I have done a search but can't find a thread with a problem similar to mine. I have an 82 Firebird which has I believe to be the original rear axle. It has 10 bolts on the plate. The problem is there is a knocking sound coming from the rear when travelling over rough road surfaces, When decelerating its bad, When the transmission is shifting from 1st to second gear its also bad. I jacked up the car and checked the usual, transmission mount, driveshaft, control arms, Panhard bar, stabilizing bar and all are tight. The one thing I did find was movement of the rear wheels in and out, the driver side is worse than passenger side. Up and down is fine so the wheel bearings should be okay and driveshaft shouldn't be worn. I believe this is my problem But why is this happening. Is there any adjustment on the drive shafts I could do to stop this movement. Is there any other checks that I can do. Could someone advise please. Thanks.

 

Check the torque arm mount. Right above the transmission mount.

Also look at the upper shock mounts. Take out the rear seat bottoms, pull back the carpet, pull out the 2 big foam blobs. The "mount" is just a stamped-out place in the sheet metal, which the shock bends up and down constantly until it literally punches a hole out of the floor pan.

Some in/out movement of the axles is normal in rears of this type; all sizes, all models, all mfrs. Anything less than 2 - 3 mm is pretty much OK.

 

Thanks for your reply. Will put it up on axle stands tomorrow and check the transmission mount.

 

RE-checking the trans mount is a good idea. Of course, the only foolproof (ME-proof: I freely admit I'm an idiot) way to check it, is with a known good one... I'm not seeing where you successfully completed that RIGOROUS and FOOLPROOF test. Meanwhile you also have SOMETHING ELSE to check. Your assignment is:

Don't forget.

 

YES. This happened on one of my 3rd gens. And...it made a racket.

 

Put it up on axle stands, checked torque arm, shock tops and all fine. Everything is fine and tight under the car. One thing I did notice when I had the wheel
off is that there is a little movement up and down on the axle. I know there is a wheel bearing there that the axle runs on. I didn't notice it before when the wheels were on.
Given the age of the car I presume that a little movement is normal. What do you think. The car has done 84K miles.

 

Did you notice any oil leaking around the axle that seemed loose? I haven't seen any vertical movement of the axle before but if it was excess it would mess up the seal I'd think.

 

No oil leak. All dry there.

 

Keep looking. If the sound is strongly correlated with bumps, then something is loose. You need to find it. Since it's related to deceleration, I'd really scrutinize the tq arm/trans mount, like Sofa suggested.

 

If u have any movement of the axle, up & down or side to side, the bearing is shot. Replace both sides with bearing + seal.

 

The axle bearing doesn't hold the axle along its length. The C-clip does that. The axle just slides right through the bearing.

 

Thanks for your replies. Will check underneath again tomorrow for anything loose.
will put a new set of wheel bearing on also.

 

If you swap out "wheel" bearings, which are REALL axle bearings, take a REAL GOOD LOOK at the place on the axle where the bearings ride.

The Deal is, the axle itself, IS the bearing inner race. If the surface of the axle that rides on the bearings isn't PERFECT, your project is doomed. The axles must be replaced, otherwise nothing has been repaired or even "fixed".

Butt that makes NO DIFFERENCE WHATSOEVER to the axle end play. The axle slides completely freely through the bearings, such that the bearings have no bearing (hahahaha) WHATSOEVER on the end play. The C-clips inside the pumpkin control that. Which of course, you'll have to remove, to get at the axle bearings. The secret of this design of rear axle (C-clip type, widely used by practically all mfrs of RWD axles) is that, there's nothing holding it together; it, ... ,,, just, ... can't quite fall apart. You take out the little itty bitty teeny tiny screw that holds in the cross shaft, and the shaft falls out; with the shaft in place, the axles can't slide inwards enough for the C-clip to fall out, but with the shaft fallen out, you can push the axles in and the C-clips will fall out; once the C-clips have fallen out, the axles can fall out; then you can change out the bearings and seals. You'll see. The bearings don't quite fall out, you actually have to bonk them somehow, butt it's kinda trivial. I usually use about a 5 foot (1.5 m more or less) piece of electrical conduit or water pipe or some such equally highly technical piece of ... something, to bonk them out. Stick it through and use your BFH to klong the bearing and seal on the opposite side out of the axle.

Hardest part will likely be, removing the little screw that starts the whole falling-out cascade. It's 5/16", which is arbitrarily close to 8mm; use a 6-point box-end wrench and a hammer. NOT a socket, NOT a 12-point, NOT an open-end wrench, NOT apply gentle continuous torque, NOT NOT NOT NOT NOT NOT NOT. A 5/16" or 8mm 6-point box-end wrench and a hammer. If you do this wrong, the screw will either strip its head or break off, and once that happens, it becomes MUCH harder to get the axle to fall apart. Like, 2 orders of magnitude, if not more. Things like TOOLS of various sorts, like drills, torches, and so on, need to be used to overcome this failure, and other parts are likely to be destroyed in the process, even apart from the obvious expense (though the great personal gratification) of the use of TOOLS. So be sure to get it right the first time. A 5/16" or 8mm 6-point box-end wrench and a hammer.

 

Incidentally, you can't "check" the shock mounts from below. You need to pop the rear seat bottoms out.

It's REAL HARD; takes me like a minute and a half. You're obviously smarter than me though, probably you can do it in far less time. It's ONE WHOLE 10mm bolt on each side, then ONE WHOLE 10mm nut per side. Took me longer to type that than it does for me to take out the seats and LOOK AT the "shock mounts".

When mine failed, I had a shop (at that moment I had no welding eqpt) weld in acoupla big washers and otherwise brace the weeeeeeeeenie sheet metal that had broke out.

 

Thanks sofakingdom for your detailed reply, a lot of useful information there. I was in contact with a guy that is going to let me use his car lift next weekend to check out the car. Crawling under it with it on axle stands is okay but is better to be able to stand underneath it to give it a good check. Don't want to have to go replacing anything in the axle if I can as that process scares me so hopefully It will be something simpler.

I did check the rear shock mounts from the top, took out the rear seats and lifted the carpet. All tight with no damage to the sheet metal that the shock goes through.