Burnt slip yoke.

[Danny Gutierrez]

Developed a strong vibration over 40 mph. Determined it was the driveshaft. Pulled it and the slip yoke is burnt blue on only one side. I Balanced drive shaft and new yoke but I assume it's the output shaft. Maybe its bent? Also is there a bushing in there? Its a 727.

[XH29N0G]

I see your other post.  I wonder if you can measure runout on both ends of your driveshaft to see if it is rotating off center.  I am one on here who gets more advice than I am able to give, so others may have a better suggestion.  I have only tried to measure runout once, I used a micrometer (the one I used to degree my cam) and mounted it to the underside of the car and then rotated the driveshaft by rolling the car.  I have seen demonstrations of measuring runout on the web with the car on a lift.

Others may have a better way of determining whether everything is rotating true.

[RallyeMike]

Yes there is a bushing in there, but the bushing does not ride on the yoke, therefore the bushing itself should not be the cause of imbalance or vibration.

A tailshaft can be bent, but normally they don't just bend by themselves. It normally takes some kind of impact event. Unless something happened that you can recall, I'd look at everything else before the tailshaft: tires, u-joints,  trans mount, etc.

[John_Kunkel]

Is the tailhousing bushing installed with the oil hole pointing straight up? I've seen lots of them installed with the oil hole pointing off to the side starving the bushing of lube.

[XH29N0G]

Questions related to the vibration:  Does it change going up/down hill or acceleration/deceleration?  Coasting or in neutral?  Have you confirmed that the frequency matches that of the engine in the final 1:1 drive ratio?  Does it steadily increase with speed, or does it go away and come back.

[68CoronetRT]

Is the tailhousing bushing installed with the oil hole pointing straight up? I've seen lots of them installed with the oil hole pointing off to the side starving the bushing of lube.

The hole is supposed to go up for sure? When I took mine out and replaced it, it was lined up with what looks like an oil passage but it's on the side not the top.

[John_Kunkel]

Yep, I see a lot of them like that. In the photo, check the rib that runs the full length of the top of the inside of the tailhousing, this rib carries fluid by capillary action to the hole on the top of the bushing.

As the fluid runs out the rear of the bushing it is trapped between the seal and the rear of the bushing, when the trapped fluid level rises sufficiently it drains back through the slot to the left in the photo.

[bakerhillpins]

Yep, I see a lot of them like that. In the photo, check the rib that runs the full length of the top of the inside of the tailhousing, this rib carries fluid by capillary action to the hole on the top of the bushing.

As the fluid runs out the rear of the bushing it is trapped between the seal and the rear of the bushing, when the trapped fluid level rises sufficiently it drains back through the slot to the left in the photo.

Ok, totally off topic but man you gotta love that engineering a simple solution crap that you described right there. That's just a brilliantly simple "oil pump".  Unfortunately it's not exactly obvious either which means it gets missed or improperly setup a lot as a result.

Thanks for that explanation!!    Learned more than just how it works in that situation.. now I have a different outlook on the interior design of some of these parts that I didn't even think about before.