Diff yoke specs

bac · Jun 4, 2018

Hi all,

Looking at putting some shorter gears and maybe an LSD in the diff of my '71 M code and currently weighing up the options of buying the parts and taking it to a shop to have them fit everything vs. buying a reconditioned diff center with the specs I want and doing the job myself.

Question for the forum is: what are the factory specs for the '71 M code diff yoke? I've heard Ford used a mix of different universal joints and yokes from '67-'73 and I'm confused as to what I have. There is a long yoke and a short yoke as well as universal joints with the same bearing size all round vs. mixed with 2 small and 2 large bearings as an option with the 1310 and 1330 universal joints.

Would be grateful if anyone can shed some light on this. ::thumb::

Carolina_Mountain_Mustangs · Jun 4, 2018

I do not have the specifics on the joint but I can tell you this. Ford installed the wrong one in my 1973 Q code Mach 1 4 speed. I ordered the car new and I broke 3 rear U joints from May to July. This was a bone stock with just the stock F-70 14" tires. When they figured out it was wrong size U joint the changed it and did not break another one. I have LS in mine or what Ford called a Traction-Loc, uses springs and clutches. Have another that has a 31 spline Detroit locker. They make clicking noise since they have the ratchet style locking device. You can spine the car around in the blink of an eye and get into trouble if you do not know how to control. I would just buy one already built unless there is a big cost savings.

Maybe a member with parts books can give you details.

David

Hemikiller · Jun 4, 2018

Ford essentially used two yokes for the 9" rear. If you had 3.25 or numerically lower gears in a 351 car, you had the smaller yoke which took a 1310 series U-joint. If you had a 3.50 rear or numerically higher, which was normally a 31 spline axle unit, you received the larger yoke and driveshaft for the 1330 joint. U joint applications varied by engine, transmission and rear axle type.

As usual, exceptions apply - it is Ford after all.

The smaller 1310 yoke is 3 7/32" across the flanges, the 1330 is 3 5/8".

If you want more specific info, I need to know transmission type, rear axle ratio and preferably the code off the diff carrier.

73pony · Jun 4, 2018

Ford Also used what is called the 1310BC (which was on mine - 351C 2V, FMX, 2.75 open)

Here is a thread where it was discussed.

https://www.7173mustangs.com/thread-1310-bc-ford-u-joint

bac · Jun 5, 2018

Ford essentially used two yokes for the 9" rear. If you had 3.25 or numerically lower gears in a 351 car, you had the smaller yoke which took a 1310 series U-joint. If you had a 3.50 rear or numerically higher, which was normally a 31 spline axle unit, you received the larger yoke and driveshaft for the 1330 joint. U joint applications varied by engine, transmission and rear axle type.

If you want more specific info, I need to know transmission type, rear axle ratio and preferably the code off the diff carrier.

Thanks for that info. My 1971 351 4V running into a C6 transmission still has the factory 3.00 open diff gears, so if I understand your summary correctly I should have the smaller yoke with the 1310 U-joint.

Unfortunately I don't have access to the car at the moment to check the diff code, but would you expect I would have the mixed bearing size (1-1/8" and 1-1/16") yoke & U-joint or the other one with 1-1/16" bearings all round? The other thing I read somewhere was Ford made both a long yoke and a short one, do all Mustangs have the same type or does that vary as well?