My 67 Cutlass has a a Chevy 12-bolt rear in it that I'm pretty sure is not original. I put a new engine and transmission in it so I replaced the u-joints to hopefully add some reliability. The yoke of the differential uses the larger u-joint and the driveline uses the smaller. I have installed the conversion joint from Auto Zone but when I tightened the caps on the diff yoke I noticed that the u-joint caps have a little extra room between the centering tabs. I moved it back and forth and tightened the bolts down with the u-joint centered as close as I could get it. This is not giving me a warm fuzzy feeling because if it is slightly off it will probably vibrate. Maybe not enough to feel during normal driving but I will always wonder... Anyone else had this problem or know of a u-joint that fits the diff yoke better?

 

It might help if you said which rearend you have (Chevy 12 bolt or O-Type) and the part number for the u-joint that you installed.

 

Edited. I'm not sure if I used the Moog 348 u-joint or a different brand. They should all be the same size but that doesn't always happen in the real world. I installed it over two years ago and with the move to Virginia and all that it entails, things like a project car get put on pause so I don't remember.

 

I've got a 1972 Chevy 12 bolt under my 1970 442. Its been years since I changed the U-joint but I got one from NAPA that had the different sized caps. I do remember the Olds was wider across, from end of cap to end of cap and the Chevy was narrower. You might measure the distance between the stops on the yoke and take that measurement to the parts store. I agree with you that it should be tight against the stops to be sure its not going to wobble.

 

Ok well CHEVy 12 bolts had 2 different WIDTH 1 1/16" caps. 1310 and 1330 yoke
IS the yoke 4 bolts and 2 straps ? or U bolts?
YOU CAN NOT run the u joint that way EVER...IT WILL FAIL and Vibrate.
So if you have some pics that would help easier BUT which ever way you can will figure it out
So if the caps are the correct size you have a 1310 to 1330 issues. If the caps are rocking in the yoke the chevy rear has a BOP yoke and you have a chevy drive shaft and had a it changed when the 12 bolt was swapped??

Or your 12 bolt Chevy has an AFTER market 1350 yoke and your trying to fit the BOP 1 1/8" joint in the yoke?
Like I said Pics will help alot and measurement.
You are just using small large wide etc.
ALL that does not help.
Measurement will help.
The diameter of each joint cup and the saddle of the yoke across the saddle will give a diameter cap that fits it. 1.062 or 1.125 or 1.188 Thise are the 3 it can be.
THEN there is width of joint 2.556 or 3.625

Jim JD Race

 

Ok, so it looks like I have a large yoke on the drive line and a small yoke on the differential. 4 bolts and two straps. The u-joint is supposed to be a transition joint so they can be used together. I have no idea when the Chevy diff was installed or what it came out of. The diameter of the cups all fit their respective yokes, the only problem is the side clearance in the differential yoke. One pic shows the amount of side clearance. Guess I need a wider transition u-joint. Pics...

 

Here are the markings on the diff if it will help identify what it came from. The cast-in numbers are 0 282, and the stampings are KDC 123 2. Definitely a Chevy 12 bolt though. Joe P helped me to see the light on that one.

 

If thats the stock drive shaft you need a 3r to 1350 conversion u-joint
https://www.dennysdriveshaft.com/c14...0Query=2-3011p

 

That is a conversion u-joint! Either the yoke is too wide or the joint is too narrow. 3.625 inch would never fit that yoke.

 

So, I took the drive line out again and was going to measure the saddle that the u-joint fits into and found that it is just completely worn out. Like many things about this car, it has been sorely abused at some point in its life. The guy I bought it from said his Uncle was a "Master Mechanic." That means because Uncle had been helping him with it the original carb leaked, the cooling system leaked, the head gaskets leaked, the transmission leaked, and so on.
Anyway, by centering the u-joint I was actually getting it settled into the saddle of the yoke properly. The alignment tabs are just so worn and the hold-down straps were so distorted that it would slide around quite a bit. I straightened out the straps that hold the caps into the yoke and it now holds the u-joint in place properly. Makes me wonder what happened in the past that made the the yoke so worn out? I'm glad I haven't been able to drive it any more than I have.

 

Yep, I get that with rears all the time. OH A PROFESSIONAL ASE mechanic installed all the parts. RIGHT!... Just because they passed a test does not mean they know how to use the info .
ANYWAY... The tabs like you said on the yoke are abused. You will need a NEW yoke or a MUCH better used one. MAny years of abuse and parts breaking and someone just reassembling each time bending twisting and hammering parts back together...
So at least you figured it out.
The u joint is what we refured as a BOP to chevy conversion joint
Moog 372
Mechanics 3R one way (1.125" cap) in the driveshaft and 1310 the other way 1 1/16 inch cap in the yoke.
Jim
JD Race

 

chevy also had a 1330 yoke with a joint width of 3 5/8" too same size cups. They were used with BIG BLOCK chevy cars. 1970-1972
IF this chevy rear was original to a BOP car it would have a CHEVY BOP yoke on the pinion.
SO this is a CHEVY rear that was from a CHEVY car.
The BOP to CHEVY u joint was very common way to swap rears from BOP to chevy chassis.
Jim

 

YOU can see the damage / dents in the saddles where the u joint let go some time in the past. That yoke is totally junk. Get rid of it and get another or a new one.
Sorry it is just not repairable.