The Stovebolt Site Forums The Shop Area Engine Shop Two piece driveshaft to One piece

I am installing a 700r4 in my 61 longbox. I was thinking of going to a one piece driveshaft and ditching the carrier bearing. The main reason is cost. I think I can get a driveshaft out of a suburban and modify it. The trans is 8 to 10 inches longer than the stock. Can I get away with this or is it going to give me trouble?

It still has to go through that crossmember doesn't it? Not sure it's big enough to allow a full range of motion without a carrier there,
Scott

There are maximum lengths you can have a single drive shaft. The best is to consult a reputable driveshaft shop as for the maximum length you can go with your driveshaft at the rpm you expect to run at.

Drive shaft performance varies with length, diameter, tubing thickness and tubing material.

The longer the drive shaft the larger around it needs to be in order to work smoothly at a given speed.

I'm sure you can make a drive shaft long enough to do the job but in doing so may be limiting your top comfortable speed because of drive shaft vibration. And if the drive shaft is vibrating you'll loose bearings and seals and u-joints.

I agree!
If you're curious what all goes into designing and installing a driveshaft check out these manuals
http://www.stovebolt.com/techtips/driveline/setup/index.html

Grigg

Less than 5 feet seems to be the magic number, or at least it was on my 1959 GMC longbed. I believe I am running a 4 inch tube. The shop that initially made my driveshaft didn't do a best job as I had a bad vibration at 3000 RPM. I ended up having that driveshaft made 3 times. The third time was because it dropped when the rebuilt rear end failed.

One thing you might want to check out is Chevy Vans. I had a 1991 Chevy Van with the short wheelbase, and a 700r4 tranny. It had a fairly long 1 piece drive shaft, and IIRC it was also made of aluminum. I think that would be your best bet since it is lightweight, and is made for the 700r4.

-Nick

Thanks for the tips guys. The trans is actually out of a early 90s chavy van. there is a decent amount of room for the shaft to move but I won't know for sure intil I get everything bolted in.

I had a trans guide with dimensions earmarked, but I can't find it. This is a guess, but isn't a 3spd column shift trans with bell about 2 1/2" shorter than a 700R4. In another thread you said you had to make side mounts for the engine and was planning on moving it forward.
The 3spd and the 700R4 both use a 27 spline slip yoke. Find a truck like yours with a 3 spd and see if the front half of the drive shaft will bolt up.

I used to go to Jeep Surplus in Lexington Kentucky when I lived there. They had a drive shaft mounted on the wall off of a large truck someone made one piece. It was sort of pretzel shaped.

My other concern besides cost was that my original driveshaft has the slipyolk between the carrier bearing and the rearend while my 700 has it in the trans which means I would have two which I believe is one to many. I only moved the engine forward about an inch.

It will be about 6 feet long.

6' is getting pretty long. Below is the recommended tube thickness at various lengths. I would would strongly recommend 2 drive shafts however, if you have a slip joint at the transmission, it is a problem. You really should have a U joint at the back of the transmission and a slip joint between the center bearing and the third member. If you go the 1 piece route, I would certainly put a guard around the drive shaft. A 6 ft drive shaft can really be wicked.
The general length limitations are as follows:
* Installed length u-joint center to u-joint center.
ACS = Adjusted Critical Speed
Suggested factors for Adjusted Critical Speed:
Safety Factor = 0.75
Correction Factor
Outboard Slip = 0.92
Inboard Slip = 0.75

TC = Theoretical Critical
CF = Correction Factor
SF = Safety Factor
Tube O.D. Maximum Length *
3.0 in. 60 in.
3.5 in. 65 in.
4.0 in. 70 in.
4.2 in. 72 in.
4.3 in. 73 in.
4.5 in. 75 in.
5.0 in. 80 in

I had a 63 C20 lwb with a TH400, and a single piece drive shaft. The previous owner had replaced the 292, 3spd, with a 350 olds. I still have the drive shaft.

Larry