Whole rear suspension replaced, now there's a small clunk

[Gibby_SVT]

Ok, I've been digging through various sites and posts and I think I have the problem narrowed down, but I wanted to get confirmation from you guys and hopefully suggestions on where to go.

Summary:
Installed Eibach Sportline springs on stock shocks (for now, Eibach Pro-Dampers coming soon)
Installed J&M LCAs
Installed J&M Adjustable panhard
Installed J&M Adjustable UCA

My car only has 1275 miles on it, so I reused the stock hardware for everything, using Red Lock-tite on all the threads. I adjusted the left-right fitment of the rear-end and reefed down the panhard, so no issues in that area. I tried to get correct pinion angle after installing the UCA, but I'm really not very confident that it's 100% correct because I had to use jacks to get the car off the ground and the suspension, though it was on stands on the front A-arms and rear diff, may not have been all the way down and seated. So I'm thinking my pinion angle of approx -3 (pinion flange read 87*), may not be really -3 because there is still a slight clunk coming from the rear when I roll on the throttle. It doesn't happen when I hit a bump or anything, just at low RPM and low speeds when I roll on and off the gas I hear a slight clunk, one I would not even hear if the music was playing fairly quietly, but definitely noticeable otherwise. This is why it confuses me because, from the research I've done, most people complain about the clunk being quite loud.

The J&M UCA seems right - I installed the anti-cluck washers and the rubber bumper is facing down! - so I thought it would fix the noise, but no joy. The only thing I think it can be is the pinion angle may not actually be correct.

Other than this barely obtrusive clunk, there are no other noises and the suspension seems tight and responsive.

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[Gibby_SVT]

And to note, the clunking noise was there BEFORE I installed the UCA, but after I did everything else. I was hoping the new UCA would fix the issue, but again, not sure if it is simply NOT the pinion angle at all or it's still wrong.

 

[skyhighsd]

Did you tighten everything with the suspension loaded? Also look at your panhard bar for the clunking, with the car on jack stands have someone push the car left to right at the 1/4 panels and see if you hear it or feel it in the bar. Just have to rock the car a bit not a ton. I installed some parts for another member and he was having somewhat of the same issue, ended up being the bushings were junk (made from the wrong material) for the panhard bar.


Also as for your pinion angle, if the car was level and the susp. loaded your reading would be correct.

 

[Aron]

The car doesnt have to be level to figure pinion angle, as long as the rear suspension is fully loaded. The actual angles dont matter, it's the difference that matters. As long as the suspension is loaded, the driveshaft and pinion angles will still have the same difference whether the car is level or not. If I remember correctly I had a noise from my panhard bar when I tightened it down without the suspension under load. I loosened it up and tightened it back up under load and it went away.

 

[TCG Member 5219]

stock two piece drive shaft thump. my car did it too. its the extra play in the two piece shaft.

 

[Gibby_SVT]

Thanks for the input guys. I am also thinking along the lines of the D/S, but I will double-check the panhard and retorque the UCA bolts.

 

[VNMOUS1]

your pinion angle should be -1*

bj

 

[Aron]

-1 is common, but since every car is different you really have to experiment to see what gets you the best results in 60' at the track. -1 is a good starting point though

 

[Gibby_SVT]

Thanks. I read that the pinion angle should be between -1 and -3*. It was at -3* when I checked it so I left it there.

 

[VNMOUS1]

On a lowered gt500, with stock or SVT or d-spec struts, -1* has ended up being the angle that 90% of people that hook run. Evolution, Lethal, yours truly (been known to rip off 1.5s and a couple of high 1.40s on drag radials )

100% ? No.

Bj

Sent from my anti-iPhone.

 

[skyhighsd]

The car doesnt have to be level to figure pinion angle, as long as the rear suspension is fully loaded. The actual angles dont matter, it's the difference that matters. As long as the suspension is loaded, the driveshaft and pinion angles will still have the same difference whether the car is level or not. If I remember correctly I had a noise from my panhard bar when I tightened it down without the suspension under load. I loosened it up and tightened it back up under load and it went away.

I Beg to differ but you own a camaro

 

[Aron]

Come on now! lol

Think about it, if the rear end is jacked up and sitting on jackstands under the rear axle, all the drivetrain angle differences will be the same as if it was sitting level on the ground.

 

[Aron]

On a lowered gt500, with stock or SVT or d-spec struts, -1* has ended up being the angle that 90% of people that hook run. Evolution, Lethal, yours truly (been known to rip off 1.5s and a couple of high 1.40s on drag radials )

100% ? No.

Bj

Sent from my anti-iPhone.

I never said you were wrong, I was just saying... not all cars are the same. -1 would work just fine, all I'm saying is that if you want to try and get the most from it, try other angles and see if they work better!

 

[skyhighsd]

Come on now! lol

Think about it, if the rear end is jacked up and sitting on jackstands under the rear axle, all the drivetrain angle differences will be the same as if it was sitting level on the ground.

agree to disagree

 

[Gibby_SVT]

Figured out that the loud ass smack is indeed my suspension (the bumpstop mount) hitting the frame. I can see the mark on the frame rail where the bolt from the bumpstop hits. The Eibach replacement bumpstops are too soft. I did a hand-squeeze test on the Eibach compared to the stock bumpstops and even that simple test showed a big difference. I cut down the stocker and going to put that in and see how it works.