Projects TH350 Swap Question for 58 Chevy

I have a '58 Chevy Del-Ray I inherited from my Grandpa before he passed away. Recently the transmission went out. Luckily my grandpa must have known about it, because he had a rebuilt one in the trunk. My issue is that the old one is a TH350 with 9" tail shaft and the new one has a TH350 6" tail shaft. Will I need to get my driveshaft lengthened/replaced or do I just need to find a longer yoke?...or will the 3" difference not be an issue?

 

will need to be lengthened

 

^^^x2, unless you can swap out tail sections of trans. I have never done it so I don't know.

 

I would want to be 100% sure that the shorter tranny is rebuilt before getting a new driveshaft made. There may be a few other minor differences like cooling line locations. The cost of a re-built tranny might not be in your budget, but the time and cost to make the necessary changes should be considered.

 

the tailshaft housing and output shaft of the transmissions can be swapped....but i believe they have to come completely apart to do so

the housing is simple, just four bolts.....but the output shaft needs to out through the inside of the case

 

I would guess the cost of the new drive shaft or rebuilding your trans are pretty close. There is a guy by me that will rebuild a TH350 for about $650. (You r/r) That way you know what you have for sure. Current guarantee ect. You put in a different trans and a new drive shaft and have a vibration you might go nuts until you figure it out. Just my thoughts.

 

I'd buy a gasket set and pull the transmissions apart and swap the output shaft. But I'm abnormal.

 

I altered the wheel base on a 54 Chevy truck after a trans swap once.

 

Ok well I opened up the rebuilt tranny, and it was indeed rebuilt and clean. The cooler lines lined up perfectly and the tranny is fully installed minus the tranny mount and driveshaft install, which I intend to do this morning. I guess I will first see what my drive shaft gap will be, take measurements, then probably go the route of buying a longer yoke as it seems to be the easiest and cheapest route.

 

Do they really make them three inches longer? Interesting....but I'd still want to put the correct driveshaft in it.

 

Yes they have quite a variety of yoke lengths for TH350 and other transmissions, this way I keep my original shaft and not have to worry about balance issues.

 

Speedway has slip yokes for the th350 in stock length , 1/2 " longer , 1-3/4" longer and 2-1/2 " longer

never tried one. i may be wrong, the extra length sticking out doesn't give me a good feeling

 

Make sure you seat the torque converter properly. Be a shame to mess up a new trans. The longer yoke does seem a bit wonky to me too, but what's the difference in using a longer driveshaft? Six of one, half-a dozen of the other.

 

A 3" longer yoke would scare me too. That is a lot of yoke sticking out the back. I would get a longer driveshaft.

 

I wouldn’t say your abnormal, rather very talented! I’m not that talented, but there are guys that would do that very reasonably.


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Do yourself a favor with your decision. Be sure the bushing in the tail housing that the yoke rides on is good and or replace it so the longer yoke won't dance around so much. Good Luck

 

^^^^that explains why a longer driveshaft could be a better choice.

 

Don't go with a longer yoke, it places the U joint too far from the end of the output shaft. It magnifies any loose tolerances with the yoke and output shaft, so the U joint will do orbits around the trans centerline, instead of spinning on the centerline, if that makes any sense. This will cause a vibration, maybe not right away, but it will happen with just a little wear on the tail shaft bearing. Change the trans output shaft or get a longer driveshaft.

 

B ad idea with longer yoke. The correct way to do it is remove the yoke from the driveshaft and insert into trans until it stops. Slide yoke out about 1/2''. With the car sitting on all 4 tires measure from the center of the u-joint caps front to rear. This will give you the length you need.

 

Hmm ok, well I haven't done or bought anything yet...right now I am gonna put in the driveshaft and see what the gap length is.

 

Well the yoke is exactly 3 inches off when fully inserted to the tranny, but when I seat the shaft to rear axle, the yoke does insert into the tranny about 1/2 an inch. My dilema is, how do i get the drive shaft out (X-body Frame). Do I really have to take the tranny back out?

 

i have never done it, but can the shocks be disconnected so the rear drops? or can the rear be jacked up to allow the shaft to slide under?

 

Measuring from weld point to weld point on the shaft its approx 52 inches long, I guess I need to research if a 3 inch longer one exists, or if its cheaper to take it to get extended.

 

After you remove the U joint bolts to the rear end, take a pry bar and pop the U joint away from the rear end. Then just pull out the driveshaft either under or over the rear end, left or right of the center of the rear end.

 

Not sure what cost are in your area, but last year I had a driveshaft made 60 inches long, 3inch diameter, I supplied the ends, for $125.00.

 

It would probably have been simpler and less expensive to swap the tail shaft. You would have to have taken both transmissions apart to do it though.
Do not use a long yoke in hope of fixing it or you will end up knocking the rear bushing out of the trans and possibly break the tail shaft. Been there done that.
you can't add a piece in the front half of the driveshaft to lengthen it but you can take it to a driveshaft shop and have a new tube put in to get the right length. Since you have or can easily have the exact difference in length of the tail shafts getting the right measurement is a non issue.
On getting the driveshaft all the way out it, if I remember right it helps if you put a jack under the rear axle and raise it up so the shaft will pull out under it.

 

Got me lost. You talk like you had the shaft out with the trans swap, but then you ask how to get it out?
In any case , you just unbolt the center support from the frame and pull the whole thing out. Actually easier in some cases, because it flexes in the middle.

 

I forgot about the two piece shaft in those years so only the front portion needs attention.

 

Just curious; does the car still have the two piece driveshaft? I wonder if Gramps used the longer 9" extension housing TH350 in order to swap to a one piece driveshaft? It would help with the geometry to use the longer TH350, getting the end of the transmission out past, or closer to, the "X" frame/bearing support. Just a guess on my part. I am Butch/56sedandelivery.

 

Well mine must be custom cause it is one piece, and the X-body frame is a complete tunnel around it. I tried everything besides unbolting the shocks and dropping the rear.