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1942 Flatfender build up project

136K views 206 replies 75 participants last post by  Brian1 
#1 ·
Well the time has come that I finally posted a build up thread about my 1942 Ford GPW flatty. This Jeep sat in the same place for 20+ years before I took it in for a build up. This Jeep had seen alot of backcountry roads in New Mexico when it was my fathers and grandfathers hunting rig. It had been rebuilt before with parts from later model CJ2's. I was inspired to build it by seeing a built flatty in Telluride and seeing pics of Dimitri's old flatty. I wanted one too and I already had a free starting point :D

Here is what I started with:




Stage/Plan 1 - What did I want to do with it?
Well A resto was out of the question. Alot of the origional GPW parts were missing and the body work had been 'worked' on. I thought a retro wheeler would be fun to start with. The plan was a SOA with stock axles, 31's to 33" tires and stock drivetrain. I pulled it into the garage and started work to get the engine running. Most all of the wiring on the Jeep was trashed from sitting so long in the weather. It had been re-done by my Dad and grandfather and converted to 12v over 25 years ago.
Working to get the engine started:

Well I spent a day or 2 screwing with it and never could get it to fire. Enough was enough. I decided I would swap in a 350 SBC. So much for Plan 1 and off came the body to proceed with the work ahead of me.
 

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#3 ·
So now on to Plan 2:
Swap in a 350 SBC, front and rear full width Dana 44's, and keep the T-90 and Dana 18. Run some 35" tires. I quickly came to my senses and decided to put in a SM420 in place of the T-90 to handle the HP and torque of the new V8. Also decided to convert to power steering and put in a steering column. I was off to the overpriced junkyards in town to get the 'new' parts from a J10 truck. I came home with F&R Dana 44's, power steering box, pump, steering column, leaf springs, and power brakes.

Now I needed to beef up the frame so out came the rest of the parts from the Flatty's chassis.

I was left with the frame.

I decided to strap and box the frame. The GPW frame was partially boxed from the factory but that wasnt going to be good enough for a V8. The whole frame was boxed and strapped with 1/4" steel. The straps were stitch welded the length of the chassis. If I were to do it all over again I would make a new frame from rectangular tube. I spent alot of time cutting steel and forming it to the frame. A new frame would have given me alot more options later in the build but oh well. Lessons learned.
Strapping the frame:

Boxing the front frame:

I would have to outboard the springs to run the axles. I used stock 5-leaf Wrangler leaves at all 4 corners. I picked up some ConFer shackles cheap at the local swap meet so I used those as well. I made up the front mounts:

And then welded them on in the driveway:
 

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#5 · (Edited)
Well after getting the front axle mounted on the newly boxed frame I changed my mind again and went in a new but similar direction with the project.

So now on to Plan 3:
Still use a 350 SBC, SM420 and front Dana 44 but I decided I didnt want to break stuff so I bought a 14 bolt full floater and a Dana 300. I also decided to go to a bigger tire - 38's. Everything else pretty much stayed the same as plan 2 so I didnt loose too much time.

This change in plans left me with an 8 lug rear and a 6 lug front. More on this later.

Start to hang the rear axle:



Once the axles were mounted my wheelbase came out to be 89" using 1" offset plates at all 4 corners. This is 9" longer than stock.

Once the chassis was rolling on 4 wheels it was time to move on to the drivetrain. I bought a donor 76 GMC truck and got the engine out of it. I also ordered an adapter from Novak to mate the 300 to the 420. Rear driveline length was a concern and Novak had the shortest adapter avail. at the time.

All for now, more to come later.
 

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#6 ·
Getting ready to put the drivetrain in i had to put the tub back on to fit the engine against the firewall.

Time to make the tranny and t-case look good so they got powerwashed, new gaskets and paint:

Next they were bolted together using the Novak adapter. Tight clearence between the 2.

Clocking was not an option for me. First I was dealing with a very narrow frame, the clearence between the tranny and t-case was too tight - I would have had to cut the shifter off. Also the bottom of the t-case was almost flush with the bottom of the tranny.

The entire drivetrain got bolted together and ready to drop into the chassis.
 

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#8 · (Edited)
Dropping the engine, tranny and t-case into the chassis



I decided to make a bolt in engine cradle and crossmember to give the chassis a little more torsional strength. I used a 2" poly bushing for the motor mounts and made my own mounting brackets. I mounted the engine centered and I cut a hole in the firewall to fit the HEI and gain enough clearence between the water pump and radiator. If I would do it over again the engine would get moved back about 1" more and moved to the pass side 1" more.

The picture below shows the new tranny/t-case crossmember and the temp crossmember :D The new crossmember acts as a skid plate as well as a mount. It is made of cut and welded 1/4" plate with holes drilled for access to the tranny mount bolts and drain plugs. It also has some speed holes. It will have some bars welded onto it to make it resist bending later. It sticks down from the frame about 5" total. The whole drivetrain was mounted a little low to keep the COG down and not have to hack the tub or use a body lift.
 

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#10 · (Edited)
Now that the drivetrain was mounted it was time to focus my attention towards the body. I put the 38's on the rear and I would have to cut the rear fenders back to fit them.

I traced the pattern of the front curvature and then transfered the curvature pattern to the back of the fender and wrapped it around the back to the body seam. I marked another line 1" lower than my origional line. This would allow me to form a lip just the same as the front of the fender and keep from cutting the tire if contact was made. I made the cuts using an air body saw - it worked the best. Below are the before and after fender cut pics


This eliminated the GPW rear toolboxes so I removed the lids and put some 1/8" plate over the hole and welded it up.
Next I moved on to the floors and the tub sub-frame. The floor was very rusty and the sub frame was in bad shape. It had steel hat channel with strips of wood under for extra support. The wood was completly rotten. I cut the rear floor out first leaving a 1" border to weld the new floor to.

I welded in a new rear floor after using the torch to put a bend in it to match the origional. I also made a new sub frame for the front out of 1"x2"x1/8" tube. I made it almost the same as the stock configuration but I moved the back a little farther to make room for the t-case yoke. Here it is with the new rear floor:

After that was done a new front floor was put in. I also cut it out leaving a 1" border to weld the new floor to. Here is the front floor out:


I also cut out a portion of the fenders and boxed it back in to get more leg room by moving the seats back.

After the new floors were put in and the sub frame stitch welded to the floor I put it back on the chassis to drill the body mount holes.
 

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#11 ·
Now that the body was back on the frame I decided I wanted to keep my fenders and tub straight when it comes into contact with rocks so I made some diamond plate corner guards. Since it was a custom fender cut and aftermarket guards for this old of a Jeep are hard to find I made them myself. I ordered a full sheet of 1/8" diamondplate. I traced a pattern onto cardboard then cut it out of the diamond plate with my plasma.

Cut out and ready to bend:

Next came out the blue torch wrench and some clamps and hammers. I heated it up and bent it around the tub clamping it every 4"-6". This of course destroyed the paint but I didnt care it would get a paint job later. I used 1/4" button head bolts to attach it to the tub.
Here is the finished product:


In this picture you will notice the fuel cell. It is a 20 gallon aluminum Summit Racing fuel cell attached to an angle iron sub frame then bolted to the floor. A hole was cut for the sump to sit down into.

The tub was then hurculined inside and underneath. Here is a view of the inside:
 

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#13 · (Edited)
Now with the tub done I moved onto the pedals and brake system.

I got some swinging pedals from a 91 Wrangler and modified them to fit the flatty. I added a custom push rod with female rod end, an electric brake light switch and an adjustable brake pedal stop. I bought a 68 Vette brake master cylinder and a Wilwood 3/4 clutch master cylinder. I had no room to run a vacuum booster.



I made a re-enforcement plate and welded it to the firewall and then bolted the clutch and brake MC's and pedals together.


I made an excel spreadsheet to keep track of the quantities and part numbers I was going to need as well as the suppliers. I am running -4AN brake lines and hardware. I also am using an electric line lock on the rear axle. Heres a pic of most of the brake plumbing parts


And the line lock mounted on the rear frame. -4AN braided line goes from the output to a T on the rear axle housing
 

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#14 · (Edited)
A little while after I got the 14 bolt axle I went to work on it. I cut out my own brake caliper mounts and did a disc swap on the cheap using parts from the donor truck mentioned above. I made a diff guard for it as well. Looking back I should have just made a whole new HD cover.

Attached are some pics of the disc swap and diff guard
 

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#15 ·
As I mentioned above when I changed my plans I had a 6 lug 44 front and an 8 lug rear end. I found an 8-lug Dana 44 from a chevy truck with internal hubs for sale so I bought it and swapped the entire axle in. I initially used some thin hi-steer arms but eventually went to some 1" thick double arms using 1 ton TRE's and 1.25" x .219"wall tie rod and drag link
 
#18 ·
way to drop the ball right in the middle brian!! LOL.

i'm sure he'll be back soon to finish up the thread.

its completely painted/caged/driving/stoping at this point. just tieing up the loose ends for completetion mid next week.
 
#19 ·
MrWillys said:
Looks great, nice to see well thought out project. . . .
Congratulations.
You're not kidding. Brian thoroughly planned & engineered this rig and everything that results shows the benefit of doing so. It's tight, the tree-fitty is schaweet and the MB has mad flex. I won't spoil things else to say: Dayam, that rig is badass! Can't wait to spot for him . . . .

I dare say there's more to follow . . . .
 
#21 · (Edited)
Jeepdude_Jay said:
Very cool build. :smokin: Do you have a picture of how you notched the fenders to move the seats back? I will be doing this to mine very soon.
As requested-

The cut, I cut it all the way to the hat channel support and to the point where there was a corner "patch" on the fender. It also goes back on the bottom about 4".

The new box made of the same sheetmetal as the new floor

And welded in, a view from under the fender. It was the best pic I could find. I couldnt find one from the inside of it finished.
 

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#22 ·
MrWillys said:
Looks great, nice to see well thought out project. Is the master cylinder from a non-power car?
Yes, it is from a 68 Corvette without a booster. This way I got a deep hole for the pushrod so it wouldnt fall out. It works good with small street tires but when the 38's are on it takes a little longer to stop. That will all be changing soon, I just got a hydro boost setup in the mail yesterday from Van @ Vanco Power Brakes
 
#23 · (Edited)
Moving on to the power steering conversion. I bought a Saginaw '76' box from the junkyard and used it on my flatty.

Because I was using the stock frame with a stretched wheelbase my front axle was pretty far forward leaving me to have to put the box far forward. it took me a good day to decide on the right position and make the mount plate.
Here it is with a plywood mockup and PVC draglink :D :


And here is the fabbed bracket with gussets made of 3/8" plate:


and here is the steering box painted and tapped for hydro assist ready to go:


And here it is mounted up with the 1" solid steel round bar output shaft support:
 

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#24 ·
Moving on to the radiator- I decided on an Afco N-series aluminum radiator in the GM configuration. I welded in a new crossmember under the radiator and then made supports with rubber isolators to hold the radiator in place and allow for any frame flex and any thermal expansion. The radiator is supported by the tanks per the instructions. By the suggestion from Geesh here is how it turned out:




I did have to cut parts of the grill so I could move it forward. I bought a taurus fan but I couldnt use it because the distance from the water pump to radiator was so small. I eventually swapped to a short water pump and an electric fan off ebay. The verdict is still out on if the radiator will keep the engine cool. I may have to make a shroud and move the radiator farther forward.
 

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#185 ·
how did you build the clamp for the radiator? What type of rubber or plastic did you use to clamp it in place? I like how you mounted it. I may try and copy it, is there anything you would have done different.
 
#26 ·
Now for the fuel system. I already mentioned my fuel cell above. I bought a 20 gallon summit aluminum fuel cell with sump. I went 20 gallons because it needs to feed the V8 on long off road excursions. I didnt want to have to carry Jerry cans for longer trips. I also went with aluminum because this Jeep was going to be stored outside and I have heard of poly cells disforming from sitting outside.

I mounted the cell in a rubber lined angle iron base to help support the weight and keep the small aluminum feet from taking all the weight. The feet themselves are mounted via springs around the bolts. My dad suggested this after working around fuel trucks and seeing mounts crack all the time. Since this Jeep is offroad and will see alot of flexing and vibes I figured it would be a good idea. It is limited to around 1/8" maximum movement at each corner. I also mounted it centered in the rear of the tub. It gives just enough room to mount a military ammo can on each side if I wanted to.

Here you can see the base and the spring mounting. Also you can see the hole I cut in the floor for the sump.


I used AN fittings up to the electric fuel pump. Here is a shot of the fittings out of the cell:

they are -8AN and 1/2 fuel hose to the pump. I am running a -8AN fuel filter before the pump. The fuel pump is an electric Holley red pump that was rebuilt with a lifetime warranty. Out of the pump I run barbed fittings and 3/8" fuel hose I believe (it has been a while since I did this). It runs all the way to the carb with a clear fuel filter right before the carb.
here is a pic of the rear frame area with the AN filter and pump.

I run the cell vent line to a 1/2" ball valve for a roll over shutoff then to a small filter that you find in the ricer isle at the local parts store.

This pretty much sums up the fuel system.
 

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