I noticed a clunking sound/feel from the rear of my 99 while shifting gears.. or if im cruising and step on it alittle I can hear/feel it. Is that normal for the IRS??

Could it be a bushing issue??

I am new to the Modular 4.6 and IRS scene so any help would be great.. thanks
Jim

 

You have the good 'ole "Cobra Clunk". Its basically driveline slop from the soft rubber bushings that Ford used for NVH reasons. The first step would be to install poly or aluminum diff bushings and work from there.

 

If not that it could be too much slack in the driveshaft ive seen it happen in trucks many times

 

i have it also, its the bushing and other IRS issues, doesn't hurt performance though

 

You need 14mm bolts put on where Ford put in 12mm bolts on the IRS.

 

14mm diameter or length??? How do I check for slop in the drive shaft??

Im glad it doesnt effect peformance.. I was worried that the rear may fall out on me

 

That's only an 03/04 thing. The 99's and 01's didn't have that problem.

 

i had that same clunking sound... til i let the hooker outta my trunk.. lol

ya mine makes that sound too, kinda freaks me out, but i have the whole "please break, i wanna upgrade" mentality so i just ignore it haha

 

IS this the proper set to replace the Diff bushings??

http://www.steeda.com/products/cobra...l_arm_bush.php

 

Those are control arm bushings, while they will help stiffen the IRS this is what you want:

http://www.steeda.com/products/cobra_diff_bushings.php