Damaged Diff, Recoverable? [Pics]

[Earendil]

Center will always expand when using Belleville springs. This is normal as the top cap compresses the springs against the steels.

On old steels one can often see the pressure marks left from Belleville spring behind it.

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Thanks for that piece of mind :)
And I can indeed see the marks left by the belleville springs.

So, I'm still struggling to understand how backlash is so far off (negative) to the point that it binds and I can't move it. I just finished finger tightening the pinion gear side and then turning each bolt 1/8 turn, which is so far below torque spec I don't have a wrench that'll measure where it's currently at. However, in this configuration I have the slightest bit of backlash. I'm temped to just put loctite on the bolts and see what she does in a car :-\

My other option is to try and get a hand full of shims and re-shim it, but how the heck did the internal components get bigger with time? The stock configuration should work...

[Earendil]

Without further advice, I think I'll shim it the tiniest bit with tin foil, and then loctite the bolts even though they aren't torqued to spec. I guess my hope would be that over time things sink into place, creating more lash, which would allow me to tighten the flange bolts to torque spec and still have proper lash. It's either that happens or it explodes, either way I have some closure.

I obviously can't run the diff with so little lash that it binds, but I also don't understand why it would bind on reinstallation when nothing has changed, so I don't just want to try and shim it because then I'm changing the pre-load on the bearings.

[Wanganstyle]

Did you get the top cap closed all the way?

Or is there too much metal thickness in the center stack?

You could try fitting it with gutted center lsd and see if the shims you have fit proper- if it was fine before coming out than why is it not fitting now?

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[Earendil]

Did you get the top cap closed all the way?

Yep. I even took it back apart to double check and really make sure they're tight. They are, and there is no space between the top and the stack.

Or is there too much metal thickness in the center stack?

There might be, but not too much to keep the top front sitting flush.

You could try fitting it with gutted center lsd and see if the shims you have fit proper-

I have nothing else to try, so why not! At this rate I'll be able to tear down a diff and reassembled like some sort of gun fanatic. Thank God for the impact wrench I got for Christmas ;-)

if it was fine before coming out than why is it not fitting now?

I guess that's the million dollar question. Maybe the bolts were already loose and I didn't notice.

[Earendil]

Progress update #2

So, if the dog years that were in there were actually the 2.1, that means the final thickness over stock should be:

dog year x2 + clutch x2 - Grinding x2
(0.1mm + 0.1mm) + (0.5mm + 0.5mm) - (0.25mm + 0.25mm) = 0.7mm above stock

Update: in order to get the smaller rings in the right order I have removed the 8 Allen bolts. When doing so, the center assembly popped up 0.5mm.

Without further advice, I think I'll shim it the tiniest bit with tin foil, and then loctite the bolts even though they aren't torqued to spec. I guess my hope would be that over time things sink into place, creating more lash, which would allow me to tighten the flange bolts to torque spec and still have proper lash. It's either that happens or it explodes, either way I have some closure.

Turns out this might have worked, or blown up.

Did you get the top cap closed all the way?

Or is there too much metal thickness in the center stack?

You could try fitting it with gutted center lsd and see if the shims you have fit proper

You nailed it. As posted in the primary diff thread, removing the center stack allowed the side flange bolts to be torqured to spec, and the center turns freely and smoothly 360 degrees, with what I would guess is the proper lash.

Conclusion: my center stack is too thick, and is affecting the way the bearings mate against the flange.

Now the question of a solution comes up. I have three things I could do, but without knowing how much needs to come out of the stack, I'm not sure what the best method is.

1. Pull my 3.73 diff out of my car. Remove the dog ears from it and hope they are stock 2.0mm. If I install these in the refreshed diff, I should lose 0.1mm per side. Final over-stock thickness per side 0.25mm from 0.35mm.
2. Order two 1.9mm dog years. Replace both 2.1mm dog ears with these. Final over-stock thickness per side 0.15mm from 0.35mm.
3. Have my 4mm spacer ground down X amount. Final over-stock thickness .35mm minus X, but only on one side.

#1 is free, just puts the car in more down time and really crowds my work bench ;)
Can I assume that removing material from just one side of the stack is a bad thing? If so, that eliminates #3.

Other ideas?

[Wanganstyle]

Pointless to tear apart another diff if you already have one in pieces- mystery random parts dont really help at the cost of disabling a car.

You really need to manage the centering of the stack; I suppose you have learned the hard way that its extremely sensitive to any change :)

The shims are factory oem spec range between 1.30-1.75mm on each side just to give you an idea of the play room- 0.5mm/per side for ring and pinion gap setting AND bearing load setting.

Id suggest you compare the breakdown of the original center stack measurements and see what caused the capsule to be too tall internally; obviously thicker plates and any changes will show up on the compression.

Its quite hard to calculate the stack in standard e30 format as the spring washers expand and dont let you have a direct measurement: on very complex custom built units (ie e46 fanatics post of e36m retrofit lsd into e46 non with all custom billet parts)- I switch out the 2.45mm Belleville springs during blueprint stage to 2.45mm static plates so I can test fit the center stack properly. One can have the 4mm stack spacer ground down for this. ...

Building lsd is like snowboarding; steep learning curve that often costs alot of time/money when things are not perfect. I think it took me buying/tearing apart/building and testing over a dozen diffs in my own track weapon before I got it down to a black art :)

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[Earendil]

Pointless to tear apart another diff if you already have one in pieces- mystery random parts dont really help at the cost of disabling a car.

I'll forgive you for that comment because you don't know me ;-)
I had the differential pulled from my car and dismantled on my bench in an hour. Another 30 minutes of cleaning as I went and I had the dog ears swapped.

You really need to manage the centering of the stack; I suppose you have learned the hard way that its extremely sensitive to any change :)

Quite right! I'm amazed by it, more amazed that we have this sort of engineering in such surplus that I can acquire a giant hunk of metal with this sort of precision for $200!

The shims are factory oem spec range between 1.30-1.75mm on each side just to give you an idea of the play room- 0.5mm/per side for ring and pinion gap setting AND bearing load setting.

Id suggest you compare the breakdown of the original center stack measurements and see what caused the capsule to be too tall internally; obviously thicker plates and any changes will show up on the compression.

I did not want to touch the shims, since nothing should have effected where the stack case (different name for it?) sits in relation to the input pinion gear. When I removed everything from the center stack, re-installed, and it fit perfectly I knew that it was the components in the stack somehow effecting it. I wouldn't want to re-shim it for a warped center stack :)

• I knew that each side was .35mm over stock, and that my own additions had added .25 mm per side.
• I swapped the 2.0mm dog ears in my 3.73 for the 2.1mm dog ears in the 4.10 in an effect to lesson the over stock amount.
• I also measured those "2.0mm" dog ears at 1.96mm in the contact area.
• After swapping dog years, that would make the new "over stock" amount 0.21mm per side.

Turns out this outcome of .21mm per side was an acceptable amount for my diff. Everything is now bolted back together and torqued correctly, and the diff spins freely with just the tiniest bit of lash. Since I didn't touch the shims, I'm assuming the lash is correct, or at least as correct as it was before I started messing with it :)

Building lsd is like snowboarding; steep learning curve that often costs alot of time/money when things are not perfect. I think it took me buying/tearing apart/building and testing over a dozen diffs in my own track weapon before I got it down to a black art :)

Not to mention your wrists. Snowboarding kills the wrists, taking a diff apart half a dozen times is no different :)

I'll toss (toss ) the 4.10 diff in the car after work today. If I can get it in there in a reasonable amount of time I should be able to test in on jacks tonight, and maybe even go for a drive. Jury is still out on the 3.73, though late night testing has it function A-okay with the 2.1mm dog ears instead of the 2.0, which is what we would expect.

[Earendil]

Report post first drive.

Well, she spun up just fine while on jacks without any odd noise. I took her out on the street and did a mile or so "around the block". On neighborhood streets, a 90 degree turn will cause some "noise" from the back. There is a hum/grumble when accelerating in a turn, a result of increased lock? I want to say there are other sounds and vibrations, but I'm going to have to drive some more to distinguish them. Nothing alarming though, and that's with the back end stripped out, so the diff can be heard if it wants to be :)

What are the chances that the clutches will "break in", and the sounds/increased lock will change? I'm wondering what to expect if it starts acting different.

[Wanganstyle]

You coukd break it in like a kaaz or japanese diff but honestly the zf units can just get to work right out of the box.

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[DER E30]

Any update about the clutches "breaking in???"

[Earendil]

Any update about the clutches "breaking in???"

Two thumbs up. The wheel hopping subsided quite a bit after a week, though I think it's still ever so slightly there. Enough I know but a passenger wouldn't. It has survived a couple thousands miles and 4 track days, and still locks up great. So overall a success!

[dude8383]

Nice work!

Good for referencing later :)

[DER E30]

Sweet.