Drive line vibration

[Jim K.]

I have a 61' with a munci 4 spd that has a vibration above 60mph. I had the driveshaft balanced and it got better, but it's still there. The vibration remains when I slip it into neutral and idle the engine down, so I'm thinking it's in the drive line rather than the "front" of the trannt or engine. Any thoughts???
Thanks!!!
Jim

[Ed Jennings]

Re: Drive line vibration

I had this problem on a 61, and it turned out to be a bent driveshaft. I would presume that can be ruled out since yours has been balanced. Other than that, there are u-joints, which I presume have also been inspected, transmission mounts, and lastly the bushing in the output of the transmission possibly being loose.

The way I found my driveline vibration was by taking it to a transmission shop where they had the facilities to raise the car on a lift, support the rear axle safely, and "drive" it while observing from underneath. If you haven't done something like this, it might be worthwhile.

[Jim K.]

Re: Drive line vibration

Thanks Ed!
This bushing that you mentioned, are you talking the piolet bushing in the crank or something else? The light is starting to come on. When I had a friend pick up the shaft from the balancer, she said that the shop said the bushing needed replacing, I assumed she misunderstood and replaced the seal... How hard is it to replace the bushing? and if it's better to rebuild while its apart, maybe I should invest in a correct BW T-10.

[Christopher R.]

Re: Drive line vibration

Most likely you've got the wrong driveshaft/transmission yoke in there. Your transmission is wrong for the car. When the transmission was installed, the old yoke wouldn't fit because of the different number of splines between the coarse T10 and the fine Muncie. The solution was to swap yokes on the driveshaft for the common Muncie one. But the common Muncie passenger car yoke was short. Corvettes take special long ones. There is a long Muncie yoke made, but it around $175. The usual Corvette parts vendors have them in their catalogs.

See John Hinckley's post for the correct lengths. Take out your driveshaft, and measure the yoke. I'll bet you find it is too short.

The vibration you describe typically comes in at 60 and gets bad at 75. It'll continue even though you put it in neutral at speed because the driveshaft is still turning along with the wheel speed.