1967 Deville Drive Train Vibration

[MikeLawson]

I own a 1967 Deville that has a noticeable vibration between 35-45 mph. The vibration is felt through the driver's seat. The car is an excellent 46,000 mile example that has never been wrecked or abused. I have tried everything I can think of to correct the issue but I've been unsuccessful. Here is some detail of the work I've done so far.

When I bought the car, it had a set of wire wheels on it and I suspected that they were not balanced correctly so I had them rebalanced and it made no difference. I then bought a set of new tires and had them mounted on the original rims which came with the car, again no change.

Next, I tried removing the rear tires and ran the car at the speed range where the vibration occurs and it was present. I suspected that the drive shaft may have been out of balance so I took it to a local truck garage that had a driveshaft balancing machine. The balance was checked and it was good but based on my symptoms the shop recommended rebuilding the driveshaft. All new u-joints and CV components were installed and the shaft rebalanced.

When the drive shaft was reinstalled and test run again, the vibration was still there. I removed the brake drums and ran it again with the same results. When I run it at the speed where the vibration occurs and shift into neutral, the vibration goes away. Engine runs smooth at all speeds. I had previously checked the transmission mount and it is in very good condition.

I would greatly appreciate your suggestions as to what to do next.

["Cadillac Kid" Greg Surfas 15364]

Mike,
Have you checked the transmission mount?
Greg Surfas

[MikeLawson]

Yes, I had checked the transmission mount during a previous repair of the O-ring seal on the transmission output shaft. Although the mount is the original, it appeared in very good condition not distorted or seriously cracked.

[TJ Hopland]

When you got it jacked up and are making this happen what happens if you lightly step on the brake to add some load?   How about reverse?   With the 400's 2.07 reverse ratio it should not be too hard to hit that speed, its kinda between 1st and 2nd.    For that matter will it do it in different gears?    That should help determine where its coming from because engine and parts of trans will be at different speeds vs wheel speed.

[MikeLawson]

I tried to follow your suggestion and the results are kind of inconclusive. In reverse, there is no speedometer reading but the vibration still happens about the same based on the engine sound. I was unable to really accurately maintain speed with the brake lightly applied. It seems vibration is most noticeable at about 35mph. I can feel it through both the seat and the steering wheel.

[Dave Shepherd]

Trans mount may look good, but over time they get hardened  and no longer can isolate harmonics and vibration. You could try loosening  it and see if any change. Any excess movement in the driveshaft  center  suport?

[MikeLawson]

The car has a single piece drive shaft, no center bearing is used. If I can'r come up with anything else, I may try a new transmission mount. I'm still stinging from spending $475 to rebuild and balance the driveshaft and getting no improvement.

[TJ Hopland]

How about in different gears?   That should change engine speed and parts of the transmission given the same wheel speed.

[Daryl Chesterman]

When the car was jacked up (I hope on jack stands!), did you have a helper to operate the accelerator pedal and you observe underneath to see what could be causing the vibration as the RPM was increased up to and through the  noted 35 MPH vibration speed?  Definitely do as T J Hopland said, and see if the vibration is replicated in 1st or 2nd gear.

Daryl Chesterman

[dadscad]

I know you have a low mileage car and this should not be the problem, but, have you checked the tail shaft housing yoke bushing for excessive play?

[bctexas]

Have a look at the harmonic balancer on the front of the crankshaft.  I had one go bad on a Caprice I used to own.  Took me a while to find it - i couldn't believe that it could shake the whole car the way it did.

Good luck!
Bernie

[Cape Cod Fleetwood]

Stupid chick comments:

Front end - when were the stabilizers, ball joints, upper and lower bushings (if applicable) replaced? Wheel bearings?
Any play in the linkages? Assuming your new tires are correct and quality for the car, I like having speed
shops do the balancing, YMMV. $475 was about right for a quality drive shaft rebuild.

You'll need a HELOC on your house to try all the well meaning ideas here.
OR, find a reputable vintage car restoration shop, have their lead mechanic drive the car and tell you what's wrong.

Occam's Razor is my BFF.

[MikeLawson]

I know you have a low mileage car and this should not be the problem, but, have you checked the tail shaft housing yoke bushing for excessive play?

Thanks for this suggestion. I just did a quick check for the bushing play by pushing and pulling on the driveshaft yoke. There was a very slight amount of perceptible play. Should there be any at all?  I had the tailshaft housing removed last year to replace the O-ring seal on the transmission output shaft. I did not measure the bushing ID because I didn't suspect this problem at the time but visually it looked good. My understanding is that when the bushing becomes excessively worn, it can cause leakage at the yoke seal. The original yoke seal was not leaking and the replacement I installed at the time has been fine. This is a very frustrating issue to resolve for sure!

[Big Fins]

I might suggest what we do with Class 8 tractors. That driveshaft should be able to be clocked in a 12, 3, 6, & 9 o'clock position. IIRC, it has a machined mating surface to the rear pinion. Try it in a 180^o position to its present one and see if that works. It costs nothing but a little time.

[TJ Hopland]

I'm waiting to hear the results of the different gear test.   That should tell us if its trans-engine side of things or trans-rear side.   Different gears will mean different engine speed vs ground so if it stays with the ground speed its drive line or if stays with engine then you know its in the engine or trans.

[Big Fins]

He's also going to need the weight of the car on the rear once it's up in the air. Not jacked up by the frame with the diff hanging there.

[MikeLawson]

He's also going to need the weight of the car on the rear once it's up in the air. Not jacked up by the frame with the diff hanging there.

All the tests I've done so far have been with the rear axle housing supported on stands at approximately the same height it would be with the wheels installed.

[scotth3886]

I know you have a low mileage car and this should not be the problem, but, have you checked the tail shaft housing yoke bushing for excessive play?

My vibration issues on my 66 is mostly gone, but not completely.  However, I was never able to find a tailshaft bushing.  I suspect that's still an issue. 

We did the front u-joints and centering kit and the tailshaft seal.  Couldn't even find a another centering kit to do the rear joints.

Any idea of where to find a tailshaft bushing.  O.D. of the yoke is 1.58" IIRC

[dadscad]

Try FATSCO transmission for the bushing an Rockford Driveline for the ball centering kits. HTH

https://www.fatsco.net
http://www.rockforddriveline.com/catalog

[scotth3886]

Try FATSCO transmission for the bushing an Rockford Driveline for the ball centering kits. HTH

https://www.fatsco.net
http://www.rockforddriveline.com/catalog

Thanks !!!