We ran a Ford 9" with 4.10 gears behind the 6 before we changed out the engine, it was a BLAST to drive and the heavier components did not seem to slow it down a bit. I think it come down to "better is better" in this case.

I will change my prior answer and defer to Kalli's expertise on the u-joint sizing.

We used the I-6 driveshaft behind the 408W, but I had the ends changed to 1350 on the rear for the 9" rear, and then the front to a 1310 style for the Tremec TKO.

It would make more sense and be cheaper to just buy a new shaft if changing both joints at the same time.

 

Got the front drivers side done. Working on passenger side now. Then rear end. I am going to make a writeup for those who have a 67-68 I6 and want to go 5 lug.

 

Front is done. Going to start on the rear today or tomorrow, not really sure.

 

http://mustangsunlimited.com/itemdy0...atKey=EMUSTANG

Is this the one I need. My driveshaft was to small and these are too. So what u-joint do I need for the driveshaft to make it fit the 8"?

 

You might be able to buy a "hybrid" U-joint at a driveline shop.

It is big on one end and small on the other...

If you can figure out what series yokes you have it MIGHT be a simple matter of getting a conversion joint.


The BEST fix is to have the shaft modified to have the right yoke, should cost about a Franklin...

Kalli probably has it right 1210 shaft, 1310 rear...

I did a quick internet search for "conversion u-joints", I did not find any 1210/1310 hybrids.

 

Kalli said there were no 1210/1310 u-joints. My grandfather has 2 V8 driveshafts he is only going to use 1, so I will try and get one from him.

 

even if there was, this would be something you wouldn't want as the difference between the 2 axis is nearly and inch. There has been claims that tehre are conversion u-joints from 1210 to 1310, but noone ever came up with one when asked.

Depending if the driveshaft is a 1250, and the yoke 1310 you will find a hybrid in a syhop that'll fit you.

If you pass measurements as above (cup dias and length) of driveshaft and yoke I can tell you what you'll need.

edit: those u-bolts you posted should fit a stock V8 rear yoke. even if cap is 1-1/16 it'll do

 

All done except getting the driveshaft or u-joint, getting V8 u-joint u-bolts, and bleeding the brakes.

 

I guess one of the previous owners swapped out the pinion yoke on my 7.5"? Mine swapped with no problems.

Sorry for the confusion!

 

Well if the yoke fits...

This would be a viable option as well..