***Rear knocking even after changing bushings,etc
 

Hey guys, so after doing some reading on here I confirmed that the rear knocking sound on my 1992 XJ Sovereign (SLS swapped for standard shocks before my time) is likely due to the rear shock bushings. I ordered new bushings, the top hat and the spring isolator. The upper bushing was destroyed. Being foam and original from when the car was new, I was not surprised. After it was all replaced, the car drove quietly again. Sad to say that after only a few hundred miles, the noise is back. I had the shop pull the entire assembly out again and they are saying everything looks to be in order. Any ideas on what else it could be?

Check the spare and jack are firmly fastened and secure. The spare retainer can work loose.

Thanks for the tip Lawrence. I did that and even went as far as to remove everything from the trunk\boot. The noise still persists. I also made sure everything behind the trunk\boot carpets was also secure and not loose.

Oh well was worth a try. Probably the metal top hat part is worn/sharp and has destroyed the rather soft bushing that fits in there. If my suspension was 92 style (I have late 94 car with different rear setup) I would do away with the soft "cowboy hat" bushing and make up some teflon or "friendly plastic" duplicates ...

I looked myself at the top of the shock when they removed it from the car. Everything is intact an tight as it should be with zero play. I agree that the top hat would be better as a polyurethane or similar component but I am fairly certain that isnt what is causing the noise unfortunately.

Maybe one of the bump stops has fallen off? Just a WAG. Pull back the side trunk liners and see if there's any electrical gumph hanging down loose? oh and sometimes one of the exhaust hangers gets distorted/rusted away and the pipe knocks against the body.

I had the same issue once I renewed spring and shocks on my XJ12, always had a knocking from the rear. I think the only difference I found regarding the old spring assembly was the mentioned 'cowboy hat' bush (no. 14), it was either missing on the old assembly or was made of a softer material. I left it away/exchanged it against the old part and the knocking was gone.

Thanks for the suggestions guys. Hey Lawrence, I did remove everything from the trunk and checked behind the liner. Also checked the exhaust and hangers. When you say one of the bump stops may have fallen off, where should I look for that?

Thanks V12, they are all new on that end.

They are rubber blocks, I think they are mounted on the frame, should be just visible in front of wheels but it's been a long time could be obscured by the wheel also. Shaped like a hollow inverted triangle with the peak cut off IIRC.

ETA, You didn't say you replaced the shocks, so could it be that the spherical bushing fixed into the bottom of the old shock is loose? Play in that bushing might not be obvious until the weight of the car is acting on it. And it would definitely cause a clunk. New shocks have that bushing preinstalled.

Hey Lawrence, the bump stops are there and like new. No visible marks or signs of damage or wiggle.

Hi Sleekjag, the shocks werent change since they still seem to have life in them. The bushing you are referring to is also pretty tight. I thought the same thing and checked it as well. Maybe worth replacing either way.

I think you are both talking about the bushing that I referred to in my post (see included link to JCP parts catalogue). It was that bushing that was causing the noise on my car even though it was brand new and came with the new shock. I left it away (like it was on the old shock) and the noise was gone. May sound strange but that's what happened here.

So eliminating this piece altogether sorted out your knocking noise?

Maybe I have to row back, I just had a look at my work bench where I put together the spring and damper assembly and I couldn't find these hard rubber bushings. Instead I found a series of these foam bushings in different sizes, so I can't tell exactly what I left away as it is too long ago. Sorry.

No worries. Thanks for your input either way!

Hi on my my tuto see if you have put all parts ! TUTO

Great write up and awesome pictures, even if it is in french! I did replace all of that however and checked it out of the car after it was done at the shop. Both sides are super tight and the foam bushings show no signs of failure.

Minor update. So today I tightened the straps that hold the gas tank down but this did not make a difference. I took the spare tire out of the trunk, the carpeting and jack kit and had my brother drive the car and take bumps while I stayed in the trunk with the lid closed. I can now confirm with certainty that the sound is coming from the passenger side of the vehicle in the rear.

So I am curious, before i go spending money on new shocks, is it possible that the shock could somehow be to blame despite still holding weight and bounce perfectly fine? Ive never seen this before and am dumbfounded. Thanks in advance!

I think it's your exhaust system. Check the clearances

Hey Lawrence, I also checked that as well and all the clearances, hooks, exhaust clamps and all. Everything has amply clearance and the exhaust doesnt have much play. :(