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  #1  
Old June 28th, 2009, 07:44 PM
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Clark Bowen
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4.75 gears

I know that the topic of 4:75 gears has been kicked around before with the general consensus that they are too weak.
Since 4:11s aren't much different than the stock 3:54s for my trail purposes (modified 1991 RR with 35" Nittos, auto, LT230 and an ISKY cammed 4.6 liter) I'm hoping that maybe someone has a new idea or supplier for the lower gears. I realize I'm probably pissing in the wind on this one.
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  #2  
Old June 28th, 2009, 07:51 PM
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4.11 is a good jump from a 3.54, especially for a 35" tire. There are also 4.71s available from GBR now that are supposed to be stronger than the 4.75s.
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Old June 28th, 2009, 08:33 PM
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Stronger,..maybe. The problem is the small pinion on a Rover third. If you think you need lower gearing, it's time to step up into something better. Try Toyota, that pinion makes Rover stuff look plain silly.
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  #4  
Old June 28th, 2009, 09:00 PM
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Quote:
Originally Posted by EWR
Stronger,..maybe. The problem is the small pinion on a Rover third. If you think you need lower gearing, it's time to step up into something better. Try Toyota, that pinion makes Rover stuff look plain silly.
Toyota for sure. There are so much more gears available and they are so reasonably priced, if you do break them it's not a huge deal.
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Old June 28th, 2009, 09:13 PM
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Either get an Ashcroft underdrive or call Bill at GBR and regear the transfercase. I have 4.11's in my ST with 35's and it does pretty well. With 33's and the 4.11's my truck moves out pretty well.
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Old June 28th, 2009, 09:30 PM
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I'm trying not to bury myself in the RR like I did with the D90 (300 TDi, underdrive, 4:11 gears, etc) otherwise the Toyota stuff would be great. Also, the underdrive doesn't work with the auto trans because it, combined with the T-case is too long. It really did quite well on the Rubicon last week, but a 4:75 would make it that much easier. It is a trail rig and the Nittos are so loud I had to wear an earplug in my left ear when I drove on the highway or I was functionally deaf when I arrived.
So, I'll check with Bill at GBR.
As a side note, the bolts holding the ring gear in the rear diff on the D90 worked loose and 4 were chewed up. They had not been loctited, but hadn't unscrewed for 7 years and 33,000 miles. These were Ashcroft R & Ps and they have the weirdest size bolts - 9mm x 1.25 x 30mm. Nobody in the US has them as far as I can tell and the ring gear is too hardened to tap for a 3/8ths - 24 pitch. If Ashcroft doesn't have them I'm hoping a friend can make some.
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  #7  
Old June 29th, 2009, 08:48 AM
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Quote:
There are also 4.71s available from GBR now that are supposed to be stronger than the 4.75s.
This is the way to go. The old 4.75s had something like 47 ring teeth and 11 pinion teeth, the new GBR 4.7 have like 33 ring teeth and 7 pinion teeth. That allows for a more beefy setup, much more beefy in fact.

There is someone on eBay selling the old 4.75 ring and pinion sets for under $100 each with free shipping. I ran those in my old Disco on 33's for a long time with no breakage, and great acceleration or course. In my current truck on 36's I made it about 20 minutes on the trail before stripping a big chunk of ring gear teeth off. So my comments about the old style 4.75s: they are OK strength wise for 33's but a bit overgeared for highway use. 34s probably a bit better on the road- 35s start getting worried and 36 be ready to break the gears.
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Old June 29th, 2009, 10:31 AM
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Quote:
Originally Posted by cdb
I'm trying not to bury myself in the RR like I did with the D90 (300 TDi, underdrive, 4:11 gears, etc) otherwise the Toyota stuff would be great. Also, the underdrive doesn't work with the auto trans because it, combined with the T-case is too long. It really did quite well on the Rubicon last week, but a 4:75 would make it that much easier. It is a trail rig and the Nittos are so loud I had to wear an earplug in my left ear when I drove on the highway or I was functionally deaf when I arrived.
So, I'll check with Bill at GBR.
As a side note, the bolts holding the ring gear in the rear diff on the D90 worked loose and 4 were chewed up. They had not been loctited, but hadn't unscrewed for 7 years and 33,000 miles. These were Ashcroft R & Ps and they have the weirdest size bolts - 9mm x 1.25 x 30mm. Nobody in the US has them as far as I can tell and the ring gear is too hardened to tap for a 3/8ths - 24 pitch. If Ashcroft doesn't have them I'm hoping a friend can make some.
I would avaid the 4.7 no matter if they are new or old. There are mechanical limits to making something so small, strong. Have you looked at the new t-case regearing options? They are not that out of line, maybe even cheaper than regearing the diffs. Would keep your freeway rpm down as well.
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  #9  
Old June 29th, 2009, 10:58 AM
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Quote:
Originally Posted by cdb
Also, the underdrive doesn't work with the auto trans because it, combined with the T-case is too long.
I have seen an Ashcroft Underdrive in a 95 D90 that was converted to an Automatic. I am considering doing it to my truck too. I like that choice better than re-gearing the TC. That way it is selectable.
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Old June 29th, 2009, 02:12 PM
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Quote:
Originally Posted by Buckon37s
I would avaid the 4.7 no matter if they are new or old. There are mechanical limits to making something so small, strong.
I would avoid passing judgement on something until you know just what the fuck you were talking about, but its never stopped you before has it?


(old 4.75s on the left, new GBR 4.71s on the right, so you all can base your own opinion on how "small" it really is)
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  #11  
Old June 29th, 2009, 03:20 PM
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mmmmmm slim jims....
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  #12  
Old June 29th, 2009, 04:23 PM
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Since we are on the subject.....are all rover diffs created equally? I.E. are gear sets from series trucks compatible with Defenders, Discoveries 1 and 2 ?

Thanks
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Old June 29th, 2009, 05:22 PM
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Quote:
Originally Posted by crown14
I would avoid passing judgement on something until you know just what the fuck you were talking about, but its never stopped you before has it?


(old 4.75s on the left, new GBR 4.71s on the right, so you all can base your own opinion on how "small" it really is)
Before you shoot your mouth off you tool. Buck and myself are talking about the pinion, NOT the ring gear. Besides, just adding mass doesn't make something stronger.
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Old June 29th, 2009, 05:37 PM
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I talked with GBR today (Bill is gone for a month) and they say that the problem has been incorrect installation by the mechanic. They suggest shipping the diffs to them and they also weld something on to hold the ring against the pinion. She was insistent that the gears were not a problem.
Thanks Joel for showing a picture of the difference. Very helpful.
Buck... on the TC do you mean maxi-drive low range gears?

Follow-up Post:

Scott...

On using an underdrive: They are quite expensive and you'll need a 1.4 t-case or different gears in your present case too.
I've found with the underdrive in my D90 that it is really helpful descending stable high traction surfaces (Moab slickrock) but really doesn't make much difference ascending. (I usually use low box second or third with the crawler box and that is about the same as low box first without the crawler).
I suspect that this would hold even more true for an automatic.
Also, was the floorpan aft of the transmission tunnel modified in the 1997 you saw?
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Old June 29th, 2009, 05:56 PM
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Clark "pinning" the pinion is what she was talking about, its pretty interesting once you see it. Had my 4.75s been pinned I might not have broken that ring gear like a $2.99 ratchet. Then again, I was backing out of a hole, unlocked, on 36 in tires with the 11 tooth pinion 4.75s.



3 times for the slow readers in the class


Quote:
The old 4.75s had something like 47 ring teeth and 11 pinion teeth, the new GBR 4.7 have like 33 ring teeth and 7 pinion teeth.
Quote:
The old 4.75s had something like 47 ring teeth and 11 pinion teeth, the new GBR 4.7 have like 33 ring teeth and 7 pinion teeth.
Quote:
The old 4.75s had something like 47 ring teeth and 11 pinion teeth, the new GBR 4.7 have like 33 ring teeth and 7 pinion teeth.
If its possible, think about it- fewer pinion teeth means bigger pinion teeth, bigger teeth means better contact with more strength, more strength means less snap crackle pop. Pinion and ring gears still exist within the same physical space.

Quote:
Originally Posted by buckon37s
There are mechanical limits to making something so small, strong.
And according to GBR, this is it.

Also there is a new 20% stronger GBR replacement for the old type 4.11 gearset that comes out to be 4.14 and follows the same path to a simple solution as the 4.71 set. Pic of the 4.11 compared to the 4.14 attached
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  #16  
Old June 29th, 2009, 06:09 PM
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Congrats! You are a tool. Using a Rover 4.7 whatever is just dumb when running a 36" tire. Switch to Toyota and be happy.

The word for today class is..."TOOTHPICK". Can you say toothpick, I knew you could do it.


You might as well tell us you're into tall narrow tires and love mud while you're at it. That's alright y'all.


Leave it at Dweb.
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Old June 29th, 2009, 07:56 PM
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*polish* *polish*


...


Yup, still a turd.
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  #18  
Old June 29th, 2009, 09:17 PM
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Carey....

What are you running?
Have you ever used the GBR 4:75 or 4:71
What did your Toyota conversion cost?
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Old June 29th, 2009, 09:18 PM
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RoverTracks has the kit... Give Keith a call.
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Old June 29th, 2009, 09:36 PM
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Quote:
Originally Posted by cdb
Carey....

What are you running?
Have you ever used the GBR 4:75 or 4:71
What did your Toyota conversion cost?
Excellent question(s).
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