I have recently built '30 A coupe, highboy, fenderless, 455 Olds/Muncie/9inch. Lots of squeaks and rattles yet (it is a Model A after all), but one particular noise has me stumped, and I've searched here and elsewhere for anyone who's had a similar symptom. Best I can describe the noise is that it is similar to a howling gear, but the problem is that it is only present when the drivetrain is very lightly loaded. If I accelerate so the engine pulls the car, noise stops. If I decelerate so the car is pushing the engine, the noise stops. All the gear noise info I can find talks only about noise when gears are loaded, whether accelerating, decelerating, or both. But never only very lightly loaded, and that's the puzzle. It is not wheel bearings - if I shut the engine off and coast in neutral, no noise. So it has to be (a) in the Muncie, (b) in the rear end or (c) maybe not in the drivetrain at all, and I'm just getting some engine/bell/trans contact with chassis or body in certain situations. (Bad engine mount maybe?) That seems a stretch, and I cannot visibly find any such contact. So, short story long: Can a Muncie or 9 inch rear have a problem that only creates noise under very light load?
Muncies whine even when they are put together proper. I think it is due to straight cut gears which is done for strength. Some reading - https://www.google.com/search?q=Mun...+whine&rls=com.microsoft:en-US:IE-ContextMenu
If it only occurs under light load why can't you rack it at a shop or jack up on jack stands and walk around and listen for the noise? At my shop it would be up on a two post rack in a second. With my guy in it to work the gas pedal I'd walk around with my stethoscope until I found it.
I've read that the M-22s ("rock crushers") have straighter cut gears and whine more than the 20s and 21s. (That's a good whine to most hot rodders.) This is an M-20. I've had a few cars with Muncies, and this noise is not normal, nor would I describe it as a whine. Plus the rest of the car is so noisy (exhaust etc) that any normal tranny gear whine should not be audible over the rest of the racket.
I'm not sure there'd be enough load to create the noise, but that's actually a pretty good idea. Nothing to lose by tryin' but a little time. I shudda thought of that. Thanks!
Only thing I can think of is the input shaft bearing , that would not be turning w/ the motor shut off & the clutch engaged. dave
sounds strange but, i just had my clutch master whining. a little oil cleared it up. clutch throw out clearance? pinion nut to tight ?
Bad U-joint? You could apply light brake pressure (possibly the parking brake) to mimick a light load on the rack.
If you have a GM posi rear end, drain the fluid and add the Posi-trac additive and finish filling with fluid. My 69 427 Vette did the same thing. Soon as I changed and added the additive, it was gone.
my m-20 in my O/t firebird whines like a small blower and its a stock rebuilt unit , all muncies whine a little , but the m-22 is a pronounced whine almost superchargerish sounding , the alumiinum case doesn't dampen the noise like the iron case saginaws do.
You could distinguish a M22 rock crusher, by the straight cut gear sound when underway. Regular old M20 & 21 yes, but less prominent. I'd try the rear diff oil change mentioned first.
What oil are you using in the transmission? Some of the synthetics are pretty thin. A thicker oil might quiet it down. You could use the old used car trick of putting sawdust in the transmission.
Interesting opinions, thanks fellas. Using the e-brake for a slight drag while running on jackstands is another idea so simple that I can't believe I missed it. I'll do that tonite or tomorrow and report. RE the u-joint comment, mebbe I haven't described the noise well. Nothing like a u-joint, too high a freq. And they are new - 800 miles. Angles are right (~3º both ends). Tranny input shaft bearing is another possibility to check, but I'd have thought it would be noisier with more load, not less. We'll see. Tranny oil is conventional 80-90. Same for the 9", and it's not a posi. RE clutch master? Sorry, lost me there. The TO bearing BTW is hydraulic. Pinion nut? A possible, but from what I'd read, that would cause noise on deceleration, and that's not the case here. But worth checking while up on the stands and running. Gonna make me a little nervous under there poking around with the wheels turning. If I don't post again tomorrow, it means my car ran over me.
The springs in the clutch disc center can cause the noise problem.. Back in the day, I had a muncie in a car and when it had a disc with the many small springs in the center of the disc. It would sound like you describe. A change to a disc with fewer, but larger center springs and it went away. I tried this back and forth a couple of times and every time the small spring disc was in the car it would make noise/vibration under light load..
Just so nobody wonders, I didn't get to it today as planned, but thought I shud post so you know nothing happened. I don't want my multitudes of fans worrying about me, haha. Tomorrow's Saturday - hopefully with some available time.
My 9 inch with 4.11's in it howls on light acceleration only. Only when I get up past second gear as well. I can feather the throttle a bit to stop it when it gets annoying...
Sounds like it is probably a little noise in the R&P.... Does it come in at a given speed and you drive thru it and then it goes away? Try driving it at the same speed in 3rd and 4th... that will eliminate the trans. If it were the output bearing you would hear it pretty much all the time loaded or not. ALL ring and pinions will make a little whining noise. Some, the harmonics set in at a low enough, or high enough speed that you normally would not hear it. But they all do it. Will live forever like that too. But then, that is why there are radios and wives.... drown out the rest of the noises.
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