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Discussion Starter #1
Happy Veterans Day and thanks to all who have served! This 68 was restored at an Army base MWR shop I’m blessed to have access to and many vets helped me along the way ??

I decided to use the Day off here to do research and finally tackle this unpleasant vibration.

First can anyone tell me if this kind of tail shaft end play is excessive on a C4 or is it normal to have some at the end of the output shaft?

Did this on the ground, set in park.


Found researching old threads the top things people have fought are:
1) U-joints - Mine came new and unused from previous owner and appear to be solid.
2) Flywheel and Torque conv - been there done that. They rev up smoothly w/o shaft spinning and are new. Put those in myself.
3) C4 was put in as a fresh rebuild. Previous owner had it rebuilt. New seal in tail shaft no leaking. Unknown if bushing was done
4) Prothane polyurethane trans mount - I have this, it came with the tranny. Planning to swap in a rubber one since that fixed issues for many.
5) Balancing the shaft. Planning to do this soon. PO says it was balanced but weights look as old as the shaft itself.

Another thing I was wondering about this OE shaft....it’s only visibly metal on the outside. Any way to tell if this was one of those shafts with rubber dampers. I’ll be pulling it for balancing next week.

Jonathan
 

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You sure have a lot of slip yoke exposed there. You only need 3/4"-1" of freeplay until the slip yoke bottoms out in the tailshaft. Your excessive freeplay may not be allowing much engagement between the splines in the slip yoke and the splines on the tailshaft.
 

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Discussion Starter #3 (Edited)
So are you saying that the yoke appears to be too short? If it slid inside the tail shaft more would this cause it to snug up more?
I guess I can test that when the other end gets unbolted.

There is no engagement issue. The car goes like it should under light or heavy load. Vibration is felt strongest at 50 & 70 mph. Throw into neutral and it reduces to normal tire chatter levels. I can feel no endbplay at the pumpkin side. Fluid is good in there too.

The only thing that’s changed is that there is a 74’ 302 in there now instead of the original 289. Unless they gave me a different drive shaft and/or yoke than what was in there previously.
 

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Discussion Starter #4
So something just crossed my mind...Is the amount of travel that the slip yoke slides into the shaft adjustable??

I recall when attaching it that it had to come out to a certain point to have u-joints engage the pinion at the pumpkin side and get bolted in. Does that side have some way of taking up slack?
 
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