322 clutch vibration

[DaveZ]

This one has me puzzled and I can usually figure most anything out. Even pops scratched his head and he has been working on these Cadillac's and LaSalle's for 70 years.
There is a vibration that you can hear and feel in the car driving down the road.  I have verified it is not the engine. I had the pressure plate and flywheel balanced new clutch disc. Here is where it gets weird. If you push the clutch down and let it back you can find a sweat spot where the vibration completely goes away. May have to do this three or four times. Each time you stop and shift gears up to third wash rinse repeat. The only thing I can think of is a possible bearing in the transmission. Since I know the engine is good and that it can completely go away it cannot be the PP or flywheel as that is a constant. Clutch plate has no loose parts or broken springs. Got under it and nice and even all the way around etc.
Anyone ever hear of this?

[z3skybolt]

Dave,

Let us know what you determine. I have a similar, modest, vibration in my 40 LaSalle at about 40 mph. Above or below that speed it is smooth.  Letting it coast seems to make the vibration go away. I've wondered if it is the drive shaft or universal joint.  Normally I avoid that speed and all is smooth.   She loves cruising at around 50 mph.

Bob

[DaveZ]

Hi Bob,
We also have a 40 52  that I rebuilt the engine, new clutch and smooth as silk. That's what irritates me. The 37 should be just as smooth. Your issue might actually be wheel balance. On our 32, albeit a solid axle, it used to vibrate at 40 and when you got it above that the vibration and shimmy went away. I went through the arduous task of static balance and it went away.

[fishnjim]

These things can drive one crazy.   Sometimes they go away on their own, sometimes they'll get worse and then easier to find.   
Could be something completely unconnected to the clutch.   Without some monitoring equipment to detect, it's anybody's guess.   
Ears, etc. are connected to the brain and brain does funny things when it senses and makes up a story to explain it.
Ask yourself, what you're prepared to do about it, that you haven't already, if you find out what it is, and if it's a major task?   That should guide your interest in it.
Search for mechanical perfection can be a long and winding road.

Sometimes it's our perception.   eg; I had a nice new shotgun and I leaned it in the garage to melt and dry off after a days duck hunt before I cleaned it after changing clothes and cleaning the birds.   Neighbor came in garage carrying some presents to hide, didn't see it, and knocked it over and chipped the stock and put scrap in the barrel.   I was livid and never liked that gun again as the chip reminded me each time.   After a while, it developed a rattle in the chamber, too.   Could not figure it out.   I finally sold it to a guy at work for less than I paid for it and he took it home and came back the next day and told me he found a pellet in the chamber, cleaned it out, and was fine.   No more rattle and he could look past the imperfections, as he got a gun he wanted for a good price.   Those guns were worth double what I paid for it when I sold it and still appreciate today.   So don't get too emotionally involved with "stuff" if it doesn't meet our expectations.
I had a minor vibration in the 4x4, it was driving me nuts, so I took it to the garage.   They figured it was the drive shaft center bearing and changed it, couple hundred $.   No difference.   I took and put a load of something on it a week later and offloaded.   Noise disappeared.  A leaf spring had over extended from a chuckhole or being offroad and spring tension causing misalignment was relieved.   I could've spent a fortune trying to figure that out unsuccessfully.

[Big Fins]

Pilot bearing? Thrawl bearing? Are you sure it's in the clutch and maybe not the runout in the final tailshaft bearing that just may find it's center when the load is released? Front mainshaft bearing?

[DaveZ]

Yeah I'm thinking transmission because of the variables. Whatever it is will find a sweet spot where it stops. The 37 has a hyaat bearing between the clutch pilot shaft and mainshaft that may be flaky; who knows? Probably a good idea to go through the trans anyway. I have an extra for parts just in case.  Good winter project.

[LaSalle5019]

I’ll  throw this out. What if your clutch disc’s rotational position is what makes the balance come and go? One way to find out is mark the edge of the disc and have someone depress the clutch, then rotate it into different positions. Just start the engine with the trans in neutral and rev it without depressing the clutch. Seems like an easy test to see if the disc balance is aligning with something else that is or isn’t out of balance.
Scott

[Jay Friedman]

My '49 once had a "mysterious" vibration at 50 mph which no one could diagnose.  It was finally found that the driveshaft was out of balance because of many small dents it had accumulated over the years.  I brought it to a driveline shop who replaced it and the universals and cured the problem.

[The Tassie Devil(le)]

How in heavens name does one get dents in their driveshaft?

I have been over very many rough roads, and never dented a driveshaft in my life.

Bruce.

[Jay Friedman]

Haven't the foggiest idea, but they were there.  Who knows where the car had been during the 35 years before I bought it in
1984.

[DaveZ]

I’ll  throw this out. What if your clutch disc’s rotational position is what makes the balance come and go? One way to find out is mark the edge of the disc and have someone depress the clutch, then rotate it into different positions. Just start the engine with the trans in neutral and rev it without depressing the clutch. Seems like an easy test to see if the disc balance is aligning with something else that is or isn’t out of balance.
Scott

Hi Scott,
Yes that is the first thing I thought of, but how on earth could a clutch disc be that out of balance?  I have never had a disc be out of balance, or knew of it anyway because this has never happened before, but I supposed more bizarre stuff has happened. It's not the drive shaft because it has nothing to do with the speed or RPM. Not the engine because it goes away after depressing and letting up on clutch x amount of times. I will check the front mounts though as I do have new ones, but I highly doubt it's that. To Jay's point if you ding the driveshaft enough I could see it possibly bending which would for sure cause a vibration, but it would have be be enough force to actually bend it and it probably doesn't have to bend a lot to get a vibration.

[Jay Friedman]

Have you checked out the bolts holding the pressure plate to the flywheel?  These should be a balanced set.  Look on ebay if you need them.

[Bob Schuman]

Have you checked the rear motor mount, located behind the transmission? If the rectangular metal can that contains the rubber mount is touching the frame crossmember, the rubber has collapsed and you have a metal to metal situation, which frequently causes vibration. New rubber mounts are available form Terrill's and Steele's, and are not difficult to install.