Recommendations for IRS donor parts

[OregonDave]

I'm expecting delivery of my MK4 this week and working to source the IRS donor parts. I've read a few threads on ffcars so I know what I need, namely the 8.8" carrier and spindles, but I may also need the axles and brakes if I don't go with aftermarket parts. Of course I also need the CV joints, mounting HW, etc.

I called Mike at Cypress and he said only the Supercoupe is a good option. He was busy, but quickly said the Thunderbird V8, Mark 8, and Cougar carriers all had issues. Wish I had asked him for more details. Wouldn't be a problem except he says the complete Supercoupe donor package would need to be ordered and would cost me $700 plus shipping. Normally these parts run $300 to $400 so this adds another $300 or so onto the costs of rebuilding and cleaning up the parts.

So, I'd like to get some opinions on whether the Supercoupe carrier is superior or whether I can get away with the Mark 8 setup. I don't need the aluminum carrier from the Mark 8 . . . all I want is a like-new IRS when I'm done and steel is fine.

On a related note, does anyone sell refurbished IRS kits that are less than the ~$2300 or so that new parts cost? If I recall correctly from a poll on FFcars, a lot of people are opting for the IRS and the newbies like me should be very interested in understanding alternative to expensive new parts.

[timp2]

The 8.8 IRS assembly was used on 89 through 97 Thunderbirds and 93 through 98 Mark VIII. The reason that people are recommending the Super Coupe IRS is because almost all of them were positraction whereas most, but not all, of the other applications were not positraction.

[OregonDave]

Mike said there were mechanical issues with non-Supercoupe IRS setups. I said I didn't absolutely need the limited slip differential so his reasons for recommending the Supercoupe were technical faults with the Mark 8 and Cougar. However, if most people are using the Mark 8 or Cougar IRS without issues then I could go that route.

[rich grsc]

His comments are incorrect, the only issue is the limited slip differential. I am using a Mark 8 setup, and the only thing I did was change the gear ratio and add the limited slip. The Mark 8 may have a better set of brakes.

[PhyrraM]

I thought the V6 models were 7.5", while V8 and Supercoupes were 8.8?

[Jim Schenck]

Agreed, there are other good choices besides the Supercoupe. The Early XR7s were identical to supercoupes (engines and all) and have good parts but any of the T-birds or Cougars with the 8.8 and disk brakes will work. Many of these along with the MKVIII may not have limited slip but they can be added either Ford Racing or aftermarket. The differentials are similiar to Mustnag 8.8s but must have the notch machined in for the CV clip to lock into. We have used both Auburn and Torsen diffs that have these grooves already in them. Also the MKIII is nice because the center section is aluminum.

Something to look out for is the later Cougars were all called XR7 so make sure of the parts unless you are sure there is a supercharged 3.8 V6 under the hood.

[RyanH]

There is a persistant misconception around about axle shaft diamiter..Theres a thin and a thick version out there but both use the same CV joints which is all you will use.

Apparently several of the ford IRS cars of that era use the same knuckles so brakes are changeable to a certain extent...so your not necissarily locked in to the same brake package that comes with your donor. Research.

Other than that, an 8.8 IRS pumpkin is a 8.8 IRS pumpkin..other than your choice of steel vs aluminum...limited slip can be added if you get one without.

[Bob Cowan]

Many of the parts you need can be purchased new from Ford: knuckles, bearings, housing, etc. Not exactly cheap, but brand new.

[rich grsc]

Brand new knuckles and housing isnt one bit better than used from a donor, only a lot more $$$$

[Ophitoxaemia]

I advise a limited slip rather than an open diff.

I've got a Lincoln Mark VIII aluminum pumpkin with a Torsen T2 limited slip. The rest of the parts were from a 91 T-bird Super Coupe. I've seen the insides of 12 or more 8.8's all but a few looked like new.