Strumming rhythmic vibration...

I get a strumming “vruum vruum vruum” when I drive. It vibrates the seat and it stops when I go into neutral and coast.
I thought it was the u-joint… so had them changed. But still happens.

Is it the new harmonic balancer on the engine? Is it the drivetrain?

Seems to me that harmonic balancer would do it in neutral too… may be unbalanced drive shaft?

You have a harmonic balancer for 28oz imbalance? They make them for 50oz, too,and you can’t use that one.

We have 50 in there. Needed it for the new 302

Check the driveshaft, maybe the balancing weights came off? Sometimes happens, look for a shiny spot.


I had a similar problem, with that happening around 60mph.
on the driver’s side axle, there is a breathing tube for the differential.
When I added a leaf, the guy showed me that it was disconnected, and the nipple was clogged. Said it was to eliminate the excess heat
My problem was solved.
Actually, it was more of a quick cycling hum.

That remembers me of last year when I had a vibration come and go like that, not to the extent to shake the seat but enough to be noticed. Then one day the transmission mount broke and needed to be replaced: no more vibration thenafter… There are so many possible causes!

Thanks all. I figures since the mechanic took off the driveshaft to put the u-joints on… maybe I should look for something else before I tackle that again.

Johnboy. Do you have a picture of where that breathing tube is?

OK, did you get the companion flex plate?

It sounds soothing, are you sure you want to get rid of it?

Yes. This one.

I keep falling asleep at the wheel!

Following up again. Did you have any photos of the nipple I should be looking for?

Should look something like this:
Not my picture. Found it online.

i’m not sure the other end is connected to anything on mine. Nipple on the the bottom is a tad different connected to a black hose with a clamp just like that. The fixed clamp at the top is there too.
Of course, nothing under mine looks as good as in that picture…

The other end of the vent hose is not suppose to be connected to anything. It is to remain open so that it can vent off any built up pressure or heat from the rear axle. It disappears up into the frame rail to try to keep any dirt from getting into it and clogging it.

Randy Goodling
CCOA #95

Issues with tires show up at 62 mph.

A guy that shows up at cruise-ins with a Cheby Comparo suffered for years with a hum/vibration when under load, not coasting. After having a new clutch and all that goes with it plus the rear re-built with no help, his rear man for the heck of it changed the axle shafts and noise/hum gone. Upon inspection the shafts were bent.

Thanks all.