Crazy vibration over 110mph

So i've been having this 'slight' vibration issue for a little while now, i used to not have it. I didn't change anything when it started happening either.

It used to happen on acceleration & deceleration but i rebalanced my wheels and now it just happens on deceleration. it used to be a 'slight' vibration over 110 when i was off the gas / in neutral but today i went cruising with a few buddies and we did a few top end runs and now my vibration is REALLY bad.

I was going WOT up to about 160mph with no vibration, but as soon as i let off the throttle it felt like something in the rear end unsettled and my car was about to fall apart... i got back on the gas and it went away.

I would get on/off the gas (around 140mph) and i would feel a weird clunk, like something was coming loose but as soon as i get below 110mph its fine.

It only happens when i'm coasting down, when its unloaded... The vibration was so bad at the time i wasn't sure if i was going to make it home. I stayed under 80mph the whole way back and it was fine.

Any ideas?


I have a 1 piece aluminum driveshaft, rebuilt rear with 3.90s, Steeda competition rod end LCAs, Steeda relocation brackets, CHE adj. poly UCA, and Fays2 watts link.

id start with checking out the bushings.i had to replace my lca bushings on my BMR's,they were busted up nasty.

re check your pinion angle

pinion angle, uneven tire wear, and the obvious one, make sure all your lugs are tight

When i rebalanced the wheels, i also rotated them to the rear.

I think i'm going to re-check the pinion angle, that was my first though along with the slop in the UCA

check your relocation brackets...i know we tightened them down but gotta recheck them if they havent been welded.

is it the whole car or in the steering wheel? seat of the pants or wrist rocker?

also how do you balance your wheels? roadforce or just regular? i had this vib from my car when i installed my steeda wheels and tires and i balanced them 5 times the regular way and it still did it, roadforce balanced them and its now gone...one was way out of whack.

are your rotors OK too ?

kevinatfms said:

check your relocation brackets...i know we tightened them down but gotta recheck them if they havent been welded.

is it the whole car or in the steering wheel? seat of the pants or wrist rocker?

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They are welded in Steeda relocation brackets now

I can feel the vibration in my seat

kevinatfms said:

also how do you balance your wheels? roadforce or just regular? i had this vib from my car when i installed my steeda wheels and tires and i balanced them 5 times the regular way and it still did it, roadforce balanced them and its now gone...one was way out of whack.

Click to expand...

I road force balanced them

MexGT said:

are your rotors OK too ?

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I'd assume so, going WOT up to 160mph i had no vibration, only when i let off the gas did it vibrate like a MOTHER FUCKER

pinion angle being can make the ds vibrate

jroc07gt said:

pinion angle being can make the ds vibrate

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ya but if thats the case, it should vibrate in accel too or while cruising.

I guess start with the simple things, i'll re-check the pinion angle and go from there.

Do you guys think the drive shaft being out of balance would cause an issue like this only on deaccel?

mine vibrated only on high deccel when the pinion angle was off.

Check the U-joints while you're under there as well. In my fox I had a U joint go at the strip, felt fine under power on a 109mph run but shook like hell after I lifted at the stripe.

Kaldar142 said:

I guess start with the simple things, i'll re-check the pinion angle and go from there.

Do you guys think the drive shaft being out of balance would cause an issue like this only on deaccel?

Click to expand...

have you checked the slip-joint on the DS you may have ripped that or some thing and it is sticking when not under load

When you were coasting down from 160 mph, was the clutch engaged?

yes and no. I coasted in gear, in neutral, with the clutch in... etc all vibrating

ever get this fixed?