C1 U-joint angles and trans shimming

[Karl #35089]

I understand the importance of U-joint geometry and I gather that C1s have a tendency for vibration if not properly set up. I've heard something about shimming the transmission tail mount on C1s. Is this a matter of some people not using the right mounting hardware or does each individual car need to be measured and shimmed accordingly? Is there a proper way of getting this right? Even if it's a little extra work for me, now is the time...

Thank you,
Karl

[John H.]

Re: C1 U-joint angles and trans shimming

Karl -

Although not called out in the A.I.M., C1 trans mount crossmembers were apparently shimmed to the flange on the frame where they bolt up, on a "pattern" basis (as opposed to measuring), and this came and went; after 40 years and many transmission changes, very few cars show any remaining shims or evidence of shims. Several of the C1's I've done have required up to 3/16"-1/4" of shims to ensure clearance of the ends of the yoke U-joint to the sheet metal shield in the tunnel above the yoke, and there were several Service Letters to the dealers outlining procedures to shim the trans mount crossmember down (and to install axle mount-to-spring tapered shims) to correct driveline vibrations.

[Ed Jennings]

Re: C1 U-joint angles and trans shimming

Prior to shimming, it might to be prudent to check other causes of vibration. I beat my brains out on a 61 a few years back looking for a driveline vibration, only to ultimately discover that the driveshaft was slightly bent. he bend was so slight it was not obvious until I observed the shaft turning with the rear wheeks raised.
Another potential source is the trans tailshaft bushing. Also be sure the driveshaft has the correct lenght yoke. Many replacement yokes are too short.

[Karl #35089]

Thanks guys! Now for measuring...

Thank you for the replies.

I am not trying to correct a vibration so much as prevent one. I am assembling a fresh rolling chassis and now's the time to get it right.

Lacking a better approach, I plan to use a digital protractor and pick up on the sides of the U-Joint yokes, front & rear. Is there a better way to go about this?

Thanks,
Karl