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Rick Johnson

R200; What is the minimum backlash possible between Ring & Pinion

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Guys,

My 73 240 with a R200 installed has unacceptable gear whine in the Cruise Mode. No noise under acceleration or deceleration. I set the backlash at .008 many years ago. I believe the spec is .004 to .008. I am hoping that reduced backlash will reduce the kinetic energy gained as the ring bounces back and forth against the pinion in the cruise mode. I would like to try .003. This would reduce the oil film and minimize the gear rattle. Has anyone tried this to reduce gear noise in an R200?

 

Additionally, some body panel or suspension component in the 240 seems to resonate at 460 Hz which is the tooth mesh frequency of my 3.54 ratio at 49 MPH. So between about 42 to 55ish MPH the gear noise is amplified by this component and the noise is almost deafening (obnoxious to say the least). I have bolted on the 'mass damper' that Datsun used as a countermeasure back in the 70's to no avail. Has anyone figured out which component is resonating (acting as the speaker) somewhere in the rear of this vehicle?

 

I have had 3 different diffs in this car that all produced similar levels of noise. I have used different ring and pinion patterns which just moved the noise to cost or accel. Ideally I could damp the offending body panel but can't figure out which one it is. It is such a shame that this noise is spoiling an otherwise great car.

Edited by Rick Johnson
Want to share my findings on backlash and noise characteristics

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I agree with Mongo, it's more likely the diff mounts or driveshaft alignment.

 

What type of diff mounts are you using? The solid aluminum type transmits a huge amount of noise to the car.

 

jt

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The quietest backlash setting is going to be right where it was when the gears were originally run in at the factory. In the future any time you take a diff apart, measure the backlash before disassembly and try to match the same setting when you reassemble. If you've run the thing with the backlash opened up for years, it will be damn near impossible to find that setting by pattern, you'll basically have to play with it if it matters that much to you. I would not run it tighter than factory spec. It will get hot and possibly ruin the gears. In general longnose R200s are not quiet differentials, and I think the other guys are right that mounts are probably the most important thing you can do to quiet them down. The softer the mount the less noise you'll get. I again agree with the other guys that your harmonic issue is more likely a driveshaft angle problem than a differential problem.

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Thanks for your input. I am using the softest mounts possible. The front is original rubber. I constrain it under accel with the strap and a Hook under the crossmember. Decell is constrained with some snubbers. Cruise floats between the 2 constraints and is very soft. The rear mustache bar uses the softest serrated looking rubber mounts (not the solid ones) on the top and bottom. I spent enormous amounts of time getting the driveshaft angles equal at the transmission and the diff. At cruise the angles are exactly even - I think it was about 2 1/2 degrees. My lateral angles are within 1/2 a degree. (All this driveshaft alignment minimized the U-joint vibration under accelleration but did nothing for the gear whine)

The noise is being amplified by some rear component. Interestingly I hear the same amplification between 15 to about 25 MPH. The vibration input for this speed is surely the close tread block pattern in the tires. Once the tires are inputing a higher frequency above the resonant point the noise is gone between about 25 to 42ish MPH. Then the noise comes back as the gear mesh frequency input approaches 460Hz and peaks at 49ish MPH. A friend at work suggested I built a speaker with a metal rod attached and drive it at 460Hz and touch it to all the components in the rear and see which one buzzes. I have already tried the hammer ping test. Both the mustache bar and the lower control arms seem to ring at about the right frequency but it is hard to be sure.

The factory just bolted a big weight on the diff mount crossmember to absorb the pinion vibrations and change the resonant frequency, but this did not make much difference on my car.

Do you think the gears on later model diffs from the late 80's might be machined better and produce less vibration??

Has anyone noticed a change in rear cross members, control arms, or body bracing that might illustrate how Datsun tried to minimize these rear diff noises through the 80's??

Thanks for any comments.

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Sounds like you've got the mounts and driveshaft well covered.

 

Jon is correct that changing the backlash from whatever it is from the original wear pattern usually makes a noise worse. However, out of numerous R200's, I've only had one that was noisy enough to be heard in the car. It's unlikely you would get three bad ones in a row.

 

Have you tried changing the rear ride height, to vary the angles of the halfshafts? How are you determining the frequency?

 

jt

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http://www.tootechracing.com/TooTechCarSection/Vibration%20Calculator.xls

 

This a link to my vibration calculator spreadsheet that I used when in the 'buisness'. With a 25" tire at 50MPH the driveshaft is turning 39.66 cycles per second. There are 11 teeth on the pinion gear so the teeth mesh 39.66 x 11 = 437 times per second. I remember having a vibration analyzer attached anywhere near the rear of the car and the amplitude peaked at 460ish cycles per second (maybe it was 440 - it was years ago). This indicates that the noise frequency coincides with the gear mesh frequency, thus the initiation of the noise is clearly the gear teeth. Unfortunately back then and today I never figured out which part of the car is resonating (acting like an efficient speaker) at that frequency. Because the frequency is so high it should be some sheetmetal somewhere. I was hoping that someone might have analyzed or stumbled across the culprit.

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Well, I have to admit my assumptions were wrong.... I took the rear apart and found the backlash still at .007". The gears are worn on the drive side. The pattern was perfectly centered but a bit high on the tooth. I pushed the pinion in .006" and cut the backlash down to .003". The pattern is lower but the cost and drive patterns are opposite one another. The gears now are reasonably quiet/noisey until about 55 MPH but then get steadilly louder up to about 70 MPH then start to get quieter. I guess the noise is all coming from noisey gear mesh and maybe the rear suspension components don't necessarilly have a distinct resonant point. My next try will be about .012" backlash to see where that makes the noise peak.

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One thing I've tried is sticking a big magnet to various parts to see if that changed the frequency. Worked pretty good on sheetmetal, sorta inconclusive on other stuff. Might be worth a try.

 

Does it resonate at the same mph if you use third gear? Have you tried putting the car up on a lift and running it?

 

I spent a lot of time, effort, and money chasing a vibration in a vette I used to own. It can be a frustrating experience.

 

As a side note, do you know of a good source for R200 shims? Last one I worked on I had a heck of a time finding any shims.

 

jt

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jt,

Thanks for the idea. I put the car on jacks with the control arms at the correct angle and ran the car at 50 MPH. We had to apply slight braking load to simulate a cruise condition. The noise is VERY audible. With a metal rod at the end of a stethoscope the rear of the diff was quiet and the rear spindles were quiet, but the nose of the diff was screaming. The front mount isolated some of the noise but it still continued down the cross member and into the frame. I found my front diff mount was grounding out a bit and not offering as much isolation as it should but after correcting this only a mild improvement was noticed. Although no longer awful, it still definitely needs improvement.

The differential experts say this type of cruise noise is usually caused from inadequate pinion preload or bad pinion bearings. My bearings don’t show any signs of wear and I made sure to preload my pinion bearings to about 10 in #s of torque to rotate.

I bought a used diff. The backlash is set at between .008 to .009" - very consistent. The pattern is a bit high on the tooth and the drive side shows a contact patch across 80% of the tooth indicating drive side wear. The coast side shows a perfect pattern favoring the Heel of the tooth slightly. One knowledgeable source said a pattern towards the Heel is quieter than a pattern leaning towards the Toe. I will first install the diff exactly as it came from the factory.

Interestingly the backlash on my current diff with the LSD varies .003". Either the carrier is not flat or the gears are machined poorly. Since I have had this LSD in all 3 of my noisy diffs, I am starting to think that the LSD may be contributing to the noise. When I put this new diff in, I will disassemble and indicate all aspects of my current LSD carrier. If it is out more than .001" I will make a trip to Vellios (my local machine shop).

Regarding the diff shim source: I have saved the shims out of all my noisy diffs. I do not have a source.

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I think it's an excellent idea to put the new (used) diff in just as it is and give it a try. The variance in back lash in your current diff is a big red flag to me. Either the carrier is off, the gears, or maybe a bent pinion shaft. Can you see a difference in the pattern that coincides with the backlash variance?

 

It might be worthwhile to set up a dial indicator on the ring gear of your current diff, check it out, then remove the ring gear, reassemble the diff, and indicate the seating surface of the carrier.

 

I've also been told a pattern towards the heel is quieter, but I've never played with it any myself. Most of my junkers are so loud I probably couldn't tell the difference anyway.

 

jt

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If you've already tried 3 different differentials, replaced the bearing in the nose (which is the one that goes bad most frequently), and tried various pinion depth and backlash settings, I have an idea for you which might work out better, and although inflection is hard to read sometimes, this is not tongue in cheek advice. Consider buying a car that isn't so horrible on the NVH. Find a Mercedes or BMW with big gushy insulators between the chassis and driveline and drive in peace and quiet. Japanese tin cans from the 70s are understandably not for everyone.

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Wow - I installed the new Diff exactly as it came to me and it is as quite as a mouse.:redface::redface::redface::redface::redface::redface::redface:

 

Since the only common part to the last 3 diffs is the LSD unit, I must assume this is the cursed piece. I will pull the ring gear off and measure the radial and lateral run-out where the ring mounts and report back.

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My 3.7 LSD out of an '88 300 ZX is much louder than the lightly muffled LS1 at cruise. It's brutal loud and gives you a headache without earplugs. I bought all new bearings to rebuild a 3.54 this winter to swap it out with. After your experience I hope it's not the LSD unit itself :( as I wasn't planning to touch it.

 

Cameron

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My 3.7 LSD out of an '88 300 ZX is much louder than the lightly muffled LS1 at cruise. It's brutal loud and gives you a headache without earplugs. I bought all new bearings to rebuild a 3.54 this winter to swap it out with. After your experience I hope it's not the LSD unit itself :( as I wasn't planning to touch it.

The LSD isn't doing anything when you're driving straight, so if anything it would be a runout issue, which could be fixed.

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I have a 4.11 R180 that whines between 55 and 65 mph under heavier load. I set the backlash to .0065" when I installed it with new side bearings. I've found that if I lower my head (which is usually near the headliner) the noise is reduced a lot, so it seems to me that it's a resonance type of issue.

 

Back in 73 apparently there was a TSB that involved adding some large weights to the front diff mount. I've tried that and I think it helped a little, but not much.

 

My point is that our early Zs transit all kinds of resonances and someone shorter than me probably wouldn't give my car's a second thought. Glad you found a diff that's as quiet as you want - I think you should consider yourself lucky :)

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Re: Is there a clunk

Yes, I do hear a clunk when I let off suddenly. It does not bother me too much since it is a one time event. I would like to reduce it to .006 or .007 but am afraid to upset the pattern.

 

LSD Carrier

It has .002 radial run-out - the large diameter that centers the ring.

It has .001 latteral run-out - the flat suface with the 12 bolt holes.

I would have thought that this was not too bad; but it is at the machine shop now for truing

 

Found the noise:

Well it is quiet now - it will be interesting whenthe LSD goes back in???????

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The limited slip carrier is in and the diff is still quiet with the new set of gears.:)

The machine shop set the carrier in their lathe and confirmed .001 lateral runout but only found .001 radial runout - not the .002 I had measured. They skin cut the 2 surfaces and produced 000 runout. When I mounted the new ring gear in the LSD and checked the backlash, the variance was now only .001", the same as it was when these gears were in the open carrier. The OTHER ring gear had .003 variance before the carier was remachined, but since the ring gear was changed, it was not an apples to apples comparison. I also put the bearings from the open carrier onto the LSD. Although visually I could see no problems, the open carrier bearing felt a tiny bit better than the LSD bearings.

I carefully shimmed the LSD bearings to produce about 6 inch pounds of rotational resistance. I previously torqued the pinion nut to produce the same 6ish inch pounds of rotational resistance.

BOTTOM LINE:

In the future, if I had to look for the cause of gear noise in a diff that had originally been reasonably quiet, I would FIRST confirm that my rubber mounts were providing the proper isolation and not somehow grounded out. SECOND I would change all the bearings. Note: I may have been ignorant about how a seemingly insignificant bearing issue can somehow exacerbate a 'gear mesh' frequency noise. THIRD I would measure the variance in backlash. If the backlash was ABOVE .002" I would have the carrier re-machined (I know this may seem insignificant but why not after spending all the time and effort on the bearings). LAST, if this failed I would start looking for a new gear set.

I have learned alot and hope this information helps the rest of you'all on HybridZ.

Rick

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