Slight IRS Wobble

[stprorolla49]

About a week ago, I swapped an IRS into my Bullitt from an '03 Cobra. Whenever I'm on the highway at speeds above about 50mph, I get an intermittent slight swaying of the car to one side or the other. The only way I can really describe it is that the car sort of feels like it's tramlining, but the road is flat. I did some research and some people say it could be the wheel bearings, and others say it could be a loose axle nut, but none of those symptoms really relate to mine.

I have a hard time believing its a wheel bearing considering how intermittently it happens (probably every 10-20 seconds, if that). I haven't jacked the car up and checked side to side play, but I literally just installed this IRS, and I have had the wheels off 3 times since I installed it, and I never noticed any play in the wheel.

I am new to IRS's so any help would be great, thanks.

 

[Kilgore Trout]

Did you have a rear end alignment? With IRS you have to be very specific or they will only do a two wheel alignment.

 

[stprorolla49]

Did you have a rear end alignment? With IRS you have to be very specific or they will only do a two wheel alignment.

I did an alignment myself on my uncles concrete floor in his garage which level. I have been doing this for years on both my cars and always had even tire wear. I made some DIY alignment tools from a thread on Corral, and did my rear alignment on Saturday. The camber was perfect and 0 degrees, straight up and I didn't change the toe from what the previous owner had and I called him tonight and he said he never had this issue. Even if the alignment is not 100% perfect, I don't think it could make this big of a difference, could it?

 

[mustang50v8]

i would look into the bushings where the subframe bolts to the body. they are just rubber. i am going to swap mine out for some urethane ones soon.

 

[Kilgore Trout]

Agree could be bad IRS bushings they can cause a problem usually described ad tail wagging but it is usually observed on a hard launch not when cruising at 50.

 

[FEARNO1]

I agree with it possibly being a bushing. I would also check the bolts to make sure they are tight and torqued down. I know when we did the swap on a buddys car we had to actually close up the bracket that it bolts into because it was spread to far apart

 

[stprorolla49]

Thanks for the info guys. Yesterday my friend and I jacked up the car and inspected everything on the IRS. When shaking the drivers side rear wheel back and forth, there was about 1/4" side to side play. My friend got under the car while I shook the wheel, and noticed the inner tie rod end on the drivers side is completely shot. That explains everything. So we went to Ford and they don't sell just the inner tie rod end, you have to buy the whole tie rod assembly for over $200 bucks.

This was not good news for me, especially after being laid off from my job yesterday morning. Yesterday was one of the worst days of my life. I'll press on and search for a new job, but the design field is not looking up right now which is why this sucks so bad.

 

[slayerripkdc]

Sorry to hear about your job. Keep your head up!

 

[mustang50v8]

Thanks for the info guys. Yesterday my friend and I jacked up the car and inspected everything on the IRS. When shaking the drivers side rear wheel back and forth, there was about 1/4" side to side play. My friend got under the car while I shook the wheel, and noticed the inner tie rod end on the drivers side is completely shot. That explains everything. So we went to Ford and they don't sell just the inner tie rod end, you have to buy the whole tie rod assembly for over $200 bucks.

This was not good news for me, especially after being laid off from my job yesterday morning. Yesterday was one of the worst days of my life. I'll press on and search for a new job, but the design field is not looking up right now which is why this sucks so bad.

you can get set to fix both sides from maximum motorsports for $150

IRS Adjustable Tie Rod End Kit, 1999-04 Cobra [MMIRSTR-1] : Maximum Motorsports, the Latemodel Mustang Performance Suspension Leader!