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Suspension Problem - Seeking Advice


Bushmaster

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I'm really hoping someone else has had a similar problem to mine and can advise me. I bought my '09 GT500 in December and the previous owner had installed Shelby Watts linkage and Shelby upper and lower control arms. The car still had the stock wheels and ride height and drove and rode very nicely with no issues at all.

 

A couple months ago I installed 20" BMC Black Mamba wheels with Nitto NT555 tires, and at the same time installed a set of slightly used FRPP lowering springs. I got the desired look but immediately noticed a problem. When going over anything bigger than a small bump, I got a loud "thunk" from the rear of the car. On the way home from doing the install, I had put one of the original wheels and tires in the trunk to use for a spare on trips, and I thought I might be hearing the wheel/tire bouncing in the trunk - that's what the noise sounded like.

 

I asked around a bit and found a great deal on a set of new Eibach Pro springs, which I bought. Before installing them, I noticed that there was not much clearance to the bump stops in back, so we cut them down, hoping that might be the cause of the problem. No improvement - still the same loud thump over bumps. So I decided to go ahead and install the Eibachs, since I had already purchased them. We did that last weekend, and unfortunately, that didn't cure the problem.

 

Now that I've eliminated the springs as a cause for the problem, I'm pretty sure it must be a result of the lowering itself, since it was just fine before the lowering. We did a visual inspection and didn't see anything amiss, so now I'm wondering about the Watts linkage. I'm not very familiar with Watts linkage - is there adjustment that is necessary after lowering the car, since the linkage was installed when the car was at stock ride height? Is it possible that the linkage could be causing this problem, or do any of you have similar experience or advice you could give me about any other potential cause? The car drives nicely now - the ride is just a bit harsher than before but certainly nothing extreme, about like my '08 GT-C was on its suspension and 20" wheels. But whenever I hit any kind of real bump, I'm getting that loud and unacceptable "thunk" from the rear of the car.

 

I really appreciate any input from any of you who might have similar experience.

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Thanks - I will definitely take a look at those when I get home. Any indication why the bushing(s) on your wife's car failed? Would lowering the car cause something like that?

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You can't tell by inspection. Looked fine on the car. Her car is stock and 30k commuting miles. I don't know what caused it except our less then ideal roads in CT. When I took them off the thumping went away. It's a known issue with the '11's. I'm in process of installing new polyurethane bushings. Not sure about the '09's and your mods. Start by removing what you can to isolate the noise.

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Do you have the factory upper control arm bracket (sheet metal) or the Shelby (welded steel plate)? If it's factory the bolt for the control arm is 14mm and the hole in the bracket is 16mm. It moves and thumps. The solution is the welded bracket, or a special bushing that I don't know if anyone makes anymore.

 

Steve

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Do you have the factory upper control arm bracket (sheet metal) or the Shelby (welded steel plate)? If it's factory the bolt for the control arm is 14mm and the hole in the bracket is 16mm. It moves and thumps. The solution is the welded bracket, or a special bushing that I don't know if anyone makes anymore.

 

Steve

I just installed the special washers on my upper control arm to make up the difference between the bolt and arm. Let me know if anyone needs the part number. It's made by Steeda.

 

Just found it. 555-4110 Stepped Spacers. I bought them from Jeg's.

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Thanks for the input, guys - I definitely appreciate it. I think I'll go ahead and order the sway bar bushings just in case. Do you think the problem was caused by the lowering? It was fine before so all I can assume is that the lowering process caused it.

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Bushmaster your car looks fantastic. The stance is perfect. Keep us informed if you figure out where the sound is coming from. I'd make sure it wasn't the large bolt that holds the upper control arm bracket to the floor pan. It's located under the rear seat. I've heard if those not being torqued properly causing the sane issue. Also, since lowering it have you checked your pinion angle to be sure your within spec? GL.

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Thanks - I appreciate it! I love the looks and now I just want to get it to drive as good as it looks. I will definitely check that bolt this weekend, along with everything else I've read here. The pinion angle is good - haven't done anything about the alignment yet as I wanted to make sure this problem was solved first.

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  • 4 weeks later...

Well, finally got a chance to get the car out to the shop and have a look, and the problem was immediately obvious. When the Watts link was originally installed with the car at stock height, they installed the bars angling up. Which was fine at stock suspension height. But after lowering the car, both bars were in conflict - the driver side was hitting the exhaust and the real culprit, the passenger side, was hitting the Watts link bracket in a big way. So big, in fact, that the bar was wedged against the bracket and we had to pry it loose with a crowbar. Once we changed the angles of the bars (level for both, as per the Shelby Watts link instructions) there's no conflict, the car rides beautifully, and I can enjoy life again. Best of all, the fix was free.

 

Probably something for people to keep an eye out for if they're lowering cars with Watts linkage.

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