IRS back bolt not threading

[stuchman1]

Hi everyone,

Apologies if this is redundant but I've scanned the threads and don't see my problem previously discussed.

My son and I worked on the IRS today. Got center section in place, bolts all started, all good. Both front bolts went into place easily and threading the first back bolt was no problem, but the other back bolt, not so much. Threaded fine at first by hand, but we quickly hit more resistance than I liked once we got out the wrench.

I changed out the bolts to see if it's the bolt or the hole, and the new bolt also didn't want to go in. The others are fairly loose so the unit still has some play, which is to say that if it was slightly misaligned, it should be able to correct itself. The hole in question in the center section goes all the way through, so just to test the threads, I inserted the bolt from the front side, just to see if I could thread it. Again, lots of resistance and now I know the resistance is not an alignment issue.

Finally I figured that maybe it's just one of those bolts that's tighter than the rest and as long as I can hub it without hitting desired torque of 100 lb-ft, we're OK. Well, not so much. We hit 100 lb-ft and there's still probably 3/4" of bolt that needs to go in.

Seems like there's a problem with the threading of the hole in the center section. It's a new unit so I find that to be pretty surprising.

Anyone else run into this and/or have thoughts?

Thanks,
ST

[Gizmosrcool]

Stuchman.

Staring at the rear from the rear. The bolts closest to the front of the car should be M16.20-130mm. They do not screw in. It goes through the arm on the diff, through the sleeve, out the back, and there a flange nut goes on it. The front arms on the diff needed to be enlarged. Did you do that?

The bolts closest to the rear of the car have threads. They are M14-2.80's or 90's. The manual states the exact.

I just put mine in. I used a jack to take pressure off when getting these in.

I hope this helps. Good Luck. Tom

[Kbl7td]

Tom, I feel like I’m reading the manual and it states the opposite of what you said. The rears screw in and the front(pinion side) slide through.

[Gizmosrcool]

Corrected. I should not post when tired. Thx KbI7td.

[Hoooper]

The rear bolts dont go all the way through in the factory installation (the mustang), so the threads in the front half might be pretty dirty which would give you more resistance. See if you can spray some cleaner through there to get any dirt or debris cleaned out. In my experience the rear bolts are pretty tight pretty much all the way through, but I didnt try to clean mine either time before installing

[stuchman1]

Thanks all for the input. Tom, yes I drilled that out but I'm talking about the threaded hole in the back, not the drilled out one in the front. I'm getting a lot of resistance trying to screw in the bolt in that back, pre-drilled hole.

Hooper, thanks a lot. Will try that. If all fails, will end up trying to rethread the hole with a chaser. My best guess now is that the threads are damaged.

Thanks all!
ST

[Ted G]

Just helped out two friends install their IRS and did mine about a year ago. Trick is to get one side (passenger or driver) in and then work the the other side threaded bolt first. Then, the last bolt should be the other front bolt. It may take some force but you'll get it.

[JohnK]

If you don't already have a set, I'd recommend picking up a set of thread restoring taps/dies. They are different than thread forming taps/dies. The latter is designed to cut new threads, while the former is designed to clean up existing threads without removing a lot of material. I picked up this set (https://www.amazon.com/gp/product/B09KZQ95R3/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1)a while back and it has come in very handy many times. It doesn't have the M14 and M16 thread sizes for the IRS but I'm sure you can find those separately. This is the best way to clean up any defects in the threads in the IRS so the bolts will go in properly. If you're encountering that much resistance getting that bolt in, continuing to force it will just strip the threads and make for a real PITA repair.

[CraigS]

I can remember quite a few threads where the ears on the frame w/ the plastic bushings seem to be just a little to wide apart. Or maybe they were a little too close. In either case, the solution was to get one bolt in pretty far but not tight. Then move the diff sideways compressing the plastic bushing on the side w/ the bolt already in somewhat. I think I remember some pulled it w/ a ratchet strap, some used a prybar w/ a cheater pipe for extra leverage. I know you don't want to do this, but I would drop the diff at least part way out so I could access that threaded hole to check the threads. If they are OK, or you can make them OK, slather them w/ some silicone or synthetic grease or Neverseize. Reinstall and try again.