Crewcab LWB to SWB conversion

[2quick4u]

I have an 81 crewcab 3/4 ton LWB and I have an 81 reg cab 1/2 ton SWB on hand (chassis and bed only). My goal is a 1/2, 5lug Crewcab with SWB. I"ve seen several around and know it's been done a lot.
My question is: Cut the crewcab behind the cab and graft on the 1/2 SWB rear section, or shorten the frame of the crewcab and use axles from the 1/2 ton. This will be a daily driver, and will possibly tow a jet boat on occasion. Don't need the load capacity of the 3/4. Fab and machining is not a problem. Just trying to weigh out the merits of each direction. I have the 16 gal fuel tanks, brake lines, etc lined up. I noticed the 3/4 ton chassis is approx 7-1/2 C section, whereas the 1/2 ton is 6-1/2". I plan on boxing the area with either approach.
Ideas? Concerns?

 

[kleedus]

read threw my crew cab build thread I shortened the frame to a short bed and swapped the spring hangers so I could use a 3/4 ton axle

the spring hanger swap is pretty easy and makes it so a 3/4 or 1/2 ton axle will bolt up

I think that would be better than putting two different frames together

there is a link to my build thread at the bottom of my posts

 

[2quick4u]

Well, decided to do the frame graft. Went very smooth, total swap time approx 4hrs.

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[2quick4u]

About to start on the front suspension conversion. Have all the control arms rebuilt, and ready to swap everything out this weekend.

 

[J Knight]

Nice! Got any pics of grafting the 1/2 ton frame to the 3/4 ton frame?

 

[2quick4u]

yes, but forum says files are too big. working on that and will post up. May need to move thread to projects?

 

[MadOgre]

AT 4 hrs I would say you chose correctly

 

[2quick4u]

lol, yes, went much easier than anticipated. Measure twice, cut once. I tried to have everything ready. TIG'd the joint, root, filler and cap in ER70S, went very nice. Fishplate rear plate and boxing interior of frame with MIG. The time includes swapping fuel tanks, and fuel and brake plumbing, but not driveshaft. BTW, I had 3 buddies helping (drinking beer). Don't know if that helped or hurt the timeframe though.

 

[MadOgre]

I think most guys just cut out a section and then push the same frame together, and just swap boxes.

 

[2quick4u]

Update:
Front end conversion 3/4 to 1/2 (2wd)
I was hoping to just swap ball joints and install the 1/2 ton spindles. I know the stems are different. Research on ball joint sizing came up empty. So, I tore it down, looks like the 3/4 lower A arms have a larger diameter mounting hole for the ball joint. Also appears the upper 3/4 is usable with just a ball joint swap. The lower cross shaft diameter is the same from both units, so still moving forward. Current plan is swap to 1/2 lower A arm, and install 1/2 ton upper ball joint in existing upper A arm. I will post exact sizing differences as I get them.
I couldnt find this info while researching, so thought I would post for future reference. I will go over Tie rod differences later.

 

[89Suburban]

Nice work and good info

 

[2quick4u]

Ok, to convert a squarebody frontend from 3/4 ton to 1/2 ton you will need the following:
1. new upper and lower ball joints. I going to 1/2 ton, so I used 1/2 ton joints. Conversion will go either way.
2. lower A arms from a donor 1/2 ton with cross shaft.
3. 1/2 ton spindle, and rotor with bearings.

The lower ball joint mounting boss is larger on the 3/4 requiring the lower control arm swap. The cross shafts (where it mounts to crossmember) are the same, shocks, sway bar, etc., all the same.
Upper control arm requires a ball joint swap only.
Tie-rods are the same between 3/4 and 1/2 tons.
Brake caliper is also the same and does not require any mods.
I went with the 1/2 ton coil spring, because I was lowering anyway, but you have your choice of coil spring, as either will fit, and work correctly.
As I come across anything else, I will post up.

 

[MadOgre]

I have an 81 crewcab 3/4 ton LWB and I have an 81 reg cab 1/2 ton SWB on hand (chassis and bed only). My goal is a 1/2, 5lug Crewcab with SWB. I"ve seen several around and know it's been done a lot.
My question is: Cut the crewcab behind the cab and graft on the 1/2 SWB rear section, or shorten the frame of the crewcab and use axles from the 1/2 ton. This will be a daily driver, and will possibly tow a jet boat on occasion. Don't need the load capacity of the 3/4. Fab and machining is not a problem. Just trying to weigh out the merits of each direction. I have the 16 gal fuel tanks, brake lines, etc lined up. I noticed the 3/4 ton chassis is approx 7-1/2 C section, whereas the 1/2 ton is 6-1/2". I plan on boxing the area with either approach.
Ideas? Concerns?

So I was pretty certain that 1/2 and 3/4 ton frames are identical except for a few bolt on braces. In my experience they measure the same and use the same thickness as well.

I also had the understanding that all crew cabs were 1 tons.

Perhaps a 3/4 ton crew would measure differently then a short regular cab, but I am wondering if that crew you have is a 1 ton and thus the difference in measurements and front end components?

 

[2quick4u]

Dunno. Has C2500 on fender, but also is a "Camper Special" with a 10,000# GVWR. It's titled in Tx as a 3/4 ton.
I'm having zero results in all my research, so I'm posting my findings in case someone else needs the info.
Would my VIN determine if it was hatched as a 1 ton or 3/4? Or does it just go by GVWR? I've noticed some 3/4 tons with a higher GVWR than a 1 ton due to option pkg.

 

[MadOgre]

I dunno. But I was fairly certain that any crew was a 1 ton