The Stovebolt Site Forums The Shop Area Engine Shop Is it possible to install a driveshaft 'backwards'?

Single piece driveshaft on a 1966 pickup. Is it even possible to install it "backwards"? I believe the front and rear U-joints are the same.

I ask because I'm curious as to if this could be causing the vibration problems I'm experiencing at 70 mph and up.

-ftyler

Never thought about it before. Looked in autozoned, they show the same u-joint on both ends. So I guess you could get them in backwards. In theory, it shouldn't make any difference. However, there could be a slight twist in the shaft. Or excess wear in the splined slip joint. If you didn't clean the shaft, you might be able to tell which end was where due to oil leaks.

Ftyler, push in the clutch at 70 mph, if the vibration goes away, it's the engine, or clutch. If it's still there,look at the driveshaft, rear end,trans internal problems or wheel balance.Or maybe you've already done that, so you're looking at the driveshaft?

Tony,

That's so simple - simple common sense. But do you think I've tried it? - NO! :rolleyes:

I'll try it tomorrow, first thing after I get my son in pre-school.

Thanks,
-Fred

I agree with Fred T and Tony. I went to Advance Auto, and I'm sure they listed the same u-joints for the front and rear. Have you checked to see if your tires are balanced? John.

Looks like it's either the tranny or driveshaft. I had all 4 tires spin balanced. No difference. It actually may be a tad worse. But anyways...

I pressed in the clutch 4 different times while on the interstate and the vibration going on. Each time the vibration continued. I guess the next logical step is to put the tranny in neutral and see what happens. If the vibration subsides (which I actually hope it doesn't) then the problem is with the tranny. If not, then we move on to the driveshaft.

Thanks guys!
-ftyler

You let the engine idle with the clutch pushed in at 70, right?

With the clutch in and the engine idling most of the transmission wasn't spinning any more. I would think it is alright like the engine.

Can you put the front tires on the rear?

Alignment.

Tony,

I held the clutch in for 4 or 5 seconds. Don't know if that was enough to go to idle but it did decelerate a good bit, and the vibration continued.

The more I think about it, the engine had to go to idle. Even at 85 mph in overdrive I'm only about 2780 rpms so it wouldn't take long at all to drop to idle (around 800-1000 rpms, I'm guessing).

I'm almost completely convinced now that it's the driveshaft. But then again I've been wrong before. :p Many times.

-ftyler

Check for any missing weights that may have come off the drive shaft. The next move is to check under the caps for dirt that may through it out of balance. Did you make any changes to the drive shaft angles, new rear axle or engine mounts? I have heard of problems with vibration in the driveline when using overdrive transmissions but I don't remeber what the problems were or why. Best bet is send it for a balance check... Joe

Since you think you might have the driveshaft in "backwards", I assume you replaced the u-joints. If so, that should rule them out. You're on the right track by eliminating things, just need to do it one item at a time. Possibilities include:
unbalanced driveshaft
pinion bearing
tranny tailshaft bearing
front yolk to tailshaft spline wear
pinion bearing - differential
rear axle bearing
tire balance - even though they were just spun, it's still a possibility, try swapping them.

I'd start by finishing your driving test. Assuming the vibration is still there, I would crawl under with a prybar or huge pliers, wheels blocked with weight on them. See if you can find movement at either end of the shaft. This will check the u-joints and bearings. Then put the rear end on stands, tranny in gear. See if the rear wheels have any side to side movement. Check the front u-joint and tailshaft for slop. If you have a dial indicator and stand you can check the driveshaft for straightness on the truck.

If all this has failed, I would then go to a driveshaft shop, and I hate paying someone to work on my truck.

With the clutch disengaged and the truck still rolling, the tranny main shaft is still spinning along with the gears if the trans is still in gear, yes try it in neutral, also both with the clutch in and out.Loose tranny gears or bearings can set up a vibration, generally goes away when you release the gas pedal with the truck coasting in gear ,clutch engaged.If it wasn't allready mentioned, check the bushing in the tailhousing that the driveshaft yoke fits into. Try to move the yoke around to check excessive clearance.
The OD vibration thing is more asociated with the motor mounts being unable to deal with vibration from a low rpm ,high load situation, like pulling a slight grade while in OD.At least that's what I think.
You know Fred, the vibration may have always been there, in the past the low rear end gears probably stopped you from driving fast, now you can and the drive shaft is spinning just as fast as it would befire the OD tanny installation.

Actually it is spinning faster since the rear end is still the same gear. The OD makes the change in the tranny right?

So, the driveshaft is spinning maybe 15% faster than before and faster than it was designed for. Maybe that or the rear end is the limiting factor?

edit: I see what you mean now, you mean the driveshaft spins the same speed at any given mph. Ofcourse the top speed has been increased only compared to engine RPM.

Quote from Tony:

Tony I think you hit the nail on the head. Since the speedo stopped working I'm not sure how fast I'm actually going, but easily 75 mph+, when the vibration starts. With the old setup (pre-overdrive) I got the truck up to 80 mph one time and noticed no vibrations. The investigation continues...

-ftyler

ftyler,

in the family 1884 Olds 98 Oldsmobile - rwd , we had a similiar problem... it would vibrate between 50-60 or so mph... it turned out the rear(axle end) 'u' joints and the metal clamps were slap worn out... and it was jsut a vibratin' around back there and was close to coming loose

Pop replaced them with new joints and life was good.

Anyway, it is something to check...

-W

Bring your drive shaft to a shop that balances. They normally will check it out free.

I read that the vibration can be checked with a container of water placed on the floor board then drive it at the speed the vibration starts. If the water ripples it's the drive line. If it splashes around, its the tires/rims/bearings?

On the wifes '70 Chevelle, I had an annoying vibration. I replaced the front end with an alignment, all four wheel bearings and even the complete rear end. I had the driveshaft and all four wheels balanced.. still had the vibration. Rechecked everything and had the wheels checked again but this time I watched COSTCO balance it. I noticed that one wheel wobbled and asked if the car would vibrate with that wobble. The tech didn't know, he said that he just puts the weights on where the machine indicates. I then replaced that rim and guess what....vibration is gone .
Upside is that my drive line are all new .

No one has mentioned checking to see if the u-joint timing, yes they can be off if the slip-yoke has been taken off the main shaft and not put back on in the right position. Some driveshaft tubes are small diameter and a person can look down the side of the shaft to see if the u-joints are alligned (timed) properly.
The diameter of mine is too big so I need to use a straight-edge or a long length of string.
Always check the position of the slip-yoke and mark it before disassembly so it can be put back together properly.

The slip joint should be at the front or trans side of the shaft. the u-joints should be in line with each other and the two yokes onthe drive shaft should be pointed the same way, one way to check is get one yoke so it is pointed at the ground, then see it the yoke on the other end is too, if not it's out of time, and if the drive shaft yoke at the rear axle is poitner down, and the yoke at the trans end is pointed to the side, that is wrong too, its off 90 degrees. Some drive lines you can't this wrong on, they have one wide spline inthe slip joint, but most don't and I have a bunch of them out of time, it will eat u-joints like crazy.