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So, I am at my whits end with making a r-200 diff work in my 1978 280z with a 5-speed. When I first bought the car, it had a really loud noise coming from the diff. This is no slight whine either, it is OVERBEARING. The car is straight piped right now and it is still overbearing. Later on I tore into it and found nothing really wrong at all.

Installed an M-factory helical diff and rebuilt the whole unit with all new bearings. I closely followed the factory service manual. Almost the same exact noise occurred with the same volume. I gave up and had a shop tear in and rebuild the diff, install and it was exactly the same. Bought a whole unit off ebay with the same ratio, checked backlash, everything looked ok. Same story, unbearable noise.
The car has the factory mounts but with urethane bushings. Everything else looked and felt good, u-joints, mounts, wheel bearings. The noise I am hearing is from the differential as it changes under load, being the loudest when the car is coasting.

I'm not sure where to go next, ive already wasted 2k trying to have a functioning differential.

Any and all tips or suggestions would be greatly appreciated at this point.

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That's a tough one.  Based on what you have done, I would conclude the noise is coming from somewhere besides the diff, but I am sure you have already investigated that possibility?  I know bad bearing howl can be quite difficult to pinpoint.  Any chance you have a fried wheel bearing?  Could the noise be from the transmission?

 

Apologies if these are stupid questions, but it sounds like you have addressed potential diff problems four times over....

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Sounds like the gears aren't meshing well.

3 hours ago, 17brpeterson1 said:

 r-200 diff work in my 1978 280z with a 5-speed.

 

really loud noise coming from the diff. This is no slight whine either, it is OVERBEARING

 

tore into it and found nothing really wrong at all.

 

Installed an M-factory helical diff and rebuilt the whole unit with all new bearings.

 

had a shop tear in and rebuild the diff, install and it was exactly the same.

 

Bought a whole unit off ebay with the same ratio, checked backlash, everything looked ok. Same story, unbearable noise.


The car has the factory mounts but with urethane bushings. 

 

If you don't get the differential isolated from the body you'll hear the gear howl.  I'd focus on the mounts.  The front mount and the mustache bar bushings.  What do you know about them?  Do the urethane mounts have the proper metal sleeve inside?  Are they compressed against the body?  Does the diff have a solid front mount, or a collapsed front mount?

 

You want the path from the diff to the body to be interrupted by rubber or urethane.

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9 hours ago, NewZed said:

Sounds like the gears aren't meshing well.

 

If you don't get the differential isolated from the body you'll hear the gear howl.  I'd focus on the mounts.  The front mount and the mustache bar bushings.  What do you know about them?  Do the urethane mounts have the proper metal sleeve inside?  Are they compressed against the body?  Does the diff have a solid front mount, or a collapsed front mount?

 

You want the path from the diff to the body to be interrupted by rubber or urethane.

It appears the factory rubber has been replaced with urethane. I've had the front mount off a handful of times and can see no issues there. I'll have to unbolt and check the mustache bar mounts, but they looked fine from the outside. If I can make some rubber insulators to stick between the bushing and body, I'll try that just to see if anything changes.

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11 hours ago, Ironhead said:

That's a tough one.  Based on what you have done, I would conclude the noise is coming from somewhere besides the diff, but I am sure you have already investigated that possibility?  I know bad bearing howl can be quite difficult to pinpoint.  Any chance you have a fried wheel bearing?  Could the noise be from the transmission?

 

Apologies if these are stupid questions, but it sounds like you have addressed potential diff problems four times over....

I've had the half shafts off and the wheel bearings seem fine as well. The transmission is rebuilt with all new bearings and nothing wrong with the gears. I am almost certain it is the diff based on the sound and location of the noise. The u joints feel smooth with no slop, but even then the sound is a definite gear whine.

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I meant to edit out the part about the gears.  When I was trying to get rid of the clunk/thump I found that the more I tightened up the diff mounts the more gear noise I got in the cabin.  If you got a stock R200 from eBay then any gear weirdness probably stayed with the old diff.

 

You can't just eyeball the diff mounts.  Former owners do weird things and the parts are over 40 years old.  You really need to get up close and make sure they're correct.  The rubber in the front mount collapses and the metal from the top piece can rest on the crossmember.  Metal to metal contact. 

 

4 hours ago, 17brpeterson1 said:

I'll have to unbolt and check the mustache bar mounts, but they looked fine from the outside.

 

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Try and get a quick video on your phone and upload it to YouTube or a video hosting website of your choosing, hearing the sound is a lot easier for us to diagnose than a description of a sound (though I will admit I’ve helped a few friends out of a jam with cars and boats based on a description of what they were hearing). Start with 30s of the sound filmed from right next to the diff (but not directly behind the straight piped car for the sake of everyone’s ears), and then 30s of the sound from in the cabin with the windows up.

What immediately stands out to me is the fact you can hear the sound in the cabin even with an uncorked I6 which makes me think it’s a vibration being transferred directly to the body. My half-shaft joints and front diff mount were incredibly worn out and I would regularly get a roaring clattering noise when driving at speed on any sort of crappy road, but smooth roads and highway never made more than the normal sounds you’d expect from worn pieces. When I took my Z apart last year the bushings looked fine when unbolting pieces but turned to plastic crumbles as I slid them off.

Edited by Sanchez
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5 hours ago, jonbill said:

you've either been incredibly unlucky or its not the diff. 

anything unusual about the suspension or gearbox setup? 

whats the noise like coasting out of gear? in gear with the clutch in? 

Nothing unusual, all stock. I'd say it whines the most while coasting, in limbo between engine braking. But there is still a pronounced whine in all situations.

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36 minutes ago, Sanchez said:

Try and get a quick video on your phone and upload it to YouTube or a video hosting website of your choosing, hearing the sound is a lot easier for us to diagnose than a description of a sound (though I will admit I’ve helped a few friends out of a jam with cars and boats based on a description of what they were hearing). Start with 30s of the sound filmed from right next to the diff (but not directly behind the straight piped car for the sake of everyone’s ears), and then 30s of the sound from in the cabin with the windows up.

What immediately stands out to me is the fact you can hear the sound in the cabin even with an uncorked I6 which makes me think it’s a vibration being transferred directly to the body. My half-shaft joints and front diff mount were incredibly worn out and I would regularly get a roaring clattering noise when driving at speed on any sort of crappy road, but smooth roads and highway never made more than the normal sounds you’d expect from worn pieces. When I took my Z apart last year the bushings looked fine when unbolting pieces but turned to plastic crumbles as I slid them 

I should be able to do a few tests this week checking those and making up some rubber washers and insulators. 

Does anyone happen to know if rubber, not urethane, bushings are still available? Would there be much a difference between the two?

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Well, I checked and unbolted all my bushings and mounts and they look good. I slipped some 1/8" rubber in between the body and mustache bar mounts and where the front mount bolts up to the body and cradles the swing arm pivot.
Test drove and no noticeable difference.
I think my next step is going to be messing with the backlash. With both of my diffs, they were on the higher end of the tolerance with backlash at .007". 
I also noticed that it whines a lot louder while coasting. While under power, its not bad, something I could live with.

From what Ive researched, it appears that too much backlash can cause a whine while coasting.

The tight end of backlash tolerance is .005", Ill try and aim for that.

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Update

 

 Went one size down on the shim size according to the fsm. That brought me to .002-.003" of backlash, a little tight but I figured I would try it anyways given the circumstances. The gears patterned good, both drive and coast side of the teeth. 

 

But alas, still overwhelming noisy. A slight difference in its characteristics, whines on acceleration, still a whine on coast too. 

 

Unfortunately, this means I'll probably abandon the r-200s I have for a ford 8.8. Which will be better anyways with cv axles, better mount design, and better aftermarket.

 

 

 

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On 10/18/2021 at 3:44 PM, Sanchez said:

Try and get a quick video on your phone and upload it to YouTube or a video hosting website of your choosing, hearing the sound is a lot easier for us to diagnose than a description of a sound (though I will admit I’ve helped a few friends out of a jam with cars and boats based on a description of what they were hearing). Start with 30s of the sound filmed from right next to the diff (but not directly behind the straight piped car for the sake of everyone’s ears), and then 30s of the sound from in the cabin with the windows up.

What immediately stands out to me is the fact you can hear the sound in the cabin even with an uncorked I6 which makes me think it’s a vibration being transferred directly to the body. My half-shaft joints and front diff mount were incredibly worn out and I would regularly get a roaring clattering noise when driving at speed on any sort of crappy road, but smooth roads and highway never made more than the normal sounds you’d expect from worn pieces. When I took my Z apart last year the bushings looked fine when unbolting pieces but turned to plastic crumbles as I slid them off.

Sorry for the delay but here is a video. Its the best i could get with my phone. You can really hear it at the end where I cruise at 60-70mph.

https://photos.app.goo.gl/9eYmMMQzgDpRsHGGA

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Just listened to the video it’s definitely a pronounced whine which has me partially agreeing with @bunkhouse.

But maybe a few more questions and tests would help pinpoint the problem area. 
1) Find a good long on/off ramp to a highway that has a good curve to it where you can safely keep the the speed where it whines throughout the turn. Does the whine change, get worse, or go away?

2) Lift the rear end so all weight is off the suspension, start her up and take it through your common drive cycle where the whines occur. Does it go away or still persist?
3) If you have a friend who can safely get under the car with a stethoscope they may be able to pinpoint the exact area the whine is coming from. I’m sure I don’t need to stress this safety point but do it safely with a 2 post lift, not with the back on jack stands.

4) You said you replaced all the bearings in the diff and have tried 3 different ones, but did you reuse the same stub axles between all of them?

 

My next thought is that from my understanding is the R200 is just a very noisy diff even when everything is totally fine with them. The cars they came in had a lot more sound deadening and thicker metal in the trunk so if your car is untouched/unrestored maybe start probing around the trunk area for some rust holes (spare wheel well most likely culprit) or missing material that could be letting excessive noise in. The tar insulation and undercoating combined has a history of making the car look solid until you press somewhere and find a softball sized hole.

Edited by Sanchez
Clarification on question 1
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39 minutes ago, Sanchez said:

My next thought is that from my understanding is the R200 is just a very noisy diff even when everything is totally fine with them. The cars they came in had a lot more sound deadening and thicker metal in the trunk

 

This is rational.  My diff noise reduced a surprising amount when I lined the back deck with bubble foil insulation.  As Sanchez says, the less material you have over the metal deck the more noise will get through.

 

 

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12 hours ago, walkerbk said:

What kind of diff fluid are you using? Diff fluid can make a huge difference. 

Agreed, forgot to mention this in my post. There are even quite a few modern cars that release TSB’s for diff fluids to combat chatter and whine.

 

Another additional comment I didn’t put in my last post:

You can’t go wrong with an 8.8, InvincibleExtremes, Apex Engineered, or TTT all have options and they’ll all give you option to run off the shelf parts that will continue to be fairly cheap and easy to source for easily 30+ years from today.

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