Rear clunk under hard acceleration in 1st gear

[FocusSTGuy]

Hey Guys,

My car has developed a weird issue. If I launch hard, or stab the throttle hard from a roll in 1st gear, the car will clunk very hard. I swear it feels like the drive shaft hits the floor pan in the back. It does not do it in any other gear.

Anyone have any ideas? I was under the car and checked all the mount points and torque specs of all bolts and everything looks fine/nothing feels loose.

I ran out of time to check DS angle again but the bolts for the UCA were not loose.

 

[gt5.0coyote]

Hey man,

We had this same exact issue. When the car it in 1st gear ready to sift to 2nd it had a big bag. We had multiple issues. The first one was that the BMR relocation bracket didn't come with the spacers to install in the top of each bracket, so the brackets were bent. Got some spacers and it was straight. The second issue is that our gt500 lower control arms were bad. The bushings were just shot and one actually looked bent. Got some BMR lower control arms and that was fixed. The third thing was is that our swaybar end links were a little loose so those got tightened. Not sure what the exact issue was but something of the 3 straitened it out. Hope this helps man. PM me if you need more help because I might forget to check the thread.

 

[BLKSUNSHINE13]

Its sounds like your hitting the bump stops to me. Trimming them down might help, then you might consider upgrading springs.

 

[gt5.0coyote]

Its sounds like your hitting the bump stops to me. Trimming them down might help, then you might consider upgrading springs.

Whats wrong with the frpp springs?

 

[BLKSUNSHINE13]

Whats wrong with the frpp springs?

Uh I don't know, maybe nothing, other then bottoming out on the bump stops. A stiffer spring rate might help him out.

 

[gt5.0coyote]

Uh I don't know, maybe nothing, other then bottoming out on the bump stops. A stiffer spring rate might help him out.

I'd hate to have a stiffer spring rate than these haha.

 

[GBCoyote]

Upper control arm or driveshaft clunk

 

[BLKSUNSHINE13]

I'd hate to have a stiffer spring rate than these haha.

Sorry if I offended your K springs, but 199.5 lb./in. rate progressive springs are not especially stiff. Considering high quality BMR parts are installed that have passed inspection, if it was me I would install FRPP bump stops trimmed down a inch, as well as, linear springs.

 

[gt5.0coyote]

Nah man you didn't offend me at all. I was actually looking at some linear springs for weight transfer and to mabe get some better traction, but everyone I talked to said it would rub in the rear.

 

[BLKSUNSHINE13]

How low can you go, it's the age old dilemma, isn't it? Anyways, as I understand it a progressive spring is softer during its initial compression to maintain ride quality then progressively stiffens to achieve compliant handling characteristics. Being lowered 1.5 inches’ certainty isn't slammed, but you have to consider how much room is left between the chassis and the bump stops for suspension travel. If it’s only an inch or less contact with the bump stops might occur during hard acceleration while the spring is still in its more compliant area of travel causing a very loud clunk/bang, as he has described. Just my two cents, peace...