Strange noise coming from the rear

[Ken92SVX]

Hi all,
I posted a tread early about a high pitch whining noise while driving. I finally had some time to do some further trouble-shooting. I checked underneath the car and did not find any vibration related causes.
I then rotated tires- no change in noise.
Put in FWD fuse and noise went away.

For now I am pretty convinced the noise is coming from somewhere in the drive train. I had also changed the fluid in the rear differential and checked the plug. I found no evidence of gear damage there.
I also pushed and pulled on the drive shaft all the way back and everything seem to be OK from what I thought.
The strange noise appears to change pitch/frequency when driving the faster I go the higher the frequency.
It is throttle related- if I let of the gas, it changes briefly, and then it comes back.
Any thoughts as to what in the rear/drive train that could cause the noise?

[Manarius]

Clutch packs are the only thing that really have anything to do with the rear driveshaft. Perhaps these are worn out. However, a high pitched noise doesn't really go with them being worn out, but it's possible.

[Ken92SVX]

Jason,
Thanks for the reply. When you refer to clutch packs, are you talking about the clutches in the transmission or what? If so I assume these clutch packs transfer the load/torque to the rear wheels as needed, is this correct?

[TomsSVX]

Yes, but to be completely honest, it sounds like a differential failure in it's premature stages. Are you showing any transmission codes?

To

[Manarius]

Yes, but to be completely honest, it sounds like a differential failure in it's premature stages. Are you showing any transmission codes?

Tom
Could be differential as well. I counted that out because of the FWD fuse causing the noise to go away, but if the center diff is going, then it could just be a fluke that it goes away under FWD. I thought clutch packs because they're "turned off" when you put in the fuse.

[Ken92SVX]

Thanks to all who replied,
I do not have any codes that I got out of the car. I went through previous maintenance history on the vehicle that previous owners left. It looks like the rear differential had leaks and it may have pretty much run out of oil before. The vehicle last summer went from Colo Springs to Alaska and back. I am afraid that the rear diff may have been oil straved at some point.
How much would it cost to have the rear diff rebuilt? Does anybody have an estimate?

[TomsSVX]

I have several in house, $125 + shipping will get it to you

Tom

[Ken92SVX]

I sent you a PM on one of your rear differentials.
Please check your private messages.

Thanks, Ken

[Yoda3000]

I have a similar problem. When I drive with my windows down (next to a curb) I hear a buzzing noise coming from the rear. It is speed (and not throttle) sensitive. Best heard at 30 mph and up. I haven't tried the FWD fuse but I will.

I suspect it's the rear diff. How do I change the fluid and how difficult is it to swap a rear diff? I have a spare, with all 3 axles still attached. Thanks.

[Suby Fan]

changing fluid is pretty easy other then the fact that you have to support the car by 4 jack stands to keep it level (some thing i dont need to worry about) :p just remove the bottom drain plug and let it drain put it back in and remove the top plug and fill it untill fluid is coming out...

[Yoda3000]

Ok, I tried the FWD fuse. WOooooo 2WD svx is funny! :p

Nope, noise persisted. Then I lifted the car and looked underneath, no fluid from rear diff. so I can only assume it isn't leaking. This must be a different problem from yours. Either way I'm taking it to the dealership on monday for something else, i'll have them check this out too.

--Mike

[nipper]

Could be differential as well. I counted that out because of the FWD fuse causing the noise to go away, but if the center diff is going, then it could just be a fluke that it goes away under FWD. I thought clutch packs because they're "turned off" when you put in the fuse.

If these are like the rest of the sooby line (correct me if i am wrong), there is no center differnential, just the clutch packs. The manual soobys have a center diff.
A rear diff will roar as it gets worse (and i do mean roar), and it usually takes a long time for it to self destruct. The reason that it went away with the fuse in is because the differnential was no longer being driven by the driveshaft, it was now driving the driveshaft. This changes the force of thrust from one side of the gear to the other (which has less wear).
Its hard to determine a bad diff by examination if you dont really know what your looking for when it first starts. You usually need to but a dye on the gears and see how they mesh. Thats why mechanics take a wait and see attitude with the diff. If it is the diff, it will get worse with time.
Just an FYI there is also a carrier bearing on the driveshaft on most soobies, as the driveshaft is in two peices with a set of universals. When this goes it is a clunk in the middle of the car.

nipper

[Ken92SVX]

I finally got around to changing the rear differential and luckily it fixed my problem. I no longer have the hi pitched noise coming form the rear of the car. :o