Heavy vibrations

[alsriv2]

I had a similar issue with an '83 C-10 I used to own. Seems when I replaced the Ujoints, doing the exact same method I had used many times, I bent the driveshaft. Not enough to visually see damage, but enough to cause a vibration at a certain speed on the highway. Ended up having to replace the drive shaft...no other way to solve the issue.
Worst part? I didn't need to change the Ujoints...I did it only because I was heading out for a drive cross country (Northern Maine to Arizona). Everything was fine before I did that work.

[Cdubvw]

New update, I felt some play in the rear wheel bearing so i changed the bearings and seals and put fresh fluid in the diff. I also shifted the driveshaft forward to make sure the yoke at the transmission was not sticking out too far as mentioned earlier, now it is back one inch. Took it for a spin and sure enough the problem is still there. I got it up to some higher speeds and shifted to N and the problem is still there at speed... thinking I might need to take it to a shop somewhere so I don’t keep throwing money at it! Anyone have any recommendations in the high desert area of so cal?

[CC69Rat]

Sitting stopped, the truck running / idling and in park. If you rev the engine to the same RPM where you start to feel the vibration does it do it in park?

[Cdubvw]

Does not happen when stopped only when driving about 55ish mph. What do you guys think about this. The rear driveshaft has 3.5” of splines exposed when installed. Maybe there isn’t enough engagement here? But would that mean at the same rpms the problem would be present and not speed dependednt?

[LockDoc]

Originally Posted by Cdubvw

Does not happen when stopped only when driving about 55ish mph. What do you guys think about this. The rear driveshaft has 3.5” of splines exposed when installed. Maybe there isn’t enough engagement here? But would that mean at the same rpms the problem would be present and not speed dependednt?

That looks like a lot of exposed splines too. If you push up and down on the shaft in that area can you see movement between the rear and front shaft? When you shifted the shaft forward it would have made that worse.

I think I would start over on that whole shaft and re-do it, front & back.

LockDoc

[Cdubvw]

I think that’s what I’m going to have to do. I just hope I’m not spinning my wheels thinking it is the driveshaft. I talked to my father in law about it ( he owned it from 96-2016) he said that he had the driveshaft made when he swapped the engine and trans to a 350/th350 from the i6 and manual. To me it looks like the shaft is not long enough so i guess I’ll get a new one made up. I also talked to the guy who balanced it a few months back about phasing since his registration marks to put it back together made the u joints not in phase. He said that’s where h balanced it and to leave it that way. But is it even possible that this can be done? Can the shaft be properly balanced but out of phase?

[LockDoc]

Originally Posted by Cdubvw

I think that’s what I’m going to have to do. I just hope I’m not spinning my wheels thinking it is the driveshaft. I talked to my father in law about it ( he owned it from 96-2016) he said that he had the driveshaft made when he swapped the engine and trans to a 350/th350 from the i6 and manual. To me it looks like the shaft is not long enough so i guess I’ll get a new one made up. I also talked to the guy who balanced it a few months back about phasing since his registration marks to put it back together made the u joints not in phase. He said that’s where h balanced it and to leave it that way. But is it even possible that this can be done? Can the shaft be properly balanced but out of phase?

I would say it is too short overall. I don't know anything about the phase stuff.

LockDoc

[harpo231]

I'm with doc looks screwy

[Steeveedee]

I went out and crawled under my truck for a look, because that driveshaft looked to have way too much spline showing, but mine looks just like it! I've had that truck up to 75 MPH with smooth drive train results...except for deep secondary roar and a sweet exhaust note. That was many years ago. I don't want to try that with this new shell that is 10" taller. I'd run out of gas in a couple of blocks.

[davepl]

My problem was different in that it showed up at low speeds, but it turned out to be the splined section of the slip joint was worn. Or at least that's the last thing we did before the problem went away. So the whole driveline seems pretty sensitive and that slip joint in particular. I can't explain the harmonics or magic that made it shake, but it shook back until we fixed that. I still don't understand it though.

[Steeveedee]

I've had that driveshaft out in that truck's lifetime for u-joints and a center support when it belonged to my FiL. But that's decades ago, and I don't remember how much more of the splined shaft is available. Anyone have one in a position to tell how long that splined portion is? I'm drawing a blank. I know for a fact that that is the driveshaft that was in it in '81 when I got married, so I'm expecting it to be original. It'll be interesting to get to the solution.

[stsalvage]

I'm having this problem in my 1972 3/4 ton.I have a manual choke in it drilled a hole in my new plastic dash cluster to put in the manual choke of the 1967--70 trucks.My Vibration comes from sitting still and driving.When i have my truck in park It vibrates really bad at high speeds to warm up the motor.Kick it back down nothing.I feel I might have a fly wheel that might be wrong.

For a side note the guy in the high desert.I have a 1967 3 door suburban i'm not using at the moment If you want to barrow my drive shaft you can.Not sure on the U joints how good they are but I need to replace them cus in my 1968 3 door The PO put in a 1 peace alum drive shaft I think its 52 inches or 58 inches .I know its way past what the law requires.The 1967 has the old carrier not the 1969-72 I have the one that was used in the 1964--67 trucks.Let me know send me a Email I'm in Moreno Valley not to far from you

I have 9 of these trucks from 1964--72.

I have every one trying to buy them off me But I'm trying to keep my Easter EGGS for as long as i can

[Cdubvw]

UPDATE!!!


So after taking a break with this issue and talking with the guy who balanced the shaft I decided that the driveshaft was not the issue... so I put a new transmission mount and of course it did not solve the issue. But hey new mount! Next I moved on to the tires again... since the issue is dependent on speed not rpms or anything else, the faster I go the faster the tires spin right? So I swapped the front tires to the back and figured I might as well throw the old drums back on so rule them out. The new rear drums looked to be of good quality and were from Napa. Upon removing the rear drums I observed that one had balancing weights and the other did not. Hmm grab my old made in USA drums and both had weights ( reason they were removed was because they did not have enough surface to machine ) torque the wheels down and rip it. 20...30...40...50 bracing for the shaking now.... 60....70.... wait what’s going on! No shaking!!! The thing is driving nice and smooth! Wow so I’m pretty stoked at this point.

So I still have to swap the rear wheels back and make sure it wasn’t the tires or wheels but I’m pretty confident that the drums were causing this mess. Hopefully this can help someone else in the future.

Thanks for the help guys 👍

[GASoline71]

I agree... your slip yoke up front is barely engaged on the splines of the output shaft of the transmission.

Gary