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Old 05-08-2012, 07:21 AM
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U-joint Inspection Question

I've replaced U-Joints before, but they were always obviously sloppy, so there was no question that replacement was required.

I have one now I am suspicious about. There is no sloppiness at all, however, the center cross can move side-to-side a litle bit; maybe as much as 1/16".

The cups are tight in the yoke, and everything seems to rotate smoothly.

Is this side-to-side movement a common condition that does not cause trouble, or does it indicate some sort of unusual wear?



ps: the yokes are heavy duty Spicer units and I doubt they've spread apart.
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Old 05-08-2012, 08:40 AM
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Something is wore, bent, or the wrong part has been installed.
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Old 05-08-2012, 03:04 PM
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Quote:
Originally Posted by lmsport
Something is wore, bent, or the wrong part has been installed.
X2 sounds like the wrong part.
Why were you checking it in the first place was there some noise or popping sound or some vibration ?

Cole
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Old 05-08-2012, 04:24 PM
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Quote:
Originally Posted by eloc431962
Why were you checking it in the first place was there some noise or popping sound or some vibration ?
Actually, I was trying to determine the cause of a slight thump when I let out the clutch in 1st gear (and sometimes a tiny bit in 2nd gear).

To be honest, the thump seems to be coming from up front somewhere, not from the transmission tailshaft back.

The engine mounts are solid as can be, however the transmission mount is a little soft. I did change the transmission mount last year, and the thump seemed to be gone, but the mount was higher and the clutch fork would scrape on the inside of the tunnel, so I put the old mount back on.

I'm looking at other causes, and this u-joint sidways movement (which may be closer to 1/32" vs the 1/16" I quoted...probably in-between; enough to easily see, at any rate) was one thing I discovered.

My next step is to get the car back up in the air and check the drivetrain angles. I bought a small digital magnetic inclinometer for the purpose. I'm sort of thinking the transmission tailshaft might be bouncing up and down causing the thump (More of a thump than a clunk) if the angles are off too much.

As far as parts go, here's the drawing and I've add in the part numbers that seem to have side-to-side movement. The driveshaft is a custom unit.

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Old 05-15-2012, 07:24 AM
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Time for a new u-joint,seems like the wrong one,never seen one wear out like that.Like your drawing.Is their still greese inside the cups?
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Old 05-15-2012, 08:06 AM
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I double-checked the u-joint problem over the weekend, and it's not quite as bad as I remember from last year, but there certainly is discernable side-to-side movement, that I havn't seen before in other u-joints I've inspected.

I managed to check my angles, and they aren't perfect. The pinion axis to transmission axis check (vertically) shows the pinion is pointing down at 1.2 degrees from the tranny/engine axis. Left to right axis angle measurements were a little less precise (i.e. difficult to measure), but I got about a 2 degree offset. I doubt either of these angles are causing me any trouble (like the thump), but they may have contributed to the u-joint wear. Driveshaft is only about a foot long.

I did manage to get some dimensional data on the mounts, and it looks like my original one has either collapsed, or was made wrong. The new (taller) one meets the spec. So I'll put the new mount back in and see if I can do a modest amount of trimming to keep the clutch fork from rubbing on the tunnel.

At least changing the mount will confirm whether the thump really did go away as I seem to remember form last year.

I'll give the u-joints a squirt of grease, although there's only 6000 miles on them since new, and I greased them really well then.

After a road test, if the thump is still there, I'll look at installing new u-joints and seeing if there's anyhting I can do to improve the angles. Actually, the new taller tranny mount should help with the vertical angle issue.
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Old 05-15-2012, 09:19 AM
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Nominally the engine should show something like 3* down as measured at the tranny output flange or spline. The differential input should then be just the opposite, ~ 3* up. In the real world, those numbers may not be possible as shown with my now long gone T-bucket with a 9" long drive shaft. My cure was every year or two, just spend the $20 +/- bucks and just replace both of the u-joints whether they were bad or not (they were bad only once) just for reliabilities sake and call it part of a normal 'tune up'. Yeah, I know that's not the right way, but to change the relationship of the engine to the differential would have been very difficult and time consuming (the engine was "off" even tho it was a Total Performance motor mount install problem) - much more so the the cost of a u-joint.
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