chasing a vibration

[Paul A]

I have been chasing a vibration in Ol Blue. It occurs between 50-55 mph in both 4th and 5th gear. Tires have been balanced and rebalanced. I even switched to a spare set of tires - no change, same vibration. U joints are tight and lubricated. Steering wheel does not exhibit any vibration so my assumption is the issue is not related to front tires or front end. Recently installed a new rear wheel bearing on passenger side but I do not see how that could cause any vibration. A head scratcher.

The car is certainly driveable at speeds under 50 and over 55 as the vibration does not happen at those speeds.

thoughts?

 

[alpine_64]

Exhaust touching the pass through at that rev rage perhaps?

 

[sunalp]

Maybe motor or trans mounts?

 

[Paul A]

Exhaust touching the pass through at that rev rage perhaps?

thanks I can check for clearance. I had not considered that.

 

[Paul A]

Maybe motor or trans mounts?

I will check the motor mounts today. Tranny mounts are good. I will also check bolts attaching bell housing to engine.
thanks!

 

[Barry]

Chasing a vibration can be difficult and frustrating.

The only things that turn the same RPM in BOTH 4th and 5th gear at 50-55 MPH are the driveshaft and the rear axle parts. At 50-55 MPH, your driveshaft is turning about 2,270-2,500 RPM, so balance and straightness are important. The rear axle parts are only turning about one-fourth of the driveshaft RPM and are less likely to be the problem.

Most driveshafts are (or should be) balanced with one or more weights that are typically spot-welded to the main tube and sometimes get detached. Another possibility is a "loose" transmission tail shaft or rear-end pinion bearing that allows unwanted driveshaft "wobble". A good driveshaft shop can check the driveshaft for balance and "straightness".

Putting the car on jack stands and "running" 50-55 MPH in both 4th and 5th gear might reveal the source of the vibration. You may need to "load" the driveline by applying the rear brakes to replicate highway conditions.

 

[hdar5702]

Barry has some good suggestions.You mentioned that your u-joints were tight and greased.I would check them to see if one is not seized or binding.
Did you have the vibration before replacing the rear wheel bearing?

 

[Paul A]

Barry has some good suggestions.You mentioned that your u-joints were tight and greased.I would check them to see if one is not seized or binding.
Did you have the vibration before replacing the rear wheel bearing?

not that I remember so, no

 

[hdar5702]

If you didn't have the vibration before I would jack up the rear end and with jack stands check the left rear axle for excess play.Then with the engine running and in gear watch the spinning left rear wheel and tire for any wobble.If it isn't true it could only be the axle(unlikely) or hub or wheel(unlikely).Like Barry says vibrations can be difficult to diagnose.I have found over the years that it helps to have a friend(or brother) over to help or just be there to talk to. Good Luck with that

 

[belmateo]

I would lean towards U joint or Transmission bearing depending on how many miles and how long it has been sitting.