The Stovebolt Site Forums The Shop Area Driveline Drive Shaft Length

I recently took my 55 to a front end specialist to figure out a vibration when I get over about 35 mph. This truck has a 55 Corvette 265 in it with a 70's transmission (auto). The place told me that they thought it was in the driveshaft. After looking at it with a gearhead friend we saw that the driveshaft needed to be about 1.75" longer. It is probably getting the vibration there. I'm thinking ??? get the new measurement and craigs list the dimension for a used one.

All thoughts WELCOME

A bunch of things come to mind, so bear with me...

How did you measure to figure out that it's 1.75" too short? As long as you have sufficient amount of the yoke engaged with the transmission output shaft, it doesn't matter if the yoke sits further out that it would have in the vehicle it was originally in, if that's what you're checking. What was the driveshaft originally from? Do you know if it was ever balanced?

Are you running a TH350 or TH400?

Before you go the driveshaft route, have you checked that the driveline angles are correct at ride height? Is the vibration only at certain speeds, or all the time, and does it seem to be in the seat of your pants/pedals (driveline) or the steering wheel (front end)?

If you do need a longer driveshaft, I would either go to the local wrecker with a tape measure and find one suitable, or go to a driveshaft shop and have them build one..

Where would one find a used driveshaft for a 55 truck with a 70s transmission?

This is from a driveshaft shop.

"In most applications the minimum is 3/4 inch and more than 1 inch is not necessary. This is measured with the rear suspension supported on safety stands or with the rear end on the ground.

Or
With the weight on the rear you should be able to slide the yoke in no more than 3/4" - 1". More than that and it will wobble & damage the output shaft."
I believe they are speaking of how much of the yoke is outside the tranny. The bottom line is how much will the female spline hold and how long is the male spline. Leaving room so as not to bottom out inside or outside.

I agree with T-Nix and I think 46GMC was going to say "go to.... driveshaft shop", but fell asleep :), I also do not think you will find the correct length with the correct ends. I would first be sure it's the driveshaft causing "bad vibes", then check the web for proper engagement dimensions (to verify what I found), then go to a driveshaft shop, tell them your engagement to double check your thinking, then have them use your ends to create proper shaft. In my experience, it's not that expensive.

The shop that looked at it to see if it needed a front end alignment took off the driveshaft and ran without it connected. They said the shaft was too short. I looked at the front yoke and appeared that it could be 1.75" longer. Which may be causing the whip/vibration. The vibration happens after about 30-3mph all the time. Seems the cab shakes not the steering wheel.

If the motor and rear are correct year and the tranny was the only variable, how could the driveline angles be off? If so, how would I know and how would I correct?

You have 5 trucks, so you are not a rookie and I'm not trying to tell you what to do, just my 2 cents. We have all been fooled by vibrations, the shop could be correct (too short will cause wobble) but check engagement per advice above. Also if you have any number of other causes, like tires, or motor mounts or loose steering components or bad Ujoints, they may not show up on static test.
As far as pinion angle, we don't know if you have lowered or jacked it up or other mods which could change pinion angle. As far as how you would know: measure with angle finder.(3-4 deg at both ends). How to correct: post/decide after measure.

The main issue with Forum help (not directed at you) is that we don't know when it started, what was done recently, mods, changes, etc? Another person had vibration and found it to be the tranny output spline/bushing. I think we all decided that at that bushing there should be very, very little radial movement (sideways slop). The sliding in and out is axial movement.

Mark, some driveline shops may be different than others but here is a sheet showing how the driveline shop I use wants you to measure. Tom knows the rest of what works and don't. He's been doing this for 30 years. He has some "spares" standing around and can pull one and shorten it, put what ever ends you want on it and balance it. Here is how most are measured.
http://i140.photobucket.com/albums/r19/LutherParris/52Panel/img011.jpg

I work part time for Tom and he is a super guy. He makes and ships driveshafts everyday. Vintage, racing, off road vehicles and many many more. If you have a driveshaft and not have a shop close by call Tom.

Here is their web address.
http://carolinadriveline.com/