C1 Drivetrain Vibration

[Christopher R.]

Installed a rebuilt T10, new U-joints, and balanced the driveshaft over the Winter. Took it out for a ride yesterday to test, and discovered a pretty severe vibration over 40 mph. The kind of vibration you get in the seat of your pants when U-joints are bad. But they appear good, and were new. 'Course I could have screwed them up on installation or got a bad one.

On installation, one thing that bothered me was that it was very difficult to get the yoke into the transmission. Had to whack the other end with a hammer a few times to get it to go in far enough to hook up the driveshaft at the rear end. When the transmission was rebuilt, the output shaft was replaced with a new one. (The old one was twisted.) I assumed that the yoke and output shaft would work it out over time.

Another thing that bothered me is that the new (T10) transmission has increased the driveshaft/yoke angles. In a C1, they're bad enough to begin with. The new one is much higher up in the tunnel than the old (Muncie) one was. I had the Muncie dropped down approximately 1 1/2" from the frame. By having the new transmission so much higher in the tunnel, the driveshaft angles have increased. I do have the shims installed. The rear end in this car is not original. It had been replaced before I got the car. Wondering if the rear end angle was set up for a Muncie. It's been a long time since a T10 was in this car.

How do I test for these things, and what else should I look for?

[Terry D.]

Re: C1 Drivetrain Vibration

Try jacking up the rear of the car, get someone to drive it to 40mph and crawl under and see if you can see any wobble anywhere. Just make sure car is supported properly. Do you have the right transmission mount? When the car is sitting does the drive shaft appear to be on an excessive angle? Do you have the right rear end under the car? Without a little more info hard to say what's wrong.

Terry

[Wayne P.]

Re: C1 Drivetrain Vibration

Most likely you need a new yoke to go with the new output shaft. If you had to drive them together I doubt they are sliding in and and out as the rear suspension move up and down.

[Christopher R.]

Re: C1 Drivetrain Vibration

Thanks for your replies, Terry and Wayne. I really can't diagnose this by getting the wheels off the ground and running it. I work alone, and have had too many Homer Simpson type experiences to dare to attempt this.

I suspect the yoke/output shaft interface because I had to force it in the last 1/4-1/2 inch when the driveshaft was installed.

Is it possible that the old yoke twisted to match the twist of the old output shaft? I thought that the yokes were stronger than the output shafts. That if twisting occurred, the output shaft would be the one sacrificed.

I also thought that 1/4-1/2 an inch isn't much - that they'd work through it. Figured it was just a little rust or crud in the splines. The rear end was not hanging down when the driveshaft was installed. The rear end had the weight of the car on it.

I know twisted output shafts are common on T10s. Trying to get other peoples experiences with them. Also trying to eliminate some variables. There's a rebalanced flywheel, new (balanced) clutch, new roller pilot bearing, rebuilt transmission, 2 new U-joints, and a rebalanced driveshaft in there.