Rear end clunking

Scott Long

Registered User
My 5-speed SC is making a clunking and banging in the rear when you accelerate suddenly or after shifting a gear if you get back on the gas about half way.

Under very granny style driving its fine but hit the gas and then BANG. It sounds like its right under the rear seat or in the trunk. I am not sure what it could be. My first guess is the rear diff is hitting the bottom of the car when the pinion angle shifts. I have about 2 year old poly-diff bushings and u-joints, so I wouldn't think they would wear out that quick but maybe the bolts came loose?

Another thought is that I tore the rubber tranny mount and that is causing it to smack under the car when the motor shifts. My friends Z28 was doing this before I changed the trans mount on it.

I had new tranny and motor mounts put in about 2 years ago but they were crappy liquid filled. If I have to do it again I'll buy the solid rubber ones. Now that I'm not working I don't have extra money to spend on the car for anything other than gas and oil changes. So hopefully this is something I can fix myself and cost me nothing.

Anyone have any hints at what I should look at? I'll be under the car this weekend to change the oil so after that I'll back it onto the ramps and slide under the back of it to see if anything is loose.
 
A couple of things to check...

1) check the bolts that hook the driveshaft u-joint assembly to the IRS. They tend to work themselves loose, and
2) check the rubber bushings where the IRS is mounted.

These are the most common causes of rear-end clunk...
 
Those damn bolts...

You are more than likely hearing the 4 bolts that mount the driveshaft to the pinion flange.... mine kept coming loose, i put some blue loctite on them, havent heard noise since.

Kinda tricky to get a socket in there... i found that a 12 point 12mm box end wrench works pretty good, i know snap-on sells a special flex socket just for that application... thats snap-on tho.

$0.99 tube of blue loctite :)

Those differential subframe bushings too... damn things. garbage.

Dylan Roth
 
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i had what sounded to that exact thing. i took it to les schwabs and jumped under there. the passenger side irs bushing was msashed so flat it was nothing but a thin layer. Id start with that. there only 30 bucks.
 
Scott,

Jack your car up, crawl under it and look at it.:rolleyes:

I had the driveshaft to pinion flange bolt issue before and it was more of a clunk than a bang. There's got to be a bolt or bushing messed up under there. However, I broke my differential housing once where it bolts to the front bushing mounts and it made a "bang" noise when I got on it or let off quick.
 
I'll get under it tomorrow. If the diff housing is broke around the holes where the bushings and bolts go, can it be welded or do I need to get a new pumpkin?
 
Figured out the problem

Took a while looking at the control arms and diff. Finally put my hand up near the diff bushings and the passenger side upper bushing fell out. Well the 1/4 of it that was left. The rest was completely gone. So.... I bought these from Super Coupe Performance in the spring of 2003 and the car hasn't had but maybe 15,000 miles put on it since then mostly highway trips to St. Louis for WFC and some TBU meets, it sat all last winter for about 8 months total, and recently my girlfriend has been driving it to work.

Why wouldn't these poly diff bushings hold up better? The stock rubber ones lasted 11 years. What gives. The car hasn't been down the race track since I've owned it so its not abused. I'm dissappointed.

How can I change these out? I don't really want to have to pull the axles out.

Can I remove the bolts for the driveshaft, remove the rear housing mounts, and then loosen the two diff mount bolts and just tilt it down or let it drop slightly and slide the new bushings in and then slide the bolts back in and tighten them down?

I'm hoping that when my new bushings arrive I can do this in the driveway with the rear subframe supported on my jackstands, and then not have to pull the axles.
 
Ive had the same thing happen to mine twice and the to a couple other cars around here. No big deal in changing them out... If you an air gun it is cake but if not still no biggie. You dont have to remove the axles to but the diff bushing in. I just pulled the bolts and slide mine in then tightened them down. I know you need to make sure you dont have any jagged edges or rocks that might cut the new bushings. (especially Poly)
 
Cool, I have air tools.

I found a picture how to on mn12performance.com so I have an idea. It shows the axles out but doesn't mention that you have to pull them. I can drop the exhaust if its in the way its just clamped on in the rear.
 
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