Another driveshaft question

[bobcooter]

I have a 79 C-20 with a TH-400 and a two piece drive shaft. I have been toying with the idea of replacing it with a one piece driveshaft. I have a couple but they are either too long or too short. One is out of a 77 C-10 shortbed ( too short by 1 1/2"  and not very strong looking for a C-20) and the other is out of a 78 GMC C-15 long bed with the TH-350. That's why it's too long. . My question is, surely Chevy built some C-10 longbeds with the TH-400? That would be an easy swap after matching the crossover u-joints. Any thoughts.. There a place down the street that will shorten one for $100.00 but i'd rather skip that step if I am able to. Any thoughts? Thanks,

[Captkaos]

From most of the data I have, most Heavy duty trucks 3/4t and up (and some hd 1/2's) recieved 2 piece driveshafts, because of their strenght and because of load.

If you really want 1 driveshaft, it is best just to have one made instead of trying to find one as you would need one out of the exact same truck to work.

[bobcooter]

Yeah, well I don't do any hauling or towing. I measured eveything and if I swapped over to the TH-350 and used the shaft I have it would work nicely. I just don't want to change transmissions.
Thanks,

[hotrodpc]

Anything wrong with your current driveline? Whats the advantage of a single over the 2 piece. Just asking. Both my 3/4 have 2 piece, and my 4 half tons have singles.

[Layne]

Far as I know the only advantage of a one piece is less U-Joints to service and replace. Maybe, maybe less driveline noise. Somebody once told me one pieces rob less hp, but I dunno.

[hotrodpc]

Thats what I am thinking Layne. I less u joint, less carrier bearing and about it. One big advantage to a 2 piece is less wear on the on the output shaft and seal of the trans too. Although that can also work in reverse too in some cases. I like a 2 piece when its done right and balanced. Many people do not mark them if they seperate them, and it can makes things a bit rough at times. I always stamp arrows on my 2 pieces when pulling them apart to be sure they go back together the same way.

[bobcooter]

I don't know really. I just had some driveshafts lying around from some half ton trucks and thought about replacing the two piece with a one piece. Sometimes I think it's the "quest" for a part that gets me going. The two piece works fine, but I think you may get a little more power to the ground with a one piece. The thing is, I really doubt the difference is noticeable.
  I 've had a two piece before on a Longhorn and didn't really ever have any problems except the carrier bearing going out. 

[81C20]

U-joint angle and balance.

Quoted from UTI Heavy Duty Truck Systems 4th ed:

"The longer the driveshaft, the greater the weight and therefore the greater the radial forces, especially as driveshaft rpm increases. At high speeds, balance becomes more critical. This why manufacturers limit tube length. For example, at 3,000 rpm, the length of any single driveshaft section, measured between the center line of the u-joints at either end, should not usually exceed 70 inches."

You also have to take in consideration the working angles of the driveline throughout the entire range of movement of the rear axle. The shorter shafts with more joints will have less of an angle, and permit a higher working speed (while also ensuring longevity for the joint and the rest of the driveline) vs a single long shaft with severe joint angles.

[Layne]

We watched a movie in school about driveshafts. Pretty interesting stuff. Scared me enough to spray paint a dot everywhere on the U-joints and couplers and whatnot.

[hotrodpc]

Then you ask yourself, so what is the differance in a 1/2 ton and 3/4 or 1 ton that the 1/2 ton gets a single but 3/4 and 1 ton get 2 piece. Above would explain that, if you consider a 3.73, 4.10 and 4.56 rearend ratio, that shaft is going to be turning alot more rpms than a half ton with 3.42, 3.08 or 2.73's. Also the load weight and geometry when the truck drops too must be taken into consideration.

[team39763]

We watched a movie in school about driveshafts. Pretty interesting stuff. Scared me enough to spray paint a dot everywhere on the U-joints and couplers and whatnot.

What does spray painting a dot do?

[hotrodpc]

Until he responds, I'll take a wild guess and say it has to do with balancing if taken apart, and to see if anything has moved or twisted. I use a metal stamp kit and hammer, and put marks on 2 piece drivelines, to make sure they go back together EXACTLY the way they were taken apart should the 2 pieces become seperated.

[beastie_3]

I think hotrodpc is right. a driveshaft is balanced, whether one piece or two piece. A two piece will be out of balance if its put back together wrong.

[hotrodpc]

An unbalanced driveline can cause a few differant problems. 1 being vibration and uncomfortable for the passengers, but that is the minor issue. It can also cause premature tailshaft bushing and seal wear in the trans, and can also cause pinion seal wear and premature pinion bearing wear. Also can wear out U joints and carrier bearing too. Just best to keep it balanced. For what its worth, it really does not cost alot either. Trying to go off memory here, but about 10 years ago, I took my 2 piece driveline out of my 93 Ford E-350 Retired Ryder box van, to the driveline shop. I had them replace all 3 u joints, new carrier bearing, and balance both pieces. They considered that a total refurb on the driveline which actually it is, so they also had vatted it, and painted it nice and shiney black. If memory serves it was like $138 and it was like a brand new driveline again. I didn't think that was to bad for a 2 piece heavy driveline like that.

[VileZambonie]

Witness marking the driveshaft is known as driveshaft phasing. It is critical to maintain proper balance. The other important thing to do is witness mark the companion flanges so the driveshaft goes back in the same way it came out. The most important reason for this is to ensure no new noises or vibrations arise after R&R. Even if there is an existing vibration people tend to get used to them. If the pitch or rpm changes after you R&R a driveshaft you will get the infamous "ever since you worked on my car..."

We had a thread on this a while back

http://forum.73-87chevytrucks.com/smforum/index.php?topic=10814.0