About U-joints...

[canyncarvr]

On the rear-end end of my driveline I noticed the U-joint moves 'some' between the cups. 'Some' as measured by my dial-indicator is .008", on axis.

Does that indicate a problem? I haven't noticed it before. Does not seem reasonable that a new joint would be necessarily any different as such movement is not in a wear pattern. There is no such movement on the prop-shaft end.


As a btw, it's a 7290 (large u-joint) driveline w/zerk-fitted u-joints. The two cups I can easily see the insides of look fine; no dimpling on the cross, well greased. Both joints are loosy-goosy movement-wise, no binding and they rotate completely.

After I greased the joint that had the movement, I could not move it as before it was greased. I'm not saying greasing it 'fixed' something...just that the movement can no longer be felt/measured/seen.

I did take the driveline out looking for a vibration source. Around 100mph/6000rpm something is buzzing/shaking the car. LOTS of things it could be, but having just resolved a vibration issue in another rig by replacing u-joints (that I didn't 'feel' as bad), I thought I'd check 'em.

Tanks!

 

[AJ/FormS]

Hmmmmmmmmmmmmmmmmmmm
"Some between the cups" is normal,but .008 seems to indicate that the cups could be closer together, or the cross, a little wider. Depending on which method your yoke uses to locate the cups, this cannot usually be changed. Greasing it, of course, filled the internal gaps with grease which "cured" it. Of course soon enough the play will be back.
So, what to do about it? IDK.
If your yoke has cup-stops and straps, I guess theres nothing that can be successfully done,short of shimming the stops.But I fear the shims will fly out, as there is nothing to keep them in and the straps do not have a whole lot of clamping force.
If the cup-stopping is done by snaprings, I suppose you could inspect them for flatness, and thickness, and try to hunt up some thicker ones.I doubt you'll find any tho.....
But if you have the U-bolt type of cup retainers, they clamp pretty hard.I suppose you could shim the outside of the cups on those before securing the U-bolts. And then pulling the shims out.
All-in-all, IDK if there is much you can do.
Modern U-joints are well machined, and I bet you could measure a hundred of them and not find much variation among them.
Hmmmmmmmmmmmmmmmmmmmmm

 

[canyncarvr]

Hmmmmmmmmmmmmmmmmmmm
"Some between the cups" is normal,but .008 seems to indicate that the cups could be closer together, or the cross, a little wider. Depending on which method your yoke uses to locate the cups, this cannot usually be changed. Greasing it, of course, filled the internal gaps with grease which "cured" it.

Yep.

Of course soon enough the play will be back.
So, what to do about it? IDK.
If your yoke has cup-stops and straps, I guess theres nothing that can be successfully done,short of shimming the stops.But I fear the shims will fly out, as there is nothing to keep them in and the straps do not have a whole lot of clamping force.
If the cup-stopping is done by snaprings, I suppose you could inspect them for flatness, and thickness, and try to hunt up some thicker ones.I doubt you'll find any tho.....

The joint cups do have inside snap rings...but the snap rings are of no consequence. The cups do not move. It is the cross that moves between the cups. The snap rings fit as they should in the cup grooves. In order to move the cups closer together, the snap rings would have to have two different thicknesses..or a thicker ring would need to fit in a wider machined slot in the cups. I understand your point as far as the snap rings moving the cups, but that isn't going to reasonably happen.

But if you have the U-bolt type of cup retainers, they clamp pretty hard.I suppose you could shim the outside of the cups on those before securing the U-bolts. And then pulling the shims out.
All-in-all, IDK if there is much you can do.
Modern U-joints are well machined, and I bet you could measure a hundred of them and not find much variation among them.
Hmmmmmmmmmmmmmmmmmmmmm

What is the outside distance between ears on a 7290 driveline? What is it supposed to be? **edit** The 7290 is spec'd at a 2.625" snap ring span. My measurement was taken with the u-joint installed and at the outside edge with a caliper. There is likely some corrosion on the yoke tabs. **edit** The three of mine that have no movement are 2.615". The one with the 'slop'? 2.618" I should have measured that before. It doesn't allow for the .008", but it's wider than it should be based on the others.

I'm sure the end could be replaced. That's a good bit of money for nothing if the .008" doesn't matter.

And not even any chicks!


I'll ask the opinion of the local driveline service shop. They built it (a couple decades ago)! Obviously it's their problem!!


Note: 2.615" does not equate to any inch fraction.

 

[canyncarvr]

Threads that start with questions and end with no answers bother me, so while it's not really an answer, this is the end of this issue.


I noticed later my u-joint cups moved inside the slip yoke ears. There was no slop that I could feel or measure (using calipers..not a micrometer). I could see concentric movement between the cup and the ear.

Brewer's were nice enough to respond to my question about that issue, the result being I ordered a new slip joint from Brewers.

I'll put the driveline together with new u-joints so I will not be able to affirm or otherwise determine that the replacement of the one u-joint with the movement had any effect.

The measured movement having 'disappeared' after greasing that joint, it would have been hard to tell if any improvement of replacing only the joint was permanent anyway.

Thanks for listening!

 

[RustyRatRod]

Here's an answer. Wait until the u joint goes bad. Because now it's not.