techs with rear end setup experience please read

[island03z]

If youve worked at a shop that installs and repairs differentials id like to know a couple things.
Ive just installed my first limited slip today and i didnt have as wide an assortment of side bearing shims as i needed so i tried to get it as close as possible but sadly theres a harmonic oscillation noise in the 45-55mph range.

Notes: Total preload was about 1 foot pound. I dont have a beam type tq wrench in inlbs and no one on the island seems to stock them(spec was 26-33in lbs)
Backlash was .0041-.0051in measured in 4 spots (spec is .0039-.0059)
Contact pattern was showing toe bias on both sides of the teeth
1. Does a shop buy an entire shim set for each vehicle they work on?
2. Each shim costs me 22 dollars. Is there a way to calculate what shims i need to buy before i buy it?
3. Would using brake cleaner to clean the case out contaminate the gear oil when i fill it up later?
4. My contact pattern bias says i should increase backlash but my backlash is within spec. Where should i go from here?
5. Is my car driveable for a while until i can get the shims needed or would i damage my brand new differential?

Any help with these questions is greatly appreciated. Thanks

Topic

[island03z]

Awesome, thanks for the replies. Definitely a learning curve but im glad its finally right.

[EricTheCarGuy]

IDK. If I look at the pattern on the gears it seems to move from the outside to the center and then inward. The depth looks good but the pattern is off, at least to my eyes. It should remain consistent over the entire ring gear. This might indicate that either the ring gear is warped, the carrier is not installed correctly, or something with the bearings. You usually put the carrier assembly in the freezer for a while before you install the ring gear to help it go on better. You want to avoid drawing it down with the bolts. Take a close look at the pattern and you’ll see what I mean. This inconsistency may be the source of your oscillation.

Perhaps my eyes deceive me. If you don’t have any issues after you’re done then I would ignore everything I just said.

[island03z]

Hey Eric, I see what you mean in the picture. Honestly I can’t remember if it was like that in person. From what I recall it looked pretty uniform. You bring up an interesting point on the installation of the carrier and ring. The original Nissan carrier had a tight fit with the ring but this aftermarket Quaife didn’t. In fact I don’t remember having a problem mating the ring to the backing of the Quaife but I did finger tighten the bolts in opposing patterns and then gradually torqued them to spec in increments. At one point it did seem like there was a variation somewhere when I had zero backlash, the gears could spin on majority of the teeth but in a certain section it would bind.

At any rate I installed the diff and it’s VERY quiet now and all the oscillation noises are gone. I do hear a bit of chatter sometimes at 50mph at low throttle position but I’ve attributed it to the polyurethane subframe bushing that I had to replace transmitting more noise through the chassis. Unless you think I should go back into it and reseat the ring gear to the carrier, I’m pretty happy with my first rear end setup. Thanks to everyone who helped out I appreciate it.

[EricTheCarGuy]

If things are working now I’d leave them alone. If they get worse and the bushing you spoke of does not solve the problem then you might consider going back to recheck things afterward. Thanks for the updates. Keep us posted of any new developments.

[Author]

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