Driveshaft questions.

[brimac50]

Trucks having TH400's usually have 2 piece driveshafts with a bolt-on yoke at the transmission. The needed spline slippage is in the 2 piece design.   What is the set-up for trucks having a Th350 and a 2 piece driveshaft?   If they use a slip yoke, at the transmission,  is that 2 piece driveshaft designed "solid' or for no slippage,  since the slippage occurs at the yoke?   Basically, does each transmission require a different driveshaft?

Also, if I wanted to use a car TH400, designed for a slip yoke, (without provisions for the bolt style),  in one of these trucks, ......  what modifications /parts would be needed for success.  Any specifics, such as donor vehicles for parts etc, would be helpful  Thanks for the info. I'm trying to get familiar with these trucks,  and assume nothing.

[Irish_Alley]

no 2 piece will slip at the yoke for the transmission but at the joint were the two halfs meet. and they should require a different shaft due to the different transmission lengths. not really sure what your asking about the second question or first but are you asking can you use a two piece shaft for a transmission thats originally a one piece? if so yes you can no mods needed just make sure its the same spine count. Or are you asking can you drill and tap the tail shaft so you can put in a bolt in it for a shaft slip style shaft?

[brimac50]

Irish_ Alley,     Thanks for the response.  I'll try to clarify my questions.   

1).  Is it possible to use a 400 trans, (w/no bolt provision for yoke,  in an 80' 3/4T with the original 2 piece (slip together) driveshaft?  Besides, drilling and threading the output shaft,  on the trans, ... is there any other way to make it work, including modification to the driveshaft?   I'm assuming that drilling by hand, with a fully assembled transmission, is not possible. Am I right or wrong?

2).  With this same model truck originally equipted with a Th350 trans, ... would that have used a bolt-on yoke also, or a slip,  with the two piece driveshaft?  If a slip,  what are the differences between the 350 and 400 driveshafts, besides spline count and maybe length.

Thanks again

[Irish_Alley]

Still confused as heck lol. But you can take the yoke off one drive shaft and mate it to another drive shaft that being said you can take the 350 bolt on yoke and swap it with the 400 slip yoke. My 350 was a slip one piece I swapped it with a 2 piece slip. If I can remember right the tail shaft on mine was drilled but I didn't use a bolt on yoke

[brimac50]

Sorry for the confusion.  My current set up is: Th400, bolt-on yoke & 2 piece driveshaft,w/center support bearing.  I might replace the current transmission with another 400 having no bolt hole.   If I switch the bolt-on yoke with a slip yoke, .....  will I be good to go?

Could not using a bolt-on yoke, create any problems?   

Thanks

[Irish_Alley]

 Ok. Yes you will be good. Once you put the new shaft in Jack the frame up to Max out the leafs and you should have more than a inch left of the tail shaft still I'm the yoke you will be good

[brimac50]

Now,    I'm a bit confused.  Wouldn't raising the chassis,  only  cause the splined connection, of the 2 piece driveshaft, ... to move, and not the yoke?    The center support bearing is pressed onto the front shaft, and bolted to the frame. That should restrict most movement of the front shaft & yoke, I'd imagine. 

 However,  the center support bearing is seated in a rubber gasket, so there is not a 100% solid connection to the frame. In theory,   that slip yoke could "walk"on the transmission spline,  .... if force is applied to the support bearing's rubber gasket,  .... as the driveshaft spins.  That's my concern.  I'm trying to determine if replacing the bolt-on with a slip yoke, and using the 2 piece driveshaft,...could cause any problems, like vibrations. 

Have you, or any of your friends,  successfully used a slip yoke with a 2 piece driveshaft?    I'm trying to do my homework up front, so I won't have any surprises.  Thanks again.

[Irish_Alley]

Yes my 2 piece was a slip yoke well it wasn't bolted to the output shaft and the second piece of the shaft after the bearing would slip. We actually made a longer shaft by sliding most the yoke off the splines. We had to make it longer cause I went from a long tail 350 to a short tail