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| | | | Joined: Feb 2017 Posts: 43 Wrench Fetcher | | Wrench Fetcher Joined: Feb 2017 Posts: 43 | Anyone out there changed a 3/4 ton to open driveline? I have a 1940 Chevy 3/4 ton with 1957 235. Trans appears to be original 3 speed. The torque tube has 2 ball joints. The chassis is 10 inches longer than 1/2 ton. Can I run a one piece open driveline? | | | | | Joined: Mar 2011 Posts: 1,146 Shop Shark | | Shop Shark Joined: Mar 2011 Posts: 1,146 | Yes you can but you would have to change the transmission and rear axle to accept a open drive shaft.
Heavy modifications.
| | | | | Joined: Feb 2017 Posts: 43 Wrench Fetcher | | Wrench Fetcher Joined: Feb 2017 Posts: 43 | I'm thinking about auto trans. and a rearend from a later open drive truck. I want to keep my 6 lug wheels. | | | | | Joined: Jan 2017 Posts: 37 'Bolter | | 'Bolter Joined: Jan 2017 Posts: 37 | Crowejam- When I changed my '52 3/4 ton GMC from half and half, to open driveline (taken from a '59 1 ton Chevy), I had my SM420 rebuilt as well. No comment on the auto trans, but not too long after the driveline change, I ditched my 4.57 for a 4.10... It's nice! Unless I'm mistaken, 6 lug wheels aren't normal for a 3/4 ton.
Jorb- Agreed! I thought about a 1 piece driveline, but when I discovered how much it would cost, I kept my 2 piece setup.
Last edited by Baronobeefdip; 04/08/2017 7:52 AM.
| | | | | Joined: Feb 2017 Posts: 43 Wrench Fetcher | | Wrench Fetcher Joined: Feb 2017 Posts: 43 | I have to change transmissions anyway if I go with open driveline because I'm told there is no way to convert my 3 speed. I'm pretty sure my 6 lug 15 inch wheels are original. I think the 1/2 ton has 5 lug. | | | | | Joined: Mar 2004 Posts: 6,228 'Bolter | | 'Bolter Joined: Mar 2004 Posts: 6,228 | 6-Lug = 1/2 ton 8-Lug = 3/4 & 1 ton Mike B  | | | | | Joined: Jun 2011 Posts: 5,096 Crusing in the Passing Lane | | Crusing in the Passing Lane Joined: Jun 2011 Posts: 5,096 | Some GMC 1 tons came with 6 on 7.25 artillery wheels.
Ed
'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires.
'47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle.
'54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed.
'55 GMC 370 w/270, 420 4 speed, grain, dump bed truck from ND. Works OK.
| | | | | Joined: Feb 2017 Posts: 43 Wrench Fetcher | | Wrench Fetcher Joined: Feb 2017 Posts: 43 | 1940 3/4 ton is 6 lug. There is also a 3/4 ton Special which was the heavy duty 3/4. Maybe it had 8 lugs but the standard 3/4 has 6. | | | | | Joined: Jun 2016 Posts: 236 DLBrooks | | DLBrooks Joined: Jun 2016 Posts: 236 | If 6 lug, you might use a 12 bolt from a 67-70 or 8 lug use a srw 14 bolt. I used a 70's srw in the 46 3/4 ton - 3.73 gear behind the 54 235 with a 4 speed crash box from a 41 1 1/2 ton dump. I believe the 46 3/4 had a 4 speed enclosed on first half and open on second to rear diff. pre 47 3/4 rear drums are hard to come by. The 41 dump 4 speed was open on both halves. Had to move perches and shock mounts on both.
My 46 3/4 ton had 8 lug wheels oem.
I have a 12 bolt ready to go - already set up for a 46 3/4 ton, but is a long drive from Oregon to Cincy. 8-)
Last edited by 42465967; 04/09/2017 9:58 PM.
| | | | | Joined: Feb 2017 Posts: 43 Wrench Fetcher | | Wrench Fetcher Joined: Feb 2017 Posts: 43 | Thanks for the info. I'm still in the "thinkin bout it stage" but every time I get on here I learn more.
Jim | | |
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