IRS Driveshaft Adapter thread size?

[cc2Arider]

Hey Y'all,

I decided to pre-fit my IRS driveshaft adapter and reached out to FFR to get help. I'll try here also...

The Build Manual states that the "clear" zinc adapter is for an automatic trans, and a "yellow" zinc is for the manual transmission (specific years).

My build delivered the "clear" version, and I'm pairing it with a 351W-based SBF and Tremec TKX transmission...

When I hand-thread the supplied M10 Allen-head bolts into the rear-end input shaft, thru the adapter plate, the threads match but the space for the Allen-head seems tight...so far, so good...However, when I attempt to thread in the shorter M10 Allen-head bolts into the threaded part of the Adapter (for the driveshaft yoke flange, I can't get more than a few threads to engage before it gets very tight.

1) Is the "clear" zinc Adapter Plate correct for my build?
2) what are the threads supposed to be for that Adapter Plate? M10, 3/8"x16? Did you have to "chase" the threads due to the zinc coating?
3) Did you get the Driveshaft bolts in the box with your driveshaft? The Build Manual says so, but my Driveshaft box only contained the driveshaft...


Appreciate the Feedback!

Craig C

[Hoooper]

The automatic adapter is right unless you have a used manual diff from some time in 2018 or earlier.

[cc2Arider]

Thanks Hoooper,

I'm using a Forte'-sourced brand-new 8.8 IRS rear-end (at least I think it's brand-new). Here's a picture of the box label...
189456

Did you have to chase the threads?

Craig C

[Hoooper]

I didnt have any issues with the adapter threads or the bolts for mine. I would definitely pull the adapter back off and inspect the threads in it, then use a thread checker to make sure youve got the right threads on both.

You can measure across the inside of the flange and make sure its 110mm on both the diff and the outside of the adapter, but basically if it fits into the flange and its a relatively snug fit thats the right adapter. There is a 3mm difference in diameter between the two possible adapters.

[cc2Arider]

Thanks for the reply -- Yup...fits snug!

I also think that the threads just need to be chased...

Craig C