Transmission Choice.............. - The 1947 - Present Chevrolet & GMC Truck Message Board Network

HiLift · 04-26-2005, 12:16 PM

Hello All!!
Finally had my '50 3/4 ton Chev and '51 1/2 ton GMC delivered this past weekend.

After much contemplation, bending over, rubbing my chin and beer drinking, I finally came up with a couple of questions.

I'm gonna take the cab off of the 3/4 ton and place it on the 1/2 ton frame.

The 3/4 ton has the four speed tranny, the 1/2 ton came with the three speed.
Can I place the 4 speed into the 1/2 ton frame? Should I? Are there any advantages to this swap?

Is there anything else mechanical I should salvage from the 3/4 ton for my project?

Thanks Guys!!

Fred T · 04-26-2005, 01:16 PM

Tranny will swap, but I'm not sure about the driveshaft. Is the GMC an open driveshaft? The Chevy 3/4 should have a driveshaft that is closed on the front end, open from the carrier bearing aft. Also, length will be a problem is the GMC is a short bed.
http://www.oldgmctrucks.com/

HiLift · 04-26-2005, 02:16 PM

Hey Fred!
Thanks for the response.
The 1/2 ton has the torque tube, closed driveshaft that is common with this model.
The 3/4 ton is as you say. Closed from the rear of the tranny then open from the carrier bearing to the differential.
Even if the transmissions were the same length is there an advantage for doing this? I know that in top gear both will be 1:1 ratio so no gain there but does it help in mid gears/speeds?
Was not the 4 speed an extra cost option for the 1/2 tons?

Fred T · 04-26-2005, 06:52 PM

Yes, the 4 speed was an option. What I don't know is if you can swap the bell on the trannys. I know the u-joint is different. The 4 speed has lower gears for 2nd and 3rd than 1st and 2nd for the 3 speed. For daily driving I would actually prefer the 3 speed.
3 speed ratios 2.94, 1.68. 1.00
4 speed ratios 7.06, 3.48, 1.71, 1.00

HiLift · 04-27-2005, 09:16 AM

Excellent response Fred, just the info I was looking for!!
Looks like I'll graft the three-on-the-tree into the 3/4 ton cab.
Thanks Fred.

Just noticed the ratio for first on the 4 speed - - Truly a stump puller!!!

3100 special · 04-30-2005, 11:04 PM

Welcome to the board!
Good luck on your project!
Jon

04-26-2005, 12:16 PM	#1
HiLift Registered User Join Date: Jan 2005 Posts: 3	Transmission Choice.............. Hello All!! Finally had my '50 3/4 ton Chev and '51 1/2 ton GMC delivered this past weekend. After much contemplation, bending over, rubbing my chin and beer drinking, I finally came up with a couple of questions. I'm gonna take the cab off of the 3/4 ton and place it on the 1/2 ton frame. The 3/4 ton has the four speed tranny, the 1/2 ton came with the three speed. Can I place the 4 speed into the 1/2 ton frame? Should I? Are there any advantages to this swap? Is there anything else mechanical I should salvage from the 3/4 ton for my project? Thanks Guys!!

04-26-2005, 01:16 PM	#2
Fred T Cantankerous Geezer Join Date: Aug 2002 Location: Bel Aire, KS Posts: 6,264	Tranny will swap, but I'm not sure about the driveshaft. Is the GMC an open driveshaft? The Chevy 3/4 should have a driveshaft that is closed on the front end, open from the carrier bearing aft. Also, length will be a problem is the GMC is a short bed. http://www.oldgmctrucks.com/ __________________ Fred There is no such thing as too much cam...just not enough engine.

04-26-2005, 06:52 PM	#4
Fred T Cantankerous Geezer Join Date: Aug 2002 Location: Bel Aire, KS Posts: 6,264	Yes, the 4 speed was an option. What I don't know is if you can swap the bell on the trannys. I know the u-joint is different. The 4 speed has lower gears for 2nd and 3rd than 1st and 2nd for the 3 speed. For daily driving I would actually prefer the 3 speed. 3 speed ratios 2.94, 1.68. 1.00 4 speed ratios 7.06, 3.48, 1.71, 1.00 __________________ Fred There is no such thing as too much cam...just not enough engine.

04-30-2005, 11:04 PM	#6
3100 special Street Rod Dreamin' Join Date: Feb 2004 Location: Work:Batam, Indonesia/ Home:League City, Texas Posts: 1,241	Welcome to the board! Good luck on your project! Jon __________________ 1954 Chevy 3100 Panel Truck 2004 GMC Yukon 2007 GMC Sierra 4X4 "I am for doing good to the poor, but I differ in opinion of the means. I think the best way of doing good to the poor, is not making them easy in poverty, but leading or driving them out of it." Benjamin Franklin, On the Price of Corn and Management of the Poor, November 1776

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04-26-2005, 02:16 PM	#3
HiLift Registered User Join Date: Jan 2005 Posts: 3	Hey Fred! Thanks for the response. The 1/2 ton has the torque tube, closed driveshaft that is common with this model. The 3/4 ton is as you say. Closed from the rear of the tranny then open from the carrier bearing to the differential. Even if the transmissions were the same length is there an advantage for doing this? I know that in top gear both will be 1:1 ratio so no gain there but does it help in mid gears/speeds? Was not the 4 speed an extra cost option for the 1/2 tons?

04-27-2005, 09:16 AM	#5
HiLift Registered User Join Date: Jan 2005 Posts: 3	Excellent response Fred, just the info I was looking for!! Looks like I'll graft the three-on-the-tree into the 3/4 ton cab. Thanks Fred. Just noticed the ratio for first on the 4 speed - - Truly a stump puller!!!



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