U Joint questions
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Cross-Country
Joined: Sep 2014
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U Joint questions
Hello all- I have a 75 F100 shortbed and have discovered a u joint is out in the rear. The drive shaft is one piece, with a u joint in the front and in the rear. I just replaced them both around the 1st of the year and truck gets driven not so often. Any idea what could have caused the rear one to fail? It had lots of slop and was on the verge of destruction. I measured the inside of the 2 notches in rear yoke where the cups rest and it is right at 3 1/4 wide. Only did this since I was ordering a third member from quick performance and needed to know which yoke. The engine and trans are not original to the truck, although I have no idea what years or what they came with. The engine is a 351M and the trans is a C6 auto that is recently rebuilt. Am i overthinking this? I read a lot about cup size and not sure if I had the correct ones? BTW the front one seems to be good and tight
Hotshot
Joined: Feb 2004
Posts: 10,842
Likes: 2,612
From: The Shenandoah Valley
There are several U-joints used.... and then Ford also uses a "big cap" joint at the rear often times. There's the 1310 series .... then there is the 1310 BC series.
Your driveshaft's yokes and the very front yoke at the transmission likely have 1-1/16" OD bearing caps, but there at the rear axle, the yoke with the two U-bolts holding the caps in ..... very likely 1-1/8" OD caps. They do that to add material to the cap to resist crushing by the U-bolts which don't have to be super tight .... but many still overtighten them.
Measure the old ones or measure the yokes. Here is a link to start you. When you figure out what you need, you can get the right ones easily crossed at your auto parts store.
U-Joint series identification
In use, you'll see 1-1/16" expressed like 1.062" and 1-1/8" expressed as 1.125". That 3-1/4" you mentioned is likely 3.219" across the joint cap top to cap top when squeezed by hand. That's "outside lockup".
Your driveshaft's yokes and the very front yoke at the transmission likely have 1-1/16" OD bearing caps, but there at the rear axle, the yoke with the two U-bolts holding the caps in ..... very likely 1-1/8" OD caps. They do that to add material to the cap to resist crushing by the U-bolts which don't have to be super tight .... but many still overtighten them.
Measure the old ones or measure the yokes. Here is a link to start you. When you figure out what you need, you can get the right ones easily crossed at your auto parts store.
U-Joint series identification
In use, you'll see 1-1/16" expressed like 1.062" and 1-1/8" expressed as 1.125". That 3-1/4" you mentioned is likely 3.219" across the joint cap top to cap top when squeezed by hand. That's "outside lockup".
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