2 zones of vibration.

RobR'35

RobR'35

Well-known member
I've totally rebuild the complete drive line on my roadster. It has a vibration starts at 25 mph and is worse at 30 mph. as speed increases it diminishes until I get to 55 mph and at 60 it's worse and remains to 65 mph. Ive not driven it faster because the vibration is terrible. Tires balanced. Wheels checked (Kelsey hayes) with a dial indicator for out of round max was .068 on one the rest were in the .040 or less range and the faces were .048 at the worse.
Transmission, original to the car rebuilt using Macs book to exact specs. All new bearings. Wherever it needed parts and wherever I could aquire nos it got it.
Rear axle is a '46-'48 with the columbia. All new bearings,Timken, Bower or Ford script, ring and pinion nos. All spec's and pre loads checked and rechecked. All the mods to update the Columbia had been done to the axle before I bought it, I checked and spoke with a few Columbia guys. John Connelly being one.
Driveshaft hollow type, modified with 6 spine to mesh with the pinion. These things done by a reputable drive shaft shop and set straight and true. I had the torque tube checked for straight and to make sure the end that bolts to the axle center was 90° to axis. Nos bearing and race. Bearing area on the shaft wear area was only .0015 wore.
U joint was an old used Ford one. I checked it the best I could. Used a feeler guage between the trunion bearings and trunion pins. .002 max I could fit. Spline fit was great!
I do notice with all of the u joints I have and the one installed that they all wiggle laterally. Slide from trunion to trunion across from each other all 4 points by about 3/32". When all installed and coupled to tha trasmission it was packed and grease added after it was coupled. Corn head grease.
I've got about 600 miles only on it and don't know what to think.
U guys have any ideas, experiences to help me out?
 
It would help to isolate the vibration, but easier said than done! Few questions:

1. Did you have the engine balanced when it was rebuilt?

2. Was the flywheel, pressure plate balanced?

3. Was the driveshaft balanced?

4. Have the tires been dynamically balanced?

It could be a lot of things, but I would start with the easier ones. Sounds like the driveshaft would be a good place to start. Tires would be another one, have them spun up on tire balancer.
 
If you push the clutch in at one of the bad vibration speeds, does the vibration stop or lessen noticeably? If it stays the same, it is likely a wheel/tire problem. If it diminishes when the driveline is not loaded I would look at U-Joints and drive shaft. That seems like a lot of lateral play in the U-Joints. Second suspect would be less than perfect alignment where the drive shaft was cut and welded for the spline change. And what is a hollow-type drive shaft? All of the drive shafts I have wrung off were solid steel shaft.
 
I haven't touched the engine in respect to rebuilding.
I did match mark and checked the clutch and pressure plate visually when I rebuilt the transmission. All was in good condition and reinstalled. I didn't have them balanced.
When I bought the car I ran it a bunch. It never vibrated until right before I heard the sheared pin rub on the torque tube.
What caused me to go through the drive line was the spline coupler on the drive shaft to pinion had sheared the through pin. On inspection it wore both male and female splines way to far.
When I had the drive shaft work done the guy at the shop told me it ran true. It didn't have balance weights on when I took it to the shop and none were on when I picked it up from the shop. It made me wonder actually.
Tires I had balanced at a Pomps tire business locally.
I asked to go in the shop and watch. I was concerned of run out on one of the tires. Visually I didn't see anything over 1/16".
 
It does continue to vibrate when the clutch it pressed. I tried pressing the clutch while vibrating on a load up a slight incline on a smooth road and on the return down hill.
It'll still vibrate at those speed ranges.
 
I've looked and never seen any specs. for the u joints.
Anyone know what the specs. should be?
Anyone else notice this lateral play in the u joints.
Out of the 3 use ones I have. All are very close to the same.
 
Sounds like you are answering your own question! The driveshaft/ u-joints sounds like the most likely cause.
 
Lateral play is normal--- the bearing centers the shaft

Perhaps remove the floor boards and drive and have someone feel the torque tube-- or if you can find a place with old style 2 post axle lift and run it on the lift
 
Thing is with all the care and time and money spent to make it right. I really don't know the true cause and a few specs for reasurrence.
I took it to a reputable drive shaft shop. I don't want to doubt their work without some kind of proof.
As to the u joint. It's the only thing not new put back in.
 
With the clutch pressed in there is no energy going through the u-joint and drive shaft to feed a noticeable vibration, unless the joints or shaft are so grossly out of balance or alignment that being turned by the continued motion of the car causes them to shake hard enough for you to feel.

Next clue would be frequency. Wheel RPM at 30 mph is about 360, or 6 revolutions per second. That is a pretty low frequency, like a rumble. Drive shaft speed will be about four times that, like 24 cycles per second; about half of a neon light hum. Which is it at 30 mph, rumble or hum?

Test suggestion. Jack the rear end and set it on stands. Chock both front wheels. Push, pull and try to jerk the wheels up, down, left, right. Any vertical, horizontal or axial play is a bad sign.

If that is all fine, start it, put it in high and slowly set the throttle to 30 mph. Whether or not the vibrations occurs, watch the wheels from the sides for any sign of out-of-round or shaking. Look at them from the rear for any sign of lateral wobble. If no tire wobble or shake, move on to the next test.

If there is little of the vibration experienced on the road, that leaves the u-joint a the one component whose ability to cause vibration if dependent on the energy it is transmitting; that is, the load it is driving. If that is the case, you should have noticed more vibration going uphill than downhill.

Last test: If you do not have a tachometer, note the pitch of the engine at 30 mph. Put the transmission in neutral and brake the rear wheels to a stop; run the engine up to about the same speed as 30 mph, approximately 1500 RPM. if you still have the vibration, you may have an engine balance problem, anywhere from the fan through the clutch pressure plate.

Good luck!
 
On the driveshaft, have you talked to the folks that did the work? If it is a reliable shop they should be able to provide some input. A lift would remove the wheels as a source and tell you it is drivetrain.
 
I haven't spoken to the drive shaft shop yet.
Was hoping to eliminate things by suggestions on here first.
I did jack the rear tires off the ground with front wheels chalked. Securely set on heavy blocks.
I ran the car in high gear and unreal how the one wheel and tire was out. Looked out of round more than wobble.
I tested the speed ranges and the vibration was there in both places.
I exchanged a front wheel and tire and ran it again. Considerable difference (better) in both speed zones! Wobble and out of round considerably better as well.
Im unable to take it on the road and test it today because its raining. Im anxious to try it tho.
Interesting how it can act so differently under actually running it vs when I took dial indicator readings off the wheels.
Thanks everyone for ur ideas and suggestions.
I hope this will be the fix.
 
A wheel vibration will have a longer period than something spinning a lot faster such as a driveline. Harmonics will cause things to vibrate at certain speeds...lower or higher speeds may not vibrate. Having two zones of vibration is interesting to me and I can't wait to hear what you find.
 
In all of my years working with vehicle repair, nearly always, the vibration that sets up at the speeds you note is driveshaft related. 99.9% of that time, it's a bad u-joint or two. On occasion the drive shaft inclination is too severe.
With what you have described - check the shaft and joint very carefully.
 
One thing I did when the local driveshaft shop welded in a new spline was to check it in my lathe BEFORE fitting it back in the car!the shop told me it was spot on true,in the lathe it was..140 in runout., how I checked it was to hold it by the front part of the shaft with the u/joint spline and see what you have,once I did that and fixed the play in the front roller bearing it was good.
Lawrie
D me
 
If you can, try a different set of tires and wheels-all four. I have had tires that looked good, ran true, were balanced several times, and still had weird vibrations. I had checked and adjusted wheel bearings, checked steering linkage, adjusted steering gear, etc. Finally put new tires on. Problem solved!
 
40 Deluxe:
Tires would be the easier of the two to change and try.
I don't have a spare set of wheels unfortunately.
 
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