IRS swap issues.

[fly4navy117]

I swapped the IRS from an 03 Cobra into my GT this weekend and I've had a couple of issues. I'm getting a knock every time I shift gears. It's almost like a thump. I think is because the preload at the pinon flange is off. I had another guy suggest the drive shaft being an inch or so too long not allowing it to slide properly and bottoming out inside the trans. I didn't think that was it because I hadn't heard of that being an issue, but I'm not entirely sure of anything at this point. It's not too bad and I can just about eliminate it with smooth shifting, but I don't want to leave it alone. Any ideas on how to sort this out?

 

[Charles236]

Welcome to the "Cobra clunk". It is pretty common for the IRS to have a bit of clunk, or "thump" as you called it. There are several things that can contribute to the clunk, like worn bushings on the front of the pumpkin, wrong size bolts in the front IRS subframe mounts, tolerance stack up (play) in the halfshafts (mostly in the inner CV joints), excessive backlash in the ring and pinion setup. There is always a little bit of tolerance stack up in a driveline, even in cars with automatics, but the IRS seems to exacerbate this in the Cobra. These factors can occur in different combinations or singly and cause the clunk. The driveshaft length is not a real problem, since the differential is mounted in the subframe and does not move up or down a significant amount (which cause the driveshaft to move in and out of the tailshaft housing). I have an '03 IRS swapped into my Mach 1, it also has the "clunk", and after four years, it has gotten no worse and I usually don't notice it.

 

[Root1022]

Very normal!

 

[fly4navy117]

Welcome to the "Cobra clunk". It is pretty common for the IRS to have a bit of clunk, or "thump" as you called it. There are several things that can contribute to the clunk, like worn bushings on the front of the pumpkin, wrong size bolts in the front IRS subframe mounts, tolerance stack up (play) in the halfshafts (mostly in the inner CV joints), excessive backlash in the ring and pinion setup. There is always a little bit of tolerance stack up in a driveline, even in cars with automatics, but the IRS seems to exacerbate this in the Cobra. These factors can occur in different combinations or singly and cause the clunk. The driveshaft length is not a real problem, since the differential is mounted in the subframe and does not move up or down a significant amount (which cause the driveshaft to move in and out of the tailshaft housing). I have an '03 IRS swapped into my Mach 1, it also has the "clunk", and after four years, it has gotten no worse and I usually don't notice it.

Thank you so much. I've been really worried the IRS was going to have a catastrophic failure.

 

[ac427cobra]

I swapped the IRS from an 03 Cobra into my GT this weekend and I've had a couple of issues. I'm getting a knock every time I shift gears. It's almost like a thump. I think is because the preload at the pinon flange is off. I had another guy suggest the drive shaft being an inch or so too long not allowing it to slide properly and bottoming out inside the trans. I didn't think that was it because I hadn't heard of that being an issue, but I'm not entirely sure of anything at this point. It's not too bad and I can just about eliminate it with smooth shifting, but I don't want to leave it alone. Any ideas on how to sort this out?

Couple of things. If you were able to slide the driveshaft forward far enough into the transmission to get it onto the pinion flange of the differential, that is all you need. An IRS car is not like a stick axle where the axle moves up and down and the driveshaft has to slide in and out of the trans. The trans and the IRS diff are fixed and do not move. (well with the exception of flopping around in the rubber mounts! :fart:

You most likely have bad differential mounts, just like every other Cobra IRS owner. Replace those crappy OEM differential mounts and you should be good to go.

:thumbsup::coolman::beer:

 

[Charles236]

Thank you so much. I've been really worried the IRS was going to have a catastrophic failure.

Really, the IRS was one of the best mods I have done to my Mach 1. It actually makes it smoother riding and better handling. Plus, I don't have to use a Panhard bar or Watts Link to keep the rear axle from swaying from side to side.

 

[fly4navy117]

Thanks for the input guys! As for upgrading the diff mounts, is there a good kit out there already put together?

 

[ac427cobra]

Thanks for the input guys! As for upgrading the diff mounts, is there a good kit out there already put together?

Full Tilt Boogie Racing Shopping Cart

:thumbsup::coolman::beer:

 

[V6&V8SHO]

Full Tilt Boogie Racing Shopping Cart

:thumbsup::coolman::beer:

I have to above in my 03 IRS. Big fan!:rockon: