Hi all,

So I'm looking at my rear axle again, figuring out how to tighten it up. (It gets a bit bucky and jiggly sometimes.) I had previously noted that my passenger side half-shaft had a lot of play in it, so I knew I had some work to do there.

Today I jacked up one wheel, left the other on the ground, put the transmission in gear, and turned the lifted wheel back and forth to figure out where I had play. The outer U-joint on the passenger side is pretty well shot, as I can see it rocking and wobbling around. The rest of the half-shaft joints, both left and right, look OK. They might be worn, but they're not a major source of play. Unfortunately the wobbly U-joint isn't the whole story.

When I rotate the wheel back and forth, I get about 1.5" of rotation along the circumference of the tire. Approx. 0.5" of that is due to the U-joint. The remainder of the slop (1") seems to be within the differential itself. So is that amount of differential slop within normal limits, or do I need to consider rebuilding (or buying a used R200 in good shape)? As some of you might recall, this is the same differential that had filings in the oil when I changed it out. I've recently obtained service records from the dealership that did 99% of the service on the vehicle, and the last differential oil change would have apparently been about 70,000 miles and 18 years ago.

Any advice is greatly appreciated. Thanks, guys!

Peace,

Sarah

One more check would be to raise both rear wheels, (block the front of course) in neutral set the parking brake and rotate the drive shaft to check slop in the gearset. I would worry about those grindings in the oil. They are most likely from the bearings. A worn set of gears will sing at highway speed under light load and stop when you ease off. The rear wheel bearings will sound like a train car on the tracks, a constant that increases with speed.

Clunking can be caused by U joints or bad bushings in the mustache bar or front diff.

I'm still rather surprised that the only way to assess backlash is to remove and open up the differential. When one half shaft flange can turn 5 deg while the other half shaft flange and the drive shaft flange remain stationary, that DOES imply something about the total backlash in the gear train, does it not? It might not nail down the exact source of the backlash inside the differential, but doesn't it provide any useful info at all?

Hypothetically, if I could just turn one of the flanges around and around while the other two remained stationary, wouldn't that imply something about the internal state of the differential? Would I really need to open the thing up to assess the fact that it's shot?

One more check would be to raise both rear wheels, (block the front of course) in neutral set the parking brake and rotate the drive shaft to check slop in the gearset. I would worry about those grindings in the oil. They are most likely from the bearings. A worn set of gears will sing at highway speed under light load and stop when you ease off. The rear wheel bearings will sound like a train car on the tracks, a constant that increases with speed.

Clunking can be caused by U joints or bad bushings in the mustache bar or front diff.

I feel like I keep saying the same thing over and over, so this will be my last attempt.

If you turn the halfshaft and watch for motion elsewhere, you are introducing slop into your measurement. Slop from the halfshaft splines to the side gears of the diff on the input side. Slop between the side gears and the pinion gears, slop in the halfshaft splines on the other side, a bad U-joint, etc is being included in your measurement. That is more than enough to throw you WAY off. The backlash is .005" to .008" if I recall correctly. That is a very small amount of lash. Trying to feel that through the halfshaft would be very hard to do even if there weren't all the other slop. Trying to feel it at the ring gear even takes a little attention. You have to rock the ring gear back and forth without actually moving the pinion, and moving the pinion is pretty easy to do.

When you put the parking brake on and rotate the driveshaft, you also are not checking ONLY the play at the gears. Again you are adding whatever slop may be in the driveshaft to tailshaft splines in the transmission, driveshaft U-joints, the side gears and halfshaft splines, the cross pin shaft and the pinion gears, halfshaft U-joints, potentially the splines on the stub axles, plus whatever elasticity there is in the brakes during your test. There shouldn't be a lot of play in any of those places, but there often is. Another thing about measuring at the pinion: The measurement of .008" at the ring gear does NOT equal .008" at the pinion flange. The movement at the pinion is greater than the movement at the ring gear because of the cut of the gears. I think this is the number one reason why people pull their diffs, they rotate the driveshaft, are surprised when it turns more than they think it should so they assume that backlash is the problem and start pulling the diff unnecessarily.

This is from a thread on Hybrid Z. This guy checked his backlash at the pinion and then went on to find out where the perceived slop was:

1st Biggest Culprit: (bjhines called it)

The axle splines are definitely not a snug fit into the diff. They were somewhat loose in the spider gears and equally loose in the OBX.

2nd

The ZX Turbo CV shafts that I am using had noticable play in the outer tulips when I cleaned out the grease.

3rd

The OBX has some lash inside of it because of the nature of the backlash of all the helical gears involved....and relatively loose tolerances in manufacturing.

4th

The rear u-joint in the driveshaft has a tiny tiny bit of lash to it.

5th

My rear wheel bearings have some play...within spec but it's there.

If you want to know if your backlash setting is OK (and it probably is just fine), the way to check it is to pull the diff, pull the cover, and measure it directly.

As far as bearing noises, I think whine on decel is typically pinion bearings and wheel bearings growl, and the growl changes pitch with load, so swerving side to side will help to identify if it is a rear wheel bearing and sometimes which side needs replacing. I agree that the little metal bits are probably bearing material. That doesn't mean that the whole diff needs to be torn down or replaced.

For more diff noise ID:

http://www.ringpinion.com/ContentFrame.aspx?FilePath=Content%2fHowTo%2fGeneralInfo%2f%2fDiagnosing_Noise_%28Part_1%29.inc

http://www.ringpinion.com/ContentFrame.aspx?FilePath=Content%2fHowTo%2fGeneralInfo%2f%2fDiagnosing_Noise_%28Part_2%29.inc

Yeah, your right. I should have been a little less vague about the results. You can drop the DS and rock the pinion flange. This does not give you a backlash reading, it only helps you make the decision to just change the oil and U joint or go through the hassle of pulling all the parts from the ds to the wheels on a car that has never been apart. Bandaid or complete R&R. If I found bearing chips in a diff I would change the oil and start gathering parts untill I could fix it right. JMO

Tom

Thanks, Jon and Tom.

Jon, I very much appreciate your taking the time to address the issues I'm seeing, and I apologize if this is becoming a frustrating process. I do feel as though we may be discussing entirely different things. If there's any failure in clarity, it's probably mine.

There's nothing like experience with the Z to help a person diagnose a Z. I suppose I should get my Z into the local specialist for an evaluation of the problem. I know at the very least that I need some work on my half shafts, and hopefully that shop can do the work. Used parts do seem available enough, if that's what I need to consider.

Anyway, again, I appreciate your endulging me. Thanks, guys!

Peace,

Sarah