I just completed this 2WD to 4WD on my Cummins crew cab conversion. The frame was from Florida and was a former US Navy truck. There are cases where it takes years to locate a really decent truck frame especially if you live here in the northern rust belt states. It also took 5 years to locate a near perfect crew cab body which came from SW Texas but was a 2WD with a stretched rear frame.
My member name over on DTR is Trebor
which is Robert
spelled backwards. Here is what was involved in doing the conversion which was going from a 2WD automatic gasoline truck to 4WD 5 speed diesel:
I would imagine most consider this as an easy modification but I was not able to find any documentation on doing one. This may fill in some of the dark areas for somebody considering how difficult it is to actually do this particular type conversion.
This pertains to a crew cab frame that I converted this past fall. The same information should apply to a standard length frame, club cab, etc.
Everyone knows how to grind or burn out frame rivets so I will not go into that area. I used an acetylene/oxygen torch set up with a small tip to avoid burning up the frame and a pneumatic punch to pop them out while they were still glowing hot! If you use this method be careful as the glowing rivets can set something alight if the fall in the wrong place! Oily rags are a prime target.
When I did the 2WD to 4WD crew cab frame conversion I CHEATED on the measurements. I initially removed all of the cab frame brackets because 3 0f the 4 were broken. No surprise there. I ordered grade 5 washers from www.Mcmaster.com
that were slightly larger than the original hole size and welded them to the top side of the brackets.
The front spring hangers are located by using the original predrilled factory holes located just behind the bumper bracket mounting holes.They share an identical frame mounting pattern with the bumper brackets and in my case the rear cab mount frame bracket mounting holes. This keeps the front axle located in the proper location in the frame. When I started to measure the dimensions from the cab frame to the front spring rear hanger location the measurements differed by almost a quarter inch between the left and right sides. The rear bracket location for the front spring is not apparently as critical as it first appears and is demonstrated by the tolerance that was acceptable on the 1992 donor frame. At this point I decided to use the original 4WD frame sections as a donor for making frame templates. I whacked the 4WD frame BEHIND the cab body mounting brackets and using a torch removed the the flat upper and lower sections leaving only the flat vertical faces of the frame. Then I ground the slag and wire wheeled the surface rust before bolting the new templates to the 2WD frame by using two of the cab bracket mounts and the front bumper bracket bolt holes.
At first you need to get all of the bolts in where they are loose. Then in the transfer areas for the location of the new hole you need to use bolts to draw the template to the 2WD frame. In the shock mounting area there are two larger holes that will accept a 3/4 or 7/8 inch bolt with washers. The trick is to draw the template in close by tightening the center most bolts outward to the end portions of the bumper end and the cab end. There will be gaps because you are clamping outside radiuses to inside radiuses between the frame and template. Template bolted to the 2WD frame to locate engine crossmember mounting holes:
The actual large holes for the brackets are easily drilled using a high quality bi-metal hole saw.
The holes may require a small bit of tweaking using a high quality round file. The original holes are oval shaped but are located by placing the hole saw in the cab end of the oval and drilling through. Mine worked out perfectly with just a bit of deburring required using a round file.
I also used a 7/16 inch transfer punch and a 7/16 inch drill bit to transfer the mounting rivet holes for the rear spring bracket and the engine crossmember. I replaced the all the rivets with grade 8 7/16" bolts and grade 5 hardened washers in conjunction with self locking nuts. There was one hole on each side of the 2WD frame that was touching one of the new holes for the new shock bracket mounting holes that I welded up on each side of the 2WD frame. This hole is the rearmost rivet hole that goes through the 2WD inner and outer mounting brackets on the frame. The other option would be to mount the bracket and add a third hole by drilling through both parts.
On the front spring hanger bracket mounting brackets there was an 1/16 inch gap between the hanger and frame because of the very slight differences between the crew frame and the 92 frame. I simply made shims that that were drilled for the hanger bolts to pass through which keep the shims in place. For me this was the easiest method for locating the new holes.Transmission crossmember brackets and mounting; 2WD automatic to 5 speed 4WD:
Also if not already noted the 4WD passenger side upper crossmember mounting bracket brace has a relief formed for exhaust pipe clearance that the earlier gasser may not have. Since I went from a 2WD automatic to 4WD 5 speed the transmission crossmember needed relocating. Again I cheated by setting the engine and transmission assembly in the frame and used the mounts to locate. What I found was there was only two of the original holes (1 0n each side) lined up. The other 2WD hole is circled in this picture. This is looking at the passenger side of the frame. F=front of frame. I mounted the crossmember using those holes and then used the crossmember as a template to the new holes using the same method mentioned earlier.
Then you end up with the new circled holes for the 4WD crossmember and upper frame brace:
Then I removed the engine & trans assembly and mounted the upper frame brackets to the center section of the crossmember. Then I staggered two new upper bracket holes by drilling through the frame and upper bracket for one hole and just drilling through the remaining hole that already lined up in the frame with the bracket below. Everything now fits exactly as it was in the 1992 frame. Note the exhaust pipe relief that is visible in the upper support brace for the 4WD transmission crossmember in the final picture.
And as a side note, ALL of my metal cutting tools were made by Morse which held up quite well compared to Wallymart or the Harbor tools.
My completed truck, provided I live long enough, will be a W250 crew cab with 6 foot bed. The bed BTW came from Arizona.
The Cummins donor truck that I scrapped was from here in PA. The body from that truck actually shed enough rust to fill up a 6 gallon plastic bucket. There are justifiable reasons to do a 4WD conversion especially if you are an older person that may not have an unlimited amount of time to complete the project.