Thread: 4.11 Diff Ratio Conundrum

I've never owned a 90, and I'm not into rock crawling.

However I do have experience with defenders and TD5s.

The stock gearing in the diff is fine off-road in low range, you would need to be doing some serious stuff to need to go slower.

Many people seem to focus on what they will do with the vehicle when they go off-road, which is fine... But I also think about the trip getting there.

The setup you have sounds awful for that part of the adventure.

You have bigger than Stock tyres, so I'd probably leave the transfer ratios the same, but I'd be changing the diff ratios back to stock.

That should be tolerable on road and a weapon off road.

If you changed to smaller tyres I'd also look at going to Discovery 2 transfer ratios for high range.

There is also a taller 5th gear available that will reduce revs on the highway, but it's not a common modification.

But that's just my opinion!

Originally Posted by Max Headroom 2.3m

What set up do others have with 4.11 ratio diffs?

The Defender 90 TD5 (Hue) that I bought at the beginning of last year, came with heavy duty 4.11 ratio diffs and front & rear air lockers. Great….but it is noisy (even for a Defender) and a bit of a pig to drive on the road. Great for off road in low range but high revving with unpleasant vibrations and woeful acceleration in high range (i.e. most of the time it gets driven) on black track. I managed to contact the original owner who fitted these diffs (not the guy I bought it off) and he informed me that they were made by Quaife UK and have straight cut gears. That would explain some of the noise. I can live with that but the acceleration, vibrations and cruising speed is unacceptable. So I can see two options:

Option 1: change the diff ratios back to standard helical 3.54’s. This would solve the on road drive-ability somewhat but I would lose the impressive low range off road capability and I would still have fairly high engine revs at highway speeds as it still has the original, unmolested Defender 1.41 ratio LT230 transfer box. There will be some faffing around with the air lockers, no doubt.

Option 2: Rebuild the LT230 with Ashcroft 1.10 ratio high range (low range unchanged) intermediate gear cluster. This, I believe will give me the best of all worlds but means that I have to strip and rebuild a perfectly good LT230 which is not leaking…..believe it or not. It is also a fair bit of stuffing around and a lot more costly as I would also be “forced” to replace the centre diff with an Ashcroft ATB and fit a steel machined bush for the front intermediate shaft O-ring support (I would kick myself for not doing it while I had the chance!!). The vehicle is fitted with 285/75 R16 tyres and with this set-up, the final drive output is slightly higher geared than a standard Defender with a Disco LT230/standard tyres (i.e. slightly more revs needed for same speed).

Any thoughts, experience or suggestions greatly appreciated.

I suspect something isn't right here with the information....

Quaife do ATB's rather than airlockers
Quaife I don't think do Rover diff gears.
Nobody that I've ever heard of manufacture straight cut differential gears, they do go to a lower tooth count though which increases noise a little bit.
Quaife do straight cut gears for the R380 gearbox which would be really noisy.
The Quaife R380 gears also have a first gear which is closer to 2nd and a 5th gear which is closer to 4th.

Are you sure you don't have a quaife setup R380 gearbox. This all adds up with your description of how the vehicle performs.

Its probably also worth just confirming which diff ratio you have because of this - put the rear on axle stands, lock the diff, and spin the handbrake drum and count for 3.54 or 4.11 turns for a full tyre rotation. It would be a real shame to regear to find it already has that ratio.

Then put the whole lot into a gearbox calculator until you get a match.

Quaife ratios: R380 4X4 Transmission 5-Speed Synchromesh Gearkit - Quaife
R380 & LT230 ratios: Ratio Calculator - Ashcroft Transmissions

Originally Posted by Slunnie

I suspect something isn't right here with the information....

Quaife do ATB's rather than airlockers
Quaife I don't think do Rover diff gears.
Nobody that I've ever heard of manufacture straight cut differential gears, they do go to a lower tooth count though which increases noise a little bit.
Quaife do straight cut gears for the R380 gearbox which would be really noisy.
The Quaife R380 gears also have a first gear which is closer to 2nd and a 5th gear which is closer to 4th.

Are you sure you don't have a quaife setup R380 gearbox. This all adds up with your description of how the vehicle performs.

Its probably also worth just confirming which diff ratio you have because of this - put the rear on axle stands, lock the diff, and spin the handbrake drum and count for 3.54 or 4.11 turns for a full tyre rotation. It would be a real shame to regear to find it already has that ratio.

Then put the whole lot into a gearbox calculator until you get a match.

Quaife ratios: R380 4X4 Transmission 5-Speed Synchromesh Gearkit - Quaife
R380 & LT230 ratios: Ratio Calculator - Ashcroft Transmissions

All good info...

Originally Posted by Slunnie

I suspect something isn't right here with the information....

Quaife do ATB's rather than airlockers
Quaife I don't think do Rover diff gears.
Nobody that I've ever heard of manufacture straight cut differential gears, they do go to a lower tooth count though which increases noise a little bit.
Quaife do straight cut gears for the R380 gearbox which would be really noisy.
The Quaife R380 gears also have a first gear which is closer to 2nd and a 5th gear which is closer to 4th.

Are you sure you don't have a quaife setup R380 gearbox. This all adds up with your description of how the vehicle performs.

Its probably also worth just confirming which diff ratio you have because of this - put the rear on axle stands, lock the diff, and spin the handbrake drum and count for 3.54 or 4.11 turns for a full tyre rotation. It would be a real shame to regear to find it already has that ratio.

Then put the whole lot into a gearbox calculator until you get a match.

Quaife ratios: R380 4X4 Transmission 5-Speed Synchromesh Gearkit - Quaife
R380 & LT230 ratios: Ratio Calculator - Ashcroft Transmissions

Thanks for your experienced input, greatly appreciated, and definitely something might not be right with the info. A bit more background is that it was set up as a comp vehicle her in WA by the original owner (OO) shortly after purchase from new in early 2005 and I have only had a brief phone conversation with him after I bought it as the third owner. He sold it to the second owner (PO) around 2017 so any information was memory based from quite some time ago although there is documentation for suspension, air lockers and electrical mods. I confirmed with the second owner that he had done no further mods other than dent in the rear door and remove the interior roll bars.
So....
The air lockers are documented ARB.
OO seemed to be very proud of his diffs and said they were made by Quaife and straight cut. Again, memory can be fickle and gear freaks can embellish but it appears that Quaife do make custom gear sets ($$$$) and we are talking 2005. Straight cut vs helical is a bit of a moot and I could live with either. The ratio seems to be more the issue in terms of drive-ability.
I have confirmed the ratio as you have said for front and rear diffs, one wheel jacked up, 18 wheel rotations = 37 propshaft rotations (almost exactly). 37 x 2 / 18 = 4.11
There was no mention of R380 changes when quizzed on transmission mods. Is there a way to confirm gearbox ratios without removal. Best I can come up with is Nanocom engine revs vs road speed and compare to Ashcroft Ratio Calculator but that may have significant errors. I have changed over the speedo drive gear for a 23 tooth and now the speedo reads just over by about 1% - 2% vs GPS.

Cool, just go off GPS for speed and Nanocom for a Tach. You may need to find a quiet place so the GPS and Nanocom get time to settle. These speeds are with 32.8" tyres which is what a 285/75 approx is.

Straight cut gears are loud, really loud, you will know about it if you have these. However...

You will quickly get a Standard vs Quaife gearbox by the 1st gear speeds.

After this then check 80km/h in 4th gear for the transfer case ratio. Both boxes are 1:1 in 4th gear, so it will tell you if the transfer is 1.21 or 1.41. See below.

R380 Standard, LT230 1:41, Diff 4.11:
1st gear: 3000rpm @ 22kmh
4th gear: 2954rpm @ 80kmh

R380 Standard, LT230 1.21, Diff 4.11
1st gear: 3000rpm @ 25.6kmh
4th gear: 2537rpm @ 80kmh

R380 Quaife, LT230 1:41, Diff 4.11:
1st gear: 3000rpm @ 34.2kmh
4th gear: 2954rpm @ 80kmh

R380 Quaife, LT230 1.21, Diff 4.11
1st gear: 3000rpm @ 39kmh
4th gear: 2537rpm @ 80kmh

Originally Posted by shack

I've never owned a 90, and I'm not into rock crawling.

However I do have experience with defenders and TD5s.

The stock gearing in the diff is fine off-road in low range, you would need to be doing some serious stuff to need to go slower.

Many people seem to focus on what they will do with the vehicle when they go off-road, which is fine... But I also think about the trip getting there.

The setup you have sounds awful for that part of the adventure.

You have bigger than Stock tyres, so I'd probably leave the transfer ratios the same, but I'd be changing the diff ratios back to stock.

That should be tolerable on road and a weapon off road.

If you changed to smaller tyres I'd also look at going to Discovery 2 transfer ratios for high range.

There is also a taller 5th gear available that will reduce revs on the highway, but it's not a common modification.

But that's just my opinion!

Thanks Shack and I agree that the stock Defender diff and gearbox ratios are more than adequate for most applications. I do feel that changing the transfer box high range to 1.301 :1 is a significant improvement but really only worthwhile if the transfer box needs to come out for other work. A mild tune seems to keep acceleration sufficiently spirited for me with the bigger than stock tyres.

Originally Posted by Slunnie

Cool, just go off GPS for speed and Nanocom for a Tach. You may need to find a quiet place so the GPS and Nanocom get time to settle. These speeds are with 32.8" tyres which is what a 285/75 approx is.

Straight cut gears are loud, really loud, you will know about it if you have these. However...

You will quickly get a Standard vs Quaife gearbox by the 1st gear speeds.

After this then check 80km/h in 4th gear for the transfer case ratio. Both boxes are 1:1 in 4th gear, so it will tell you if the transfer is 1.21 or 1.41. See below.

R380 Standard, LT230 1:41, Diff 4.11:
1st gear: 3000rpm @ 22kmh
4th gear: 2954rpm @ 80kmh

R380 Standard, LT230 1.21, Diff 4.11
1st gear: 3000rpm @ 25.6kmh
4th gear: 2537rpm @ 80kmh

R380 Quaife, LT230 1:41, Diff 4.11:
1st gear: 3000rpm @ 34.2kmh
4th gear: 2954rpm @ 80kmh

R380 Quaife, LT230 1.21, Diff 4.11
1st gear: 3000rpm @ 39kmh
4th gear: 2537rpm @ 80kmh

Thanks again Slunnie. Finally had a chance to carry out tests as suggested and confirmed standard R380 and standard Defender 1.41 LT230 with 4.11 diffs, pretty much bang on the first set of numbers you posted.
The plan is to finish rebuilding the doors which are currently stripped down to fix all their attendant rattles and then do some challenging off roading to see if the 4.11 diffs are suitable for the low range work I am likely to do. TBH, I am not a rock crawler so will see how this goes.

If I am happy with the low range performance then I will change out the LT230 high range gear cluster to 1.100 : 1, giving a high range final drive ratio very similar to a manual Disco II which I really like. I am assuming changing down in gears while in low range will manage engine revs with the downside being the extra diff noise and possibly diff oils needing to be changed more frequently due the extra thermal and shear loading.

If the 4.11 diffs are over the top for me then I will change back to 3.54s. However, when (not if) the LT230 needs to come out for a leak fix, I will probably still change the LT230 high range gear cluster ratio to 1.301 : 1 as, again, this gives a final drive very similar to a manual Disco II. My son has a Defender 90 TD5 with virtually this same set up and his drives very nicely. It will be interesting to compare low range performance, particularly in soft sand, something we have a lot of over here!

Someone is pulling your leg. straight cut diff gears have not been produded for at least 110 years only some very early veteran cars had them

The 4.11 gears will be helical , most likely Ashcroft. May be Quafe ATB - but that wont be making any noise.