Engine vibration � need help diagnosing

[Rod R.]

[Mark E.]

Mark, in answer to your questions:

Yes, vibration varies with engine speed, not vehicle speed.

Yes, vibration only occurs between 3500 - 4500 rpm as I don’t want to increase the rpm anymore with the vibration.

Vibration only occurs with the clutch engaged and the transmission in first or second gear as I have not gone to a higher gear at the 3500-4500 rpm.

Yes, vibration stops when the clutch is disengaged and the transmission is first or second.

Yes, vibration stops with the clutch engaged and the transmission in neutral.

Yes, the vibration varies with drivetrain load with medium and full throttle. I can go up to speed and coast, run the rpm up to the 3500-4500 range, and not get the vibration. I have had the engine up to 5500 rpm, no load and it is smooth.

Rod

Rod,

I suspect the driveline (from driveshaft to hubs), or engine/transmission/rear carrier mounts.

It's less likely the problem is the engine/clutch assembly, since the vibration only occurs with the driveline engaged
It's less likely the problem is the transmission, since it worked ok prior to restoration.

I've experienced two cars with a vibration which seemed a function of engine, not driveline RPM, and in each case the problem turned out to be worn u-joints. I suspect the u-joints complain under a specific load, which happens within a specific engine RPM range.

Assuming the mounts and driveline wear components were replaced during restoration, the issue may be installation or part quality related, rather than due to wear. Things to check:

- All fasteners in place and properly torqued. Carefully check all u-joint trunion fasteners.
- U-joints properly seated
- Slop/play with half shafts, driveshaft
- All mounts tight and properly installed
- Wheel bearing run out/slop
- Re-orient driveshaft 180 degrees (as previously suggested)
- Driveshaft pinion angle (should be ok unless mounts improperly installed)

[Rod R.]

[Richard G.]

[Rod R.]

[Perry M.]

[Mark E.]

You can take the clutch balance off the list.
Got an old phone with a working camera? Attach it under the car, hit record in movie mode with sound. Go for a ride.

Clever idea! There are purpose-built vibration and noise sensors for professional mechanics which are mounted to suspect areas of the chassis, which do the same thing. An old smart phone is an affordable alternative.

[Mark E.]

A more practical way would be to find someone with a dynamometer in your area. You can run the car through the gears at any RPM you wish while someone is actually watching the drivetrain in motion. You can inspect every aspect of the mechanics of your car except for the front wheels.

If a careful visual inspection doesn't identify any issues, this would be my next step. This avoids running the suspension at full extension on a lift, plus load can be applied.
A

[Gene M.]

[Rod R.]

[Gene M.]

To clarify: The only reason the vibration "stops" at 4500 rpm is that I stop running the rpm any higher, under a load, to prevent any damage. I suppose I could redline the engine under a load to see what happens but the chances are something might break.....therefore, I will not do that. The contributors to this forum have given me a long list of things to check. Hopefully, the culprit will be found earlier in the process of elimination.

[Rod R.]

Will do. Thanks Gene.