IRS Highway speed vibrations on decel

[D2Fresh16]

As the title says I have a vibration with my IRS on highway speeds, mostly around 80 letting off the gas.
The IRS is all stock with 18k, stock 03 cobra driveshaft, built T56.

I'm not sure if this is the driveshaft indexing as I read if you spin the driveshaft 1/4 turn the vibration could go away (not sure how this would affect it)

OR, when I took the pumpkin out of the subframe to change the gasket perhaps I put the bushings/spacers in wrong and the vibration is the pinion angle?

Does anyone have a picture or diagram how the bushings/spacers go on the front of the differential? Any other ideas?

 

[hotcobra03]

were those stock bushings or hard replacement?


i had a issue like this..i had replaced pinion flange to fix...

try this link for pic



http://www.terminator-cobra.com/svt_documents.htm

 

[01yellercobra]

The first thing I'd check is the driveshaft bolts. I had a vibration appear out of no where and it was because of loose driveshaft bolts. Which diff bushings do you have? If it's the stockers or poly bushings they really go on one way.

 

[I'D WIN]

FTBR has many how-to's and pictorials available on their website.

 

[keith89]

Does it only happen on deceleration? Is it more prevalent when decelerating at high rpm? if so, this could be indicative of a failed pilot bearing. It happened to me when a shop pulled the transmission in using the bolts instead of making sure everyhing lined up first. I would have a nasty vibration under deceleration only at high rpm and especially in 3rd gear. I had to pull the tranny and put a new pilot bearing in myself. It was a cheap fix but took time that I should not have had to do.

 

[D2Fresh16]

were those stock bushings or hard replacement?


i had a issue like this..i had replaced pinion flange to fix...

try this link for pic



http://www.terminator-cobra.com/svt_documents.htm

Stock bushings Thanks for the link

 

[D2Fresh16]

The first thing I'd check is the driveshaft bolts. I had a vibration appear out of no where and it was because of loose driveshaft bolts. Which diff bushings do you have? If it's the stockers or poly bushings they really go on one way.

Yeah this didn't just happen out of no where, I just finished my swap so Im not sure how it was in the donor car.

Does it only happen on deceleration? Is it more prevalent when decelerating at high rpm? if so, this could be indicative of a failed pilot bearing. It happened to me when a shop pulled the transmission in using the bolts instead of making sure everyhing lined up first. I would have a nasty vibration under deceleration only at high rpm and especially in 3rd gear. I had to pull the tranny and put a new pilot bearing in myself. It was a cheap fix but took time that I should not have had to do.

Yeah only on decel but rpm doesn't really matter. It was fine with my old solid rear.

 

[Rich'sTRsvt]

If you just put the rearend and driveshaft in and they didn't have it marked on the pinion I would try rotating it a 1/4 turn at a time and testing it. I had not marked mine on another car when doing gears and had to do this to find the spot the vibration was the least. Although that was usually just going a constant speed above 60 so this maybe something different.

 

[hotcobra03]

Was any thing done on ds?

They claim there are 2 pinion flanges for 8.8

1 being larger/thicker..

like maybe flange was swapped on ds without a re balance?

Putting car up on jack stands and running it you can see if shaft is turning straight. .

I just went thru this after rear end work..pinion shaft was bent

 

[D2Fresh16]

D/S is stock, 18k miles. Im going to try turning it half a turn and see if it gets better or worse.