Projects TH350 Swap Question for 58 Chevy

Attached shows the 2 piece vs. the one piece. My car has the one piece. The old tranny was also caked in grease, assuming the engine probably leaked oil when my Gramps had it, which was resolved when he threw a rebuilt 350 V8 in it.

 

That was the route I was originally going to do, but most everyone here says it will cause long term issues. Of which I still don't understand why 3" more yoke would cause it, unless you can claim you did this a long time ago and still don't have issues.

 

The problem with the longer yoke is that it will magnify any issues with u-joint wear or driveshaft imbalance. Those issues will be magnified by lower gear ratios, like a 4.88 or 5.13, which would make the driveshaft turn faster at highway speeds, vs 3.23 or 3.54. Those numbers are just examples. It sounds to me

 

I would have a 3" longer shaft made personally, but that is just me. Like wicarnut says, you could probably just use a longer yoke and be perfectly fine.

 

Yeah at this point I am either gonna get the longer yoke and run the car until I get the old tranny rebuilt, or just find a used TH350 with 9" tail and sell my rebuilt 6" TH350 to offset. Either way the old one will be kept to eventually rebuild. I have a local junkyard that sell pulled parts, if they have a 9" tail TH350 for the right price, I will get it. I only intend to drive this car on local roads to and from work which is a 10 min drive.

 

I guess you'd have to draw yourself a picture to figure it out...Maybe a pop-sickle stick or two would help.. Not an engineer, but I know this to be true. Maybe if you mocked it up like I said earlier, you would see it.
Apparently, you did not, ..so I'm about done with this one

 

the clearance issue is when the cars rear suspension moves up and down when hitting bumps. a one piece shaft can not bend in the middle to clear the tunnel created by the x member.

 

Can that be relieved by adding spacers/thick washers under the tranny mount?

 

Virtually all transmission shops keep a ready-to-go supply of commonly used transmissions on hand. Easier/faster to just swap out a customers transmission, than to hold a repair bay up while the customers transmission is rebuilt. Maybe one of those shops would be willing to do the swap back to a 9" ext housing transmission, accept your old 9 inch and current 6 inch, plus a little $$$ to get you back to where you really need to be. I am Butch/56sedandelivery.

 

I called all the local transmission shops here. The lowest quote I got to swap the tail shafts from old tranny to new was $275. The lowest quote I got to have the old tranny rebuilt was $900. However, I didn't think to ask if they had one available, nor did they mention if they did either. I might call back and see if I'd get a better deal if I gave them the old one.

 

Clearance is an issue. The longer any item is the more clearance is needs when a pivot point is involved. Look at it this way. Running a longer drive shaft is equal to moving the tunnel in the X frame back 3'' which in return reduces up and down clearance. Don't believe what's said? Try this table top experiment. Take a toilet paper core and a piece of 1/2" pipe some 2 ft. long. Place a piece of masking tape 3/4 x 3/4 on a table, this will be your pivot point or trans yoke. Now run a piece of tape 2 ft long 1" below the imaginary pivot left to right of it. That will be a reference line so you can slide the core tube left and right along the tape. Do this with the core tube at different locations and see how the clearance will increase the closer to the pivot vs further away from pivot point. Then you will see why you need 3'' more of tranny or give your first idea a shot. Life is all about self experimenting to see what works and doesn't. It's called learning and if you can handle a failure, then do your own thing without regret.

 

Makes sense...thanks...though if you read my last post you would know I am going to swap the old tail shaft into the new tranny to bring it back to how it was when I got it. But I do enjoy everyone's input on here. I inherited this car when my Gramps passed away, so there is obviously a lot I don't know of what he did to this car. So far I know it has a 350 engine, TH350 Trans with 9" tail with custom one piece drive shaft. Thank you all for the learning experience and helping me from paying for my failures.

 

Longer yoke will not be as much of an issue if you use a new rear tail shaft bushing. It will tend to wear out the rear seal and bushing on angles that are excessive.

 

All of the X frame Chevies I worked on had the two piece shaft with a center support bearing. I would think a one piece shaft might have a clearance problem similar to a drive shaft tunnel with a long rear end travel. There are a few places that make a heavy duty center support setup for higher HP swaps that have different length shafts available.
The X frames are really flexible and need some serious reinforceing and gussets if you add a lot of power.

 

"Makes sense...thanks...though if you read my last post you would know I am going to swap the old tail shaft into the new tranny to bring it back to how it was when I got it."

Glad to see you have seen the light, and are going this direction. Gramps would be proud!

 

In your mind you've decided that, I guess? All I read into it is that you made some calls, got some prices.