TR4/4A Identifying the source of gear noise.

[Sarastro]

I'm getting a whine or buzz, which seems like gear noise and sounds like it's coming from the transmission area. It's loudest around 3000 RPM in top gear but seems to correlate with road speed, not engine speed. I think I know what's happening, but before I tear the car apart, I'd like to get some insight from any of you with more experience in tracking down this kind of problem.

The car is a newly restored solid-axle TR4A; just got it back on the road in August. I rebuilt everything in the drivetrain.

I've made the following observations:

1. The pitch of the whine does not change when I shift gears and keep the road speed constant.

2. The pitch also doesn't change when I switch the OD in and out, as long as I keep the road speed the same.

This seems to rule out the transmission and OD; the noise would have to be from the differential, drive shaft U-joints, or output shaft bearing of the OD. But the sound seems to come from the transmission, although I realize that sounds can be hard to localize--maybe the transmission cover just transmits sound better than the body of the car. I've never heard a U joint make a noise like that, especially a new one, and I spent quite a bit of time and effort getting the differential right when I rebuilt it. I reused existing OD bearings, but I inspected them closely. Nevertheless, it seems like the differential is the most likely culprit. I also wonder if it might just be a vibration, but I can't imagine what might vibrate and make a gear-like whine.

So, does anyone have any more thoughts on this, or can anyone suggest more tests I might make?

 

[CJD]

It sounds most like a bearing. If it were the differential gears, it would be noticeably more pronounced in multiples of 30mph, with the loudest whine at 60mph +- a few mph. Diff gears also change the sound abruptly when you go from accelerate to coast.

Unfortunately there are a lot of bearings it could be. Perhaps put the car on a lift with the engine running in gear so you can listen for a closer location...it could even be something rubbing on the driveshaft or axle.

 

[Sarastro]

That's interesting. Why is it louder at multiples of 30 MPH? Could you explain that?

I haven't noticed if it changes suddenly when I go from accel to coast, but I'll check that.

 

[bobhustead]

It looks from the Moss catalog that the trans cover is removable. You could pull it and get an assistant to drive while you do the "big screwdriver stethoscope" test. Put the tip on various points on the trans housing and put the handle to your ear and listen.
Bob

 

[CJD]

That's interesting. Why is it louder at multiples of 30 MPH? Could you explain that?

I haven't noticed if it changes suddenly when I go from accel to coast, but I'll check that.

I have often wondered that myself. I have driven bad gears of many ratios, and even our Diesel RV that lost a rear end...from 2.58 gears in the Olds Cutlass to the 5.90's in the RV, the loudest resonance is always at and around 60mph. If the wear is slight, it may actually go away at other speeds, with lessor resonances at 30 and 90mph. You can usually also make it go silent by coasting with just enough power to follow the speed of the car as it slows. In other words you remove the loading from the diff. The olds was the only car that I dared to take up to 120mph as a test...and it was a deafening howl at that speed too. Of course totally shot diff gears will howl at all speeds. I first learned about this from an old 1970's high school shop manual that an Uncle gave me. It has been the best book I have ever read for mechanical diagnostics...which is a lost art in our modern computerized world. Most techs don't know what to do if it isn't a sensor problem.

Bearings usually make noises that can be described as "rumbles" if they are heavily loaded wheel bearings, "hisses" for lighter loaded tranny bearings, and also "whines" or "grinding" sometimes.

 

[malbaby]

My guess would be a diff bearing. Does the whine change when the car is free wheeling.

 

[Sarastro]

I have to check what happens when the car is freewheeling or changes from accel to decel.

However, I used all new Timken bearings when I rebuilt the diff, so if it's a bearing, it almost has to be the OD output shaft bearing.

I replaced the ring and pinion with a used set, which looked good to me, but it's possible I didn't look closely enough, or got a measurement wrong, or...

 

[malbaby]

Pardon me for asking....did you check diff preloads, shims, backlash adjustment etc.

 

[poolboy]

This might be of some help:
https://www.onallcylinders.com/2012/03/30/quick-guide-to-diagnosing-differential-driveline-noises/

 

[Sarastro]

I made all the adjustments in painful detail--that's why I'm puzzled. In my (very) limited experience with differentials, the tolerances are very tight, but you still have to miss them by a good margin to get significant noise.

For all I know, I might have forgotten to tighten a bolt or didn't get a bearing race pressed on all the way and it slipped--I do my best, but I still can mess up. Maybe I'll just pull the thing--it's only a day or two of work--and recheck.

Also, Ken, thanks for the link. I did a search and found too many sites with gear-noise info, but this one seems to be better than any I found.

 

[Madflyer]

The universal would be a knock if broken. The diff as stated would come and go with load off and on. Look at the speedo gear at the trans and cable. what sound when coasting say down hill?? When holding same speed wheel bearing front or rock next to brake pads. Simple spin front wheels off the ground to check bearing for play and or stone. Can you feel the sound in the shift lever?? As it is RPM water pump or generator. Madflyer

 

[Sarastro]

Thanks, those are good ideas. I'll add them to my list of stuff to check.

 

[Sarastro]

I finally took the car out on the road to do some checks. I noticed the following:

1. The whine/buzz is only on acceleration.

2. I reconfirmed that the pitch of the whine depends on road speed only; shifting gears or switching the overdrive in and out does not change the pitch, as long as I keep the road speed constant.

3. It is loudest when accelerating lightly; not nearly so noisy when I accelerate more aggressively, but the noise is still there.

4. It was hard to tell if it was worse around 30 and 60 MPH; might have been a little worse, but hard to tell over the ordinary TR4A noises.

5. There is no clunking or anything like that when going from acceleration to deceleration.

So, it sounds to me like the differential is the strongest candidate, with the OD output shaft bearing as a second possibility. The bearings are new Timkens, but the ring and pinion gears were used. The rear wheel bearings also are new. The OD output shaft bearing is not new, but it was a quality Timken bearing and looked good to me.

So, unless anyone has any more thoughts, I think I will pull the rear axle and check the diff as soon as I get a chance (which may be a while).

Thanks much for your input; it helped a lot.

 

[Snowkilts]

I finally took the car out on the road to do some checks. I noticed the following:

1. The whine/buzz is only on acceleration.

2. I reconfirmed that the pitch of the whine depends on road speed only; shifting gears or switching the overdrive in and out does not change the pitch, as long as I keep the road speed constant.

3. It is loudest when accelerating lightly; not nearly so noisy when I accelerate more aggressively, but the noise is still there.

4. It was hard to tell if it was worse around 30 and 60 MPH; might have been a little worse, but hard to tell over the ordinary TR4A noises.

5. There is no clunking or anything like that when going from acceleration to deceleration.

So, it sounds to me like the differential is the strongest candidate, with the OD output shaft bearing as a second possibility. The bearings are new Timkens, but the ring and pinion gears were used. The rear wheel bearings also are new. The OD output shaft bearing is not new, but it was a quality Timken bearing and looked good to me.

So, unless anyone has any more thoughts, I think I will pull the rear axle and check the diff as soon as I get a chance (which may be a while).

Thanks much for your input; it helped a lot.

I worked for 12 years at an axle manufacturing facility. What you are describing is classic gear noise from the ring and pinion. Light acceleration is almost always the worst. Did you roll the gears with marking compound to check the pattern when you installed them? And honestly, even if you did, they can still be noisy.

Probably no consolation, but the noise does not indicate that the gears are more or less likely to fail. We used to have a saying where I worked: A singing axle is a happy axle.

 

[Sarastro]

I have to confess--I went by the dimensions in the shop manual, got them all within spec, but never used the marking compound. At the time, I doubted that that was done at the factory, since they had a special tool to set up the pinion depth, and simply couldn't have gone to that much trouble. Probably they just installed the tool, figured out the necessary shim thickness, and socked it all together.

Some measurements I made when setting the lateral position of the ring gear turned out to be wrong, but I caught the error and THOUGHT I got it right in the end. But maybe not.

But thanks for the benefit of your experience.

 

[CJD]

It usually takes me at least a coupe days setting a ring and pinion. Marking is pretty essential to the assembly. I don't know, but I would imagine the factory would make a quick marking check to verify the setting. The check only takes a minute...adjusting if it's off takes a good bit longer.