70 Mach 1 Rear Axle Question

04mustang70 said:

I have a 70 Mach 1 that I have had for 15 years. Finally getting around to a major overhaul. Question on the rear end. Over the years it no longer will engage both wheels, I believe it is limited slip. What would cause it to only spin one wheel now? Do I have to rebuild the rearend or do I just need a fluid fill? The rear end has never been serviced and has 130,000 miles on it (some are hard miles from my high school days) The axle code is 6. I'm pretty sure this would be a Ford 9 inch. Correct me if I'm wrong. I would like to put a steeper gear in it. What is the best (economical) way to get both tires engaging and have a steeper gear (3.75?) Thanks for all your help

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A code "6" shows to be a 3.00:1 non-locking differential for '69-'73 Mustangs. If the tag is still on the rear end's 3rd member, look to see what the first letters of the string is on the first line of the I.D. tag. Ex. "WFG-A"

If the differential is not a single track, it should be the Traction-Lok version. Ford Limited-Slip differentials ceased production in 1968. They are somewhat similar, but not the same thing, if the differentail is a Traction-Lok.

The problem is the clutch discs' friction material has worn away enough that the unit will not lock both axles together. The fix is to rebuild the differential.

If the curent ratio is 3.00:1, 3.50 gears would make a vast change in off-the-line acceleration.