Setting up an 8.8

[elgemcdlf]

I started on my journey as I have a MN12 IRS in my truck with an 8.8 center section. The 8.8 became Ford's mainstay rear end replacing the 9". The cars came with 28 spline axles, Explorers came with 31 spline & I have read that all trucks with exception of the Ranger came with 31 spline. There is an exception with Rangers being the FX4 version. It came with 31 spline axles. As with the Ranger exception the cars have 1 as well. It is the Cobra IRS. It came with 31 spline axle ends on the inside BUT the outside CV joint is still 28 spline.

You can put any carrier into any 8.8 housing but there are a few differences that must be looked at. If you put the 31 spline carrier into an existing 28 spline carrier you will need to swap to 31 spline axles. Since I have an IRS I see no need to move up to 31 spline inners when the outers will still be 28 spline. The IRS has spider side gears that have a groove cut into them for the circlips. If you are running an open carrier IRS & are swapping in another open carrier from a solid axle you can take 1 of 6 routes. You can put the replacement carrier in doing nothing & put your axle shafts in doing nothing. This will for the most part lock your axle shafts into the carrier that will be extremely difficult to remove for future service.

You can do nothing to the carrier & remove the circlips from the axle shafts. I have read of people running many passes down the track with no issues BUT I do not recommend this. For the inner CV joint to operate properly the cup portion needs to be locked into position. The next option is to simply use only the ring & pinion gear from the replacement. That is pretty straight forward. You could also swap in the spider gears from the old carrier into the replacement carrier. This is not recommended by all I read yet I fail to understand why. You are putting the full set in which are a matched set. The final option would be to have the groove machined into the side gears. You could also buy the IRS gears new for the replacement carrier.

These options change when moving from an open carrier IRS to a Traction Lock carrier from a solid axle. The spider gears are different so the option of using the old spider gears is not an option. Every other option remains. You can also buy aftermarket units for just over $400. Naturally moving from IRS to IRS you need to modify nothing. Same applies for solid axle to solid axle. The 8.8 came with almost any gear ratio you could desire. I am looking for 3.55 for my personal application. They came in Ranger trucks in both open & Limited Slip carriers. I will be looking for the Limited Slip version. I then plan on having the groove machined into the spider gears. This will give me a quicker takeoff but also increase my rpm level at highway speeds.

When working with the IRS the Mercury & Ford versions have a cast housing with an aluminum cover. The Lincoln version came with an aluminum housing & cover making for a slightly lower weight overall. I have also located a Lincoln housing which I will be swapping into my truck with the gear change. Since I also plan on moving up to a thicker anti sway bar & heavier axleshafts I expect to end up back at the same overall weight as I currently have.







Reading the rear end tag is pretty straight forward on a Ford. In this image you will see 8 8 this is the indicator for 8.8. You will also see (you can't see the 3 but it is there) 3L27. This is the Limited Slip with 3.27 ratio.



For more info regarding the 8.8 (and 7.5) rear axle you can check out this link.

http://www.therangerstation.com/tech_library/Axles.html

[ultraranger]

I recognize the last photo ...that's a picture of my SC IRS.

Cobras were not the only Mustangs that came with 31-spline axles. In fact, from 1994-1998, Cobras had solid axle housings. They didn't get IRS rears until 1999 ('99-2004 --although due to engine problems the Cobra was not produced consecutively in each of the years from 2000-2004). Only the supercharged '03/'04 Cobras had 31-spline inner halfshaves. Prior Cobra IRS rears had 28-splines on both inner & outer halfshaves.

My '03 Mustang Mach1 has a solid axle 8.8" with factory 31-spline axles along with the stock Traction-Lok/3.55 gears.

All Ford 9-inch rear end production in the Ford passenger cars ceased at the end of the 1980 model year. Ford 9-inch production in the trucks ended in the 1986 model year --which was the end of all 9-inch rear end production by Ford.

The 8.8" rear end was installed in the Mustangs at the time Ford began installing the fuel injected 5.0L engines into them --1986. All 5.0L Mustangs from '86-'93 came with 8.8" rears. 5.0L LX models came optionally with Traction-Lok but all 5.0L GTs had Traction-Lok as standard equipment. Some of the 5.0L LX/GT Mustangs came from the factory with decent ratios (like 3.27, 3.55, 3.73), but most have 3.08 or more likely, 2.73 ratios. All these 8.8" rears came with 28-spline axles/differentials.

[elgemcdlf]

Thanks for the additional info ultraranger. Something I neglected to mention is you can take the carrier out of an IRS & put it into a solid axle without making any alterations.

[ultraranger]

Thanks for the additional info ultraranger. Something I neglected to mention is you can take the carrier out of an IRS & put it into a solid axle without making any alterations.

Here's a photo comparing the T-Bird/Cobra IRS halfshafts, I thought you might like to see. Cobra is definitely much beefier in the middle.

[elgemcdlf]

The inner joint looks the same with exception being the spline count. Am I correct? If so I can simply replace my shafts with the Cobra shafts. If I need to use the Cobra inners I need to rethink what carrier I want.

[ultraranger]

The inner joint looks the same with exception being the spline count. Am I correct? If so I can simply replace my shafts with the Cobra shafts. If I need to use the Cobra inners I need to rethink what carrier I want.

From the photo, it appears the T-Bird and Cobra IRS shafts are the same length.

If this is true, you could swap in a Cobra center section, but be prepared for sticker shock! Even used, they are higher than a cat's back! The other alternative to running a Cobra (aluminum) center section would be to simply swap out the 28-spline axle gears (inside the differential) for 31-spline axle gears in your existing setup, then use the 31-spline shafts.

I'm not certain if your IRS center section is iron, like mine. If so, you could try and locate a Mk VIII IRS center section --if you were wanting an aluminum center section. the Mk VIII has an aluminum center section and supposed to be the same as the Cobra aluminum version.

Cobra center sections for sale, just to give you an idea what you would be looking at for one of them, price-wise:

1. http://www.ebay.com/itm/2003-2004-Musta ... ba&vxp=mtr

2. http://www.ebay.com/itm/FORD-RACING-199 ... a3&vxp=mtr

3. http://www.ebay.com/itm/NEW-03-04-MUSTA ... ce&vxp=mtr

[elgemcdlf]

Ok those guys are just plain silly. I located an aluminum unit from a Lincoln for $50. From what those folks want I have plenty of room to make mods. I was talking about swapping in the center section of the axle shaft using my CV joints.