1965 Valiant /6 Automatic. I have a vibration that starts at 50 MPH, kind of a whommpa - whoompa for 2 seconds-pause-2 seconds. I can feel it mostly on the drives shaft hump. I think the noise is called "chassis druming". It gets faster whomp-pause-whomp at 65 MPH.

I've put on new motor mounts, checked the front end, had the tires balanced. Had it on a lift and the little weights on the driveshaft are still there so I assume it is balanced too. My guy at the shop put it on a lift and could not find anything wrong said "U joints look & rear end look good". I am not sure he knows about, or checked the ball and trunion.... I am pretty handy but that's new territory for me too.

When I take the car out of gear and coast at 50 MPH the vibration is still there, no change If I downshift to 2nd at 50 MPH, I feel the vibration and it is more steady buzzz buzz. I am pretty sure I have heard it ever since I have owned the car, 20 years now but either it's getting progressively worse or I am getting older and more cautious; afraid something might self destruct on the highway !

I know it's hard to diagnose a sound via the net, but I am taking a shot that someone might have had similar symptoms and point me in the right direction...thanks !

Cyclical vibration like this is usually due to bad U-joint angles. Since you've made sure the front U-joint is at the proper angle by doing the motor mounts it's most likely the pinion angle. You're still advised to have the driveshaft balanced.

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Joshua

You didn't mention the transmission mount. Have you investigated there?

CJ

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Part of Tyrde-Browne Racing

Remove the 4 nuts at the front driveshaft flange, and remove the driveshaft from the trans. Install a couple of flat washers on each of the studs, then reinstall the driveshaft. This will have the front joint running in a different position in the housing (not where there has been wear taking place). Now road test.
If the fibration is improved, either rebuild the front joint (the housing should be replaced), or convert to a "normal" u-joint with slip yoke.
http://www.earlycuda.org/tech/ujoint.htm
Be aware that NOS repair/rebuild kits will have old rubber, which will not last long. It would be best to get a "reprodution" rubber boot.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

The trans was rebuilt in the last few years so the mounts are O.K. I will check the trunnion, and especially the U-Joint angles. I've had the thing in to
three local shops and no one has even mentioned checking the angles . The third shop asked me where the ECU is (just kidding). Thanks you guys....

I didn't catch the tranny type from posts. It takes the same number of driveshaft rpm to produce 50 mph regardless of what gear the transmission is in. Since the noise changes when you go to 2nd, that suggests to me is that the problem is somewhere between the engine and the input shaft. The other possibility are the engine and transmission mounts. While you're under the car, check to see that the exhaust is not flopping around too much. That's my 2¢ worth.

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You can't fix stupid. - Ron White

Should be a 904, he mentioned it was an automatic.

I agree with this. Seems like it may be a torque converter related issue.

Can you get the car to vibrate sitting still with the engine revved to freeway rpm? Say 2500 rpm?

~RDE~

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1984 D100 Shorty Custom
Certified Auto Appraiser - RevItUp Classic Appraisals
President - Cherry City Bombers CC
Part of Tyrde-Browne Racing

Yes an automatic trans. No, absolutely no vibration with the car stopped and reving in P or N.

I was wondering about the change in the vibration when I shift from D to second . I get the same buzzzz-pause-buzzz vibration in D or Neutral at 50 MPH, but it becomes a different, more steady buzz in second; Maybe the buzzz-pause -buzzz is still going on in second, but is masked by a steady buzz because the engine is reving so high.... the old gal is just saying ease off me and shift into the right D gear !

I guess the torque converter & flywheel stop spinning when the car is in Neutral coasting at freeway speeds; so this would rule those items out ?

The converter and flex plate spin at engine speed so if you shift to "N", those items would slow to the current engine RPM.
DD

Have you swapped the tires around? Tried the spare in rotation? Have you inspected the tires? I had one (new) that the tread in a small area was "bent" over and it darn near took the steering wheel out of my hands! Some times the tires are at fault.

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50 chrysler,54 Plymouth, 64 Valiant conv 4 speed, 66 Valiant V8 wagon, 70 Challenger R/T 440+6 conv 4 speed,80 Colt, 98 Neon ACR,84 Honda V45 Magna
Taking care of 57 300C conv,48 T&C conv. Missing my 67 GTX and 36 Ply coupe

This is what I did after checking wheels and tires,etc.with a similiar problem. I put the rear of the car up off the ground, ( I use stacked 6x6's), chocked the front wheels and had someone sit in it. Have them start the car,put it in drive and slowly increase speed until the symptoms begin. From the back of the car I watched the 2 rear wheels spin and low and behold, the right rear axle shaft was bent, which caused only that wheel to vibrate at higher speeds.

Well I am glad you found it (I was close!). If I think I have a bad axle or rim I will have some one drive next to me and look while I drive down the road.

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50 chrysler,54 Plymouth, 64 Valiant conv 4 speed, 66 Valiant V8 wagon, 70 Challenger R/T 440+6 conv 4 speed,80 Colt, 98 Neon ACR,84 Honda V45 Magna
Taking care of 57 300C conv,48 T&C conv. Missing my 67 GTX and 36 Ply coupe

The rear axle shaft was bent ? No visible damage on the outside of the tube ?
How do you bend an axle shaft !? Seems like even if you were off roading it and hit something HARD, the rim would deform, tire would blow etc. before the axle bent !

This was a used rental vehicle that I bought from an unscrupulous dealer. Who knows what they did or where this thing was. My fault. I learned my lesson. I'm through with dealers.

The most common way to bend the axle is to slide the vehicle into a curb or divider in the roadway... the tire / rim does get damaged... and are easily replaced but they don't go as far as checking for damage with the axle & housing.
DD