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

Yawl about got this worked out? Then I don't need to say anything? Good.

As they said in "My Fair Lady" "I think (s)hes got it." "The rain in Spain is mostly on the plain." "By God (s)hes got it."

Thanks, I think your're right, now if I can just convince my mechanic!

Kelly

Pardon me, but when I disassemble an early 6-cylinder I find the "pilot bearing/bushing" is pressed into the end of the CRANKSHAFT .

Either I don't understand the problem or "nomenclature" has taken a hike.

That sounds right, but both ends of that shaft are held in place with "pilot" bearings so if it's not the one in the flywheel than it has to be the ones in the transmission, hopefully.

The noise should occur anytime the engine is running and clutch depressed. If you let the engine idle in neutral, clutch not depressed, and you don't hear the noise then it is likely the flywheel side, if you hear the noise then it is likely the transmission side.

If you fill the transmission with oil and the noise goes away, problem solved.

Brian

I think that the problem here is one of nomenclature and everyone needs to get on the same page as to what they are calling a "Pilot Bearing". The bearing that is in the end of the crankshaft is called the "crankshaft clutch pilot bearing". If there is a bushing in the crankshaft instead of a bearing, then it is called the "crankshaft clutch pilot bushing".

Also, the "crankshaft clutch pilot bearing" (or bushing) turns whenever the crankshaft is turning.

I'm voting for the throw out bearing being the culprit. To go back to the original post, the noise occurs occassionaly and only after sitting for a while with the clutch disengaged. At that point, the t/o bearing would have been rotating for a while and, if not properly lubricated, could be building up heat and starting to "growl". Also stated was that it "....has what appears to be a brand new clutch assembly". If the previous owner had to replace the clutch because it was slipping too badly to sell, but didn't want to replace the t/o bearing in order to save a few bucks, maybe it is worn out as well. Wasn't the '38 t/o bearing the first year for a sealed bearing? I know my '37 coupe has a small inspection cover that can be removed to lubricate the t/o bearing, but that's a graphite bearing and I think it was redesigned for '38.
Lastly, I'd make sure the clutch pedal adjustment is correct and not riding on the clutch and that the t/o bearing fork isn't hitting the rotating assembly when the pedal was depressed all the way.
My 2¢

-Bob

I have a 1940 Chevy that I have owned since 1963 and have put ove 370,000 miles on it and it still has the original pilot bearing (needle type) installed. The bushings came later. I have changed many throwout bearings over the years but have never messed with the pilot bearing. And I have had the same problem you have. The throwout bearing will not always make the same noise or any noise everytime you depress the clutch. If your car is like mine it knows exactly when there are people present to hear uncalled for noises. I've read all of the replys to your questions and my vote stays with the throwout bearing.

I just hate being corrected by a dog....

Arf Arf! ha ha! :eek:

Your explanation is good enough to understand and it is correct.
To Check if the throwout bearing is causing the noise. Simply spray some penetrating oil around and into the back side of the TO bearing, then run it to see if the noise subsided. You can also remove the small inspection cover on top of the bell housing to observe what is happening at the throwout. It is obvious that the transmission and clutch assembly will have to come out, as it will not fix itself.
Secondly it is extremaely likely that the crankshaft pilot bearing (roller) is completely worn out and has destroyed the end of the input shaft. I have removed a number of crankshaft pilot bearings and bushings and the bearings do the most damage (Although they last for years) Replace it with a new bushing! With all of this wear on the front it all transfers down the line for a shaky clutch.

Sounds like what I went through with the 52, it turned out to be lack of lubricant in the pilot bearing. I relubed carefully using high temp white grease where the transmission shaft and the pilot bearing mate care not to get carried away and have had no trouble through over 3 years of driving in parades, around town etc.

And if the crankshaft has excessive end float you can get a noise when the clutch is depressed because it pushes the crankshaft forward. The source of the noise can depend on how worn the thrust is. It is an easy thing to check before you start pulling things apart.

Ken

Did you greese the pilot bearing?

Well, after replacing the motor and transmission mounts, fixing the leaks in the transmission and filling it back up with oil, my mystery clutch noise is.....still there.
The mechanic was sure it was the pulley grinding on the frame because nothing was holding the engine in except the driveline, but after I drove it around for awhile, sure enough, it came back in all it's growling glory. My wife said she could even hear it in the house as I pulled into the driveway, but at least this time I can make it happen at will. Just warm the car up real good by driving around for a half hour and then with it stopped and in gear and with the clutch pedal held down, rev the engine. Grrrrrrrrrrrrrrr until you let the clutch out.
Now at least I can take it back to my mechanic and let him hear and feel it for himself.
I'll keep you posted!

Kelly

By what I have read the bearing (bush)at the front of the gearbox in the crankshaft is the problem. The only way to fix the it is to separate box and motor. While it is all apart advisable to check condition of clutch and flywheel, repair or replace as neccessary.