Slick 60's

Hello All,
I'm trying to trouble shoot a problem on a 67' swb Ford truck. It has the 240 w/3spd manual transmission. I got the truck from my brother in law. After getting the thing tuned up and running, I'm getting a vibration in the drive train above 40mph. It's a very dull vibration and the truck doesn't much want to go past 50mph. I was told it had a new clutch in it so I thought something was screwed up there. I took the transmission and clutch out and everything looked good there. While I was at it I changed out the u joints. I also put on a different set of wheels and tires that I know are good and balanced. Still no change. I'm assuming it's something in the drive train because I get it up to 50 mph and let off the gas and I can feel the vibration instantly go away. Any ideas?
Thanks for the info.
B.

Sounds like somthing in the rear end. Does it under light to medium throttle goes away at zero throttle. Does your truck have a center support bearing on the driveshaft?

No, it has a one piece drive shaft. At low rpm I really don't feel the vibration.

Maybe your driveshaft is bent or missing a weight? Are the motor mounts ok?

Do you have the same vibration as before you changed u-joints?

The vibration is the same with the new u joints. I was going to look at the motor mounts next.

Here is something I was thinking of when I changed the u joints. When the u joints were in and the snap rings in place, it was hard to move them on the axis that was in the driveshaft. Does this make sense? The joints moved freely on the axis of the yoke. It's been a while since I changed u joints on anything so I assumed this was normal. Thanks for everyones replies.

B.

sounds like the ears on the driveshaft are closer together than they should be, so when you got it all together it is too tight.somebody may have bent them a bit changing the u-joints before.

I had a vibration in my truck in the throttle and out of throttle but not when coasting found the rear spring hanger bushings worn out. So you could say, my rear axle was walking.

Crossed spark plug wire, or some form of ignition missfire? Could cause a noticeable imbalance under load but not when the throttle is closed.
Jus' a guess. I've had it happen
Dave

maybe your flywheel has runout, this can cause a vibration.

How about the trans., A worn or low oil could be a problem.

T/D New Caney,Tx.

btalley wrote:The vibration is the same with the new u joints. I was going to look at the motor mounts next.

Here is something I was thinking of when I changed the u joints. When the u joints were in and the snap rings in place, it was hard to move them on the axis that was in the driveshaft. Does this make sense? The joints moved freely on the axis of the yoke. It's been a while since I changed u joints on anything so I assumed this was normal. Thanks for everyones replies.

B.

My guess? Driveshaft.

One time, on my big truck - freightliner, the front yoke was worn and had similar vibration , although only vibrated with a load .

T/D New Caney TX

I need a little explanation on the won't run over 50. Is this because of the vibration, or it just won't run any faster? If it won't run any faster, then my guess would be firing order on the engine. If it is the vibration, this could be the drive shaft. Any binding on the u joints, will cause a problem. Might be an abused drive shaft. I would aslo check the rear bushing on the tranny, along with the yoke. Grab you rearend yoke, and see how much play is in the pinion bearings also. Have you checked all your axle bearings for play?

Rich

So, the firing order of the engine is good. There is no play what so ever in the drive shaft between the front yoke or the rear.

If it is something with my drive shaft, what are my options? Have someone balance it? I had another driveshaft but it wasn't close to being the correct one.Also, has anyone ever removed u joints without messing them up? What is the best way to install the u joints with no possibility of messing up the ears? I pressed the u joints in and since the snap rings went in, I assumed they were installed correctly.

I'm about to take it for another test drive to see If I can get some more info.

Thanks again for all replies.

truckerdaddy66 wrote:One time, on my big truck - freightliner, the front yoke was worn and had similar vibration , although only vibrated with a load .

My '84 Mustang currently has that problem. The bushing in the transmission tail shaft is worn & the front yoke vibrates around in there. I replaced the yoke & that cleared up most of it, but there's still some slop in the bushing.
The car vibrates under a load at about 60mph, with no vibration when I lift off the gas.

If you pull the yoke out of the trans, the shaft of the yoke should be perfectly straight with a straight edge on it, front to rear...no dip in the middle. If it necks down in the middle, it's worn.

The tight u-joint problem shouldn't really cause a vibration, it'll just wear out faster than usual.

btalley,
One other sourse of a vibration like you describe could be an axle bearing , getting ready for the "happy hunting ground". I have had that same problem once , drove me crazy till I found it . "Didn`t have too far
to go". LOL Just my 2 cents worth!
Bill.

jack the back end up, with the trans in park or in gear on a stick, grab the tire and see how far forward and backward you can rotate it before it stops.
also watch the driveshaft to see when it starts to move against the trans gear so you know what travel you are observing.
the more it rotates before the driveshaft begins to turn, the more slop thats in the ring/pinion. watch the pig yoke and see if it jumps at all, not supposed to but bad pinion bearing will.