99 Tahoe U-joints..again!

I posted not too long ago with the same title, 99 Tahoe U-joints. I say again because I was on the maiden voyage into the city after all the work I had done on this truck, and the rear u-joint came apart after about 50 miles. In replacing the fuel pump I removed the drive shaft and while it was out I thought it was a good idea to replace the u-joints. Learned all about the factory "plastic injection mold" retaining method used by GM and how to deal with that. See '99 Tahoe U-joints' thread. Anyway, the rear u-joint threw a cap and all was crap after that. Here's the thing. In replacing the u-joint on the bench with the help of a vise, a hammer and my son adding squeeze to the vise while applying hammer to vise jaw, the new u-joint was a very tight fit and needed every fraction of an inch to get the clips in. After installed, the new joint was stiff but could be moved. I remembered a comment from another thread that said, "don't forget to grease the new u-joint before you put it back in". So... I greased the front joint, no problem. But made the mistake of greasing the back joint. I should have seen it coming. The 2 caps push off cuz there's nothing holding them yet. Okay, so I push them back down but they want to just slowly push back off because of the grease. I figured I cold hold them together enough to get the saddle clamps on and tightened up so that's what I did. I remember while I was putting it in the first time thinking that I'd better get this thing centered. Now here's my question and I'll have to use the "F" word here. My Ford has a ridge on the outside edge of where the caps sit in the rear pinion yoke so the u-joint is "contained" and centered when tightened. The Tahoe has no ridge and the clamps don't either. I thought sure when I pulled this shaft back down, I would see where I didn't hold the caps together enough to catch the ridges but there is no ridge. How do you know if the shaft is centered? Do you just tighten the crap out of those bolts? I don't want to make the same mistake again.

Every U-joint saddle I have ever encountered has a ridge or specially-shaped saddle that centers the caps in one specific spot. Possibly you missed finding the sweet spot.

Do not overtighten the straps that hold the caps in place. This distorts the caps, so they become oval, which seizes the roller bearings and leads to rapid joint failure.

Also, when you press in the U joint in the driveshaft it must move freely. If it is stiff, something is wrong, usually the tiny roller bearings get dislodged in installation,. Either one has become dislodges and is sitting at the bottom of the cap or they are no longer sitting parallel, which leads to quick joint failure.

BTW the first few times I did U-joints, I had to do them a couple of times over, including re-aligning all those tiny cap bearings, before I got everything right. It just takes a bit of practice. :)

Thanks MajicRat for replying. I looked when the shaft came back down this time specifically for a ridge or something. The land is flat all the way across. I'll take a picture and post if I can figure out how to get it in. I'm getting another u-joint tonight and putting it on the shaft. I'll try to post a picture before I put it back in the truck. What I won't do is grease the new joint untill it's in the truck. That didn't help.

You're right Trox, there is no "centering" device. What I always do is line the new caps up with the rust line left by the old caps on the yoke. Either I've got dozens of them prefectly centered or they're not very sensitive to being out of balance... I'd guess the latter :)

For the stiffness in the joint... I get a bit of stiffness in one direction on a lot of aluminum shafts, not sure why (I'd guess they bend slightly). But I've never had a problem or comeback letting them go like that (the first one I did I drove all over the place and then brought back and pulled the shaft again, it was free after driving maybe 5-10 miles). It's not very much stiffness, but it's not loose by any means. Usually one way it'll flop back and forth and the other way I have to shake it a bit to make it move.

When you put the caps in, always set the cap on a hard surface, hold the shaft level (either get a helper or adjustable stand), and tap the yoke to get the cap in. Never tap the cap or you'll bend it in slightly unless you hit it perfectly centered and square. So... install cap one, hold joint into cap one, rotate shaft over, set cap two on surface, lower shaft to where it's touching cap. Then (this is the most important part for not losing a roller) let the joint go so it's half way (roughly) into each cap and then tap the yoke down.

You're right Trox, there is no "centering" device. What I always do is line the new caps up with the rust line left by the old caps on the yoke. Either I've got dozens of them prefectly centered or they're not very sensitive to being out of balance... I'd guess the latter :)

It's probably the former :)
In my experience, it only takes a few grams of off-centered metal to produce a vibration. I've been able to fix a driveshaft vibration with a couple of well-placed hose clamps followed by a spot-welded washer.

As for the lack of self-centering.... thats odd. I expect the change was made to take advantage of some new assembly-line procedure when the truck was manufactured. Good to know, though for the next time I see one.