VCCA Home Forums TECHNICAL - 1945 AND NEWER 1949-1954 Ready for the nervous hospital

This all started when I replaced an oil soaked worn out transmission mount on my 51 Styleline Deluxe, 235 powerglide. Vibration in the drive line, especially at cruise, 40 mph and up. Tore down the differential, pulled the drive shaft out of the torque tube. Differential carrier bearings were pitted, replaced them. Pinion bearings were smooth, no noise or growling etc. Replaced both torque tube bushings with new ones, really not much wear. Replaced the rear yoke and u joint. U joint is a bushing style u joint. Had some play in the pin at the pinion end of the drive shaft, drilled it and installed a larger pin, tightened up nicely. Front yoke on trans is tight. Assembled ring and pinion with.007 backlash. Set up ball with three shims,not floppy loose, can move it up around with one hand, snug though. Put it all back together, and not one iota of change. Starts vibrating at about 40 mph, by 50 you can feel it in the seat of your pants, steering wheel and floorboards. Back out of the throttle slightly and you can make it go away. Give it a little throttle, its back. Floor it from the start, run it up to 70 or so, smooth untill you back out of throttle a little to maintain cruise speed. A previous owner had put some shocks on the rear with the helper springs on them. Thought perhaps they could have something to do with it, so I removed them. Vibration was almost tolerable, so I decided to install my PeeCee clamp to hopefully get rid of the rest. WRONG. Way worse. Take PeeCee clamp back off, take it back out again, vibration back to the way it was before I removed the shocks. New mount is not hitting or touching anything it shouldn't. I just can't figure out how changing the shot trans mount has caused me all this grief. Although it should not make any difference, I am ready to try a different trans mount. The car was fine with the old trans mount, no vibration at all. HELP, I'm ready to go to the nervous hospital

Have you tried shifting the trans to neutral at 50 MPH to see if the vibration changes?

What is wrong with the original trans, mount?

Steve, I have, and the vibration disappears when shifting into neutral. I can make it come and go with the throttle while in gear and moving down the road. I can put it in neutral and rev the engine in neutral while moving and no vibration. Gene, the mount was a ball of mush from the old powerglide leaking oil all over it for sixty years. If I still had it, I'd put it back in

The mount is riveted to the steel plate. I assume you chopped out the old rivets and bolted the mount to the plate.
I would suggest removing the plate and mount to see if there is a metal to metal contact aat some point
Excuse me if you have already done this.

Have you looked at the motor mounts? Maybe when you raised the transmission to replace the mount it tweeked one of the motor mounts? Just a thought.

Yes Gene that's what I did. Put bolts in the steel plate where the rivits were. I have checked for contact a couple of times, but I will have to check again, as I'm running out of things to check here.

DBT, I put new front motor mounts in it a year ago, and you can only jack up the transmission about 2 inches before it hits the access cover in the floor, so I don't think it tweaked the mounts, but I will take a closer look. It must have something to do with jacking the trans up, something must have have got moved or tweaked somehow. There are two smaller mounts attached where the trans bolts to the engine, does anyone know if these are specific to the auto trans models, or did they come with stick shift too? I'm going to wear out my floor jack before this is over!

Why not put good stands under the rear and front (four total) and operate it at the speeds giving trouble? Notice for any vibration.

Be careful. Don't worry about it jumping off the jack stands and going through the garage and making a lot of racket. After all, its just an 51.

Charlie

BTW: Could be a out of round tire, bad spot on tire, or out of balance in some way. Tires do not always vibrate the same at all speeds. Could be you have gone to a lot of trouble for nothing.

The "little" side mounts are used on all 1949-1951 cars. They do not support the weight but just keep the engine from twisting any major amount.

Charlie,I have already tried that. Problem is it will not do it under a no load situation. If I am going down a slight grade, I can back out of the throttle a little bit, and it goes away.I have never seen a tire cause this type of problem. Although it was alot of work, it was not all for naught, as the differential carrier bearing were on their way out. Thanks for the ideas, though keep em coming

You might want to check those "little" rear engine mounts. I had one that was only a couple years old and looked like new but the rubber had separated from the metal. Looked great at idle but when the engine was torqueing it lifted right off the mount. Your posting that you can go 0-70 and the vibration starts when you let up leads me to believe you have something loose in the driveline. Did you put the rear jack stands under the frame or rear axle? If under the axle you might try it with them under the frame.

I have the small side mounts and another trans mount on the way.I haven't checked the side mounts, but I'm pretty sure they are original. I had the jackstands under the axle, Steve. If I put them under the frame the axle will drop way down, putting the torque tube at quite an angle at the transmission. I suppose I could try it, though

You could take up some of the droop with a floor jack, being careful not to over do it. With the car on jacks have you tried turning a rear wheel manually to check for free play? With the car still and in neutral if no vibration when revving the engine then the only thing I can suggest is starting over at the rear of the trans. and rechecking the yoke-ujoint- and R&P backlash. Once you find the culprit it will be interesting to say the least to see what it is.

is the new trans mount the same as the old one? Could it be that the new mount is made of softer, (more flexible) rubber than the original. I would install the one the new one replaced and start there.

New trans mount was the same as the old one. Unfortunately the old one is long gone now. Just been driving the car under speeds where the vibration comes in at, and when I get to the speeds where it begins to vibrate, it seems to be getting better. I can jack the car up and try something, take it out and drive it and go wow,found it. Get in it the next day, vibration is back. Actually the new mount is alot stiffer and more solid than the old one, so that might be some of it. Just gonna drive it for right now