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Hi, my 1965 Cutlass has developed a vibration problem. It is a slowly pulsating vibration starting around 50 mph and getting worse as speed increases. I have felt this vibration on and off for some time (a year maybe) but now it's become worse and is a real problem.
I suspected a driveshaft issue so I started by replacing both u-joints (rear was original!). I also tried a different slip yoke as well as turning the shaft 180 degrees. No real difference.
I've fixed unbalanced driveshafts before so I was pretty sure this was the problem. Therefore I bought a new shaft (balanced including slip yoke) and thought all would be well. WRONG. Again, no real difference (if anything it's actually a little worse). New driveshaft is 3.5" and 1350 series, conversion u-joint (1350/3R) in rear to BOP 8.2" 10-bolt.
Vibration is not RPM-dependent, only speed-sensitive. It vibrates both on drive and coast and gets worse if I put the transmission in neutral while at speed.
I've never had a tire go bad like this before. The tires on the car right now are one year old and worked perfectly when mounted. However, car sat all winter so maybe they got "square". We'll see!
I now have a spare tire in my 66 trunk that decided to shift or break a belt causing an out of round condition. That may be your problem but in my case I still have a light hum so I believe its a couple of the rims.
Wayne
I have felt this vibration on and off for some time (a year maybe) but now it's become worse and is a real problem.
The fact that the vibration comes and goes leads me to believe it is related to tires. Driveshaft imbalance isn't going to change and then get better. Flat-spotting and tire-temp would be the first things I look at. Also, check the balance weights to make sure one or more didn't get flung off at some point.
Well, it's not the tires. I put on my old set of wheels and the results are exactly the same
The vibration has a rather high frequency (higher than normal tire shake) and it definitely feels like it's coming from the rear of the car. No steering wheel shake at all but the whole body is vibrating and humming loudly. I can't see out the rearview mirror because it's shaking so much...
You might try putting the rear end up on jack stands (on the axle tubes as far outboard as possible), or better yet, on a lift. Have a helper put the car in gear and slowly accelerate. This should help you narrow down where the noise/vibration is coming from. There are only a limited amount of possibilities to explore. Do not get under the car during this test if it is on jack stands!!
You might try putting the rear end up on jack stands (on the axle tubes as far outboard as possible), or better yet, on a lift. Have a helper put the car in gear and slowly accelerate. This should help you narrow down where the noise/vibration is coming from. There are only a limited amount of possibilities to explore. Do not get under the car during this test if it is on jack stands!!
Yeah, good idea. I'll get it up on jack stands this weekend and start checking pinion yoke, wheel bearings etc first. I'll do the "air drive" test after that
There is a mathematical way to narrow it down. There are devices that can pin down the rpm/frequency of the vibration. The most available one is called a wire tachometer. Lawn mower repair shops use them to set idle speed on small engines. You adjust the length of thr wire until it osolates in a circle and note the rpm on the scale. Then you can mathematically figure out if the vibration is at wheel speed, driveline speed or engine speed. I took a training class at the Ford training center years ago (like 15 or 20) and it was the most interesting class they ever offered. I can't remember the formulas but I'm sure you can find them online. It is basically measuring the diameter of the different rotating parts and figuring out the rpm of said parts. At a given rpm or speed. Then compare it to the wire tach reading when the vibration occurs. Not sure if any of this makes any sense but it works. If used properly it will keep you from replacing parts unnecessarily.
Hi, my 1965 Cutlass has developed a vibration problem. It is a slowly pulsating vibration starting around 50 mph and getting worse as speed increases. I have felt this vibration on and off for some time (a year maybe) but now it's become worse and is a real problem.
I suspected a driveshaft issue so I started by replacing both u-joints (rear was original!). I also tried a different slip yoke as well as turning the shaft 180 degrees. No real difference.
I've fixed unbalanced driveshafts before so I was pretty sure this was the problem. Therefore I bought a new shaft (balanced including slip yoke) and thought all would be well. WRONG. Again, no real difference (if anything it's actually a little worse). New driveshaft is 3.5" and 1350 series, conversion u-joint (1350/3R) in rear to BOP 8.2" 10-bolt.
Vibration is not RPM-dependent, only speed-sensitive. It vibrates both on drive and coast and gets worse if I put the transmission in neutral while at speed.
Any ideas? Help me out please!
check your convertor to flywheel bolts?
Bent flywheel cracked?
Trans mount? but you said it gets worse when in neutral which really this should get less if in neutral.
Do you even remember when it started? ever remember an incident? curb slide big chuck hole?? anything you can trace back?
The high frequency vibration is solved. Upon installation of the new driveshaft the rear u-joint wouldn't fit in the yoke - the snap rings were too thick (3/32"). So I reused my old thinner ones (1/16") and installed it. I thought it was nice and tight but I didn't check it thoroughly enough.
Today I rechecked everything and found out there was side-to-side play between the u-joint and the yoke. So I took the thicker snap rings and ground off 0,4 mm from each ring to make them fit (with a surface grinder). Ended up with a perfect very light press fit and no more high frequency vibration!
BUT – I still have a lower frequency vibration (perhaps 10 Hz) starting at 50-55 mph. I suspect the tires here as I have abused them pretty bad (burnouts…) and they look rather sad. I will put the old wheels back on again and see how they work this time.
Has anyone here had your tires get out of wack after burnouts?
Last edited by RocketV8; June 2nd, 2017 at 01:18 PM.
Do you even remember when it started? ever remember an incident? curb slide big chuck hole?? anything you can trace back?
Not really. My theory is the old driveshaft was slowly going bad (50 years of rust, rubber bonding deteriorating, worn u-joints) and then everything went fubar with my bad installation of the new driveshaft.
Can you buy a new u joint with the correct clips and ditch the one with the ground down clips? If one side is any thicker than the other in any spot around the ground down clip it will place the shaft out of balance and vibrate.
Can you buy a new u joint with the correct clips and ditch the one with the ground down clips? If one side is any thicker than the other in any spot around the ground down clip it will place the shaft out of balance and vibrate.
No need to. I didn't grind it by hand, a precision surface grinder (such as below) was used. I would actually bet tolerances are now stricter than original.
It could be just the picture but if you look at the left where the rubber seal of the bearing cap rests on the body of the joint, it looks like it rides a little farther out than the one on the right. About the same amount that the difference is between u joints .
It could be just the picture but if you look at the left where the rubber seal of the bearing cap rests on the body of the joint, it looks like it rides a little farther out than the one on the right. About the same amount that the difference is between u joints .
I see what you mean but it's probably just the picture, rubber or casting being a bit funky. You can see I clamped both u-joints to seat them properly while measuring. And the u-joint in that picture is the "stock" one that fit properly (MOOG 234).
Ok, I tried the old wheels again with no success. Still vibrates.
So I put the car on jack stands and started checking brakes, axles, diff etc. Wheel bearings felt good so I figured I'd check axle flange runout (axial):
Well, passenger side is 0.004" while driver side is 0.020"
I don't know how much is acceptable but that can't be ok, right?
Last edited by RocketV8; June 3rd, 2017 at 04:19 PM.
Did you check the driveshaft for run out with that gauge?
Yeah I did and the results were as following :
New drive shaft:
Front 0.027"
Middle: 0.046"
Rear: 0.046"
Stock drive shaft:
Front 0.014"
Middle: 0.020"
Rear: 0.004"
Now I know you can balance out runout but this sucks. To add insult to injury the front u-joint also has 0.009" side-to-side play in the tube yoke.
I was looking for an upgrade but my 50 years old drive shaft is actually tighter and truer. I have contacted the manufacurer.
I don’t think the vibration is primarily caused by the drive shaft (since it’s present with both the new and the old one). But the new one isn’t helping...
In the light of things there probably isn't much of a problem at all with the old drive shaft
Great info here. I have a pulsating high speed vibration as well, 75+ MPH which is 3,600+ driveshaft RPM.
My car is lowered to the point the driveshaft runs 'uphill' from the trans to the rear end, and my pinion angle was never updated after I lowered the car. I got rid of about half the vibration by adjusting the pinion angle, I am going to try rotating the DS 180 degrees next.
Great info here. I have a pulsating high speed vibration as well, 75+ MPH which is 3,600+ driveshaft RPM.
My car is lowered to the point the driveshaft runs 'uphill' from the trans to the rear end, and my pinion angle was never updated after I lowered the car. I got rid of about half the vibration by adjusting the pinion angle, I am going to try rotating the DS 180 degrees next.
My car is lowered as well - one inch. These are my driveline angles with the drive shaft as zero reference:
Both pinion and transmission are angled downward in a "broken back configuration". I run all rubber bushings in the rear so pinion should rotate up 3-4 degrees during launch leaving me with transmission and pinion running almost parallell.
Since I bracket race occasionally this feels like a good setup. Car has been smooth as silk for the last years as well (up to 100 mph).
Ok, so I have ordered new axle shafts (Yukon) to possibly eliminate that problem source. The old ones were pretty beat anyway and wouldn't hold the bearings without Loctite...
Next I crawled around and checked the rear suspension. Bolts, bushings, control arms etc. All looked good.
While I was at it I checked the front as well and found this:
Driver side lower ball joint
Passenger side lower ball joint
The driver side ball joint is loose and tilted in the lower control arm. Now if this was to cause a vibration I would feel it in the steering wheel, right? Anyway, I'm buying new lower control arms. This is not an area where I want possible metal fatigue and looseness.
May 31st, 2017, 01:40 PM
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