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1946 3/4 ton flatbed frame substitution?
#1369750 Sun Jul 19 2020 05:49 PM
Joined: Jul 2013
Posts: 133
J
JoeR Offline OP
Shop Shark
I've been slowly working on my '46 3/4 ton flatbed, very slowly. A friend of mine has a 350, 4 bolt, technically he has 3 of them, that he's been telling me would "look great" in the '46. I originally replaced the 216 with a '54 235 and a T5 trans. I keep telling him that I don't think the frame is built to handle that kind of power. Neither was the original breaking system and suspension. Of course his solution was to "upgrade" all those parts. I told him I'm happy putt putting around with it the was it is. And then . . . I came across a late 60s early 70s Chevy 3/4 ton frame, complete that is for sale near me. I've been searching on here to see a/ would it even be possible to swap out the frame, and b/ what kind of time and how complicated would it be?

I haven't looked at the frame yet, but from the photos it seems to be all there, front end, rear end, all the cross members etc. Only thing not there is the motor and trans. From what I've been reading the wheel bases could be anywhere from 115" to 133" depending on what truck it came from, 1/2 ton, 3/4 ton 1 ton and something called the Longhorn version. The original w/b on the '46 is 125".

Anyone out there have any words of wisdom, encouragement or other guidance regarding this idea?

Joe

Re: 1946 3/4 ton flatbed frame substitution?
JoeR #1369751 Sun Jul 19 2020 05:54 PM
Joined: Nov 2005
Posts: 1,368
H
Shop Shark
The width of the new frame will be way wide and your wheels will stick out of the fenders. That is why most use an s10 frame like I did.


Pictures [s300.photobucket.com]
41 Chevy
41 GMC resting peacefully
46/7 Chevy
45 GMC panel truck in line for restoration
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41 Chevy coe in line for restoration
Re: 1946 3/4 ton flatbed frame substitution?
JoeR #1369771 Sun Jul 19 2020 08:20 PM
Joined: Jun 2005
Posts: 773
V
VEW Offline
Shop Shark
I put a 350/700r4 in my 41 3/4 ton. I did put a dual master cylinder on it, with a booster. But it already had front and rear axles from a 59 -12" brakes as I recall.
Never thought the frame was an issue . . . I think it will be around long after I'm gone.
My goal was/is a comfortable road truck able to haul some weight - and stop safely. It runs and stops just fine, BUT, I haven't had it out on the road yet because I need to finish my parking brake system.
You probably know the frame width of a 1/2 ton is wider than a 3/4 ton.
I would say if you're "happy putting around the way it is", leave it the way it is and drive it. You'll know when it's time for a change.
IMO


Victor

41 3/4 Ton Pick Up (in process)
55 Grumman Kurbside (Doughboy) 235/3 on tree w/ OD
57 3100
58 C4400 Viking (Thor)
59 C4500 Short Bus (Magic Bus)
59 G3800 1 Ton Dually (Chief)


Re: 1946 3/4 ton flatbed frame substitution?
JoeR #1369780 Sun Jul 19 2020 08:57 PM
Joined: Feb 2004
Posts: 21,002
H
Boltergeist
Run, do not walk away from that frame swap. Nothing will fit right and you'll end up with another butchered up classic truck that will sit and rot for years and probably never get back on the road. You will contribute to the economy, however, with all the dollars you'll throw away trying to make it work. It will also look funny with the tires stuck way out past the fenders.
Jerry


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: 1946 3/4 ton flatbed frame substitution?
Hotrod Lincoln #1369797 Sun Jul 19 2020 11:08 PM
Joined: Jul 2013
Posts: 133
J
JoeR Offline OP
Shop Shark
Originally Posted by Hotrod Lincoln
Run, do not walk away from that frame swap. Nothing will fit right and you'll end up with another butchered up classic truck that will sit and rot for years and probably never get back on the road. You will contribute to the economy, however, with all the dollars you'll throw away trying to make it work. It will also look funny with the tires stuck way out past the fenders.
Jerry

Hey Hotrod,

Thanks for the advise. I'm an old guy so I think I'll stick with the old school frame. I was thinking about a disk brake swap but I can't find any 8 bolt systems. I've found 14 bolt rears with disks, but I'm guessing the front conversion won't be that easy. Maybe a new master cylinder with dual systems and some decent drums and shoes will be sufficient to stop it with the 235. I found an Offy intake manifold with 3 ports for single barrels online. That may give it a little more juice. I also think I've located a 14 bolt Corporate rear end with a 3.73 final drive. That should allow me to get on the freeway, at least in the slow lane. Which, after this covid mess, is just about every lane on California freeways.

Joe

Re: 1946 3/4 ton flatbed frame substitution?
JoeR #1369803 Sun Jul 19 2020 11:50 PM
Joined: Feb 2004
Posts: 21,002
H
Boltergeist
Welll- - - - - -you'll only have two too many carburetors that way, and an engine that won't perform anywhere except wide open throttle- - - - -better invest in a transmission with a lot of gears so you can run it wide open all the time regardless of road speed. Maybe put a 3 speed Brownie behind that T-5 so you'll have 15 gears. Somebody just started producing a disc brake conversion for a 3/4 ton with 8 lugs- - - - -I believe it uses discs and calipers for somebody's 8 lug rear end with some special adapters to mount the calipers to the front axle.
Jerry


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: 1946 3/4 ton flatbed frame substitution?
JoeR #1369805 Mon Jul 20 2020 12:09 AM
Joined: Jul 2013
Posts: 133
J
JoeR Offline OP
Shop Shark
LOL Jerry,

and here I thought you couldn't have too many carburetors :-) I found a company called Lugnut 4x4 that produces an 8 lug conversion kit for '76 - '97 Chevys. I wrote to them to see if they had any recommendations for a '46. I've also found some Chevy frames for sale on the ol' interweb but so far no 8 lug units.

Re: 1946 3/4 ton flatbed frame substitution?
JoeR #1369810 Mon Jul 20 2020 02:06 AM
Joined: Feb 2004
Posts: 21,002
H
Boltergeist
It would take me about 4 hours to fabricate a set of disc caliper brackets for your front axle. I've done similar things on round track race cars for 30+ years when no exact brackets exist for a particular application. Find a disc that fits your hub, use air pressure to clamp the caliper onto the disc, and fabricate whatever brackets you need to make the thing work, using the bolt holes in the spindle where the drum brake backing plate would usually mount.

I had a friend in high school who managed to fit three Stromberg 97 2-barrels onto a 51 Chevy 216. He never made it to the road since his driveway was slightly uphill. The car caught fire twice from lean backfires. He went back to a single carb after that fiasco!
Jerry


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: 1946 3/4 ton flatbed frame substitution?
JoeR #1370013 Tue Jul 21 2020 03:01 PM
Joined: Jul 2013
Posts: 133
J
JoeR Offline OP
Shop Shark
I think I may have found an outfit that makes an 8 lug conversion set for the '47 and up fronts. I'm looking at the service manual for both and it looks like they have similar mounting points for the bracket. The shop I work at does a lot of fabricating so if their bracket doesn't fit I'm pretty sure I can make one. I've also looked at some boosters that fit under the cab on the frame. Any suggestions or recommendations on those?

Joe

Re: 1946 3/4 ton flatbed frame substitution?
JoeR #1370025 Tue Jul 21 2020 03:55 PM
Joined: Feb 2004
Posts: 21,002
H
Boltergeist
The under-floor master cylinder used with most 1/2 ton conversions won't have enough volume to work with 3/4 ton components. Make sure the master cylinder can move enough fluid to get all the brakes applied without running out of pedal stroke. Those tiny booster diaphragms are also short on power- - - -they're better than no boost at all, but not by much. I'd choose a firewall mounted booster with a big enough diaphragm to get the job done and a larger-bore master cylinder.
Jerry


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
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