vibration when I let off the gas

Pa Joe

Pa Joe

Senior Member
I have a strong vibration when I let off the gas.Most noticeable going 35 to 45 mph. What would be the first place to look?
 
I agree with James, and also check the carrier bearing behind it. That is the roller bearing in the front of the torque tube. Of course to check that you need to remove the rear end. If both of these check out OK, then look for something loose in the rear end, such as ring and pinion.
 
How do you feel the vibration? In your hands through the steering wheel? In you butt through the seat?

Hands = engine
Butt = drivetrain, usually behind the ******.
 
I don't know what's normal vibration to expect with an A. But it sure seems excessive to me. Mostly around 35 to 45 mph. You can feel it in the steering wheel, floor boards, hard to pin down. What I did find so far, the front motor mount springs are tightened down so far that there is no space between the coils in the springs. And, the bottom spring below the cross member is missing all together. So, I should have a new spring kit from Snyders tomorrow. I'll see what that does. Process of elimanition. As far as the motor goes, it's a fresh rebuild with less than 100 miles on it. Stock crankshaft, stock fly wheel, rebuilt by a very reputable engine builder thats done A engines for years and years. Could spoked wheels not running true cause vibration? As I mentioned before, seems worse when I let off the gas. Like James mentioned, could very well be the universal. After the front motor mount, I'll check out the universal joint.
 
I'm betting it's the motor mount. Are the springs collapsed under the mtor weight or are they maybe tightened down too much? Maybe you can just loosen the big nut.

Max vibration on backdown is normal: high rpms with minimal cushioning fuel charge in the combustion chambers. Don't expect to be able to use your review mirror.

How did it run before the rebuild? U-joints don't go bad while motor is under repair. Are there ugly noises accompanying the vibration?

Steve
 
Steve, I never did anything with the front motor mount when I replaced the motor so I have no way of knowing if the weight of the motor is collapsing the springs. All I know is nothing moves the slightest bit when I take the nut off the bottom of the frame. I know better when the new springs come.
 
I think most A's vibrate when you back off the gas. Your motor might be worse because it is new and "tight." It may be due to torsional vibration caused by the motor "holding back" under compression. It may improve as the motor breaks in.
 
Using the Les Andrews book as a guide to replacing the front motor mount springs and other parts was not successful. The book claims I can replace it without pulling the motor out. I put a floor jack under the front of the motor until the throttle linkage just bearly touched the firewall then unbolted the front mount. Still not enough room to get the mount past the front pulley. One thing wrong a previous owner put that brass washer in wrong way. He put it in from the top down instead of from the bottom of the frame up. Forgot to mention, I did loosen up the back (float a motor) mounts before I jacked up the motor. I just put the motor in a few months and really dont want to pull it out again so for now I'm just going to put up with the vibration until maybe next winter.
 
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