4.10 LSD Whine After Swap, Bushing or Bearings?

[Sail Boat]

Hi all,

I'm hoping for some feedback on what might be causing a loud, whine/howl that's occurring after a 4.10 open to LSD internals swap.

Short story long, I pulled a 4.10 LSD from a totaled '87 325is Automatic that had 41k miles on the odo. Since the car was stored at the yard on its side, the entire diff case was awfully corroded. The insides, however, were in beautiful shape despite the mucky gear oil.

I have a 4.10 open to which I swapped the 4.10 pumpkin. The pumpkin itself was solid and bearings appeared in good shape. The install went smoothly - there was no play and I couldn't see any major gear lashing. I used Lucas Synthetic 75-90. Finally, I finished up the job by installing a Powerflex Street Urethane Diff Mount bushing.

Now there's a relatively loud whine coming from the differential. There's no clunking or grinding and no vibration of any sort - in fact it feels smoother than before. I wouldn't say it's deafeningly loud, but its definitely annoying.

I've read that Urethane diff bushings transfer gear noise, but what I'm experiencing seems a bit excessive. Albeit I have no previous experience with poly bushings.

I would note that after completing the assembly and tightening down the output seal on the crown side, the differential became very difficult to turn by hand from the pinion. I don't know if this is important or not, but its the only unusual thing that occurred during the job.

Really hoping this noise is normal for a poly bushing and not bearing related...

Thanks!

[redlightpete]

Every housing, pinion, ring gear, and bearing is a little different, so if you swapped 'pumpkins' from another diff, the bearing preload and the position of the ring gear could potentially be wrong. If you're saying that the diff became very hard to turn by hand, there's probably way too much bearing preload. Or, maybe the ring gear is forced into the pinion gear. There should be some gear lash.
I'd recommend putting the lsd parts back in their original case if that's still an option.

[e30davie]

I am a big DIY advocate, but differentials are one thing I leave to the professionals.There is alot going on inside the differential with not much margin for error.

In my limited experience a whine that comes and goes with throttle is worn out contat patch/teeth on the gears themselves. and a constant whine that changes with speed is bearings.

Remembering that a bung pinion bearing will eventually wreck the teeth on the gears, so one whine often leads to another...

As mentioned you cant just swap parts from one to another cause every diff is a little different.

If it were me, id get my favorite diff ratio, get the LSD and drop it all off at a diff shop for bearings, seals and setup. Pay the man and get a diff that is setup correctly and never have to worry about it again.

BTW, if you did have the backloask on your gears too tight (as you suggest), you have probably wrecked your pinion and crownwheel, you may be able to save them by getting them lapped but there is only so much lapping will do.

[Sail Boat]

What a bummer. I've done this in the past on Subarus, was much more successful in those instances.

I'll buy a rebuilt LSD that is in working order. It will cost me a lot more than what I paid for this project, but it will probably be worth it.

The question I have here is how long I can drive on this unit until it is unsafe or destroyed? I may need to transport it places throughout the week.

Thanks for your input.

[Bmwdayz]

You should be able to turn the pinion fairly easy by hand. you definitely tightened it to much and have a whining pinion bearing. You'll need to replace the bearing and get a new crush sleeve.

[TobyB]

I'm still trying to figure out why you didn't just stick the whole diff in intact...

so: Did you use a new crush sleeve, and follow the crush procedure for either reused or new bearings?
: which shims did you use for pinion, and for carrier alignment and bearing preload?
:did you do a gear contact pattern marking? (bluing, lead, sharpie, whatever)

The BMW diff uses shims to move the carrier side to side to set how deep the teeth mesh and to set carrier bearing preload. They look like nothing special, but they are-
ground rings available in about .002" inch increments.
Likewise, the pinion depth is set with a shim in the pinion stack.

I have had some luck keeping the spacers with the gears as I swapped them into different cases-
it seems that the gears are more variable than the cases.
But even then, I've had to adjust a bit- and once, it was so bad that I just gave up
and grabbed a different set of parts. Yes, it could have eventually been dialled in,
but either I messed up the shims completely when I tore things apart (possible)
or the case the parts came out of was very non- standard. I'm far from a pro,
don't keep shim sets around, and use the results for racing, so I'm pretty cavalier
about it, compared to a real shop. But it usually works. Mostly.

t

[Sail Boat]

I swapped the internals because the case was in terrible shape. I transferred the shims, but I used the pinion from my existing 4.10 Open... I'm assuming this is where the issues have originated.

No big deal, in the end I really didn't expect this to be so simple, but for $50 it would have been nice! I've got a fully rebuilt 4.10 on the way that I found for $750. At first this seemed a little expensive, but considering my local shop wants $1,000 to rebuild this existing case, it doesn't seem so bad.

Hopefully it's the last diff I'll buy.

[TobyB]

You used the pinion shims from the open diff, or the pinion gear itself?

If you mixed gears, yeah, that doesn't usually work so well...

t