"whinning" or high freq sound from rear diff...

[nsbone_1988_520i]

my e32 has got this "whinning" sound from rear diff i think. This can be heard from inside the car during car moving at any speed...

I have changed rear wheel bearings... so my next action would be changing rear diff or i could change some bearings inside the rear diff?

tia,
rahman

[joshua43214]

Find a nice flat or slight incline that you can drive at a steady speed that provides stready load on the differential. Aply light throttle and listen for a whine. let off on the throttle and listen for the whine to go away. If the whine comes at load but goes away with no load, this is indicative of worn pinion bearings.

verify that the carrier bearing is not the cause of the whine.

You will need to raise the rear wheels and have an assistant run the car in drive while you listen to the differential with a stethoscope to isolate the pinion bearings from the side bearings. The carrier bearing can often be diagnosed with out doing this.

The pinion bearing is not a do-it-yourself job, but you can maybe do the side bearings if you are brave. There are ways to replace pinion bearings with out all the special tools, but none I would recomend to someone who has never had experience with diferrentials.

[shogun]

Well, first of all you have to be sure if it is the differential
http://www.nmia.com/~dgnrg/page_16.htm
Or could it also be the driveshaft end which goes into the differential?
There is a repair on Johan's page under driveline, but at the moment the link does not work. Try later again
http://bmwe32.masscom.net/

[nsbone_1988_520i]

Joshua,
I think the sympthon more like worn pinion bearings as in your post below... would i be better of get another one from junk-yard?

Shogun,
i was also contemplating to change to Redline diff oil... should i do this first?


Find a nice flat or slight incline that you can drive at a steady speed that provides stready load on the differential. Aply light throttle and listen for a whine. let off on the throttle and listen for the whine to go away. If the whine comes at load but goes away with no load, this is indicative of worn pinion bearings.

verify that the carrier bearing is not the cause of the whine.

You will need to raise the rear wheels and have an assistant run the car in drive while you listen to the differential with a stethoscope to isolate the pinion bearings from the side bearings. The carrier bearing can often be diagnosed with out doing this.

The pinion bearing is not a do-it-yourself job, but you can maybe do the side bearings if you are brave. There are ways to replace pinion bearings with out all the special tools, but none I would recomend to someone who has never had experience with diferrentials.

[shogun]

Well, you can try the stuff.
On the other hand a diff is not that expensive from the junk yard.

[AllGo'n'Show]

Have you replaced the diff anytime in the last little bit?

When you swap one diff out for another but keep the same gears in there, atleast this is true for domestic modding, haven't looked at a BMW diff but pretty sure they all the same design, anyways... if you keep the gears but change the diff out, you have slightly changed the telerances and clearances of bearings, location of the diff to the gears, therefor when the gears were first put in, the worn down in one spot on every tooth, making smooth mating surfaces, no noise. If you change the diff, then it may be out by just the tinyest bit cause that worn spot to no longer be the place of contact, creating noise, creating a whinning.

If thats the case, no problems, just noisey.

[joshua43214]

Have you replaced the diff anytime in the last little bit?

When you swap one diff out for another but keep the same gears in there, atleast this is true for domestic modding, haven't looked at a BMW diff but pretty sure they all the same design, anyways... if you keep the gears but change the diff out, you have slightly changed the telerances and clearances of bearings, location of the diff to the gears, therefor when the gears were first put in, the worn down in one spot on every tooth, making smooth mating surfaces, no noise. If you change the diff, then it may be out by just the tinyest bit cause that worn spot to no longer be the place of contact, creating noise, creating a whinning.

If thats the case, no problems, just noisey.

The comments about replacing the differential are actualy about replacing the entire final drive assembly. generaly BMW final drives are not repaired by the DIYer but are replaced as an assembly, or sent out for repair.

Many people don't understand that the "differential" is actualy and assembly inside the final drive, and the folks who do, toss the word arround loosely since they can tell when someone is talking about a differential or a final drive by the context.

You are more or less correct that they all share some common parts such as a ring and pinion gear, and that the ring gear is attached to the differential. after that there are many variations as to what is actualy inside the differntial. If you have whining after replacing parts, then the dif was not reassembled properly, and it will wear faster.

[AllGo'n'Show]

Never heard any of the mechanics or enthusiasts I work with or know call ti final drive, maybe in another language or slang. Diff = 2 axles in, spider gears and springs/clutches *varies between LSD, Open, designs, etc...*. Final drive I could see being all new pinon gears and such, but not just the diff unit alone.

[nsbone_1988_520i]

Hi,

I just finished changing the whole rear diff with another one (from junkyard). Took me and my helper about 12 hours. Well he did most of the job, except the difficult ones. (He's a mechanics himself, but he's been learning lots of tricks to fix BMW from the very little knowledge that i know).

Wow! THis 7-series is very different from my 520i e34 and e21 models... and so so much difficult especially when putting it back, and that gasket at the universal join... i just did one test drive and there's no more whinning sound... well it's 11pm and i've been working since 11am in the morning to do this one... Perhaps i should ask a workshop to do it for me next time...

I just used 75W90 LSD rear diff GL-5 grade (non-branded) and i hope it's ok.. Tomorrow morning will be busy day for a full test.. i hope it's all fine...