Driveshaft end yolk compatibility

[87CrownVic]

Hello all, it's been a little bit! I searched through alot of great info on driveshafts and spacers and universal joints from over the years, but nothing regarding my current situation.

I am finally installing the 8.8 disc brake rear end in my '79 LTD and running into a few issues. It was originally a 7.5 rear end with FMX transmission and a silly, odd little driveshaft. The rear flange coupling on the original driveshaft does not bolt onto the new 8.8 input flange. I will just be dipped in shit if I can figure out where to obtain an appropriate coupling (if it even exists) for the driveshaft so i can run the original for the time being and maybe actually drive the car this summer. Has anyone come across this situation before? Please advise!

[Mustang Eddie]

The easiest way to make it work is take the pinion flange off the 7.5 & put it on your 8.8. You can also change the rear flange on the driveshaft to match your pinion flange but it may require a combination u joint depending on whether your driveshaft has 1310 or 1330 u joints.

[87CrownVic]

I should have specified - I am hoping to avoid taking the 8.8 apart so i don't have to replace the crush collar and retorque it and blah blah blah. OH, and I already scrapped the failed 7.5 without removing the flange. Like an idiot. I wonder if the trans end is correct from any of the old aluminum 351 PI with 8.8 or '96-'02 (4R70W??) aluminum driveshafts. I would upgrade to the later aluminum shaft with the correct flange end on it in a heartbeat if the FMX accepts it in front...

[Mustang Eddie]

Trans yoke from 4r70w is larger in diameter so it won't work. Really not that hard to change the pinion flange. 351PI driveshaft is still going to have the wrong flange on the rear. I'm pretty sure the later driveshafts are about 1" shorter so they won't work either. A Marauder driveshaft is the same length as some boxes 55 1/2" cl to cl but will have the wrong yoke on the front. I can help you out with the correct rear d/s flange but it is for a 1330 u joint so you'll probably have to buy a combination u joint because I'm pretty sure your d/s has a 1310 joint. I also have a Marauder shaft here I can sell you that I can change the front yoke on to work in your application.