2010 GT500 Clunk

[CaliGT500524]

Hi all,

So a few things. I have been noticing a clunking sound that appears to be coming from the rear of the car. It happens mainly when I transition from a "coasting" condition to giving substantial throttle input quickly. I dont normally drive this way, however, I can replicate the condition basically on demand. Also, I get a rapid clunking sound when going onto a driveway, which could potentially be related. I had it on a lift today and noticed some wear in the sway bar mounts and noticed what seemed to me like a lot of rotational play in the driveshaft. Also, the passenger side wheel seems to not be centered in the wheel well. The driver's side seems to be more centered but the overall appearance makes it seem like the axle is crooked in its position. The car, to my knowledge, hasn't been in an accident, although anything is possible. Would adjustable lower control arms potentially aid in this situation?

The car has been lowered, maybe 1"-1.5" I am not sure by how much since I purchased the car with the suspension mods installed. The car has Steeda Lower Control Arms, Steeda Control Arm brackets, BMR Adjustable Panhard Bar, stock driveshaft and stock UCA. I have been modifying the engine namely with a 2.6 upper pulley, Lund tune, JLT CAI, 65MM Throttle Body, VMP Inlet Elbow and colder plugs.

I guess I want input on whether this could be a driveshaft issue, or perhaps a axle gear backlash issue, or maybe just plain old extra NVH from the added stiffness of the aftermarket rear suspension in combination with more power? I haven't been able to find a good forum post that satisfied my want to find out what causes the noises.

Thanks in advance.

 

[RedVenom48]

Check your rear lower control arm bushings. Ive had two poly bushings blowout from drag racing that clunked on the street till I could get it fixed. I run rod end control arms now. Louder, but also much more durable as a street strip car. even if you dont drag race, poly can crack overtime. Prior owner could have begun that process.

Worn sway bar bushings will clunk a little if the rubber has completely worn though to metal. typically they will squeak when the suspension articulates when they begin to wear.

Blown U joints on a driveshaft would cause a bad vibration at speed. Excessive backlash from your gears would cause an VERY noticeable howl while driving, usually at speed on the freeway in addition to some rotational clunking. You *might* have a drive shaft issue, but if its the stock 2 piece, you should consider upgrading it anyway.

The rear axle will shift to one side when raised in the air due to the geometry of the panhard rod. Wouldnt worry about that. Definitely matters when its on the ground, so check it then. I dont think its an alignment issue.

 

[CaliGT500524]

Thanks for responding.

Right, I'll have to take a closer look at the control arm bushings, didnt have much time when it was on the lift for something else.

That was my thinking, that the sway bar will squeak when it starts to go bad, I'll look into that further.

In relation to the gears, I dont have the typical howl but there is most certainly a clunk when I turn the driveshaft from one direction back over to the other direction. Seems like more than the .008"-.012" that Ford recommends however, I have yet to actually measure it. I have heard that when owners change out the gear for a 3.73 or even a 3.31 they have the backlash made tighter and it remedies the issue. However, I wanted to hear from anyone if that was true.

I want to upgrade the driveshaft anyway, but I wanted to potentially identify if it was an immediate problem first.

The rear axle doesnt stick out per say side to side but looking top down on each side of the wheel well it seems like that axle is crooked (wheel forward more on the driver's side and wheel rearward more on the passenger side, however more extreme on the passenger which I have yet to understand why that is the case with a solid axle).

 

[ShelbyGT5HUN]

I can get a clunk sound, just as you describe, but it's only noticeable in 5th and 6th. If you go from a coast to a full throttle application, you can hear it. IMO, this it totally normal. Hard to nail down noise descriptions online, but I think you are fine. There is very little sound insulation in these cars, and the carpet is thin as well so a lot of noise gets transmitted into the cabin.

If you had it on a two post lift, that would explain why the wheels were not centered because of droop.

 

[RedVenom48]

Thats the thing about a solid axle, it should definitely not be like that. From the factory and even with upgraded boxed lower control arms, there is no wheel base adjustment available. The adjustable panhard rod centers the rear axle under the body. Assuming both lower control arms are in good condition and equal length (undamaged), the thrust angle should be zero when centered and wheel base even and in spec.

Id say that the passenger control arm has the blown bushing, given the clunk and visual cue of its alignment.

Now, the not so fun theory. Its entirely *POSSIBLE* that the prior owner ran the car hard and bent the rear axle housing. High RPM clutch dumps at the track on drag slicks or radials can do that kind of damage. *IF* this were the case, youd have a higher chance of your alignment being off, abnormal pulling and generally terrible handling in addition to noise.

I would have both rear lower control arms removed and inspected as a starting point. I have a feeling thats your issue right there. If they are pulled and they look fine, you'll need to have a professional inspect for rear end damage.

 

[RBB]

Good advice from Lexustech. I've also blown out a couple poly bushings racing....everything is rod end or spherical now. Since you're lowered, check your pinion angle and make any adjustments to the UCA if needed. That can cause some unwanted banging back there over bumps.

Other thing to look for is to make sure the bolts on your UCA mount are tight. I know that sounds ridiculous, but a buddy of mine had a UCA and mount installed on his GT at a shop in the area. He told me it was clunking all the time so he brought it over to the house. I don't know if the shop forgot to tighten one of the mount bolts or it somehow came loose....whatever the story was, it needed to be tightened to spec. Check all your bolts back there and make sure nothing is loose. Sometimes the overlooked solutions are the simplest ones.