Drivetrain vibration

[Michael G.]

I seem to have some vibration in the drivetrain of my 63 L84 car. It becomes very noticeable at 60 MPH (about 3000 RPM with a 411:1 differential). The car feels 'rough' above that speed and the shift lever vibrates like crazy.

Anybody know what is the most likely cause or what to check first?

Thanks

[William C.]

Re: Drivetrain vibration

First question is if you are running at "vibration" speed, and you push the clutch in and coast while off the gas letting the engine speed fall, does the vibration go away? There are many possibilites, but you need to start with "is it engine/clutch, or transmission/drivetrain related?" I believe there are similar discussions in the archives regarding vibrations.

[Jerry B.]

Re: Drivetrain vibration

Had a similar problem with vibration. It turned out to be a tire balance problem...... cause was one of wheels flipped a weight.

[Robert S.]

Re: Drivetrain vibration

I had a similar situation in my 60. Turned out that the pilot bearing was about 1/8 inch oversize and the clutch disk would be clamped off center. Trans probably needs to be rebuilt. It's hanging on the wall waiting. New trans and pilot bearing solved my problem.

[Michael G.]

Re: Drivetrain vibration

Thanks Bill, I'll start with that, I didn't push the clutch in at 60 today, I'll try it tomorrow.

The radial tires and knock-off rims are new, I can check the balance, but I don't feel the vibration in the steering wheel or the seat like I normally would with a tire or wheel balance issue. I once had a bent driveshaft (after an accident), and it feels a bit like that did.

[Michael G.]

Re: Drivetrain vibration

I was just reading some old posts about unequal driveline angles causing vibrations, when it occurred to me that my car had been more than an inch above normal height, so I just had it lowered to the recommended height. This is a pretty big adjustment, but since the change is just lowering the car to the expected geometry, I don't see that this should be the cause.

Is this enough of a variation to cause a problem?

[Michael G.]

Re: Drivetrain vibration

I just finished driving the car again. I took it up to 60 MPH, at which point the vibration in the shift lever got much worse. I then let off the gas, which made a little difference, but not much.

I then pushed the clutch in, which did not affect the vibration at all. The frequency seems higher than a vibration of a rear tire, so I assume this means the problem is in the trans, u joints, or differential. (or perhaps driveshaft alignment?).

Anyone know whats the next step?

Thanks,

[Timothy B.]

Re: Drivetrain vibration

Michael,

If you turn the steering wheel one way or the other and the vibration stops there could be a bad front wheel bearing..

Got to be a process of elimination at this point but don't rule out tire and tire balance.

[Dick W.]

Re: Drivetrain vibration

I just finished driving the car again. I took it up to 60 MPH, at which point the vibration in the shift lever got much worse. I then let off the gas, which made a little difference, but not much.

I then pushed the clutch in, which did not affect the vibration at all. The frequency seems higher than a vibration of a rear tire, so I assume this means the problem is in the trans, u joints, or differential. (or perhaps driveshaft alignment?).

Anyone know whats the next step?

Thanks,

Did you let the engine drop back to idle when you kicked the clutch in??

[Gary C.]

Re: Drivetrain vibration

Michael, any vibration in the steering wheel - usually means something's out of balance in the front suspension/wheels or any vibration in the seat bottom - usually means something's out of balance in the rear; tires, rear wheel bearing, etc. If it's only the transmission shifter, might want to check your motor or transmission mounts? Putting on a lift and running might help with the diagnosis. Gary....

[Dick W.]

Re: Drivetrain vibration

Michael, any vibration in the steering wheel - usually means something's out of balance in the front suspension/wheels or any vibration in the seat bottom - usually means something's out of balance in the rear; tires, rear wheel bearing, etc. If it's only the transmission shifter, might want to check your motor or transmission mounts? Putting on a lift and running might help with the diagnosis. Gary....

Real dicey running a rubber axle car on a lift. You not only have to support the chassis, but both trailing arms. A little on the scary side for me.

[Michael G.]

Re: Drivetrain vibration

Tim, I'll try turning the wheel at speed (judiciously) and see what happens

Dick, yes, I let the engine go to idle and the vibration was still present.

Gary, there really is no appreciable vibration in either the steering wheel or the seat. Sounds like my first suspect might be the trans mount....

Thanks,

[Dick W.]

Re: Drivetrain vibration

Does it seem to be engine speed, faster or slower?

[Michael G.]

Re: Drivetrain vibration

Dick, I think its pretty much independent of engine speed, but I can try running it up in third gear and comparing the vibration at a given speed.

[Michael G.]

Re: Drivetrain vibration

Update on vibration issue: I drove the car about 100 miles over the last two days, so I've got a better picture of the vibration issue.

The vibration starts to be noticeable at 60MPH, but get worse as you go faster. It is intermittent, sometimes it starts at 60, sometimes it doesn't happen at all and the car seems fine well past 70.

When I drive 60 and feel the vibration, if I push in the clutch, the vibration stops. When I let the clutch out again after a few moments, sometimes the vibration comes back, sometimes it goes away completely sometimes its worse. If I'm driving 60 with no vibration, if I push in the clutch and wait a moment, when let it out again the vibration may start, or it may not.

I have no clue here, but my best guess is that maybe the flywheel and clutch are both out of balance, that random rotation angles sometimes cancel the two out of balance conditions and balances the whole thing.

Opinions are welcome.

Thanks,