MN12 IRS install in a 1970 F100 SWB

This thread will walk through the install of a Ford Thunderbird IRS into a F100 SWB pickup. This swap can be done on virtually any truck with a 34" wide frame. The process remains the same regardless of make. The IRS was put in 1989 - 1997 Ford Thunderbirds, Mercury Cougars and Lincoln Mark VIIIs. They are readily available in multiple configurations. They came with either disc or drum brakes and the Lincoln units came with an aluminum third member housing. They can be easily purchased used for between $150 & $400. I paid $125 for the unit used in this thread.

These IRS units come completely mounted on a subframe that is mounted into the donor vehicle with 4 main mounting bolts. HD aftermarket sway bars and axle shafts are available. With the 8.8 third member almost any gear ratio you would desire is available along with locker units. If you have the fabrication skills required to do this installation you can easily fabricate an additional third member support as well.

The bolt circle is 5x4.25 and can be swapped out using bearing units from Mustang IRS units for a 5x4.5 bolt circle. The 5x4.5 circle was only offered with disc brakes to my knowledge. The 5x4.25 came with either disc or drum brakes.

I will be using a mount kit from Truck IRS. At the time of this article the mount kit cost was $395 plus shipping. The kit includes:

(2) rear mounts
(2) front mounts
(6) gussets
(4) upper shock mount ears
(2) sleeves

In addition to the mount kit you will need to purchase:

(1) 2x2x33.6875 steel tube
(2) shock absorbers
(2) standard to metric brake line adapters
(1) U Joint
(1) MN12 IRS Unit Complete

Shock absorbers:
The shocks are not being mounted as in the Thunderbird so shorter shocks are required. There are plenty of options available. I bought mine at Advance Auto. They are front shocks from a 1970-1982 Chevrolet Blazer. The Monroe shock built for Advance is part number is 59041. The Monroe part number is 33033. The Monroe shock built for Napa is part number 94005. If you would prefer something different you are looking for a shock with a compressed length of 10 1/8" & an extended length of 14 5/8". You want 1/2" eye type mounting on both ends.

Brake line adapters:
The brake lines in the Thunderbird are metric. The brake lines in the F100 are standard so an adapter is required. The adapters are Edelmann 271300 although any adapter with matching specifications will work.

U Joint:
As it turns out Ford for the most part uses 2 basic U Joints. A large and a small. The drive shaft in the pickup used the small version while the Thunderbird IRS uses the larger version. Any good parts store can find you the proper U Joint to mate your driveshaft to the Thunderbird IRS. I have seen this install done putting the old 9" yoke on the front of the 8.8. This pickup will be receiving a 460/C6 swap soon so a new driveshaft will be needed. At that time I will have it built using the Thunderbird U Joint on the rear. This will make servicing in the future easier as parts will be standard and not a blend of 2.

I am not employed by Truck IRS nor have I ever been. I have no vested interest in Truck IRS. The pickup used in this thread is my personal pickup. I like the swap and wanted to share the process with others should they desire to do something like this to their pickup.

Still Interested? Read more on the subject here....
http://www.customcarforums.com/f13/m...976/#post43601