I had 4.08 gears installed and the diff is humming. I bought the gears on here and they were used. I paid a mechanic to install it. Is the humming due to a mistake during installation or because they're used?

 

Basically wondering if I should get this mechanic to fix it or if i just have to deal with it. The hum is not super loud but its noticeable even with low music on. They were used but looked to be in great shape.

 

IIRC, the humming could be because they are shimmed incorrectly or the driveshaft might not be 100% aligned.

 

So is it possible that the set of gears they sent me are not correct? Like the ring gear is 4.08 and the other gear was from a stock set? Would that work at all or would it work and hum like i have? Now I'm hoping that more than likely something is just not aligned perfectly? If that were the case I would not feel bad taking it back to him.

 

If it's humming, take it back before the diff. goes out. It's not right.

 

Thanks that's what I needed to know. I drove it for two days I hope its not screwed or anything. Hopefully the mechanic guy sorts this out for me.

 

Its most likely a backlash issue or the pinion depth could be wrong. Also where new bearing installed? If not worn bearing( pinion bearings) can give you a high speed whine.
I put my money on improper gear setup.

 

Did you also install new aftermarket bushings?

 

I had all new bearings and everything. I bought a z1 motorsport install kit. I gave the guy the car this morning and he said something about pinion gear depth so hopefully thats it.

 

Yea, hes going to have to tear is down and rebuild it to fix pinion depth issues.
How did he mess that up I wonder?

 

I'm no mechanic so I have no idea...

 

Voboy asked the right question, did you install aluminium bushings

 

I'm 99% sure that its a ring/pinion setup being done incorrectly (in ref. to backlash, pinion depth and contact patterns).

 

Getting the correct tolerances with exact shims and/or combo of shims is critical to the entire pinion/ring gear install, that is why the parts list of the various shims available (as I found out) is so large. I'm lucky to have a great mechanic who races, master mech. etc. and he explained a lot to me when installing my 3.9 fd, he put gears in and back out about 3 times while diff. was on the table and we had to try several shim sizes; he said mine is actually now better tolerances than factory and I've had zero issues. *Not everybody who says they can install new gears can do it right and slap it all together with just the stock shims, etc. I wouldn't doubt that the "hum" sound is due to ring/pinion engaging way too deep and needs to be backed out even a few .000's!

That is why you don't get any shims when you order your gears, it can be completly different with another car that's exactly the same year/model. Good luck with this all, but like some guys mentioned, I'd get it taken out and done right; and man, don't drive much at all. *the shims were about $18 per and I bought a few extra ones that ended up not being needed, but well worth it to give your mechanic any and all that he may need to get it dialed in right.

 

I hate this forum anymore...

The reason why we bring up the bushings is because if you have aluminum bushings, it will hum and howl...

 

Bushing will not make that big of an issue. I'm taking a wild shot in the dark as you probably have never been inside a diff. ( yea I was going to say rear end haha). It is a issue with how it was setup. I know for a fact that I have seen race car (dirt track and drag) cars with gear setups completely quiet and with solid mounts.
Ring and Pinions noises make a very distinct sound, along with worn bearing. I'm not going to get into the pissing battle with people of this forum, I offered my option base off my experience with setting up the countless Dana and Ford rear ends (this meaning turning wrench not CTRL C CTRL V off the internet).

 

This is why I hate this forum...

 

This reason I dislike this forum is due to 95% of the stuff up is is ******** bickering,I am willing to be over 3/4 of the people who are on this forum have never even gotten their hands dirty, most wont even change there own oil.

 

Alright, because I have never worked on a car or been inside and out building a 350z... I will offer some information that more experienced people would know, the aluminum bushings for the 350z/G35 are notorious for making alot of howling noises... Mine howled like crazy. Is there a chance he did not shim it correctly? yes, but if he answered this very simple question we could at least rule out that it is not a bushing replacement issue.

 

My statement was more generalized for the people of the forum, not you specifically.
We will see, hopefully he will tell us what the fix is. I might be wrong, it wont be the first time.