I have a 1965 mustang 200ci 6 cylinder and I am going to upgrade the rear axle and the whole car to five lug. First question is should I use an 8 inch or a 9 inch rear axle. Second question is if I change the rear axle do I need to change the driveshaft. Thanks

This car may later be upgraded to a 289 but the plans for now are to keep the 200ci 6. Thanks

 

Unless you want to test your fabrication skills or your wallet the only 9" that is going to fit is the one from the Lincoln Versailles. (which traces its platform right back to the early mustangs and falcons) I have read that some of those 9"ers made it into Granadas and Monarchs but still it would be a junkyard adventure or prying it out of someone's hands with cash.

So this leaves you with the 8" which is more than strong enough for 200 6 or any normalish 289 V8. The 6 can be upgraded as well. (see fordsix.com). The 8" axle could probably be sourced from a variety of small fords. Some years back I helped a guy identify the unknown 8" on his (66?) mustang. Turned out it was an exact match for the factory one on my '73 maverick, and thus he learned what it came from.

I do not know if you need a different drive shaft going from the 7" to the 8".

 

Thanks. I have been looking into upgrading the 6 as well that's why I figured that it wouldn't hurt either way to beef up some parts underneath. I was assuming that the 6 driveshaft would need to be replaced if I were to do the engine swap to the 289. Is this correct?

 

I believe in '65 the transmissions between the V8 and I6 versions were different and thus you would likely need a different drive shaft. I remember MT stuff more than AT so you'll need to double check that. By the time my car was built ford was commonizing more and more. The 250cid I6 in my Mav shares just about everything with the V8 models. Wish I could help you more, but you've run into the limits of my (remaining) knowledge of the earlier cars.

 

Thanks a lot I appreciate all of the help.

 

You are correct, I've heard the AT driveshafts are the same, but the MT ones are different. I know the V8 and I6 driveshafts on my 67 were different. However starting in 67 the transmissions were all the same. You can keep the I6 rear end even with the modded 6. I ran one for awhile and then swapped over to all V8 parts from the transmission back. Going 5 lug in the rear with a V8 rear end is way easier than the front. The front requires new spindles, hubs, and some steering components. In 67 the spindles, suspension, and steering all became universal.

Essentially the first 2 years of production were test dummies for the 67+ cars.

 

The drive shaft from a I6 with auto trans and the V8 cars are the same. The I6 drive shaft and u joints with manual trans is smaller. As BA said you can use the I6 rear end with a modded 6 but to use the V8/I6 auto trans drive shaft you will have to change the pinion yoke to one from a I6 with auto or 8" rear.

 

Ok thanks