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Need help diagnosing grinding noise in the rear of my Z


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I need help diagnosing a grinding noise in the rear of my 72 S30.

 

I just recently got the car running after an extensive engine and drivetrain upgrade and rebuild. It has polyurethane LCA bushings. RT front differential mount with GM style polyurethane mount. Polyurethane mustache bar bushings. Z31 LSD and Z31 CV joints with shortened shafts. New rear wheel axle bearings and seals. AZC Wilwood race brakes all around.

 

The car is making a constant grinding noise while driving. The sound is similar to rolling a steel wheel on concrete. It is constant - all gears, accel/decel, cruising, braking/no braking, turning, etc. The sound only stops when the wheels stop.

 

I put car on jackstands, started it, put it in gear and engaged the clutch in first gear. The sound was gone. When I turn the drivetrain by hand all I hear is a slight dragging of the rear brakes. The brakes were initially dragging and I thought that was causing the noise but I have since shimmed the calipers so there is minimal (normal?) drag.

 

Any ideas what it could be or how I can determine the cause?

 

Thanks,

Ross

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Put the car on the ground to get weight on the wheels and roll it back and forth by hand. Maybe it needs weight on the bearings, or to get the suspension in some specific position to make it happen.

 

Drive shaft rubbing something? Half shafts rubbing brake or e-brake cable? TIres/wheels rubbing springs or perches or brake calipers?

 

Do it by changing one thing at a time until you find the source. Methodical...

Edited by z240
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This happened on my 240Z some years ago. It turned out that the stub axle flange had some how become warped. You could see that it was warped when the wheel was turned. Installed a new stub axle to fix the problem.

 

You mentioned new rear wheel bearings. Recheck the assembly. Are the axles, bearings, spacers and stub axle retaining nut installed correctly? Are any parts of the stub axle/flange rubbing on the strut housing?

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Just saw a comment by JohnC on zcar.com about "brinnelling" a bearing race (see Brinnell Hardness test). I think that it means damaging a race's bearing surface by pressing the balls in to it with too much pressure. Did you have any problems with installing the new bearings? Any chance that pressure was applied to the wrong race?

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Thanks for the replies. All good suggestions. I have checked all of the moving/rotating parts and found no indications of wear or inadvertent contact. My setup is pretty simple as there is no rear sway bar or parking brake hardware.

 

I made

of my turning the brake disks as the car sits on jack stands. The sound you hear is coming from the differential. I believe this sound is normal and, like I said when the engine was running and drive train spinning I could not hear any significant drive train noise noise inside the car.

 

 

NewZed - It's been a couple of years but now that you mention it, I do remember having trouble with one wheel bearing. I did check it afterwards and it seemed to rotate perfectly smooth so I called it good.

 

I suspect that the culprit is a bearing somewhere. Question is, where?

 

Does it make sense to you guys that a bearing will make more noise when loaded as z240 mentioned?

 

It seems to me that the differential would make the same noise whether the suspension is loaded or unloaded. I can understand how differential noise would change relative to input load but that doesn't seem to be the case. The noise only varies with the speed of the car.

Edited by rossman
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That sound when you rotate the hub by hand is not normal. The only thing that should be rubbing is the brake pads on the rotor, and that sounds way too rough to be brake pads. You could pull the CV's and rotate the diff and the hubs independently and see if it is coming from one or both hubs.

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At this point it sounds like it is the bearings which means you will need to inspect them for possible replacement. Recommend that you do both sides if you replace the bearings.

 

 

If you are not familiar with the rear axle bearing replacement go here: http://forums.hybridz.org/index.php/links/link/13-rear-wheel-bearing-replacement/

 

 

One other thing to check is the flange that bolts to the stub axle. It has a thin outer dust shield that can get dented and rub on the axle-housing making a scraping noise.

Edited by Miles
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The R200 pretty commonly wastes the outer pinion bearing that is right under the pinion seal. You have to pull the carrier and the pinion to get it out, but it's not that big a deal if you're not changing shims or trying to set the pinion depth. I would bet that replacing that bearing fixes your problem. The problem is that the bearing is tough to get. I thought it was NLA at one point, but the older part number had been superceded by the 300ZX part number. Check with the dealer and see what you can do.

 

One guy actually had a ceramic bearing manufactured at one point. It was supposed to hold up better. Also there was some speculation that the problem might be static electricity jumping from race to race and if that is correct then a ground strap from the diff mount to the chassis might help (normally insulated by the mounts). I don't know if that one is true, but a ground strap is a couple $$$ at the auto parts store so I was going to do it on my car. Seems to me that I've seen this problem a lot more in the 300ZX, so my theory is that the 300ZX has the diff mounted at just enough of an angle to starve that bearing for oil.

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Thanks guys, I appreciate the help.

 

A quick search came up with 3 hits for 38335-N3220. I'll call around tomorrow. Looking at the FSM, removing the bearing doesn't look too bad. It shows a tool used to remove the bearings. Since the bearing ID is 28mm, I'm assuming that I can use 1" galvanized pipe to drive out the bearing.

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Courtesy Nissan found the bearing for me. They had to get it from Nissan...whatever that means. Ordered it on Monday got it on Thursday.

 

I pulled the differential apart today and found that one of the side bearings is also bad.

 

I'm going to replace all of the bearings. Is there anything else I should do while I have it apart?

Edited by rossman
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  • 2 months later...

At this point it sounds like it is the bearings which means you will need to inspect them for possible replacement. Recommend that you do both sides if you replace the bearings.

 

 

If you are not familiar with the rear axle bearing replacement go here: http://forums.hybrid...ng-replacement/

 

 

One other thing to check is the flange that bolts to the stub axle. It has a thin outer dust shield that can get dented and rub on the axle-housing making a scraping noise.

 

Miles,

 

Just read the lnk you provided. This is really well done. After 40 years the left rear has come loose so its time for a change. I was wondering what I was in for so the link was very helpful. I particularly liked how he mentions the 27mm socket. I could see it would have been a pain to figure that out.

 

Paul

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Miles,

 

Just read the lnk you provided. This is really well done. After 40 years the left rear has come loose so its time for a change. I was wondering what I was in for so the link was very helpful. I particularly liked how he mentions the 27mm socket. I could see it would have been a pain to figure that out.

 

Paul

 

Glad that helps. Post some pictures.

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