Just a thought, I've had vibrations caused by the brakes. The parking brake was not releasing all the way and caused a vibration over about 60 km/hr. the only reason I caught it was because I pulled on the brake cable and it released. Another time it was a slightly seized caliper and a rotor that was warping more and more because of the heat, the hot rim was a dead give away. That's a vibe that rips through the back.

I've heard that radial tires on older cars can sometimes cause harmonic vibrations. The running frequency of radials is different from bias ply tires and can cause the suspension components to oscillate at their natural frequencies. I've never experienced it for myself, so I don't know exactly what it sounds or feels like.

A pilot bearing for a manual transmission will also cause vibrations like you're describing, and disengaging the transmission doesn't always stop the vibe.

How are the wheel bearings? I've had a noisy vibe when I let the wheel bearings go, but it's not really the kind that will jostle the spine, just annoy the ear drums.

I've had a similar vibration caused by a malleable iron harmonic balancer starting to come apart. It didn't vibrate when the engine was disengaged from the transmission, but it did vibrate over a certain speed. When the engine was disengaged over that speed, the vibration would stop. You probably got the car to speed and flipped it into neutral to check this, I assume that's what you meant by not RPM specific.

With out going into the transmission, That's about all I can come up with, good luck.

 

Yeah, it's an automatic, so the pilot bearing thing is out.

A friend suggested wheel bearings, but I agree with you. Usually they just make a terrible racket, but don't cause a nice harmonic vibration--and I mean IT'S A VIBRATION. You feel it through the entire car.

The radial tire explanation I guess is possible--others have suggested it. But I've driven almost every kind of "old" car out there and invariably adding radial tires usually just improves handling without any other symptoms. I guess this could be the exception, but...

The harmonic balancer looks brand new. I haven't checked for slippage--will do that.

Speaking of the transmission, could a poorly meshed rear gear set do this? I've heard that you need the mesh pattern down right, otherwise it could be a problem.

I raise that issue because it is a fairly new tranny--not sure when it was rebuilt--but supposed to have been recently.

Another idea a friend has had is a bad or out of round axle. Possible?

 

Out of round Axle is possible, if you mean out of round at the bearing surface. I haven't heard of axles going out of round from wear or stress, and I don't know what a bad axle is so I can't comment. The ones I've worked on usually go out of round at the bearing surface, (usually because of the bearing) so If you're going to check the bearings, you'll see it. If that's the case, see if you can get an axle repair bearing. It's the same bearing, but the case is made so the bearings run a little further in (or out) on the axle surface. I don't think you're going to get off that easy though because you probably would have heard the vibe from the bearing wearing out in the first place, unless the bearing just fell apart.

Another thought is the diff. carrier bearing. My experience is with cars a little newer than yours so I don't really know how yours is set up, but I would pull off the diff. cover and check things out. Probably a good time to do an oil change and slide in that new synthetic oil. (I'm so sold on that stuff, 463 000kms on my diff. with no problems) I'd start there before checking out the trans, although checking the rear output shaft for play is pretty easy too.

I had a vibe in a chevy van that I couldn't find for the life of me, the kind of vibe that made looking in the mirrors impossible. It was the planetary gear in the trans missing a half a dozen teeth. Of course that meant a rebuild, so I'd try looking for the simple stuff first.
good luck

 

A few things to look at.

Alignment of the drive shaft U Joints.
Raise the vehicle on a lift and look down the drive shaft from the differential.
The ujoints should be in line.
If you see the front one off a bit the transmission mount has slipped.
The mount has a bolt going through a rubber mount.
After several years the rubber will deteriorate and the drive train will move sideways one way or the other.
Also check to see if the transmission isn't resting on the cross member. Again from a bad mount.
The engine mounts can cause this as well.
If one is sagged it will upset the apple cart.
Don't want to lose all your precious apples.

 

Maybe a bad torque converter? You can DEFINITELY feel a bad vibration when those are out of balance or internally damaged. Although I'd think that would be more rpm specific.

 

Does the pitch of the vibration change between 45 & 75mph?

 

For Jimfulco:

Yes, the pitch of the vibration changes between 45 and 75. The worst is dead on 60 mph. At that speed, the vibration is a nice, steady harmonic hum through the body in one second intervals with one second between vibrations.

At 75, the harmonic vibration seems to be quicker (faster) in its resonation, and sometimes you "think" it has disappeared because it is vibrating so rapidly through the car. But, you can still feel it--more like a constant hum or vibration as the car moves down the highway. Then you drop it down to 60 mph and the one second intervals begin again.

For flyfisher and Stu:

Both of your suggestions seem like possibilities. I had the car up on a lift previously and the tranny mounts looked okay, but then again, I wasn't looking specifically for that as a trouble spot. So, next chance I get I'll check that out along with the axle/wheel bearings and the diff. carrier bearing.

 

Id be interested to hear the solution as I am having the EXACT same problem. I too have replaced the driveshaft, motor mounts, tranny mount, ujoints to no avail.

In the past I had a brake rubbing the drums and am starting to wonder if this could be the case again. I also plan on inspecting the rear end here shortly and will be sure to let you know if I find anything.

Hope this gets figured out for both our sakes lol.

 

I have been fighting the same type of problem for the last 2 weeks or so on my 66 Caprice. I replaced the engine and tranny mounts, had the drive shaft balanced, had the tires rebalanced, all to no avail. Previously, while I had the brakes apart, I had the brake drums powder coated. I'm thinking the sandblasting and powder coating changed the balance on the drums. This weekend, I replaced the two front drums with a set from the salvage yard. The low-speed, 45-60 mph vibration went away, but I still feel it at around 70 mph. I'm going to replace the rear drums tomorrow to see if that eliminates the problem completely. I'll let you know what I find out.

JimR

 

I would be very interested in Vista Cruiser's results. My brakes appear to work fine, but not in reverse. That is, I really have to stomp on the vacuum assisted power brakes to make the car stop while in reverse. Braking while moving forward is no problem.

I would not have imagined that it could be out-of-round drums or brakes that could cause such a vibration.

Let us know what you find as soon as possible. I'd rather tear into the brakes than the tranny or differential.

 

I had a similar problem like that caused by a rear u-joint not perfectly centered on the mount. It was only about 1/8" offcenter, but it was enough to cause vibrations around 60mph and faster.

It was not the right u-joint. My drive shaft is custom and the ujoint lengths are different on the x-y axis. It took a while to find the right one that fit, but since then, there's been no vibration problems.

 

Wheel bearings............................

 

check drums, rotors for runout
flywheel out off balance.
loose rear spring mounts
etc.
basically anything that rotates is suspect.

 

Also.
Have a look at the pinion angle.
It could be too high or too low.

 

Id think that if the flywheel was out of balance it would be more a factor of RPM instead of speed.

How would one go about changing the pinion angle?

 

For Dawg:

Flywheel is out--replaced with a new one and made no difference.

Rear spring mounts solid.

For Poncho62:

Several others have suggested wheel bearings, but wouldn't they make a racket at almost all speeds? In the past, when a wheel bearing has gone bad on me, you can hear the noise as a loud squeak regardless of engine or automobile speed, although sometimes the squeak goes away at higher speeds.

For Stu:

I thought of the pinion angle, but I would think that would show up when checking the drive shaft. We got the rear end up and accelerated to 50 in first gear then second-third up to 60 mph by the speedo. There was no vibration through the car, no vibration/wobbling on the drive shaft. If it was the pinion angle, wouldn't it show up regardless if the car was on the pavement or not?

 

The rear transmission bearing.....?

 

No the vehicle would have to be on the ground for the pinion angle to really be a factor.
Weight, thrust etc. will determine the angle.
Just to ease your mind you can place a few shims under the front end of the spring base on the differential.
Then put them under the back side.
See if there is any difference.
Flex plates on Chrysler products aren't balanced.
Depending on the engine, convertors either have no weights or one of three weights welded to the face of the convertor on either side of the drain plug.

 

For Stu:

Flexplates are balanced on the 360 ci Chrysler engines. The engine is externally balanced using a special flexplate. The PO had used the previous flexplate from the swapped 318 and he thought that was causing the vibration, but replacement with the correct flexplate for the 360 changed nothing.

 

I'm sorry. The flex plates on these engines are not balanced.
It is the convertor that is balanced.

 

Yes, that is technically correct. But all 360 engines have to have a special flexplate to mate the 727 torque converter. As Summit Racing put it:

"Aftermarket torque converters are neutral balanced, designed for internally balanced engines. Most externally balanced engines have the balance weight on the flexplate, so this is no big deal. But on externally balanced Chryslers 340 and 360 small block and 440 big block engines, the factory put the balance weight on the torque converter. If you have one of these engines, make sure to get the appropriate flexplate counterweighted to match the engine balance. Most SFI approved Chrysler flexplates have this counterweight."

This is what I was trying to say in a clumsy way. The converter is indeed "balanced," but you have to have the correct "counterweighted" flexplate changed if you are converting from a 318 to a 360. The original owner didn't do this, but again, it made no difference. The problem is not with the flexplate nor the converter.

 

It doesn't mention which engine is in this vehicle.

 

Last night I finally got time to replace the rear brake drums on my '66 Caprice. I had done the front ones last weekend trying to eliminate said "vibration". I had hoped for the best, but I am disappointed again. It's really baffling. I think I'll look at wheel bearings next since I packed them while I had the brakes apart.

It's hard to pinpoint because I was working on about five things at once. First, I was changing the governor springs and weights on my 700R4 to get it to shift at a higher rpm. During one of the tests, it didn't shift out of second till 95 mph and it was wound pretty tight.

After I got the shifting down to about 82 mph in second, I put the car up on jack stands on removed the old factory style dual exhaust to replace it with a set of 2.5" mandrel bent pipes from pypes. Sweet setup. While I had the pipes off I spent some time pressure washing everything I could get to under the car.

While the car was up on the stands I decided it would be a good time to pack the wheel bearings. That's when I found out I needed new back brakes, and while I had the brakes off I also replaced the rear emergency brake cables. I also had the drums powder-coated at the same time.

So I have had to check and double check everything I touched. So far, the car still has a shake that comes and goes between 60 and 70 mph.

I'm still watching this thread to find out what solves some of our problems. I'll let you all know if the wheel bearings help.

Thanks for listening.

JImR

 

For Stu:

No, I didn't list the engine because I knew the engine, flexplate, and torque converter were good and had nothing to do with the vibration. Sorry for any confusion.

For Vista Cruiser:

Sad to hear of your continuing problems. I was hoping against hope that your complete swap out of brakes would solve your problem and then probably solve mine as well.

I don't have time to work on my car until the weekends, so progress is sometimes slow. I should have the car running this weekend and I'm taking a friend for a spin so he can experience the vibration. He is an excellent mechanic and can usually spot problems others just scratch their head at. In any case, I'll report back to this same thread with any new information, and I would appreciate you and any others do the same as we work through all of "shakes."

 

This weekend I tried another set of wheels and tires, the ones that came with the car originally. The vibration stopped. Now I have to figure out why my new Cragar SS wheels and BF Goodrich Radial TAs make my car shake. Up on jack stands I noticed one of the back wheels moves in and out about 1/16 of an inch so I am taking that wheel in today to have it straightened. It doesn't look like enough to cause a problem but I know something is...

FYI

JimR