I have an 89 GTA, L98 and lately I've noticed if I launch hard I get this banging from the rear. (harder I launch, I get more rapid bangs about the same interval apart)

I jacked up the car and everything appears ok. I recently replaced the trans mount. I can't tell if it's internal to the rear of part of the suspension but the car is find if I keep off the gas.

Any suggestions?

thanks,
-Dan

 

Are the torque arm bolts tight? Do you have a drive shaft loop maybe hitting the weights on the drive shaft. If all that is good, you may want to pull the diff cover and see if you have any missing teeth on the ring or the pinon gear.

 

I was wondering if it could be a worn posi. My posi hasn't been working for a while now but the only syptom was 1 wheel spin. I was wondering if the "skipping banging" I'm getting is the posi trying to work.

The rear is quiet when I'm not on it so I was thinking bad teeth would make some noise. No drive shaft loop and I guess something could be loose but those parts have never been apart.

 

Its possible, maybe a spider gear is missing a tooth, or coming apart.
Jack the rear of the car up again, and spin one wheel with the car in park, (or gear if its a stick) and see if you have any noise. If so, may be time for new spiders or a new carrier.
I'd pull the cover though and look for chunks in the fluid, or obvious damage.

 

Check carefully where the torque arm bolts to the rearend housing. Either that end of your torque arm, or the bolt mounts on the rearend may be broken. Under hard acceleration, or launching it will make the whole rearend want to rotate clockwise along with the wheels. The end of your driveshaft & pinion (at the u-joints) will bang in the top of the tunnel.

 

thanks, I'll post when I have time to investigate.

 

Car is back on the road after a complete rear diff swap - only took me a year ;-)

New (used) rear posi hooks up great but same exact rapid banging on hard launches. Any thoughts? (I replaced rear shocks and complete diff off another third gen car)

It is coming from the rear for sure and it almost feels like a hop or skip

 

Wheel hop?

 

could be but there does seem to be a bang from the rear when it happens

I think I ruled out the axle, rear, etc by replacing it and all the torques are corrrect.

maybe bushings - nothing looked obviously wrong except there was a diagonal arm which was bent that i straighened out - the arm attached from the drivers side of the axle housing to the passenger side of the body - no idea how that got bent

 

you may need lower control arm relocation brackets

 

The banging is the trans mount or the mount where your torque arm meets the trans. Mine did the same thing when I gassed it years ago when I first bought it. The bolts had fallen out of the trans mount allowing the torque arm to hit the trans tunnel. It only did it when I gassed it very hard or when it went into passing gear.

 

+1 that's what happened to me years ago

 

Mine's doing the same thing. Where can I get the trans rubber mount? Mines shot!

 

Have you checked the driveshaft slip yoke that plugs into the trans ? I've had one of those malfunction and make the exact noise you describe . Mine finally got bad enough to be readily evident , and the fix was a rebuilt trans with a new slip yoke . Under moderatly high power it would bang as the splines couldn't hold the torque , and it sure as heck sounded like it came from the back of the car . The sound probablly followed the driveshaft and appeared loudest from the back .........

 

OK, I found them on GMpartsdirect.

 

I guess I need to pull the driveshaft to check this? does the yoke pull out without opening up the trans? Really hope it isn't something IN the trans.

I was just under the car again - all looks good. all bolts torqued. No signs of anything making contact with something it shouldn't. And problem is identical before complete diff swap.

So I can believe this could be the problem. Bumps from rear seem to correlate to how hard i am hooking up. I usually get 2 to 3 bumps for launch or one hard one for a downshift.

Thanks for the suggestions