'72 C3500 GMC flatbed project

[JJorgensen52]

Today had much nicer weather than anticipated, so I started tearing down the '72 rather than wasting the sunlight blasting in the garage.

Here's where I started


First off came the side boards, rear deck, and lift frame/hydraulics



Then went the front clip



I knew this truck was clean, but I was still floored when I pulled the fenders. I'm just stunned, this is a lifetime Massachusetts/ New Hampshire truck, I've no idea how the cowl vents are so perfect!



And this will be coming on out tomorrow, provided the weather is nice. I have most of the week off


The basic plan of attack is that once I finish blasting, priming and painting all the frame bits and the axles, I'm going to strip this frame down, prime and paint, then build it back up with the new parts. Once that's done, the engine (which I'll clean and paint while it's out) goes back in, and it's getting a new front clip, rocker shells, driver's kick panel and a partial cab corner on the passengers side. Then on to paint!

Also, I figured you guys might appreciate a peek at this. Everybody is always telling me I can't change the door lettering on this truck (which is awesome vintage), but the folks I'm doing the build for want it re-lettered for their farm. I went ahead and drew up the concept sketch for them Saturday, and I've got the go ahead to lay it out on the doors once the paint is on.

As you can see, I'm still in the midst of digitizing my pencil sketch, then I'm planning to project it onto the doors (which also allows me to mirror the dog to face forward on both sides)

[JJorgensen52]

More progress. Cab is off, motor is ready to come out:

I made a support board out of some 2x6 sandwiched together and then several more pieces running front-back, so the load of the hoist was essentially distributed across the entirety of the roof, and is not touching the doors.

I lifted it 100% complete. The only thing not in the cab was the shift boot, and it had probably 60% of a tank of gas.



Tomorrow I'm pulling the motor out and then I'll work on getting the suspension free of the chassis so I can roll it out and put the new rolling stock underneath. I'm supposed to get rain Wednesday and Thursday so I will be cleaning and rebuilding the axles indoors that day, and probably painting the engine and bolting up the new trans / t-case



And rather than double posting, here's a link to a separate thread I just posted for the hydroboost modification / install I'm doing:

[JJorgensen52]

Pulled the engine out, divorced it from the trans, and pulled the front suspension today. My camera was MIA until this evening, so no photos there.

Once I got the front of the frame bare, I started work on installing the new motor mounts. Immediately two things became obvious:
1. The '87 frame is 1/2" taller than the '72 frame where the motor mounts sit
2. The '87's frame is asymmetric at the front cross member

So, with those bits of info I set about shortening the motor mounts.



I admit, not my prettiest welding by a long shot, but it's strong and that's more important at the moment. I haven't done an sort of cleanup either.

Got it all set in the frame and clamped in place



You can just see in the second photo the passenger's side front of the engine cross member is not touching the frame - this is where the asymmetry of the '87 frame became a problem. I cut and reshaped the end of it, accordingly:


Of course, not one single hole on the lower frame rail lines up properly. Oh well, I've got some drilling, filling and grinding to do.

Also test fit a front spring hangar


I had measured the rivet pattern and it looked the same, but it turns out the rivet heads aren't always centered over the holes, so it's a little bit out. When I re-drill the holes for the 7/16" bolts, this will all wash out.

You may also have noticed I have a ratchet strap across the front of the frame - turns out, when I removed the front cross member the rails sprang apart a bit, about 3/4" - I was quite surprised by that!

[JJorgensen52]

Not much progress today, slow going in this phase but I think things will be picking up soon.

Got both front spring hangars temporarily mounted (interestingly, on the passenger's side 3/4 holes line up, but on the driver's only 2/4??). This allowed me to located the front axle and then use it to reference the front cross member and get an idea what I need to do to install the rear shackles.


Springs landing on the frame to show where the shackles will go


Mostly mounted up. Had a bit of trouble getting my drill marks in the right place on the outside of the frame, but I've got a good method now and it's going smoothly.


You can see both the front and engine crossmembers were modified at the passenger's end, the frame profile is slightly different than the '87.

I think, after going through this, that it's not terribly difficult if you have a little bit of fab skill, but the front swap would be vastly easier using a '67-'72 K20 donor, as the frame components are the same in the front between 20 and 30 series trucks. That would solve all of the fitment problems I've had and make this a pretty straight forward swap.

[7dee2]

Wow, excellent progress! What a clean old truck must have never been parked under a tree.

[JJorgensen52]

Thanks!

Today, I got slowed down a bit but I did get the front shackle hangars mounted.




I also got the engine, front cross member, and engine pads drilled and fully mounted.


I decided to use the hangar section of the '87 frame as a reinforcement plate, rather than attempting to create a neat filler for the area I had to cut out where the parking brake mounted (see my post from yesterday)

I'm hoping to get the rear axles swapped tomorrow, so I can finalize all the holes I need to drill, then start cleaning up the frame for paint. I still need to weld up an extra few holes where the front spring hangars land, but otherwise it's basically ready.

[JJorgensen52]

Good news: Rear axle is under the frame and I have everything mocked up to drill

Bad news: I found a few spots under the rear spring hangars that need attention before I finish the frame work

Here's the new axle, slung and in place


Here's the rear hangar position. The front two holes of the V3500 hangar are on the rivets which held the rear of my original hangar (you can see the front rivets to the right of the hangar)


Here's the front hangar


This photo shows it better, but the front hangar actually lands in the same place as the original did. The cross member has 4 rivets I knocked out in the bottom, and I need to slot the holes in the spring hangar reinforcement just slightly to make all 4 of them line up


You can also see the nice rust-divots left by the original spring hangars where the bolt access was. I will be fishing these closed tomorrow, hopefully.

Using these hangar locations, my wheelbase has increased slightly, from 133" to about 134.5". I'm not 100% sure how the driveshaft is going to work out, I'm hoping to use the V3500 pieces but that may not be feasible without relocating the center support bearing cross member, which I do not wish to do if I can avoid it.

As another note, I've gained a LOT of height in this swap; the unsettled height right now has 20" under the main frame rail, as compared to about 14" before.

[JJorgensen52]

Not much to show today, welding up and grinding smooth all the various extra holes in the chassis was pretty time consuming, and the weather wasn't in my favor.

The major highlight is the rear spring hangar damage is now patched:
Driver

Passenger


And driver's rear hangar, fully drilled and in final position (I will remove, clean/paint, and then reinstall with grade 8 frame bolts).


I still have to trim the hangars (obvious in the photo above), and I have more holes to drill. I welded up probably 25 holes I didn't need or were in my way, plus patching the frame, today.

[JJorgensen52]

The last two days have been a bit ... scattered. Anyway, here's some updates:

1. Finished drilling the frame and trimming all the brackets. Also, replaced the bolts in both of my rear shock mounts (the threads were messed up on both sides)


2. Got a radio! I also have the usual dual coil dash speaker, I've not decided about rear speakers yet


3. Got into the rear axle. Broke it down first, replacing everything in the brakes:



4. Primed backing plates and rear axle. Traveling for Father's day tomorrow.

[junksaver]

Nice work. Just wondering why you changed out the front spring hangers on the rear spring pack instead of just keeping the originals?

[JJorgensen52]

Originally Posted by junksaver

Nice work. Just wondering why you changed out the front spring hangers on the rear spring pack instead of just keeping the originals?

Height. If I kept the original front hangers, the truck would sit slightly nose-up. The 4x4 hangers from the later trucks sit about 3" lower than the originals did.

My camera was MIA earlier, but I'm making progress. Rear axle is painted, frame is primed, and I'm hoping to have the axle and most of the frame reassembled tomorrow. If all goes to plan, I should have the cab back on Thursday.

[JJorgensen52]

Photo Dump!

Cleaned, painted and rebuilt spring packs (new bushings, new hardware on the center bolt and slide bolts and spacers)



Modified the '87 front spring hangar/body mount to accept the smaller diameter 67-72 core support mounts. '72 Mount is at the top, modified mount in the middle, unmodified (partially out of the picture) to the right. I found these conveniently sized flanges at tractor supply to weld in, quick and easy.


Frame and all the parts are fully painted and will be dry to assemble in the morning





Rebuilt rear brakes, including new drums and wheel seals. I painted the drums inside and out before assembling to prevent rust build-up.



And the axle ready to go back under the truck. I just need to install the axle shafts in the morning (wanted to double check my bearing preload torque spec was correct)



Wheels cleaned up and painted, and I straightened out the stainless caps and gave them a quick wash as well

[Tx Firefighter]

Herculean amount of work you're doing. I know for every picture there's hours of work behind the scene that you did to get to that point. Well done. I'm following closely.

[JJorgensen52]

Originally Posted by Tx Firefighter

Herculean amount of work you're doing. I know for every picture there's hours of work behind the scene that you did to get to that point. Well done. I'm following closely.

Truer words never spoken . I've kind of backed myself into a corner as far as timing on this project, so I'm racing the clock.

Now if you'll excuse me, I need to get back to work

[BLAZERMAN]

Wow! Somehow I missed this build till now. Your making great progress and it should be one Tuff truck when your done. I've been gathering parts for a few years now to do a 4x4 conversion on a C/30 and hope to get started soon.
Will be watching this one from now on... Keep up the good work

[BLAZERMAN]

One question for ya, when you set up your engine crossmember did you set it in the same 2 wheel drive position or did you move it back to where it would be on a 4x4?

[JJorgensen52]

Originally Posted by BLAZERMAN

One question for ya, when you set up your engine crossmember did you set it in the same 2 wheel drive position or did you move it back to where it would be on a 4x4?

I used the forward mounting holes. The square bodies have a slightly longer frame in front of the axle, so putting the mounts in that position keeps the geometry about the same for the wheel location.

I'm not 100% sure yet where the engine is actually going to land, because the motor mounts (later style) are entirely different, but I am trying to keep it forward so I don't have to mess with the cab floor.

[JJorgensen52]

Today I rebuilt the front axle, among other things. Mostly, I learned a LOT about the D60-F by doing it wrong. Specifically, there are 4 different ways to install the caliper ears on the spindle. They swap side to side and install facing in or out. You know how they say third times the charm... Anyway, got to practice my bearing R&R but wasted some time there.

Front axle is a roller!

Axle shafts cleaned up with fresh u-joints


Axle built up. All new seals, cleaned the bearings, full kingpin service, and new rotors and calipers. Plus tie rod ends and steering stabilizer. Plus paint to make it look nice


I really have a tough time putting the stainless caps back on, I dig the white wheel look so much



And fully assembled and ready to go back under the truck in the AM

[BLAZERMAN]

I like the idea of moving the engine forward for better firewall clearance, I believe the factory had the engine moved back so far for better oil pan to front axle clearance. Hopefully you'll have plenty but it looks pretty tight in that 3rd pic in post 54. I plan to use the forward position so I can leave my trans in the same spot that it is now but I'll be using 4" lift springs which should help.

Looks like you got a lot done today...and I agree, those white wheels look Great!

[JJorgensen52]

I failed to meet my desired deadline, but made tons of progress - frame is now a roller.

All the parts ready to go together


Just an example of the hardware. These are grade 8, flange head bolts with "keps" (self locking, distorted thread nuts), which are what GM used to install bolted in parts in the later truck frames. Never, ever coming loose!



Frame complete


With full suspension



To be honest, I didn't do much to the engine other than clean/paint and a tune-up, this truck already ran like a top. Original 350 mated to a late SM465 and NP205 combo.


To make the rear driveshaft work, I did a combination of things. I shortened the spline and yoke of the slip section from the '87 driveshaft, installed the short front section from the '87, and swapped the shortened slip yoke onto my original '72 driveshaft. Wala!



You can also see here, I had to move the center support bearing rearward about 2.5"


PTO details. Trimmed the rear muffler hangar to allow the PTO shaft to pass through to the hydraulic pump. Also shifted the exhaust relief in the '87 transmission crossmember outboard, towards the frame rail, to clear the PTO. This is a rare Chelsea driver's side PTO unit with the extended drive, to clear the reverse idler rib on the SM465




Oil pan to axle clearance still decent. The original exhaust still fits, too


All SS brake lines, new prop valve





Using the original PS pump requires some slight tweeking of the '87 PS lines, and clearancing the engine cross member where the pump sits. I may pull it back out and box this notch in, eventually.


And the finished roller, ready for the body



The stance is just killer, I'm loving it. Going to be quitting this project for about a week or so, life and all. Enjoy the update!

[Tx Firefighter]

You're a hard worker. I can only imagine the sweat you invested in getting it all put together to roller status.

Significant investment in that high quality hardware there too unless you've got a hookup.

[whitels1]

Bad ass man, great work so far! Ill be watching this one.

[rs74]

Where did you get the brake lines? Inline tube? How was the overall fitment of them. May have to send my father-n-laws 67 GMC out for you to do the same to. Just Kidding. Would love to do the same to his. Everything looks great. Looking forward to more. Oh and what did you order the lines for. I was assuming the 87 just didn't know if so how the 87 lines fit up on the older frame.

[mx289]

You have done alot of work, in the past couple weeks.

Looks great.

[JJorgensen52]

Thanks for all the compliments, guys!

Originally Posted by rs74

Where did you get the brake lines? Inline tube? How was the overall fitment of them. May have to send my father-n-laws 67 GMC out for you to do the same to. Just Kidding. Would love to do the same to his. Everything looks great. Looking forward to more. Oh and what did you order the lines for. I was assuming the 87 just didn't know if so how the 87 lines fit up on the older frame.

I did order the lines from Inline tube, for the '87. The fit is okay in the older chassis, a little tweaking here and there but nothing major. The only real problem I had was with the rear axle, they don't have a pattern for the cab and chassis (narrow) rear end, so I had to reshape those lines a good bit to get them to fit.

I also ordered the PS lines for the '87, and so far it looks like everything will fit up very nicely, but I won't know for sure until I get the cab back on and can try and hook it up to the hydroboost unit.