The Stovebolt Site Forums The Shop Area Engine Shop Drive line Vibes!!

Here's the story. Last October the truck,'51 GMC, was running just great then my crankshaft broke. HAd the engine out had all the work done and re-installed everything. Know I am getting a vibration at about 40mph. Tires are good king pins are new etc..

Here is my thought and give me your thoughts.
I kind of remember when I put the drive line back together that the ball
housing on the rear U-joint went together pretty tight. I mean I really
had to torque the bolts down on the "ring" that holds the ball into the
"socket". I did this because I used Permatex to make the seal. But I am
wondering if I way overdid it. Is this part suppose to have some flex to
it?
Also I did a Search and one comment that came up was "u-joints being "out of phase". Since I have a longbed does this mean both u-joint have to be lined up?

Thomas did you install a new clutch, when you had the motor out, if you did did you line up the marks on the fly wheel and the clutch? I learned the hard way.

In my manual for a '79 GMC w/two piece drive line, they say to mark the spline so that it is installed in the proper "phase". Not sure what that means, but they said it would vibrate if it was out of phase. Good luck.

U joints out of phase shouldnt be a problem on torque tube since it only has one

My truck had a vibe that drove me AND my mechanic nuts. He started dismissing my bitching about it. THEN I took my truck down to his shop, jacked up the rear, took the tires off started it up and ran through the gears while he looked underneath. (I removed the tires to eliminate them as a source of the vibration.) Turns out it was the trans output bushing. They screwed up the installation. VINDICATION.

A while back I had to replace the main bearing between my two piece drive shaft. they rebuild the shaft and balanced. I didn't mark the spline, followed the advise on putting the two pieces together and to this day I still have a vibration around 40mph. I tried several different settings with no improvments. Don't know how to fix but maybe thi is your problem.

..Russ

Is this a long wheel base truck with the short stub shaft between the trans and torque tube with two "U" joints?

Could someone explain the phase thing please?
And how would you know if had already been put back together by someone else incorrectly in the past?
Thanks,Jeff

Yes, This a Long bed '51 GMC. It has that short section of shaft.

[img]http://www.chicagolandmgclub.com/driveline/0404/u-joints.jpg[/img]

Sorry for the big picture. It's the best one I found.
Slipe the joint apart and turn either end 90 degrees and it would be out of phase.

Thanks Richard.
Jeff

It is posible you put one of the U joint end caps on backwards, the ones that have the mounting bolts going through them. The bevel side goes on first.

Thomas

I'm not familiar with your model truck but I have a WW2 Jimmy .These trucks all have several conventional driveshafts but also one, 2-piece driveshaft with a carrier bearing between.On normal 1-piece driveshafts the two inner yokes are assembled in line,and the two outer yokes in line;as in Richard's picture; but on the two-piece shafts, the two uj's on the front shaft are assembled at 90 degrees to each other to eliminate vibration.I don't know the principle behind this but the Jimmy manual gives specific instructions about it and also specifies that this is only for this 2-piece shaft.I can e-mail the pages if you are interested. I know this arrangement is still used today by at least some manufacturers.Hope this is of some help!

I would have to see the wording or the pictures.
It should be noted that on a two piece driveshaft that has three "U"(universal) joints the 1st U joint and the 2nd U are in phase. At the same time the 2nd U joint and the 3rd U joint are also in phase. The 1st U joint and the 3rd U joint are therefore, 90 degrees out of phase.
If any one of those three U joints is a constant velocity joint, that changes everything.