mismatched drive shaft u-joint advice

[75hang10]

Hey Gang -

Turns out the 7.25 in my 75 dart is from a much earlier car, maybe a 68 a-body if memory serves correct. The PO did this switch... used to be a built up car, but he scaled it back before selling to me.

So it seems the drive shaft isn't the right shaft for the rearend because the u-joint is off. One direction of it can't accommodate any clips so it can't be properly centered/adjusted properly. The result is that its got some slop and forcing a seal in the rear to spray fluid everywhere.

My question is, can you recommend a part number that might do the trick to fix this? FWIW, the car was a /6 but is now a 318 mated to a 904 floorshift auto. I don't know if they drive shaft is stock. It could be from a /6 or it could be left over from when it was built up to a 360. The 7.25 is from something like a 68. So, any suggestions on what u-joint I could use?

 

[Brad4406]

I'm not sure I understand your discription; a picture might make it a little easier to understand. However, I will try to work with what you have provided. The year of the rearend doesn't matter, the yoke on the rear is what matters. There are only two sizes; large and small except for when we are talking about Dana's. The way you describe it, it makes it sound like you have the wrong size U-joint on the rear of the driveshaft. However, that wouldn't cause the pinion seal on the rear to leak. To fix the driveshaft problem, measure the diameter of the driveshaft where the U-joint attaches and the outside diameter of the rearend yoke to verify that you have two different sizes. You can then purchase a Spicer conversion U-joint to match both. Just tell the part store you need a conversion U-joint for a Mopar, they should be able to set you up with the right one. As I mentioned though, that isn't what is causing the rear to leak at the pinion seal. The pinion seal sounds like it needs replaced. You'll still have to do something about that.

 

[75hang10]

However, that wouldn't cause the pinion seal on the rear to leak....

As I mentioned though, that isn't what is causing the rear to leak at the pinion seal. The pinion seal sounds like it needs replaced. You'll still have to do something about that.

Thanks! I assumed the pinion seal would have to be replaced at this stage, too. The way a guy that looked at it said, the movement allowed by the wrong u-joint probably did in the seal. Does that not sound accurate? What else would kill the pinion seal?

Thanks so much for the quick advice, I think the first part about the spicer conversion sounds spot on! Any feedback on potential causes of pinion seal failure would be really helpful in the meantime.

 

[grumpuscreature]

Check the rear end yoke for a groove worn in it by the pinion seal. If there is one that is deep enough to catch a fingernail, you will need a new pinion yoke or a repair sleeve.