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10/25/2011 5:23 pm  #1


Tbird or Mark VIII

I'm doing a Shelly Cobra project and I wanted to go with a IRS  the kit will work with  92-97 t bird or a 92-97 mark VIII I want disc brakes but I'm having problems finding a 8.8 that is a limited slip. Are all 8.8s the same?  can I use a carrier from a straight 8.8 to make a limited slip?  What else should I be looking for when I'm looking for one of these? which one is better? please educate me I'm new to IRS


Thanks in advance.

 

10/25/2011 8:40 pm  #2


Re: Tbird or Mark VIII

Most 'Birds are 7.5s.

The T-bird SCs and Cougar XR-7s got an iron-case 8.8.

The Mark VIII got an aluminum-case 8.8.  This same case was used in the Cobra Mustangs.

The SCs to my knowledge all had limited-slip diffs, the 5-speeds were 2.73 IIRC and the automatics were 3.27.    All the Mark VIIIs were open diffs, the one I had for parts was a 3.07.

Even the iron SC diffs got a very, very weak aluminum rear cover (it weighs about as much as a beer can) and a less-than-impressive mounting arrangement (two narrowly-spaced vertical-axis mounts in front and a single bonded-rubber V-mount in back cantilevered some ridiculous distance behind the carrier.)  There are aftermarket braces available to keep the cover and mount from coming apart.

All the SCs and Mark VIIIs, and the pre-blower Cobras, used 28-spline inner drivers.  The '03-04 Cobras used 31-spline inner drivers.

The Ford factory 8.8 Trac-Lok diffs are interchangeable between IRS and stick-axle housings.   Some aftermarket diffs are, some are not - if you're planning to use one, check with the vendor.

You apparently can't use one, but the '02-up Explorer used a very different 8.8 IRS center section, much MUCH stronger, with an infintely stronger rear cover and a three-point mounting (offset front bushing, widely-spaced rears that bolt to outriggers on the rear cover) more typical of German practice.   Not only is the case different, the drivers, side bearings, and seals are different too, so trying to use one in a retrofit application means custom axles.

I'm currently working on cooking up a mounting bracket to allow use of an Explorer rear cover on an earlier IRS pumpkin (I'm using an iron SC case) on an MN12/FN10 subframe, not sure if it'd fit anything else.

Last edited by JEM (10/25/2011 8:54 pm)

 

10/25/2011 9:53 pm  #3


Re: Tbird or Mark VIII

Look for a unit with the 3.27 gears. I have 3.36 in my C3, they are great. I do not have an OD, I could use it on highways however. My tires are 26.5 diameter and I run app. 3,000 RPM at I think 70 mph.

Last edited by Ralphy (10/25/2011 9:55 pm)

 

10/25/2011 9:59 pm  #4


 

10/26/2011 10:12 pm  #5


Re: Tbird or Mark VIII

Ralphy wrote:

Look for a unit with the 3.27 gears. I have 3.36 in my C3, they are great. I do not have an OD, I could use it on highways however. My tires are 26.5 diameter and I run app. 3,000 RPM at I think 70 mph.

I'd consider 3.27s the absolute shortest gear I'd run without  overdrive gears in the transmission.   3.55s, even 3.73 are perfectly acceptable with a 0.60-0.65ish top gear in the transmission.

 

10/27/2011 6:39 am  #6


Re: Tbird or Mark VIII

JEM wrote:

Ralphy wrote:

Look for a unit with the 3.27 gears. I have 3.36 in my C3, they are great. I do not have an OD, I could use it on highways however. My tires are 26.5 diameter and I run app. 3,000 RPM at I think 70 mph.

I'd consider 3.27s the absolute shortest gear I'd run without  overdrive gears in the transmission.   3.55s, even 3.73 are perfectly acceptable with a 0.60-0.65ish top gear in the transmission.

With the 3.36 gears if I do ever go with an OD, I think I would prefer .80 OD. It shifts more like having another gear. But I can see if you started to get in the high three's going with a .060.

I guess it's also what your looking for. I'm not looking to boulevard race from light to light running 4.00 plus gears.

Last edited by Ralphy (10/27/2011 6:42 am)

 

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