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Drive shaft wobble 77' C-10

My truck started vibrating a couple days ago and is getting worse. It felt like a u-joint going bad, so I set the parking brake, put it in gear, and climbed under. When I moved the drive shaft I expected to see movement in the u-joints, but instead my yoke is wobbling around where it slides into the transmission! I have had many transmission issues with these TH350’s but I have never seen this. Any ideas?

Did you pull the driveshaft? The yoke is either worn out or the output shaft is worn. Another possibility is that the driveshaft yoke is the wrong one. Are you the original owner? A good mechanic can get this sorted out for you.

Yes, since I’ve owned the truck, I’ve put two transmissions in this truck. The original(non-lockup) was in it when I got the truck. It simply stopped shifting, which is fine for a 25 year old transmission. I put a rebuilt in, which was a lockup TH350, running without the electronics. It operated well, but the metal lines were rubbing against each other. This caused it to rub through on the freeway about a year later and leak all the fluid, which destroyed it. In went another rebuilt, this time a non lockup, which worked great for about a year. First, the tailshaft bolts worked loose and the tailshaft separated while on a 4X4 trail. After replaceing the bolts it has worked fine for a couple of months, untill now.

How deeply does the yoke sit in the transmission tail piece? Measure the length of the exposed smooth machined part of the yoke that slips into the seal. Is there more than 3 inches exposed? How much?

Took my drive shaft off today and found that the output shaft that the yoke slips onto is wobbling around with about 1/10 inch of play. I assume that it needs new bearings of some kind, but do I have to drop the tranny to do this? Are they pressed on, and if so, what would be the best way to get them off?

There is a bearing in the tailpiece that the yoke slides in. With the yoke out the output shaft will have quite a bit of play. If the drive shaft has been repaired or raplaced with a salvage part it may not be long enough to reach that bearing. Before you bolt the rear yoke up install the slip yoke fully into the tailpiece and check for play. If the tailpiece bearing is bad it is easily replaced.

It can be assumed that EVERYTHING is worn out…Here are the parts you need…