Hello,
I drive a Camaro 98 convertible 3.8 auto.
I have changed my drive shaft and everything was good up to yesterday.
After driving on highway 130km/h during one hour, the rear axle is "singing". A noise like a wind noise and frequency increases with speed up to 80km/h then becomes not audible.
I suspect a wheel bearing noise and get up the rear axle to try turning wheels by hand on neutral position. No noise but of course speed is very low !
Oil in the axle has been changed same time drive shaft was, and I see they used "huile de boite" (manual gear box oil). Not sure this is good. The book says "75 - 90 oil".

Thank you very much for your help.

 

its a very good possibility they didn't use the right oil, in addition, if they didn't add any friction additive, that may be an issue as well

 

Thank you for your answer. First of all, I'll replace oil + additive. And of course a new gasket seal...

 

Additive ? for a posi rear? Posi rears in 3800 is optional but pretty rare. The axle turn test is not very accurate, in fact the bearing has to be pretty bad to feel it will almost no weight on it and turning so slow. Also you are assuming it a wheel bearing not a differential bearing or pinion bearing. You want to drain the oil and look for metal or flakes of metal in the oil. If there is a lot of metal or flakes then all the bearings in the rear are "at risk" because of the metal going through them. Replacing the bearings in the rear should be left to professionals. Setting up a right and pinion is not complicated but it is very unforgiving. One small mistake and its a complete do over.

Since the wheel bearings support the weight of the car they tend to change pitch as you add and remove weight. AKA weaving while driving. As you weave to the right the weight of the car loads on the left side. If the whining get louder then the issue is left wheel bearing. When you weave to the right the opposite should happen. At least if its a wheel bearing. If the noise does not vary much then you are talking differential or pinion bearing. We can get into how to figure out which one but if you tearing the rear a part anyways then you should just replace all of them. If the weaving shows it is a wheel bearing and there is not a lot of metal in the oil check youtube for how too replace wheel bearing in GM rear axles. You may need an offset bearing or a axle repair sleeve depending how bad it is.

Depending on you and the condition of the car the most economic way to fix the rear may be just to replace the whole rear. You could get a posi and a different gear ratio if you wanted for a few hundred dollars. Rear failures are pretty rare n the 3800 since its the same rear as the V8. Most likely you just had the luck of the draw and the bearing was not great from new. If you start with a good rear you can swap out axle seals and bearings and the pinion seal and be ready for another 100+K of miles.

 

Noise is exactly the same turning left or right.
The pinion seal has been changed due to oil leak, but not bearing because it seems to be OK. This was done 150 miles ago same time drive shaft and rear oil changing.
There was no metal parts into the old oil.
After this, the 50 first miles has been perfect. I drive to Bordeaux (90 miles) on the highway and when I slow down to pay taxes, the moise was here for the first time.

 

The GM procedure to replace the pinion seal requires a new crush bushing and a resetting of back lash and preload on the pinion bearing. Because of the cost involved most mechanics will skip this process. Just a guess but I think you mechanic did not do this and it screwed up your preload on the pinion bearing and now its toast.

Why did you have to change the drive shaft? Was the car shaking? If the car was shaking due to the drive shaft there is a chance the bearing was already damaged when you swapped the pinion seal. These early surface cracks would be undetectable for a while until the car got a few miles on it. I have seen issues show up 3 months later.

Since the differential bearing and the pinion bearing rotate a different speeds you can download a vibration app on your smart phone and see the megahertz of the vibration at 2 different speeds. You can do the math and see which vibration is running with which speed, Axle speed or driveshaft speed. If this is a automatic run the car in 3rd gear under light load the drive shaft should be turning very close to the engine RPMs with the axles turning 3-4 time slower. If you want to get pin point accurate run the car in forth gear under light load and add in the overdrive ratio then look up the your rear ratio on you options tag and you should be right on with real turning speeds. Again it may not be worth it since you are pulling everything a part IMO you should replace all the bearings either way.

 

Yes, my mechanic did not do anything but changing the pinion seal.
He also changed the shaft because the middle joint was dead and it crushed and the car was shaking.
The front and rear joints are new end the central bearing is new.
I'm waiting for a one part shaft but the truck mechanic who accepts to make it is ... in late !

Today, raised the rear on two candles so the rear wheels are free. I turn on motor and put gearbox on Drive.
The noise seems to come from the middle of the car along the drive shaft. I'm sure it's not from the wheels.

Gearbox bearing, pinion bearing or central shaft bearing (it's new !) ?

 

I would touch the center drive shaft bearing then touch the differential (gear box) housing and see in which component feels like a stronger vibration. Sure seems like seem to my like its the pinion bearing. You have two possible causes, One the vibration from the drive shaft and two the loss of preload on the pinion bearing. Either one could cause a pinion bearing failure.

Vibration speed is the only real way I know how to know if its is a pinion or differential bearing, Back in the day before cell phones I used a reed tachometer. Think Guitar tuner to figure out the harmonics . Like I said before though, does it really matter? the cost of bearings is not that high. If you need to replace any one bearing in the rear you have to set it up, Preload, back lash and you will need to check the tooth pattern. This process is the expensive part of the repair. I can not imagine reusing old bearing when setting up a rear. You are going to need to buy a bearing kit a crush bushing and a new pinion seal either way.

If I was doing a $500+ repair on a rear and the customer wanted to save $40 to reuse old bearing I would turn the job down. There is just too much chance one of the bearing not making noise has 100 miles of life left in it. Then no matter what I do my customer will think I messed it up.

 

I did exactly what you tell me.
Rear up - Wheels free - moteur running for max noise (1300 RPM) - drive position.
But this time I lay down under the car (I know it is not very safe...) and listen with a piece of wood as a stethoscope : there is no doubt, max noise comes from the central bearing yet new! May be because it has been used for a few hundred miles with a broken central joint before changing the drive shaft ?

I also understand what you said about any work on axel bearings. The two pinion bearings are conics and to change the seal my mechanic removed the central nut and then screw it up but not with the appropriate tightening torque. It's not possible to fellow the process if the pinion is not free and if it is engaged with the differential. A too much tightened conic bearing will be quickly dead !

Now, I don't know what to do. Only change the central bearing or a complete restoration of the rear axel ? My car is only 65000 miles.

 

When you say central bearing you are referring to the Carrier bearing in the middle of the drive shaft? If that is where the noise is coming from I would not mess with the rear until it is needed. A lot of mechanics get away with not following procedure on the pinion seal. I would say most of the time 90% or so the car can go another 100K.miles.

That taper bearing in the pinion likes pressure. If it fails after a pinion seal replacement it is probably from not enough load. When you set up the pinion bearing you have a sleeve between the nut and the bearing. You have to tighten that nut to the point it crushes the sleeve. That crushed sleeve maintains a spring like pressure that will not fall off when hot or with a little wear. Think of the biggest breaker bar a automotive tech would have then add a meter+ long cheater bar to that then picture a mechanic hanging on the bar. The main issue with just replacing the seal is the fact that the crush sleeve is a one time use part. It only reacts as predicted to being crushed once.