VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 Mystery clutch noise

My '38 Business Coupe has what appears to be a brand new clutch assembly, the problem is that I quite often hear (and feel)a loud deep growling noise when I have the clutch pedal depressed.
It does not occur all the time the clutch is disengaged, only occasionally, and after the vehicle is warmed up.
It only happens when the clutch is disengaged, like while idling at a light, I'll have been sitting a few moments with my foot on the clutch and then it will start growling. If I engage the clutch a little then it will stop. If I put the tranny in neutral and release the clutch it will stop. and it never happens while driving.
This is a loud noise, people have said they thought I was grinding the gears, and of course it never happens around my mechanic.
Anyone have any ideas on what might cause such a noise?

Kelly

if the throwout bearing or the clutch is assembled incorrectly it could be the cause of the grinding. This is definately a job for a mechanic, a mechanic can probably find the trouble by pulling the lower flywheel cover. But sounds like the transmission will have to be pulled

Hi bigkid,


From your description it would most likely be the throw out bearing. If it is a replacement bearing, that is actually a bearing, it may need to be lubricated. Normally, there is an oil receptacle on the side of the bearing holder that can be lubricated with an oil can. Problem is being able to access this oil spot.

The mechanic has had the cover off the underside of the clutch and inspected it as well as shown it to me, everything seems to be in order and quite new. He's observed it working while up on the stand and could see no problems. He's stumped.

Kelly

Has the grinding sound been there ever since you bought the car or did it just start? Does it make the grinding noise when the mechanic is watching it? Whatever the case is I would say replace the throwout bearing and check out the clutch for correct assmbly of the pressure plate and disk if the throwout bearing can't be lubed, it is posible the wrong parts were used whenthe clutch was replaced.

It's made the grinding/growling noise since I bought the car in Sept. but only after it's warmed up and been driven a few miles (lucky for the guy I bought it from, the test drive was short).
It hasn't made the noise in front of the mechanic or while up on the stand, it's one of those devious glitches that knows when to hide.
The front and rear motor mounts are shot and the mechanic thinks it's the fan hitting the radiator, but I know what that sounds like, and it ain't that.
We're gonna replace the motor mounts and give it a shot, but I'm not very hopeful that will solve the problem. Any other way of double checking the clutch without taking it out?


Kelly

I just went through a similar situation with a 60 Chevy, with the same symptoms. It seemed that the input shaft was binding in the pilot bushing, causing the input shaft spin with the engine while the clutch was disengaged making some real strange noises. It was intermitent, I am not ruling out what the other guys are saying, but this was causing some "grinding" noise. I replaced the bushing and the noise left. The input shaft did have bushing material on it so there was some evidence of this going on.
John

I would agree with everyone on the possibiliites. But agree most with John that the pilot bushing is more likely than the throw-out bearing. Unfortunately there is no way to check it without pulling the trans and clutch assy.

...Also, when your mechanic gets the clutch removed be sure when he checks the pilot bearing or bushing. as it is often called, is have him check the flywheel bolts and bolt holes. I hope he has a shop manual or repair manual for your particular year and model.

Has the level of the gear oil in the transmission been checked??

Great suggestions folks, I will tactfully ask my mechanic if he has considered the pilot bushing/bearing as a possible culprit and, yes, the tranny oil was very low...

What a wonderful resource, instant access to the accumulated knowledge of people in the know!

Kelly

Gene are you thinking maybe a dry or bad transmission front main shaft bearing?That sounds possible.

My thoughts would run to the pilot bearing.The original 1938 pilot bearing was a ball bearing job.It is replaced with a later brass bushing type.The brass one is used up till the present time.It does require greasing when installing.The throw out bearing is a sealed ball bearing in 1938 and cannot be lubricated.IF it was new I would doubt if it is the problem.The T.O. bearing is also still used up to a few years ago.(1938 was the first year to use a ball bearing T.O. Bearing.

If it sounds like gears grinding is something hitting the flywheel teeth-such as the starter drive??

Doesn't sound like gears grinding, but it is about that loud. What it does sound like is a shaft or a bearing rattling around in too big of a hole.
Bottom line, I think the tranny needs to come out and whole mess taken apart and looked at.
I admit, I bought the car because it just looks so damn cool, and seemed to run well, but I am no mechanic which should be obvious by now, and I don't have a great love for working on old vehicles even though I own a mid 50's panel truck and two late 60's motorcycles, but I am quickly learning the finer points of how a clutch mechanism works.
My question now is, when the clutch pedal is depressed, what part of the mechanism is now relieved of tension and would be free to rattle around? It seems that when the clutch is disengaged, the throwout bearing is forced against the diaphragm spring and is under a lot of tension and is not free to rattle, the flywheel is firmly bolted to the crank shaft and is spinning but the pressure plate is no longer holding itself and the flywheel against the clutch plate so it and the clutch gear that it is mounted to have stopped spinning and are under no tension. If the pilot bushing or bearing were too loose would this allow the clutch plate and clutch gear to occasionally shimmy around?

When you push in the clutch pedal the throwout bearing contacts the fingers and retracts the pressure plate that clamps the clutch plate between it and the flywheel. This allows the clutch plate (splined onto the transmission input shaft) to spin at a different speed from the flywheel and pressure plate. The transmission input shaft fits into a depression in the flywheel and the pilot bearing (or bushing) fits into the depression and supports the front of the shaft. The pilot bearing is neccessary when the input shaft spins at a different speed than the flywheel. So if the pilot bearing is bad then it will make noise when the clutch is depressed. The greater the difference between the input shaft and the flywheel the more potential for noise.

When you are at a stop light and you depress the clutch so that the car is not in any gear, the transmission is at a stop. Putting the car in gear and releasing the clutch will cause the drive shaft to try to rotate the transmission input shaft, moving the car.

So if you are at a light with the clutch depressed you can put the car in any gear therefor the transmission must not be moving. The only thing that is rotating is the drive shaft, throwout bearing, and the flywheel. The throwout bearing is moving with the idling flywheel and is the only bearing moving at the time the noise is made.

The input shaft would only rotate if the transmission were in idle and the clutch not depressed.

However, if the clutch plate were free to wobble around, due to worn pilot bearings, it could make a rattling sound as it is bouncing off the flywheel but I would look at the throwout bearing first.

Brian

Bigbth
You have forgotten about the engine. The flywheel and pressure plate are tied directly to the engine so they all rotate when the engine is running. If the transmission input shaft is not rotating and the flywheel is then the pilot bearing is rotating. You are correct that the other bearing functioning as a bearing is the TO bearing.

........and the driveshaft isn't turning either.

It is if your coasting

Yep, but they are talking about sitting at a stop light.....unless of course......they are coasting through it!

Chip-If I'm at a light and the car is not moving, the clutch is depressed, and the car is in gear, the pilot bearings are not in the picture because the input shaft is at rest. I know this because if the car is in gear and not moving, the input shaft has to be at rest. It is now one with the propeller shaft.

The clutch pressure plate is bolted to the flywheel so it is now moving with the flywheel. If I'm still at that intersection then the flywheel is rotating at idle speed, the input shaft is not moving (the pilot bearings are not moving), the throwout bearing is rotating on one side at idle speed and the other side at rest. When I release the clutch the pressure on the clutch plate increases and the input shaft starts feel torque applied. Still the pilot bearings are at rest. The only time the pilot bearings will be in motion is when the car is running in gear or the car is in neutral and the clutch is not depressed. Therefor I would look at the throwout bearing as the most likely culprit in the scenario provided by the esteemed bigkid.

Brian

If the engine is running and the transmission is in neutral, with the clutch pedal not depressed, the following things are rotating together,The flywheel,disc. pressure plate and front shaft (main drive gear) of the transmission.They will be turning at the same speed and the pilot bearing will not be in play.
When the pedal is depressed with trans. in any position, the disc stops spinning as well as the main drive gear.Then the pilot bearing is functioning as the flywheel is turning -actually the crank shaft, and the main shaft, which rides in it (and the pilot bearing), is stationary.

Okay, we're on the same page, just must be a nomenclature issue. When I talk of pilot bearings I am referring to "Pilot Roller Bearings" on the clutch gear (input shaft) and main shaft of the transmission.

--If the engine is running and the transmission is in neutral, with the clutch pedal not depressed, the following things are rotating together,The flywheel,disc. pressure plate and front shaft (main drive gear) of the transmission.They will be turning at the same speed and the pilot bearing will not be in play.--

The pilot bearings are rotating at the same speed as the clutch gear(input shaft not main shaft of transmission). They are what separate the input/clutch shaft from the rest of the transmission.

--When the pedal is depressed with trans. in any position, the disc stops spinning as well as the main drive gear.Then the pilot bearing is functioning as the flywheel is turning -actually the crank shaft, and the main shaft, which rides in it (and the pilot bearing), is stationary.--

The only time the crank shaft is stationary is when the engine is not running. So in this situation, when the pedal is depressed, the pressure on the disc is removed and it stops spinning at the same rate as the flywheel/crankshaft/clutch cover/pressure plate (which are spinning at idle speed, in this example). When the disc stops so does the clutch gear(input shaft) and thusly the pilot bearings.

If the sound is heard only when the car is in idle, the clutch pedal depressed and the car in gear then the throwout bearing is the only object rotating differently than at any other time, it's rotating at the same speed as the flywheel/crankshaft/clutch cover/pressure plate - idle speed.

Brian

It may be a matter of nomenclature.

From my post of November 20, 2003 7:15

The bearing (or bushing) in the flywheel is commonly called the "Pilot Bearing" (or bushing). I guess you can call it anything you want but that is what I and several others are referring to when we write "pilot bearing".

I'm not having any luck convincing my mechanic that it is any of these things that is the cause of the noise, but then he's never heard it and I have.
Here's what I'm leaning towards based on all the input I've received from you knowledgable folks, but I'm not sure I have all of the terminology correct so bear with me.

There is a bearing/bushing that is placed or pressed into the rear facing surface of the flywheel, I think this is the pilot bearing, this bearing supports the forward end of the clutch gear/input shaft/main drive gear. It's this shaft/gear that the clutch plate is attached to and the throw out bearing is sliding over.

When the clutch pedal is depressed and the car is stationary, the flywheel is spinning with the idling engine and the clutch plate and the clutch gear/input shaft/main drive gear are now not spinning. The pilot bearing attached to the flywheel is rotating around the front end of the stationary clutch gear/input shaft/main drive gear.

Now if that bearing were worn or loose then when the clutch is disengaged and the car is at idle and stationary, the front of the clutch gear/input shaft/main drive gear could shimmy around in the bearing because nothing is supporting the front of that shaft but that bearing, but as soon as the clutch starts to be engaged any chance of the front of the clutch gear/input shaft/main drive gear being able to shimmy is removed because it and the clutch plate are now becoming one with the flywheel.

Huh? whaddaya think?

Kelly