Roger60

67 Cutlass conv. 330 rebuilt, turbo 350 rebuilt 12 bolt (cover) O type rear, nor rebuilt but serviced. At speed I both feel and hear a slow vibration and hum that is far slower than anything rotating at that speed. Kinda a rrrmmm rrrmmm rrrmmm , but real slow. Hard to describe in print. Any ideas? Thanks.
Just remembered, I replaced all the bearings, races seals and crush sleeve.

76olds

A vibration, rrrmmmm rrmmm noise is often a loaded question. This can be anything from exhaust harmonics, to bearings, tires/balancing to many other area's. Difficult to pin-point and often annoying.
I would begin with checking the tires for bulging, minor belt separation , to wheel weight missing. Then go on to axle/wheel bearings, U-joint and so on.
Very difficult to nail this type of question down over the web.

Eric

Fun71

That description is similar to what I heard when a wheel bearing was going bad on my O-Type rear. The inner race of the bearing was spinning on the axle shaft and actually grooved the shaft. I got a replacement axle shaft from Brian Trick.

Ozzie

It might help if you could post a recording of the noise.

oldcutlass

I've had old tires make a rumbling type of noise.

Roger60

It is more of a vibration than a noise, I don't think it would it would show up on a recording. Feel it more thru the steering wheel on my hand, but not like an out of balance issue. Very subtle, not violent. More of an annoyance than anything. Like I said, nothing rotates that slowly especially at 70 mph. The car has gone thru a complete nut and bolt frame off resto; everything is new including tires. I have only about 400 miles on the rebuild. I have new riken performance tires on 17" turbo thrusts. Maybe the more it's driven it may go away. Maybe not. Like Captain Ron says " if anythings gonna happen, it's gonna happen out there". Thanks.

rickman

Some of the older tire shops still have the floor machine that can spin the tire/wheel while it is still on the car (even though they actually balance the tires off the vehicle on the newer wheel balance machines). I would suggest finding one of these shops and ask them to spin each wheel individually on the car and see if you have the vibration. Many years ago, I had a bad front bearing which I felt in the steering wheel but couldn't find it until an experienced guy used this method to find it. Good luck!

Roger60

I used to use one of those. Haven't seen one in years. Thanks.

SWinner

Roger60

Put the rear end of your car up on jack stands and have a friend sit in the car and run it at the offending speed while you observe the rear tires and drive line. if you have a mechanics stethoscope you can listen to each bearing individually.

Good luck,

oldcutlass

Also check your free play in the front wheel bearings. With these odd noises your just going to have to start looking at things that move.

Vintage Chief

Might offer up my own SWAG, WTH:

(1) Possibly a buffeting vibration the result of wind? Did you repack the firewall at the steering column? Anything loose along the firewall steering column assembly area which might be buffeting?
(2) I don't know the type of steering column you have. Don't some steering columns have an inner & an outer sleeve to them when you assemble them? I know they changed over the years with various types. Chance it's buffeting around in the column itself?

droldsmorland

Start with basics:
When you performed open heart surgery on the rear end how did the mesh pattern look post reassembly? These O types are picky and hard to assemble properly. Off a couple thou and it will bite you azz...end. Pull the cover and recheck mesh with marking compound.

Check wheel balance and tire/rim runout. Observe wheels on the balancer machine for both. Are the tires old?

Before pulling driveshaft check for play at the pinion and both ujoints. Then remove driveshaft feel both ujoints. One cup needle bearing assy could be frozen up?

Check front wheels, off the ground for play. If present look at front wheel bearings.

Look at each brake assembly. A frozen caliper piston or slider pin will put enough drag on a rotor to vibrate. Check shoe brake assemblies for drag or drum runout.

Then dig in further.

76olds

Sounds like everything is new and just needs to shake itself out as you mention, you may just need to snug a shock bolt or nut up since you can feel it at the steering wheel.