I'm waiting on the vid cam to charge so I can get a video of the noise, but in the meantime... has anyone noticed an odd humm after the 4.083 gear upgrade? I just got the car back from the gear install and the shop who did it swears the gears are fine. I've had an odd humm before but this is a lot louder. It typically happens on deceleration. Ideas of what/where to check? Maybe driveshaft vibration?

Any ideas appreciated.

 

They probably set the gears a bit on the loose side. This makes them whine a bit. Is the sound gear dependent or just speed dependent?

 

Seems to be speed dependent - when I decelerate you get the noise. Here's a vid I made last night.

http://www.youtube.com/watch?v=crj53Ilbcs8

Whenever I decelerate you can here the whumwhumwhum noise... especially towards the end of the vid. Make sure you're sound is up - it's a LOT louder in the car.

Ideas?

 

I noticed this morning it seems more pronounced in the higher gears. Don't really hear it in first or second but that could be because I'm not getting enough speed.

 

4.08 gears are really high strung. its probably the tranny winding down. sounded normal to me with gears that are so quick. my car makes that noise with the stock ratio gears in first or second if i let off high in the rpm range in the same gear.

 

Just climbed underneath and the rear subframe bushing is busted (have the black streaks from the silicon filling all over). Would that cause the noise change?

 

I imagine that would change the sound paths - could certainly be part of the problem. Although, it was likely that way before you changed the rearend, so, dunno.

 

sounds like you (unfortunately) need to have a talk with your installer

 

Some more data - I jacked it up on a lift yesterday, put it in gear, and "drove" it up to about 70mph. Not a hint of whine or anything - entirely quiet. So whatever is causing the whumwhumwhum on deceleration only happens when there is a load on the diff/suspension/drivetrain. Maybe a bearing in the diff?

I setup an appointment with Forged on Thursday. Hopefully they can check everything out and tell me what the hell's going on with it.

 

d

 

Did you have new bearings installed in the diff when changing out the gears? If not I would be concerned with the pinion bearing, with a noise like you are describing that is often going to be the cause of it.

 

Yep, all new bearings used - I got the Install kit #1 and #2 from Z1 (http://www.z1auto.com/prodmore.asp?m...ne&prodid=2833).

 

If you've got all new bearings I would be concerned with the preload on the bearings and the clearances in the install. Setting up a ring and pinion properly can be tricky, so it's not uncommon to have issues with the install.

 

sounds like a pinion bearing problem to me too. There is only one way to set up gears and loose is not it.Best to get it fixed pretty quick or the gear set will develop a howl that will never go away.

 

did you use a new crush sleeve? ($10 from dealer)... I think the pinion pre-load theory could be the problem - and if the old crush sleeve was used, it wouldnt have the proper load.

Here's a link that might help:

http://www.bernardembden.com/xjs/diff/index.htm

I hope the installer doesnt charge you to take appart and correct, if this is the issue

 

I will take a listen when you get here. Definately should not make any significant or meaningful noises. If it's whining, especially after just 25 miles, something is probably out of spec.

FYI, we didn't do the initial install, in case anyone was wondering.

 

Yes, new crush washer/sleeve was used. I made the decision to not go back to the installer - I'll pay someone else to diagnose and troubleshoot (Forged).

+1 to Sharif's post - didn't mean to imply they did the original work. Forged has always given me good service, which is why I'm taking it there for a second opinion.

 

Great find on the article!

 

I'm very interested in the outcome... it is a peculiar sound - and very pronounced.

 

A bit off topic, but how does the car feel with the new gears? Can you tell a big difference? What year is your car?