Rear end length problem... Need help

HDTony

Member
Oct 15, 2010
134
2
19
Plainfield IL
I posted this in the rear end sticky but never got an answer, can anyone enlighten me?

Length question.

The 9" i have is going to need to be shortened, its 59.5 axle flange to axle flange. My question is do I have it brought down to 57.25 or should I go slightly narrower. I am mounting 15x8 magnum 500's.

Is 57.25 the Ideal length?

Or will this 59.5 beast work? It's roughly 1.12 inch longer on each side. Doesn't seem like that much
 
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It comes down to wheel offset (or backspacing).

I have a '71-73 Mustang 9 inch rear (edit 61.25" flange to flange) in my '70 (stock '70 is 59.25") and it's too long similar to your issue. For my situation I used rims designed for an SN-95 Mustang (edit: 5.82" of backspacing) in the rear of my '70. I have 9.5" wide rims with the SN-95 backspacing on the rear, and rims designed for a '70 8" wide in the front (4.5" backspacing). Looks great and fits like a glove. I happen to be using chrome Torque Thrusts which are made for many different cars - Magnum 500s probably don't give you this option unless you spend a lot more.

I would recommend you mock everything up and measure carefully before buying rims. If you don't want to replace the rims, just make the measurements based on your existing parts to see if they'll still fit with the new rear diff. Every car is a little different, so that's why I'm recommending you check to be sure first. If you want to stay with Magnum 500s you will probably need to either get a different 9 inch rear or have it narrowed.
 
Moch up your rearend. Bolt on your wheels and measure how much you want to sink them in on each side. Subtract that measurement (x2) from the overall length of your diff and you are done. clear as mud.
 
How i set mine up, is i had the wheels and tires i wanted to use for my car. I mocked them up in the wheel wells where i wanted them to be. i took that measurement, (hub to hub on the wheel). I then called strange and told them my hub to hub measurement and rear end i was using (for me was 8.8). They did some math and figured out what i needed the axles to be as well as my housing plus bearings ect. so i then cut the housing down to what they told me.
 
It seems easier to order the wheels to suit your needs, than to cut both the housing and the axles. I have 15x8 wheels on the back of my car, and I had them add an extra inch of backspacing (5.5 on the back).
 
Well I am sure someone will correct me if I am wrong but that axle should allow late model wheels to bolt up directly without the use of spacers. I believe the usual spacer for late model style wheels is about 1.25" so that puts in pretty good shape if you are looking to go that way. If not I would suggest as others have and find the wheels you want first (for example if you want something with any kind of dish or big lip, then you will have to cut it down.
 
do you already have the wheels you want, or are you still waiting to order them? I got my wheels from SpecialtyWheel, and they added an extra inch of backspacing for free. They have the centers, and the outer rims seperate, and weld them together, so it's no big deal to change the backspacing dimension when they go to weld it.
If you already have the wheels, then this wouldn't be much help....
 
Moch up your rearend. Bolt on your wheels and measure how much you want to sink them in on each side. Subtract that measurement (x2) from the overall length of your diff and you are done. clear as mud.

That is exactly what I am working on now, I was hoping it would be easy to get the measurements etc from someone elses car, but I realized it's probably better to just mock it up and measure how much I want the wheels to move in.

I already talked to strange the other day, luckily they happen to be right here in Chicagoland, so once I get the measurements, the rear end is getting torn down and dropped off with them to shorten it. they are also going to supply me with new axles since mine are tapered and cant be shortened.

Well I am sure someone will correct me if I am wrong but that axle should allow late model wheels to bolt up directly without the use of spacers. I believe the usual spacer for late model style wheels is about 1.25" so that puts in pretty good shape if you are looking to go that way. If not I would suggest as others have and find the wheels you want first (for example if you want something with any kind of dish or big lip, then you will have to cut it down.

thats another reason I posted it, I could have sworn I read someone talking about having to use spacers to mount up 15x8 magnums 500's and for those that asked.... Yes I already have my wheels and tires and they are mounted. so I have to make this rear end fit, my wheels.