IRS Center Section Rear Bolt Length

[cv2065]

Just finished buttoning up the center section install. Anyone know why the M14-2.0 100mm bolts are about 1/2" short from going all the way through in the IRS rear mounts? Is that how they are in a traditional Mustang?

[edwardb]

I have no idea how long they are in a Mustang and if they go all the way through. But the length supplied with the kit is completely adequate. The boss is large and has plenty of engagement.

[cv2065]

Thanks Paul for the reply. I was tightening the bolts and just realized that. Must have missed it before. There’s over an inch of thread engagement, so as you said, it’s plenty. Thought I saw someone mention the Mustang comparison in another thread.

[TXJosh]

Thanks Paul for the reply. I was tightening the bolts and just realized that. Must have missed it before. There’s over an inch of thread engagement, so as you said, it’s plenty. Thought I saw someone mention the Mustang comparison in another thread.

I have noticed the same thing. The rear bolts do not have sufficient length to get through. I do not think that the fact that the threads are engaged an inch or so is sufficient. I plan to use a longer bolt so that I can use the flange nut — there is so much force going through this part.

[OB6]

I have noticed the same thing. The rear bolts do not have sufficient length to get through. I do not think that the fact that the threads are engaged an inch or so is sufficient. I plan to use a longer bolt so that I can use the flange nut — there is so much force going through this part.

This isn't something I'd get hung up on. Take a look at a 2015+ IRS assembly and you'll see that the factory bolts don't engage all the way either. It's likely that the FFR design uses the same specs as Ford.

[edwardb]

I have noticed the same thing. The rear bolts do not have sufficient length to get through. I do not think that the fact that the threads are engaged an inch or so is sufficient. I plan to use a longer bolt so that I can use the flange nut — there is so much force going through this part.

No need to re-engineer that connection. (1) Meets the "two times thread size nominal diameter in aluminum" rule. (2) I don't have data (obviously) but I'd bet that aluminum ear would break off before the threaded bolt connection would fail given the amount of thread engagement with the supplied bolts. Including the same as what our friends at Ford do on the Mustang. There have been multiple hundreds of FF Roadster built with that setup without any reports of failures. Mustangs with high horsepower, drag slicks, etc. report things like broken axles (big aftermarket item) but not broken housings.