I was selling one of my 1.22 transfer cases for $450 so that's why I thought that would be the most economical route. But if they're not available in your area, then the Ashcroft swap may be your only choice if you decide to go with the 1.22 gearing.

A 6-speed like Randy mentioned would be really nice. What these little diesels really need is more gears. That's why I'd like to use the OD as a gear splitter. But 28% is almost the same as the R380 4th to 5th and ZF 3rd to 4th gear changes so you don't derive any gear splitting benefit. I really don't understand why all of these OD's are geared so tall.

Escondido is about 30 miles north of San Diego.

Ryan
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Old May 12th, 2008, 04:12 AM
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Quote:
Originally Posted by Santiago
(I guess that if you tune the 2.8 engine with another intercooler and tuning the fuel pump it would be another story but I undertsand that is too risky).
If you use the appropriate tools and gauges to monitor changes you make it is not to "risky" No more risky then installing the 2.8l TGV in the first place.
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  #16  
Old May 12th, 2008, 07:15 AM
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I just built a D-90 w/300Tdi 1.4:1 T-case, 4:10 differential gears and a GKN OD. With the gearing and standard size tires it drives very nicely at highway speeds (65-75 mph). No big climbs around here though. It is a heavy truck....probably close to a 110, but is geared lower. Didn't bother doing the math on this one (gut feeling said it would be ok) so have no idea what final ratios etc. really are. "gut" would say that without a reduction in axle gearing even a 2.8 would struggle a little.

I'm hoping the damn GKN thing doesn't become an issue. The owner insisted on having it as it is a good "splitter".....we'll see.
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  #17  
Old May 12th, 2008, 08:35 AM
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I would love to see if someone comes out with a 6 speed adapter for the new LR trans...
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Old May 12th, 2008, 09:57 AM
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I have installed the GKN. so far so good... I'm using it just as a 6th gear. I didn't want to resign the nice 1st gear pull changing the transfer ratio..
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Old May 12th, 2008, 10:58 AM
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I called ashcroft in the UK to ask them about the 6 speed conversion. They said not yet....
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  #20  
Old May 12th, 2008, 03:41 PM
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Matt - Here are the numbers I ran a while back for an R380 with a 26% OD:

1st: 3.692:1
1st OD: 2.732
2nd: 2.132
2nd OD: 1.578
3rd: 1.397
3rd OD: 1.034
4th: 1.000
4th OD: 0.740
5th: 0.770
5th OD: 0.570

So you can see that 3rd OD is about the same as 4th, and 4th OD is about the same as 5th. So the only real gear splitting you get is in 1st and 2nd where you really don't need it. For the gearing you set up (1.41 TC with 4.11 axles), I can see where the OD can help (and is almost necessary for highway driving). Assuming he's running 33" tires, engine rpm at 70 mph without OD would be 3180 rpm. With a 26% OD, it drops to 2350 rpm.

Randy - Does the new LR 6-speed bolt directly to the LT230? What engine(s) is it used with? It's definitely intriguing, but may not be cost effective until some start hitting the junkyards.
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