8.8 IRS donors?

I'm thinking we'll have to go with an 8.8 ford third member for our LeMons RX7 project. I know the 2002+ explorers had them. I know they were available in the MN12 Birds and Cougars, but did all of those cars have 8.8s? Others include Mark VIIIs, Cobras, and the clones to the above mentioned vehicles. Is there anything else out there? Will a 28 spline Mustang posi unit and gears fit into a later third member? I'm thinking I'll likely use the 89 and up Bird parts for the ability to buy the cars for scrap weight. Anything I need to know?

The V8 and supercoupe/XR7 MN12's had the 8.8, the Mark 8 has an al housing 8.8.

Any 8.8 gears will work, not sure about the limited slip though, there is a groove in the IRS models to hold the stub axle in. Where are you located.....I have a complete Supercoupe IRS sitting on my back porch I will probably never use...

The NA V6 T-Birds and Cougars had the 7.5, so watch out for those. Remember too that the Lincoln, Cobra, and maybe Explorer housings are aluminum, while the MN12 housing is cast iron. Trac-Lok was an option on 8.8 MN12s, but not the Lincoln. You should be able to find a factory-equipped posi if it helps with your budget.

I've got a 3.27 posi third member from a Supercoupe I'd part with if you were closer.

know some truck guys use the entire thunderbird rear end

http://www.team321.com/truckirs/TEAM321TruckIRSInstall.html

You can buy the hubs from the IRS Mustang from ford performance parts as kit car hubs. Probably for Cobra kit cars. Then you can use mustang 5-bolt rims.

I'm in Dallas. So the SCs are probably the cheapest way out. The Lincoln was open diff only. Do all the MN12 V8 cars have the 8.8?

If you'd like a fast way to visually identify the 7.5" from a 8.8" look at this link.

There are two small relief cuts at the bottom of the 8.8" diff cover and none on the 7.5"

RossD wrote: You can buy the hubs from the IRS Mustang from ford performance parts as kit car hubs. Probably for Cobra kit cars. Then you can use mustang 5-bolt rims.

Yeah, but they are 100 bucks EACH! Can get the 'bird ones redrilled for less than one new hub.

You can actually buy the spindles new and center section too IIRC...Just a lot of $$ compared to $150 or so for a complete used one.

If it matters the Explorer diff has a 31 spline carrier the T-bird has less. The stub axles will not interchange.

btp76 wrote: Do all the MN12 V8 cars have the 8.8?

Yes. V8s could have 3.08 or 3.27 gears; Supercoupe 5-speeds came with a 2.73.

foggy memory here, but didn't the mark 8 LSC have limited-slip?

familytruckster wrote:

RossD wrote: You can buy the hubs from the IRS Mustang from ford performance parts as kit car hubs. Probably for Cobra kit cars. Then you can use mustang 5-bolt rims.

Yeah, but they are 100 bucks EACH! Can get the 'bird ones redrilled for less than one new hub. You can actually buy the spindles new and center section too IIRC...Just a lot of $$ compared to $150 or so for a complete used one.

When cash was tight, I've done this with good results. (It also could have been dumb luck and pratice on a spare axle). Do the math, with what bolt pattern you have, and want to get to, make a little jig, and redrill them yourselves. Picture is an axle, but same for a IRS hub. I put the rotor on the axle and then the jig on top, and drilled the rotor and axle together.

AngryCorvair wrote: foggy memory here, but didn't the mark 8 LSC have limited-slip?

I believe all Marks are 3.08 open diff w/traction control. Wouldn't bet my life on it with the LSC, but I think I'm right on this one.

In reply to Will:

The LSC got better 3.27 gears, but were still open. HTH

If this is a second gen I think you will be alright with the factory diff. Lots of V8 and rotary guys putting down a lot of power with no real issues. You are going to be limited to a high ratio rear end (mostly 4.10 IIRC)

Yeah, the 4.10 is the problem. In our LeMons wagon with 3.73s we never use 1st and often run out of 4th. 5th gear is .4 taller than 4th so it's nearly useless.

With the Rex we should shed 500lbs so we need less gear to get it rolling aside from the issues we already have with the 3.73s. I haven't really looked at the ratios, but my hunch is we need something like a 3.00 gear.

Also, if it would stick, we could downsize from a 245 45 17 to a 225 45 15 and cut our tire budget in half.

We have a solid 8.8 3.27 in the 1st gen RX-7 with the 5.0 T-5. Running 235/45/17 At Sebring we were runnign out of 4th on the back stretch and really only using 3rd and 4th however we were having some carb issues. I think 3.73's is what we are looking for next.

At PBIR we were running the stock 3.9 RX-7 rear on 205/60/13. Ran out of gear around 130 in 5th. I liked that set up better honestly. With the taller rear we really just ran 4th and 5th. Made it pretty easy to drive.

Given the expense and fab work of making that rear work I would probably just keep the 4.10 or find an auto rear end (3.9 IIRC)