Rear end upgraded needed, any suggestions?
 

Hello,

Okay so I thought I had a 8.8 rear, picked up some upgrades and 355 gears and my mechanics tells me the rear end is a 7.5. Now everything made sense when I needed wheel spacers in the rear. So the 7.5 will need to come out because I’m pushing 438TQ and 486HP. What generation or year are people using for the 8.8? I know I’ll get the go with a 9 inch but I want the 8.8 rear for my car.

Thanks
Paul

The car is designed to use a 88-93 mustang rear. The sn95 rears will work too. Just an inch or so wider. If you don’t already have wheels that’s not a problem.

You did not indicate if you were building with an IRS or a stick axle. It sounds like you are using a stick axle rear suspension. If that is true, then any of the 8.8 axle housings will provide you with a good starting point. Determine the width you want to use and then either trim the existing axle tubes if they are too long or remove them and install longer tubes if they are too short.

Once you have the tube selection behind you, decide the ends you want to use based on the brakes you intend to use. Weld the appropriate ends on and you are done.

Thank both!

Yes, I plan on using the original drive shaft for now. I orders everything for a 1991 Axel. Couldn’t find a 1991 axel and picked up an 98 and nothing works. I think I will look for a 91 axel housing.

Personally, if i had a CR and i already had everything out i'd go with an IRS. Just sayin.

Full transparency I am not familiar with an IRS System. Could some one send me a link or anything I can do some research? I’m open to suggestions for sure.

Heidts 58” Superide IRS

The CR was set up, as stated, for a 88-93 Mustang 8.8 rear end.

I have an 1990 Mustang 8.8, 3.73 posi in my car now. It came with drum brakes. I figured I am not racing the car, and the brakes were designed for a car about 1000lbs heavier, so they should work fine for me. The lower control arms are custom from CR. The uppers are stock Mustang items.

I would consider going to an IRS, but you will need to custom build its connection mounts and shock locations. I do believe there has been some postings of folks on here doing the conversion.

IRS suspension systems are not a race car exclusive. In fact, if you examine the currently available daily driver alternatives, a huge proportion of them have IRS suspensions for the road holding and control daily driver style benefits they bring to the table. The same is true for our roadsters. Considering the decision point you currently find yourself at, you might want to reconsider what you want for your rear suspension.

Wow, that Heidt unit is pretty but pretty expensive. Basically looks almost like a Jag setup. Plus its only rated for 400hp? I'm giving it a hard pass.

It uses a 9" Ford center section. The weak spot (if there is one) is likely somewhere else.

To be honest, I never liked the Jag design, where the axel serves as the upper control arm. Break a U-Joint, and it's gonna be ugly.

It seems to me from a foggy memory that Ford made a good IRS for an SUV that was about the right width. Maybe an Explorer? Not sure about how much Hp it could handle. My little 4 cylinder turbo SUV make about 280 Hp. I think the ecoboost V6 is about 400 Hp. There should be something available.

By the way, it isn't Hp that breaks things, it's how much Hp you can hook to the ground. Tires are important too.

Thanks everyone!

I ended up getting the Currie F9 9 inch package completely built for Foxbody Mustangs.

Horsepower does not break rear ends or, for that matter, anything else in the driveline. Torque breaks everything. If you take a relatively small 500 HP Cummings diesel, with a governed engine speed somewhere around 1800 or 1900 rpm, and hook it up to a TKO-600, you might believe the TKO had a chance of surviving until you discover the engine has over a thousand foot/lbs of torque just off idle!

Guess what happens to the TKO (or TKX) if it is hooked up to a load and asked to pull it? If you haven't guessed yet, the diesel reduces the transmission to a basket of badly broken part segments — and this happens at around 250 HP or so. It is clearly not the HP that is breaking parts; it is torque!

Most aftermarket parts providers have no idea about the safe power (torque) transmission levels of the transmissions that they sell every day because they have no way to measure it and do not, so they SWAG (Scientific, Wild, Ass, Guess) it. Because HP gets all the attention, the suitability or right-sizing reference quickly goes to HP, and no one gives a second thought to torque capacity, but they should — and so should you if you are building one of these cars.

HP will get you bragging rights. Torque will destroy drivetrain parts. If you are writing the checks for the repairs, it is to your advantage to understand the difference.

I have the Currie F9 on my CR. It was a custom order. Pics in my gallery. 350GR which works well with my TKO600.

John