V2 Diff rebuild + Gear Ratio Swap

[maupineda]

I have measured breakaway torque on the spare diff and it read 65nm or 48 ft/lb. Not sure that is ok, or too low.

[maupineda]

I took a few moments to measure backlash on what I assume is the factory setup.

it was .0025 to 0.003in, or 0.06 to 0.07mm so I know what to aim for. I was thinking the correct value would be 0.1mm, but now that sounds like much.


This is how I setup the tool


start



end

[sapote]

Yes, backlash between pinion and ring is very small.

[maupineda]

I pressed the E36 bushings, it was pretty annoying at first as I tried to use a c-clamp tool and it did work partially, but it was not the right tool so I stopped and used a small mechanical press that was available at work

a few things to note:

a) use a press, period.
b) use the front diff bushing to drive the diff cover bushings in, is right on perfect!
c) clean and file the inner cover holes as the bushing are a very tight fit.
d) press them until it bottoms out so they are flush with the back side of the diff cover

[bmwfnatic]

I have measured breakaway torque on the spare diff and it read 65nm or 48 ft/lb. Not sure that is ok, or too low.

I have a V2 diff sitting here that I measured a while back and I barely got 50Nm out of it, sometimes less, so by that logic yours is better than mine.
I believe though in their video's the Racingdiffs people state that they want to achieve 100Nm+

[bigjae46]

I have a V2 diff sitting here that I measured a while back and I barely got 50Nm out of it, sometimes less, so by that logic yours is better than mine.
I believe though in their video's the Racingdiffs people state that they want to achieve 100Nm+

120nm I believe.

[maupineda]

Specifically to the GKN V2 LSD; it is 100NM for their V1 rebuild kit, and 125NM for their V2.

The GKN V2 unit has more clutches and steel plates compared to GKN V1, however, the V2 rebuild kit form racing diffs for both GKN variants has the same number of plates (clutch and steels), but there seem to be differences within components of those as the packaging space for the clutch stack is different. My hypothesis is that the big bevel washer is what causes the GKN V2 unit to not lock as the viscous unit compresses the washer rather than locking the clutches.

My approach will be to replace as many clutches as I can (5 as that is what is in the kit) and reuse the OE clutches to maintain the same setup. as for the free play shim, I will look at whether I use flat washers to reduce lash, or go to a softer spring to avoid wearing out the spider gears. I plan to stick to the 25% rule which for the S54 is about 88NM of breakaway torque.

[sapote]

1. Specifically to the GKN V2 LSD; it is 100NM for their V1 rebuild kit, and 125NM for their V2.

2. The GKN V2 unit has more clutches and steel plates compared to GKN V1, however, the V2 rebuild kit form racing diffs for both GKN variants has the same number of plates (clutch and steels), but there seem to be differences within components of those as the packaging space for the clutch stack is different.

3. My hypothesis is that the big bevel washer is what causes the GKN V2 unit to not lock as the viscous unit compresses the washer rather than locking the clutches.

4. My approach will be to replace as many clutches as I can (5 as that is what is in the kit) and reuse the OE clutches to maintain the same setup.
5. as for the free play shim, I will look at whether I use flat washers to reduce lash, or go to a softer spring to avoid wearing out the spider gears. I plan to stick to the 25% rule which for the S54 is about 88NM of breakaway torque.

1. It makes no sense why V2 needs more preload for clutch than V1. The breakaway torque should be determined by the pump piston active travel range, not by the number of clutch plates. Ideally an LSD (or any diff) should have zero breakaway torque as this robs engine power during a turn. But since the pump once activated its piston doesn't travel far enough to lock the clutch 100% and so this is the reason why the piston needs to preload the clutch. If Racing Diff called for 125Nm preload then I agree because they use the spring washer on the clutch. Why do they want to use spring washer? It saves their labor to set the clutch total thickness for the installed pump -- cutting corner in my opinion. Having the spring washer is the main reason that the LSD might loss its locking performance down the road. We should use flat shims and take time to set preload as stock.
2. IF RacingDiff V2 kit has the same number of clutch plates as V1 then the higher locking torque of the updated V2 design is nullified.
3. the big bevel washer -- are you referring to the stock or RacingDiff part? I don't think the stock unit has bevel washer for clutch.
4. I'm confused. You will replace with new plates but reuse the old plates for what?
5. Reducing the spider/side-gear backlash -- this is not a high precision by design and so I would use flat shims to reduce the backlash down to around 1mm or 0.030" (10x more than your measurement on the pinion/ring plays), (or even 0.020" as I don't remember the stock clearance for comparison). No reason to reduce the spider plays down to zero using spring shim, hard or soft.

[bigjae46]

Specifically to the GKN V2 LSD; it is 100NM for their V1 rebuild kit, and 125NM for their V2.

The GKN V2 unit has more clutches and steel plates compared to GKN V1, however, the V2 rebuild kit form racing diffs for both GKN variants has the same number of plates (clutch and steels), but there seem to be differences within components of those as the packaging space for the clutch stack is different. My hypothesis is that the big bevel washer is what causes the GKN V2 unit to not lock as the viscous unit compresses the washer rather than locking the clutches.

My approach will be to replace as many clutches as I can (5 as that is what is in the kit) and reuse the OE clutches to maintain the same setup. as for the free play shim, I will look at whether I use flat washers to reduce lash, or go to a softer spring to avoid wearing out the spider gears. I plan to stick to the 25% rule which for the S54 is about 88NM of breakaway torque.

I never looked but the clutches and/or steels might be different thicknesses as well.

I think you're better off using the free play shim. There's no evidence that it accelerates wear on the spider gears.

[maupineda]

...
3. the big bevel washer -- are you referring to the stock or RacingDiff part? I don't think the stock unit has bevel washer for clutch.
4. I'm confused. You will replace with new plates but reuse the old plates for what?

The new kits (Version 2) have the free play shim, which is just a Belleville washer, and another on the pump side. This is something they seem to have introduced not long ago, and what they call an improvement

You can see bellow how the kits are almost identical, but one of the steel plates is thicker on the set for the GKNV2 LSD, and the big spring washer has holes.

GKNV1 Kit



GKNV2 Kit



Since the kit only comes with 5 clutches and 6 steels, I need to reuse 3 OE clutches to have the same setup. I may also need to swiss cheese steels to maintain the overall thickness the same and shim accordingly to achieve the 90NM breakaway torque.

OE GKNV2 has 9 steel plates, and 8 clutches

I used to have the count for the GKNV1, but forgot. Maybe someone that has open the GKNV1 unit can confirm how many steels and clutches there are. but for sure is less. I think that is why the V2 unit can handle the torque of the S85 V10 as is the same unit.

[sapote]

The new kits (Version 2) have the free play shim, which is just a Belleville washer, and another on the pump side. This is something they seem to have introduced not long ago, and what they call an improvement

You can see bellow how the kits are almost identical, but one of the steel plates is thicker on the set for the GKNV2 LSD, and the big spring washer has holes.

I watched their V1 rebuild video (listed in your first post) again and noticed the following:
OEM has 8/7 plates and the old worn stack total thickness is 13.26mm for that particular diff being rebuilt. No spring or any shim.
Back then their new stack had 8/7 plates also, and total thickness is 13.77mm. No spring or flat shim.

So why now their V1 kit has 6/5 plates and a spring shim? I think they tried to avoid the problem of having the breakaway torque too high or too low due to the stack total thickness a little too much due to part tolerance. So it's easy for them to reduce from 8/7 plates to 6/5 with a little thicker plates and add a spring shim for compensation. This is not a high performance end goal but cheaper way to make the kits. 5 clutches compared to OEM 7 pieces and so no way that their locking torque is higher, and the spring shim only can reduce the performance further. I would throw out the spring shim and add flat shims to get a total thickness = 13.77mm.

Can you measure the V1 kit total thickness without the shim, then measure the spring shim thickness at the edge only, not across the whole plate?

[maupineda]

I measured the V2 kit for GKNV2 unit

Steel Plates - 1.03 mm (5)



Thick steel plate: 2.02mm (1)



Clutch plates: 1.1mm (5)



Total stack based on Individual component values - 12.67mm

The big spring washer that goes on top of the stack and between the lsd pump is 4.6, and can compress flat to 2mm

so total value is ~17.27mm (uncompressed) or 14.67mm (compressed)

I also calculated the load the washer needs to compress flat and is 3300N or 320kg (~700#) of force which is meaningful, however without knowing the pump capacity I don’t know if this is much or not; hydraulic pumps have high force capabilities, so if we make an analogy to a car jack, you get the idea.

the “free shim” washer needs 2000N to go flat, so I don’t like that much preload for the spider gears. So I will go with flat shims and leave some slack (0.1mm).

[sapote]

Since the kit only comes with 5 clutches and 6 steels, I need to reuse 3 OE clutches to have the same setup. I may also need to swiss cheese steels to maintain the overall thickness the same and shim accordingly to achieve the 90NM breakaway torque.

OE GKNV2 has 9 steel plates, and 8 clutches
.

Adding 3 more of the OE plates for a total 8 clutch plates won't work, as the total thickness is too much for the pump to sit stablely.
Assuming V2 and V1 having the same clutch parts by the factory.
So V1 8-plate = 13.7mm, then V2 with 9 plates should be 15.4mm
Your masurement of the v2 kit is [14.67 : 17.27mm], "so total value is ~17.27mm (uncompressed) or 14.67mm (compressed)"
To lock the pump properly the spring washer has to be compressed to have the total thickness = 15.4mm which is achievable. But adding 3 more OE clutches will exceed the magic number 15.4mm.

[maupineda]

Another data point, the original stack height is ~14.2mm, this is on a god knows what mileage, but at least I know is not completely shot as it still has 65NM of breakaway torque.


I tried measuring the steel plates and clutches and seem the are 0.8 each

[sapote]

Another data point, the original stack height is ~14.2mm, this is on a god knows what mileage, but at least I know is not completely shot as it still has 65NM of breakaway torque.

Good piece of data. I wonder what is the thickness of the brand new stack - more than 15mm? The pump must have an internal spring to provide the breakaway torque on a used worn stack, as there is no spring washer used on the original diff.