My Mustang is a 68 straight six coupe. The PO had installed a 5 lug set up in the front. I ended up getting a rear end off of ebay from from a 68 Cougar with the 5 lugs. Seems like it will fit.

My question is, how do I tell what gears it has?

Also, should I open it up to make sure everything looks good inside before installing it? If so, what should I look for?

The drum brakes a fairly rusted and seem original- is there a kit someone can recommend for a rebuild. I'm assuming that a 68 cougar and mustang have the same drum set up.

Thanks.

 

It will fit. What is the tag # on the differential, that will tell us gear ratio. based on production thre is a good chance it will be in the 2.80:1 to 3:00:1 range. I would open it up if for no other reason than to get the old fluid out.

 

That Cougar rear ought to be fine. To see what gears are in it, set it up on some jackstands and mark a spot on the brake drum. Turn the drum one complete revolution and count the number of times the U-joint yoke turns. If the output (wheel side) turns one rev and the yoke turns 3 complete, then you have a 3.00:1 rear end.

Turn it and listen for any noises...turn it back and forth and listen to it 'clunk'..to see how tight it is. There will be some slop between back and forth..maybe 1/4 turn. Unless you feel any grinding or more than that 1/4 turn..I'd go ahead and install.

Definately rebuild the brakes before installing. New brake shoes,rebuilt brake cylinder, andhave the drums turned.

 

Ok so the gears are 2.80

Another question:

When I spin the drum, nothing happens-
when I spin the U joint the drums turn-
when I spin the U joint I'm able to stop the drums from spinning- is this normal?

 

When I spin the drum, nothing happens- Normal
when I spin the U joint the drums turn- Normal
when I spin the U joint I'm able to stop the drums from spinning- is this normal?- normal

 

You guys are great- thanks for the all the info. Another question.

So I have an inline six at the moment- It runs great and I'm planning on keeping it in there for a couple of years while I build up (brakes, suspension etc...) for a 289 or 302.
I'd like to get the most out of the 6, but as mentioned I'm only planning on having it a few years- so here's the question.

Would it make sense to drop in a better ratio of gears that will give the six a little more pick up, but also work well with a V8 in the future?
Recommendations or insight would be great.

Thanks

 

Everyone has their thoughts on this topic... If it twere meeee...

I'd spend the next couple of years working on brakes/suspension upgrading to V8 specs and 5 lug wheels. When it came time, I'd lower the rear gears to 3.40s or so AND install a T-5 behind the I6 at the same time. Then after a while, when you get ready for the V8...you can drop it in using the same T-5.

 

Why only a few years?