The Stovebolt Site Forums The Shop Area Driveline Driveline vibration after reinstalling transmission?

This spring I removed the 3 speed from my '50 3100 to reseal everything. It all went well but it seems as though I've developed a vibration going down the road at 35-50 mph. If I had to guess I would say it is coming from the torque tube/rear of the trans but I'm not sure what to even check. I used two gaskets on the torque ball collar as determined from the procedure in the factory service manual. I can think of 3 possibilities...

I lifted my torque tube upwards quite a bit to get the trans out (I removed it from the bottom as a previous owner riveted the floor access shut) and it didn't come to rest at the same angle. Is there any procedure to align the torque tube to the rear of the trans? I just had it propped up with a 2x4 and lowered it down by hand to reinstall. the rear bushings are original but it seemed to go up and down willingly.

The U-joint bolts were torqued to spec and lock tabs in place, but there did seem to be some side to side play in the joint when assembled. At the time I thought this to be normal as it was tight in the saddles and there didn't seem to be anything that would keep it from being able to move laterally aside from the torque tube itself.

The bell housing and likely front engine mounts are original and liquefied. The rear has been rebuilt with new rubber and is quite tight to get into place. This would seem like a no brainer but I drove the truck all last year this way and it went down the road nice and smooth. I plan to switch the body over to a new chassis and drivetrain this winter that I'm currently building so I'm trying to keep the amount of replacement parts I put into this one to a minimum.

Any thoughts? I'm really hoping to at least get an idea of what to look for before I go tearing into this thing again now that the snow is melted!

After you installed the trans did you pour some 90 weight into the bell of the torque tube to immerse the ujoint prior to driving the truck? If you drove the truck with a dry ujoint it could be the culprit. Other than that I have nothing else. Did you re-bearing the trans also when you resealed it?

I did add fluid to the rear. I got conflicting information on exactly how much to put in, I think the service manual said 8oz and a few places online said fill through the speedo hole until it runs out. It was a pain to get fluid in with the floor access riveted shut but I figure I put a good 10-12 oz in before I gave up on waiting for anything to run out. I didn't tear into the trans, only replaced gaskets.

There is a square head pipe plug that retains the bearing support and it is on the outside of the passenger rear side of the transmission. You didnt happen to loosen that did you, thinking it was a fill hole?

I had the same problem after having my 3 speed out. After reinstalling and filling with oil I had a vibration that started at about 35 mph. I discovered that even though I was sure I'd filled the transmission it was a bit low. After topping it off the vibration went away.

If it's what I'm thinking it is, yes I did. Is it the circled plug in the picture? I drilled out the rivets in the floor access and took a look, it seems like the bearing race hole is lined up with the peg on the plug.

That is the bearing support pipe plug. If you just loosened it or removed it without driving it loose you are probably ok, if not it could of slid out of the case towards the ujoint then it could just spin with the mainshaft causing the mainshaft to whobble in the case. When I disassembled my 3 sp that bearing support slid out really easy,not a press fit. It has been awhile but I seem to remember it had a 3/8" indentation in the bearing support for the retaining plug to center in.Since there is no seal in there, you should be able to view it if you removed the torque tube and ujoint and iinput yoke. Then you could recheck your ujoint to see if it is ok too.

I have seen where one of the U' joint trunnions was installed backwards which caused this.
The trunnions that are held on by the two small bolts are offset, and if installed backwards will keep the U' joint cross from centering its self, causing an imbalance.

That might explain the side to side play I noticed when reinstalling. It's looking like I have no choice but to open that thing up again.

There should be a fair amount of side play originally.
The cross is free floating and relies on the outer ball to keep the whole joint assembly inline.
The problem in this case is when the trunnion , if installed backwards, holds the cross off to one side, preventing it from centering.

It looks to me like both caps are on correctly. The 45° bevel matches up to the bevel on the output yoke and the saddle seems to be sitting towards the outside on both sides. Is this correct? I reluctantly ordered new engine/trans mounts in the hopes that that helps.

I took the trans out before I started driving it for the year (stupid snow) so maybe I just remember it having a smoother ride that it actually does. I do mostly city driving and really don't want to end up stranded on a busy street!

Another question, just how tight is the threaded cap at the end on the ball housing supposed to be? I thought I had mine pretty tight but it was still dripping.

That pic shows how they should be installed!

Just wanted to post an update, after replacing all 4 engine/trans mounts and rechecking fluid levels the vibration seems to be down to what I suppose are normal levels. Still unsure if it was all in my head or something was actually off, but the mounts were pretty shot so at least those are fixed!