Brothers 1973-87 Longbed To Shortbed Conversion Kit Part 1

Part 1: Chopping the Frame on a ’73-87 Long Bed Square Body Chevy Truck

By Rob Fortier – Photography by the Author

For starters, don’t get me wrong, long bed pickup trucks are cool. They definitely have their purposes, plenty of devout fans, and are an important staple in this great hobby of ours. That said, the first thing I’d do to any non 4×4 or full utility old truck is cut it down to a short bed! And to all the complainers crying “just go find an SWB to begin with,” well, let me just remind you of the current surplus versus value (there are plenty of decent and affordable LWBs available, while the same cannot be said for their SWB brothers!). I will get off my preferential soapbox now and carry on with the story at hand.

02 The finished product of shortbed conversion kit
After.
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In 2017, Brothers Trucks came out with their flagship long bed frame shortening kit for the ’63-72 GM trucks—and it instantly became popular, due not only to how amazingly affordable it is ($469.99) but because of how extremely easy it is to use and, ultimately, shorten your light- or heavy-duty 2WD chassis … without fear of f’ing up!

03 Here_s what you need for the short bed conversion kit
“Fourteen inches is all it takes …” Yep, that’s the difference between your standard long wheelbase (LWB) and a short wheelbase (SWB) ’73-87 GM pickup … and for under $500, Brothers Trucks has the goods in which to make that 14-inch magic happen! Follow along as we first document the frame shortening procedure at Brothers’ Tech Center, followed next month by the in-depth bedside shortening procedure..

Brothers Trucks accomplished their “failsafe” aspect by developing a one-time-use, dual-purpose frame rail drilling and cutting guide that gives the user little room, if any, for error. In short (no pun intended), the guide or template, as it were, is used as a metal miter box to first remove the “long box” section of frame forward of the rear axle and just aft of the rearmost cab mounts, and then the remaining section from the tail end of the frame rails. It’s also used to mark and drill the required holes for installing the frame-gusseting C-channel supplied with the kit as well as the relocation holes for the rear bumper.

04 removing the long bed off our 1976 C10
We’ll skip the photographic formalities of removing the bed but will point out the following: one, disconnect all electrical wiring; two, disconnect the fuel filler/vent; three, pre-soak all the bed-to-frame hardware with a good penetrant before removing.
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Five years later and the obvious has transpired—Brothers has finally developed and released their follow-up: the ’73-87 Squarebody truck LWB to SWB Conversion Kit. It should come as no surprise that it’s just as easy and affordable as their earlier model version … we know because we were right there as they reduced this one family owned ’76 Chevy!

05 Next, level the the long bed truck on four jack stands
In preparing the chassis for its pending surgery you’ll need to remove the following: fuel tank, exhaust (from the cab back), rear bumper, and driveshaft. Bundle the taillight harness up out of the way as well (it does not need to be trimmed). Next, level the the long bed truck on four jack stands—“without” putting the frame in a bind or under a load!

Read More: The Perfect C10 Combo!

This month we’ll cover the chassis reduction process as well as a variety of incidentals related to such. Next month, as an option to simply purchasing Brothers Trucks shortbed Fleetside bed panels and bed floor (the easiest way to finish up the job if you’re not concerned with “patina matching!”), we’ll show you how to cut down your existing longbed Fleetsides and pair them up with a new bed floor and your stock tailgate and front bed panel. Stay tuned!

06 you’ll need to remove the two factory rivets attaching the exhaust bracket on your 73-87 GM truck
In preparing the frame rail itself you’ll need to remove the two factory rivets attaching the exhaust bracket on your 73-87 GM truck (and the bracket as well, which you’ll put aside for future use). Straighten any imperfections in the upper/lower ’rail section carefully with a large crescent or hammer and dolly.

07 Straighten any imperfections in the upper_lower ’rail section carefully with a large crescent or hammer

08 The supplied Brothers cutting guide will fit over the frame rail
The supplied Brothers cutting guide will fit over the frame rail, forward of the front leaf spring hanger bracket, butting up against the rear cab mount rivets, as shown. Align your main (larger) number one guide hole in the center.
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09 Align your main (larger) number one guide hole in the center

10 Start your drilling sequence with the smaller number one pilot holes
Start your drilling sequence with the smaller number one pilot holes, then open each up to the corresponding bolt size (7/16) and secure with the supplied hardware.
11 The number two holes will follow the same process—with the exception of the hardware
The number two holes will follow the same process—with the exception of the hardware, as these holes are specifically for the C-channel you will be installing shortly. Follow the directions closely for bolt/hole sizing.

12 Follow the directions closely for bolt_hole sizing

13 When all is said and done, this is what you should_will be looking at
When all is said and done, this is what you should/will be looking at.
14 Dave here likes to use his thin-bladed cutoff wheel
After completing the drilling process (one and two), break out your favorite—and most accurate—cutting device. Dave here likes to use his thin-bladed cutoff wheel; a Sawzall will suffice as well. While a plasma cutter will do the job, unless you’re using a high-capacity machine, we don’t recommend it.
15 Cut the frame using the forward “3 CUT” guideline
Cut the frame using the forward “3 CUT” guideline, making sure the rear of the chassis as well as at the cab are still well/safely supported.
16 Finish up the cutting the long bed
This is what you’d call the point of no return!
17 Dress each cut portion of the frame where you cut, providing a nice 45-degree bevel for the weld bead
Now you can finish removing the 14 inches of frame section by cutting through the template at the rearmost “3 CUT” guideline.
18 Check fitment of the supplied C-channel on both halves of the frame
Dress each cut portion of the frame where you cut, providing a nice 45-degree bevel for the weld bead that will soon rejoin the two halves back together as one.
19 Keeping the wheels attached to the rear end makes the job so much easier!
Check fitment of the supplied C-channel on both halves of the frame prior to rolling the back half back up to align with the front section.
20 With the two halves butted up together, start by installing the C-channel into the front section of the frame
Keeping the wheels attached to the rear end makes the job so much easier! The rejoining process is now about to begin.
21 Adjust the sections of frame until the holes you previously drilled align with the holes in the C-channel
With the two halves butted up together, start by installing the C-channel into the front section of the frame—use a block of wood and hammer to help coerce. (Notice the frame bowing out on the bottom edge on the passenger side—this was/is due to the lack of carrier bearing crossmember. Once the C-channels are installed, the ’rails will square back up!)
22 Next carefully drive to a shop to be professionally welded
Adjust the sections of frame until the holes you previously drilled align with the holes in the C-channel. Do NOT use a drill to open up any misaligned holes; as the hardware is installed and tightened, use a punch to assist with hole alignment.
23 Completely weld (or, as mentioned above, have it professionally welded) from top to bottom, as shown
Technically, as long as everything’s with just the hardware and C-channel installed, your frame is strong enough to be driven (carefully) to a shop to be professionally welded—either way, we’re now ready to move onto the final “major” portion of the procedure.

24 make sure the weld fully penetrates from the outside frame rail surface all the way to the underlying C-channel

25 weld the lower horizontal edge of the C-channel to the frame lip for added strength
Completely weld (or, as mentioned above, have it professionally welded) from top to bottom, as shown. MIG or TIG, whichever is your preferred metal-fusing poison—just make sure the weld fully penetrates from the outside frame rail surface all the way to the underlying C-channel.

26 make sure the weld fully penetrates from the outside frame rail surface all the way to the underlying C-channel

27 weld the lower horizontal edge of the C-channel to the frame lip as well for added strength
For additional strength and peace of mind, Dave likes to weld the lower horizontal edge of the C-channel to the frame lip as well.

28 C-channel to the frame lip is welded

29 use the remaining section of the template to shorten the rear frame horns down accordingly
OK, now that the meat of the LWB has been reduced to SWB dimensions, use the remaining section of the template to shorten the rear frame horns down accordingly. Simply follow the cut guidelines …
30 on the rearmost end of the frame, it relocates in the SWB holes already in the frame
… and set the corresponding piece (DR for driver side, PA for passenger) on the rearmost end of the frame (at this point, the rear crossmember had already been removed—it relocates in the SWB holes already in the frame). Scribe the edge closest to the rear end and mark your new bumper bracket holes, then …

31 Scribe the edge closest to the rear end and mark your new bumper bracket holes

32 cut off the extra 6 inches of framehorn
… off with the extra 6 inches of framehorn!

33 clean up the aftermath of the cut

34 Drill out the holes you just marked for your rear bumper
Drill out the holes you just marked for your rear bumper (now as opposed to later due to the bed preventing good drilling access once it’s reinstalled).
35 Using the supplied hardware, relocate your rear crossmember in the two aligning holes
Using the supplied hardware, relocate your rear crossmember in the two aligning holes situated in the middle of the rear leaf spring hanger bracket, as shown.
36 Regardless of whether your truck has a one- or two-piece driveshaft, have it “professionally” shortened
Regardless of whether your truck has a one- or two-piece driveshaft, have it “professionally” shortened (and balanced, with new U-joints if yours show any signs of age/wear) the exact same amount you just shortened the frame: 14 inches!
37 you’ll need to use an SWB tank, such as the one shown from Brothers
As for your fuel tank, if you prefer to stay with the OE saddle-style tank, you’ll need to use an SWB tank, such as the one shown from Brothers (not included in kit). Otherwise, you can figure out an alternative fuel supply option, such as an aftermarket aluminum one to mount in the rear of the frame. (Brothers does include an SWB rear brake line as well as the correct-length parking brake cable!)
38 The short bed conversion is done for now
And that’s a wrap for the frame portion of the Squarebody shortening. Next month, Dave will show you how to cut down your factory LWB bedsides and, using a new floor from Brothers, complete the job 100 percent!

39 The 73 C10 has now officially been shortened

Ready For More: Part 2 Found Here!!!

Brothers Trucks
(800) 977-2767
brotherstrucks.com

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