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ricosan

Drive line vibration

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Hey Guys,

Well today was the big day. We installed a 2 1/2 degree shim at the springs. This unfortunately made the vibration worse! I can't understand it. I'll recheck the drive angles when we have the old drive shaft completely out to see if I measured wrong.

I talked with my mechanic about making up a new drive shaft with modern universal joints. This hopefully will once and for all eliminate the drive shaft as the culprit in this vibration saga.

If the new DS doesn't do it, we move into the pressure plate clutch area.

ricosan

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Um, it seems clear to me that if the shim made it worse, there is nothing wrong with the drive train, including drive shaft and gearbox and clutch. You proved the clutch was not involved by coasting in neutral while moving and it made no difference. Try the shim on the other side, tilting the diff. the other way.

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I apologize if these sound like a sarcastic questions. I sincerely do not mean them to be:

1) If the driveline was 4 degrees out of phase, why did you go with a 2 1/2 degree shim?

2) You did tip the differential it up didn't you?

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Hey Dwight,

Since shims are relatively inexpensive, My mechanic suggested I get both a 4 degree shim and a 2 1/2 degree shim. We decided to go with the 2 1/2 first and see how the vibration "responded" to that. Since it made the vibration worse, we felt trying the 4 degree would make it worse.

I am completely baffled as to why it got worse. I keep going over how we measured the angle and how we installed the shims. (my mechanic measured the angle too. We installed the shims with the thick part of the shim facing the front of the car. This pushed the differential up bringing it closer to parallel with the transmission.

Several of you have suggested I reverse the shim. I'm willing to try it but why do you think this might work? It does sound logical but it kinda stands the "science" on its head but it does make sense in an odd way. When I take my car in next week to measure for the drive shaft, I'll talk to my mechanic about reversing the shims.

Tomorrow, I'm going to put the car back on jack stands and take angle measurements again just to recheck to make sure I haven't erred in some way. It's not very easy to read the dial on the protractor.

ricosan:confused:

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I suggest you take the angle measurements with the car resting as normal with all its weight on ALL FOUR WHEELS, such as on a ramp-type hoist. It seems to me that when the car is on jack stands, the rear axle will not be in its normal position--that is, the axle assembly will be either hanging on the springs if the stands are under the frame, or some of the spring action is taken up if the stands are under the axle housing. Either way, on jack stands you will probably not be getting the same angle measurements as if the car is resting on all four wheels.

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Thanks for answering my questions. The shim is in the right way. I would expect it to continue to vibrate, but vibrating worse doesn't make sense. I am confused too.

George is right. If you can manage to squeeze under the car without jack stands, the measurements will be more accurate.

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It may be a stupid statement: if the vibrations are worse with an angle change, it means that the problem is there. I would try to put the shims to change to inclinaison of the axle the other way, as Spinneyhill suggested.

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Hey Guys,

We put the new drive shaft in Yesterday. Good news and bad news. The car rolls much easier and when I push the clutch in at speed, the stacatto vibration that I felt previously isn't there but unfortunately much of the vibration is still in the system.

The old drive shaft threw lubrication out at both U joints (pic). This new shaft has grease fittings so no more mess under the car.

I am going to box up the old drive shaft for sale with the car when the time comes. We made no modifications to the drive line itself so the old drive shaft will bolt back in easily.

From here we keep on working. I don't think that the problem is in the transmission. I think it may be in the flywheel/pressure plate area.

I was really hoping that this would solve the mystery of the vibration. I can't say I'm not disappointed but this new drive shaft took me just a little closer to the prize. It's one more thing that can now be ruled out.

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"We installed the shims with the thick part of the shim facing the front of the car. This pushed the differential up bringing it closer to parallel with the transmission."

That may be the problem. If the drive shaft is in a straight line with the trans and/or diff it will vibrate. The driveshaft must be at an angle, in other words the universal joints must work as the shaft rotates and they must both be at the same angle.

http://www.hotrodhotline.com/md/html/drive_shaft_harmonics.php

Edited by Rusty_OToole (see edit history)

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Rusty,

Thanks for the article. I'm going to measure the driveline angle again this afternoon. I don't think that it is exactly parallel. Maybe 1 or 2 degrees off.

ricosan

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If the problem is the flywheel or pressure plate you could make the car vibrate sitting still by revving the engine in neutral with the clutch out.

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When you push in the clutch at speed, if it is the clutch/flywheel, the vibration will vary with engine speed. From all the several pages of descriptions of the vibration, the vibration is created by something AFTER the clutch flywheel, and is dependent on road speed, not engine RPM.

I suggest that the vibration and 'staccato' noise are in the transmission or the freewheeling unit. There can be bearings that are very bad, or gear teeth missing, or freewheeling 'one way' rollers that are flat-sided, or several other possible causes of vibration in the transmission.

Did you start and run the engine with the trans either in or out of gear when the driveshaft was removed?

GLong

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Good Morning Guys,

I disconnected the drive shaft from the transmission this morning, started the engine and brought up the temperature. I brought the engine RPMs up and as I did I found a distinctly familiar vibration. I then engaged the transmission in first gear and then moved on up to 2nd and 3rd. Again as the speedometer rose I found all the same vibrations but the vibrations didn't increase when the transmission was engaged so I think that the vibration is forward of the transmission. It may be in the pressure plate or the clutch plate. It could be in the engine i suppose?

I have a Marmon get together in May that I want to travel to. I hope I can get this vibration out before then.

Thanks guys for the great suggestions. I'm beating myself up for not thinking of it before!

ricosan

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And doesn't have a stuck valve (esp. if it has sat for a while)? Is the engine vibration damper in good shape?

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First Born - The engine runs pretty good. In the past 12 months I've replaced all of the spark plug wires, new points and condenser, new spark plugs and new coil. Also had the carburetor professionally rebuilt. Compression is good. 7 cylinders 64 lbs and 1 at 70 lbs. I believe it is still using the babbit type bearings but I haven't opened up the engine to see.

Spinney - I take the car in next week to replace the leaky cork seals on the side valve cover. This will entail removing all the manifolds and most everything else on that side of the engine in order to expose the valve stems. We plan to adjust all of the valves when we have every thing off. I don't want to have to do it again.

I'm not certain but I don't think this car has a damper or not one that I recognize anyhow.

ricosan

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I don't know what's causing your vibration. But I noticed your compression readings, and they seem low. Your engine probably had a 5.5 to 1 compression ratio originally, and multiplying that times 14.7 psi (atmospheric pressure) yields 80 psi. Did you check the compression with the engine fully warmed up, all spark plugs out and a fully charged battery? I am not saying that compression is the cause of your vibration. But it's possible that the engine needs closer attention to assess its condition.

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jr,

Engine rebuild is on the agenda but just not ready for it yet. I'm thinking I'll rebuild the engine if it needs it when I have the body off for painting next year.

ricosan

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Have you (or your mechanic) given any thought to the engine mountings or exhaust/muffler causing the vibrations. Don't know anything about the Marmon engine mounts but the photo of the rear engine mount in post 59 appears to rubber insulated on the cross bar. Perhaps this needs replacing. Hope you find the cause as there is nothing more frustrating than trying to solve these issues.

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Good Morning Stude,

I think that what you see in post #59 is the support for the tail of the transmission. This is my first antique car so I am still learning every day. I've looked for "motor mounts" as I'm accustomed to seeing on most all the cars I've owned but this car looks to me as if this engine is bolted solid to the frame.

ricosan

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Good Morning Stude,

I think that what you see in post #59 is the support for the tail of the transmission. This is my first antique car so I am still learning every day. I've looked for "motor mounts" as I'm accustomed to seeing on most all the cars I've owned but this car looks to me as if this engine is bolted solid to the frame.

ricosan

The first car to use "modern" rubber motor mounts was the four cylinder 1932 Plymouth. Prior to that all cars had their engines bolted directly to the frame. Cars with more than four cylinders were not subject to as much vibration but by about 1935 virtually all auto makers were using them.

Terry

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The first car to use "modern" rubber motor mounts was the four cylinder 1932 Plymouth. Prior to that all cars had their engines bolted directly to the frame. Cars with more than four cylinders were not subject to as much vibration but by about 1935 virtually all auto makers were using them.

Terry

Not true. My 1931 Dodge Brothers had rubber insulators (motor mounts). A few earlier Chrysler products had them.

Edited by keiser31 (see edit history)

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