So I'm working on a '57 Chevy, it's got a newer Turbo 350 (1980ish) in it with the original rearend. I found a driveshaft that is almost the perfect length, maybe just a bit short. You can see from the slip yoke on the unknown driveshaft that it originally had about 1" exposed and the other 2 1/2" inside the tail of the transmission, the barrel is 3 1/2" long total. When I put this shaft into my car, I get about an 1 3/4" exposed, almost 2" I'm not experienced at all on drivelines, so I have two questions. 1. Can I assume that I should not run this with only 1 1/2" to 1 3/4" of yoke barrel in the tranny tailshaft? It's clearly not ideal. 2. Can I remedy the situation with a slightly longer yoke? I see the aftermarket offers a yoke that has a 5" long barrel length, which would give me about 3" in the tailshaft and 2" exposed, maybe 3 1/4 in/ 1 3/4" out depending. Would it hurt the car at all to have the U joint an extra inch away from the tailshaft? or is 3 1/4" too much to have in the tailshaft? This is a relatively low horsepower car with stock leaf springs/suspension travel. Here's a pic of the current yoke which you can see the witness mark on from whatever car it originally came from, and a pic of it installed in the car with a tape measure for scale. The car is standing on it's suspension with all of it's weight on the wheels, minus the seats, doors, side glass, and a driver, so I suppose it could compress a bit more once those things are added back in.
It is too short, it will whip around and cause a vibration and take out the tail shaft bushing and seal. You need a longer yoke or a longer driveshaft.
The splines on the tranny only go so far, a longer yoke may bottom out. I used a longer one on mine, but had to take out the splines in the yoke.
The correct fix is to use a longer driveshaft. Get the shaft to someone who can replace the tube with a longer one.
I get that the ideal solution would be a custom made driveshaft at the correct length, and I'll do that if I absolutely have to, but I'm really hoping to avoid it due to the cost. I understand that currently there isn't enough barrel length in the trans, but if I had a longer yoke, so the trans would have the proper 2 1/2" in it, would the tailshaft bearing really get destroyed by having the U joint slightly further away than stock? Not talking about a lot here, it's about 3/4 of an inch extra. Also, anyone know how to determine the ideal or maximum amount of yoke that can be slid into the back of the trans? The aftermarket long yoke adds quite a bit and I don't want it to bottom out. The 2 1/2" measurement is just a guess based on the wear indicated by the yoke on the unknown driveshaft, it's not original to the car or the transmission. I'd hate to have this driveshaft reworked and then find out the yoke I'm trying to use is not the correct one. Was every TH350 yoke from GM the exact same length?
Nikes' tag line says "Just Do It", you should too, believe me (all of us), it's the smart thing to do, the cost of a new driveshaft pales to the carnage from not heeding this advise. Maybe not this week or month but it will have to be dealt with!
The longer yokes are designed to be shortened, if necessary, to your needed length. Although a driveshaft of the "correct" length would be ideal, you can probably get by with the longer, modified, yoke. What you DO have to worry about when using a longer yoke, is that it's not too long, and pushes the speedometer drive gear forward, thereby disengaging it from the driven gear. It's what I did in my D.D. truck when I swapped to a short shaft TH-350 from a 9" extension housing TH-350 and a 700R4 before that. Truck should have had a TH-400 from the factory! I am Butch/56sedandelivery.
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