3 Speed to 4 Speed Swap Questions - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Hawks · 10-19-2014, 10:52 PM

Hello, been a while since Ive been on here, work takes all my time, Ive been driving my 60 like crazy and getting ready to swap the motor out, (305 done wore the cam down) but i still cant kill it, Been driving it like this for months, it will pop back through the carb at high rpm, So im swapping in a 350 im re gasketing now, I plan to change out the 3 speed OD with a truck four speed, Its a c20 custom camper, Its a wonder i haven't grenaded the little 3 speed with all the abuse it takes, My main question is i now have a one piece drive shaft and i would need a two with the truck four speed, where would i mount the carrier bearing? I don't have a two piece drive shaft in my parts trucks so i may have to make one from a 73-87 truck work, Any info will be great, Thanks

NEWFISHER · 10-19-2014, 11:39 PM

Why a 2 piece? All of the 3 and 4 speeds I have run have used a one piece.

66Submarine · 10-20-2014, 01:19 AM

Quote:

Originally Posted by NEWFISHER

Why a 2 piece? All of the 3 and 4 speeds I have run have used a one piece.

The SM420 truck 4 speed (and others like the SM465, NP435, etc.) does not have the slip yoke on the end of the driveshaft that goes into the trans, so the slip joint has to be in the driveshaft itself.

Hawks · 10-20-2014, 10:50 AM

Quote:

Originally Posted by 66Submarine

The SM420 truck 4 speed (and others like the SM465, NP435, etc.) does not have the slip yoke on the end of the driveshaft that goes into the trans, so the slip joint has to be in the driveshaft itself.

Yep, has to have a slip yoke to make up for distance when the springs are compressed with a heavy load it shortens the driveshaft distance, I'm just not sure where the carrier bearing mounts with the x frame,

66Submarine · 10-20-2014, 09:57 PM

Quote:

Originally Posted by NEWFISHER

Scratching my head...

Check this picture out; no slip joint at the trans.

Quote:

Originally Posted by Hawks

Yep, has to have a slip yoke to make up for distance when the springs are compressed with a heavy load it shortens the driveshaft distance, I'm just not sure where the carrier bearing mounts with the x frame,

Not sure either, but I'd have to guess it mounts inside the "X"? Someone on here should have a picture of the OE setup.

NEWFISHER · 10-20-2014, 10:09 AM

Scratching my head...

10-19-2014, 10:52 PM	#1
Hawks Registered User Join Date: Dec 2011 Location: Floyd va Posts: 80	3 Speed to 4 Speed Swap Questions Hello, been a while since Ive been on here, work takes all my time, Ive been driving my 60 like crazy and getting ready to swap the motor out, (305 done wore the cam down) but i still cant kill it, Been driving it like this for months, it will pop back through the carb at high rpm, So im swapping in a 350 im re gasketing now, I plan to change out the 3 speed OD with a truck four speed, Its a c20 custom camper, Its a wonder i haven't grenaded the little 3 speed with all the abuse it takes, My main question is i now have a one piece drive shaft and i would need a two with the truck four speed, where would i mount the carrier bearing? I don't have a two piece drive shaft in my parts trucks so i may have to make one from a 73-87 truck work, Any info will be great, Thanks

10-19-2014, 11:39 PM	#2
NEWFISHER Registered User Join Date: Sep 2012 Location: Oregon Posts: 3,303	Re: 3 Speed to 4 Speed Swap Questions Why a 2 piece? All of the 3 and 4 speeds I have run have used a one piece. __________________ GOD BLESS AMERICA!

10-20-2014, 10:09 AM	#6
NEWFISHER Registered User Join Date: Sep 2012 Location: Oregon Posts: 3,303	Re: 3 Speed to 4 Speed Swap Questions Scratching my head... __________________ GOD BLESS AMERICA!



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