Driveshaft/yoke query

[UKPlymouth]

Guys, I'm trying to track down some vibration and have a question. I pulled my driveshaft to inspect the yoke on it and considered replacing it.
Here's the thing. My slip yoke is unusually long (I think) as the measurement from centre of UJ to end of yoke is 9". Most listed yokes are somewhere between 6.5-8"

I wonder if my driveshaft was too short for the car (73 RR) and someone fitted a longer yoke to compensate.
This might be the reason for rhythmic vibration at 70mph plus as the yoke is too long. This would cause undue wear on the front UJ which did wear out quite quickly.
Any insights appreciated.

 

[RT K_line]

How far does the slip yolk go into the tailhousing? What is the engine combo too? I had a similar issue with a cast crank 440 before also. the weights on the converter were thin and should have been thicker. I got it close but ended up using a motor I built for a GTX that I had but ended up selling. Still kicking myself for that one LOL.

 

[brian6pac]

As long as it doesn't bottom out it the trans, it shouldn't be a big deal if it sticks out of the trans a little as long as the bushing is tight, just make sure it goes in far enough.
This works great for finding drive shaft balance problems,
first mark the shaft 1/4 turn by the front uj in 4 places mark them 1,2,3,4, around the shaft then put a hose clamp on it and tighten it so the screw is at the #1 line. then take it for a ride, then turn it to #2, then #3, and see where the vibration is worst. Put the clamp on the opposite side if one is not enough ad another one, if that is to much spread them apart. I had 2 clamps on the drive shaft of my polara for 25.000 miles with no problem , then sold it. Probably still on there.

 

[UKPlymouth]

Thanks guys. The shaft and yoke seem to fit correctly and the shaft was new when I bought the car. I did fit a clamp on the prop and left it slightly loose to find its own balance (something I read) but I can try the 4 place theory as that's easy to do.

The actual yoke has a wear step about 2" in from the end. What might cause that?

 

[UKPlymouth]

Motor is 340/727. Motor is balanced, converter is correct and all has been rebuilt as have the UJs on the shaft and the trans mount is new. Vibe starts at 3,000 rpm or close. I changed to smaller wheels and tyres and it still vibrated but at 55 instead of 70 mph so definitely rpm specific it seems.

 

[brian6pac]

RPM of what? If you rev the motor to 3000 RPM free rev is it smooth? If it is output vibration it will be speed related not RPM related!

 

[UKPlymouth]

Motor revs fine in idle. Likewise if I'm setting timing at 3,000 rpm.
I m just saying that the vibration with my normal 15 x 60x 255 tyres with 3.23 gears sees the car showing a rhythmic vibration at approx 70mph @ 3,000 rpm.
Seems to be worse on the over run, when letting off gas.
There is a long downhill highway where I let off the gas at 70-75 and the vibration is bad at that point.

 

[Fran Blacker]

Think your right the drive shaft is to short. The dark area near u-joint isn't inside the rubber dust cover on the seal? Dust cover is about 1-1/2" long and attached to the seal. Can you push your drive shaft in so you collapse the dust seal, this is to see if the splines on trans will accept a longer drive shaft using that yoke, it is long one. I put a 68 GTX Dana 60 drive shaft in my 66 Satellite with a Dana 60 and the d shaft was out almost as far as the dark area on your d shaft and had a vibration at guess what speed 70 mph at 3100rpm.

 

[UKPlymouth]

Thanks, that's interesting. I need to offer the driveshaft back up and check. That said, when I have removed it I can only push the yoke into the tailshaft the requisite couple of inches so as to clear the pinion yoke to remove the shaft. There is no great forward/rearward play in place.

 

[Fran Blacker]

I'm posting pictures or two drive shafts. The one with big donut neat yoke is a 66 and the other is the 68 Gtx one.The picture of 66 d shaft is lousy. First picture is the 68 as you can see the slip part of yoke is 4.5".

 

[PurpleBeeper]

To me, that driveshaft looks like about the correct length looking at the wear pattern on the yoke. It "sounds" like your tailshaft bushing/seal has gone bad maybe. To be sure, you should have some "up & down" slop if you grab the yoke/driveshaft & try to move it.

 

[Fran Blacker]

It's worn Late this fall going to pull tail shaft and replace bushing. Will also switch out the manual valve body while I'm at it. Why don't I do it now? Last year sold the non-original Dana 60 and opened a can of worms, not this year. It will survive another 500 miles, I want to drive it this summer. Those two drive shafts aren't for my car. One with the inertia ring on front is I think a 66 8.75 Charger shaft the other is a 68 GTX with a Dana shaft. Extra parts.