Do we have the right bolts for mounting the rear differential for 2015 IRS?

[kmseddon]

Hello - We are preparing to mount the rear differential of our 2015 IRS set up and the bolts are confusing us compared to what is shown in the instructions, in the book, in EdwardB's photos, etc.

The silver bolts that would go through the bushing and then into the rearmost part of the differential are 100 mm and appear they would end in the differential without the need for a nut. Those seem right.

But the frontmost gold bolts are 130 mm and seem to come with lock nuts. But they seem tight going into the differential and then I worry that the unthreaded part of the bolt might not even fit through the differential since it seems a little wider? Why would they bother to thread the frontmost part of the differential if they just want the bolt to thread into the nut after the bushing?

I didn't want to force anything and double check with the brain trust before I started.

Thanks,

Differential.jpg

[MSumners]

Did you drill out the mounting holes yet on the front of the diff?
They get drilled out to 5/8ths

[edwardb]

The rear cover has threads already from the factory by Ford. No additional nuts are required. The front mounts aren't threaded from the factory. But doesn't matter because they get drilled out to 5/8" as already mentioned and shown in the instructions. With that, the provided hardware goes right through and yes requires lock nuts. Not sure what you're seeing in my build threads. It's possible the provided hardware could be slightly difference now (e.g. different plating or whatever) then when I did mine. But nothing has changed in the two builds I've done several years apart.

[Traveller]

I echo what Mike said - have you drilled them out per the manual? As a side note, drilling those things out with a hand drill is tricky (at the beginning the bit wanted to bite in and the drill would try to snap your wrist...). I found that using a step drill bit to slowly enlarge the hole to 5/8", then using a regular 5/8" bit to finish the hole helped a lot.

[michael everson]

What Msumners said. You need to drill out the front holes to 5/8. You will need to do this to the spindles as well
Mike

[kmseddon]

Geez - thank you Msummers, Michael, Paul. I missed that part. I saw it for the spindles, but not the rear differential as well. Thank you!

Since you guys are so knowledgeable, I wanted to ask a follow-up. I am going with 15" wheels on our car. I hear that with 15" wheel some have a problem with a lack of positive caster and the recommendation is to cut the upper control arms by about ¼" an inch. Does that sound reasonable and necessary to you?

Paul, we are so grateful for you build blog. We are trying to follow it as best possible. Could you tell us were you got those couplers on post #26? Thank you all!

[edwardb]

Paul, we are so grateful for you build blog. We are trying to follow it as best possible. Could you tell us were you got those couplers on post #26? Thank you all!

You're welcome. That thread just keeps on giving. Some of it getting a little dated, so be a little careful... Those couplers are these https://www.mcmaster.com/90977A190/. As I mentioned in the post, I was using 7/16"-20 hardware because I had it left over from previous builds. So got the couplers from McMaster to match. Also listed as grade 5. 7/16"-14 is a more common size and nothing wrong with that either.

[toadster]

yeah go slow on the 5/8" bit - it will test your wrist strength for sure!