Intro with a driveline vibration

[AlexW]

Hi all, been reading around on here lately to learn some tips and tricks on working on my 1985 GMC 3500 dually. It's the High Sierra 3+3 package, 2WD.

The transmission went out on it, and I replaced it. I discovered a rotted out carrier bearing and a bad u-joint on the front half of the driveshaft. I had both of those pieces replaced, and put the driveshaft back together the same way that it came off. Though, it looks like it can only go back together one way...

I'm having a driveline vibration problem. I don't feel anything at all until it hits 40MPH, and then it will smooth out some by 55MPH, but it is still present. I haven't driven it faster than that since the swap. Do I need to have the driveshaft re-balanced? I'm a bit confused about what could be causing this. Prior to the transmission replacement, I had zero vibration issues with the truck at all.

On a side note, possibly related, I removed the transmission mount to get the transmission out and have been having a beast of a time getting the bolt holes to line up. Is this mount only designed to be installed one way, and it could be that I have it installed backwards?


Regards,
Alex

[DetroitIron]

Alex, I had a similar issue recently. I was assured by the transmission rebuilder that all my ujoints were good. I had a vibration that was very noticeable in the rearend at around 55 mph when my 700r shifted down into overdrive. The cause ended up being that my driveshaft was installed 180 degrees out from where it was originally. This solved my vibration issue. Wish I could help you more, but I can totally relate to how annoying that can be. Good Luck. The other thing to check is tires with a flat spot or broken belt.

[donut]

Can't comment on the vibration without feeling it.
I can help with the mount, maybe. Loosen the cross member and that way you have movement to line up the mount. It was easier for me to install my trans with the cross member out of the way anyway.

[Keith Seymore]

Take a look at this link:

http://67-72chevytrucks.com/vboard/s...d.php?t=522180

It will talk about setting driveline angles but, perhaps more importantly, will walk you through the though process of diagnosing and fixing any kind of vibration issue.

K

[Stepper86]

Im having the same problem with mine, vibrates like crazy when overdrive kicks in and smooth out as I gain more speed. Will try to turn the shaft 180 degrees and see if it helps, I had it off when I installed new exhaust so maybe it´s an easy fix (I hope)

[AlexW]

Thanks for the info Keith. I'll sift thru that and start my diagnosis. There's not a way that the driveshaft could be installed 180* out of sync since I never disconnected the rear half of it from the differential.


Alex

[AlexW]

Could it be the result of only replacing one of the u-joints and not all of them?


Alex

[AlexW]

Could it be the result of only replacing one of the u-joints and not all of them?


Alex

[Mrknowitall]

The drive shaft needs to be clocked in the orij positions, next time take some scratch all and make allighnment marks.

All u joints need to be replaced at the same time. It sounds like you cracked a needle bearing during install as well.

Additionally ujoints come prelubed but need more, grease them with a gun, allighn all zerts during install to make grease procedure eaiser.

The mount issue: the mount is there just to keep er centered, ive seen trucks with broken mounts drive fine,

Did you pull the motor and trans as one? Or just the trans? Did the tq converter click in? Was theyre space between the trans and motor? Did you force them together?

Reason i ask is if the tq converter dosent allighn with the shafts forks it will throw the entire trans back aprox 1/16-1/2 in.

Pull the drive shaft again, check for ease of movement, all weights on the same side, all zerts same side perferably opposide side of weights, grease and replace with all new u joints.

Use a press if you can, a hammer and socket will work but often can knock out and break the bearings if u dnt know how to keep the joint n the cap trick.
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[Mrknowitall]

Also; i chased shaft problems for a half year until i realized it was bad balljoints up front causing the heromic vibrations, have a buddy jump around while driving and feel the floor, the feeling shoud b stronger as you feel tward the rear. Also i cant tell u how many times my friends did a trans job and didnt lube the speedo cable, it vibrated and gave the feeling installnof trans was wrong, i almost guarnteed the driveshaft wasbjust put togetther wrong. Like i said take the drive shaft out and inspect,

Before pictures before pictures before pictures
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[motornut]

I did two when my 4X4 rear shaft was out
mine were press fit one side,u clamps the other
try turning one side u replaced, 180 degres

[AlexW]

The driveshaft went back in in the same orientation that it came out, including matching it up the same position on the transmission output flange. I had a shop replace the u-joint after it fell apart when I removed it. I figured it was a safer bet to just replace it than it risk getting dirt in there while trying to line up the needles. Too much work anyway. Its possible, I suppose that the shop could have garbooned the joint. They did also call me asking if I knew which direction the support bearing needed to be installed...

I removed the trans separately from the engine. When I remounted it, the reman TQ wouldn't touch mount to both the trans and the flexplate, so i used washers to space it off the flex plate and keep it against the transmission so that it can engage the pump.

I don't believe that all the balance weights are on the same side of the driveshaft, but they weren't that way when I removed it, so i havent changed the orientation of the driveshat from.its original position. I suppose it could be ball joints, but I'm hesitant to believe that because there was no issue prior to driveshaft/transmission removal. In my experience, these kinds of problems are usually a one-source deal. I'll regrease the fittings and have new u-joints installed on the rest of the driveshaft and see if that clears it up.


Thanks,
Alex

[Mrknowitall]

Oh boy. That tq converter needs to be corrected, other than that, the shop screwed somehing up if theyre. Asking u how to fix it. Sorry. Good luck
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[AlexW]

How so does the converter need to be corrected? It is seated directly against the transmission input shaft as well as the flex plate.


Alex

[Mrknowitall]

If you had to modify a part that was intended to be a direct replacement, then its not right. Im no saying thats ur problem, just remember aprox 200ft lbs of torque goes thru 3 bolts. They need all the thread they can get, washers/spacers are unexceptable if not orij equipt
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[AlexW]

I replaced the original bolts with longer ones to compensate for the additional spacing.


Alex