I am rebuilding my first mustang. It is my wife's first car and has been on jack stands and covered for 18 years. It is a 1971 mustang coupe and I have been working on the project for seven months. It has the original 302 that has been re-built and the original f-4 transmission that has also been re-built. I have a question that someone might be able to help me on. I noticed the other day that with the transmission in park and the dive shaft locked up, not turning; the rear wheels still spin. The car rolls freely. Can anyone help me understand why? I know according to the id on the rear axle that it is not a limited slip, just a conventional differential. Do I need to have the rear axle re-built?

Thanks for the help,
Brent from Arizona

 

reread

 

No rebuild unless the lash (play) of the driveshaft engauging the gears is large. On the 9" rears, even if the lash is large, it will still work for a long time! I have my 69 Bronco and I think the diff was rebuilt in the mid-70s... it's a little clunky, but it still works.

If you had a posi, it would not spin with the driveshaft locked, but without the driveshaft the wheels would spin the same direction. With a non-locking diff (even limited slip), the opposite wheel will be spin the opposite direction of the one you spin. Now if both wheels were on the ground and you had it in gear, it would "lock" and the car would only roll a little bit, i.e. it won't roll down a hill.

That's about the best I can explain it without finding some detailed one on the web. The whole purpose of non-locking diffs is to help cars turn better, making the outside wheel turn faster than the inside wheel.

Good luck on the resto! My Bronco is still in pieces after 3 years, it takes a long time unless you have the time and money to get it done in a short time. Hopefully you will break less bolts than I did (rusted).

 

Thanks. With a little more research, I found out that I have a open differential and what the axle is doing is perfectly normal. Also I have a C-4 transmission not a F-4. Good luck on your bronco and thanks again.

Brent