Rear Suspension Noise/Clunk When Going Over Bumps in the Road

[MoparCarGuy]

Back in 1999 I installed the Performance Suspension Technology (P-S-T) polygraphite rear leaf spring eye bushings and rear shackle bushings on my 70 Cuda. The springs are factory T/A number 3400048 that are not sagging at all. The shocks are KYB Gas-A-Just monotube. I have never been satisfied with the ride quality as it has always seemed very stiff and hard with a noticeable "clunk" when going over speed breakers or bumps in the road. I have attributed the clunk to the poly bushings. I do not suspect the shocks or the shock mounts as all appears to be good but I would consider changing to a softer, more factory-like shock absorber to improve the ride.
Any suggestions on a set of softer, more factory-ride quality shock absorbers?

I am considering removing the rear springs and installing normal rubber bushings. I have a new set of Moog K7308 rear shackle bushings. They are rubber but are surprisingly quite hard. I plan to order the front spring eye bushings (2" O.D.) but wanted input on a troubleshooting procedure before embarking on a leaf spring bushing swapout.

Do you guys think I am on track to correct the "clunk" or could there be something else causing the issue and how would you troubleshoot it?

[MoparLeo]

Get the car up in the air to inspect the mounts and any ineference that will cause the clunk.
The bushings wil not do this. Only squeek. KYB are a stiff shock. I think the rear number was KG-5512 .

[Bullitt-]

     Poly bushings would not cause your harsh ride or clunk.
  KYB shocks I've heard for years are extra stiff.  A set of Monroe shocks would be closer to stock ride and be the most economical.
  Do you feel the "clunk"? Many things could be caused to move when the suspension bottoms. I had thought there was a suspension issue that turned out to be a loose exhaust hanger   

[dodj]

Your ride quality, imo, is caused by the kyb shocks. They are known for being a rather harsh shock on e-bodies.
I really like the QA1 adjustable on my car but they chew up $1000 or so for 4 of them.
My money would be on the upper shock bolt(s) causing your clunk. You can't raise the car and jerk the shock around to check. You will need to remove the bottom shock nut and let it hang. Then try to move the shock to see if you can get a 'clunk' out of the top mount. Make sure your car is supported well before you push and pull on the shock.

[EV2RTSE]

I haven't run them yet but I went with Bilstein RCDs for my orange car, I found the best price at Kanter Auto Products. Lots of good feedback on the forums about them. They're roughly half the cost of a set of adjustable shocks.

[PatO]

I dealt with that clunk for a short time. Upper shock mount bolts. I bought some bolts at the parts store that worked . . . almost.  After a bit of trial and error I found that the diameter of the bolt was important also. Too small a diameter, even just a little, and going over a bump will cause it to clunk. I got the correct bolts from Roseville and that solved the issue.   Also make sure the mounting holes in the cross member haven't been rounded out.   

Hope that helps.

[dodj]

I dealt with that clunk for a short time. Upper shock mount bolts. I bought some bolts at the parts store that worked . . . almost.  After a bit of trial and error I found that the diameter of the bolt was important also. Too small a diameter, even just a little, and going over a bump will cause it to clunk. I got the correct bolts from Roseville and that solved the issue.   Also make sure the mounting holes in the cross member haven't been rounded out.   

Hope that helps.

Are the upper shock bolts a special diameter bolt? 

[anlauto]

The only time I've ever had a clunk like you're describing, it ended up being a loose upper shock bolt. Sometimes they use lock nuts that seem tight when they aren't.

[PatO]

MoparCarGuy Yes, the bolts from Roseville were a slightly larger diameter.  When I first started driving my car again, the clunk started after a few miles.  I re-tightened everything and drove it again. Thought I'd fixed it but in just a few miles it came back.  I removed the shock and mic'd the holes. They were round and equal diameter from side to side.  I then slid the bolt back in without the shock in place and noticed that I could wiggle it ever so slightly. I puzzeled on that overnight.   

The next day I went to rosevillemoparts.com and saw that they had different rear upper shock bolts for different cars and different years. I ordered the e-body bolts and when they arrived I fit then in the hole - again without the shock - and noticed that they fit fairly snug and with no wiggle at all. I measured the bolts with a micrometer and saw the Roseville supplied bolts where indeed a larger diameter by around 1/16 inch ?? (forgive my late sixties memory)  I used those and a thousand miles later - still no clunk.

That was my experience on a 72 challenger that I restored.

[MoparCarGuy]

Thanks, guys, for all of the responses. I summarized the replies below and it came to me that I should also check my adjustable pinion snubber distance to the floorboard. I may have it too close and that would cause a clunk as well.

Troubleshooting Plan:
1. Check pinion snubber distance to floorpan. Adjust for 3"-4" versus 1", if possible. Replace with stock pinion snubber if adjustment won't provide more clearance.
2. Check the rear upper shock bolts for a clunk by taking the bottom mount loose and moving the shock around, up, and down. Listen for clunk.
No clunk, go to step 3.
3. Remove the entire shock and inspect the upper shock bolts and the crossmember holes to make sure the bolt fits the crossmember correctly. If the bolts are the issue, replace the rear upper shock bolts with the correct E-Body bolts from Roseville. BTW - Checked and Roseville is out-of-stock on them right now. Rear Shock Upper Bolts and Nuts 1970-74 B/E-Body
4. If all is good with upper shock bolts, consider changing out the KYB shocks to the Monroe Monro-Matic 32073 Shocks. Alternately, consider Bilstein RCDs rear shocks from Kanter Auto Products or QA1.

I will let you know what I find. Maybe even take some pics.

[MoparCarGuy]

So here is what I found this afternoon.

The adjustable pinion snubber on the lowest setting was only 1/2" from the tunnel reinforcement with the car sitting on ramps (suspension loaded).
The upper shock bolts were tight with zero play in any direction (removed lower shock eye from the stud to check the play).

Snubber clearance definitely needed correction so I found my factory pinion snubber, cleaned it up for paint, and baked on some satin black.
The factory snubber's rubber bumper has MoPar on it with part number 2405906.

I installed the factory snubber late this afternoon. I think this was the problem but will confirm via a test drive to a local car show on Saturday morning. I'll post the results soon.

[MoparCarGuy]

Here are the results after changing back to the factory pinion snubber.

Drove to the local car show and no clunk. Ride is still a bit harsh for me. Rear suspension bushings (spring eyes and shackles) are polygraphite but no need to change that. Likely going to throw on some softer shocks like the Monroes and see what that does.

Thanks for all of the input. 

[HP2]

I picked up a MP snubber many years ago and after sticking under my car, noticed it was way too tall. I ended up cutting it down to get a better gap to the floor board. See that you only have two adjustment holes, it appears your has already been cut down. The OEM snubber might be the better fit for yours and if you are getting too much spring wrap with it, try using the taller MP snubber rubber pad, as its a bit taller.