4BT Cummins 4L85 Long to Short
 

I'll give the dessert first! 1968, 4BT Cummins, 4L85e transmission, Long box cut down to a short box, used a short box frame. Rear air bags for hauling, AC, Hydro boost and 4 wheel disc brakes, quick ratio power steering, the list goes on. I have put 2,700 miles on it so far, no issues. Currently getting anywhere between 18-23 MPG. It's not afraid to work either...

Re: 4BT Cummins 4L85 Long to Short
 

Long story short, I found an original short box patina truck in New Mexico. Part of the deal came with an original short box frame. Went down and drug them back to Iowa. Started the build and found this truck 7 miles from home. Bought it and used the short box frame from NM.

Re: 4BT Cummins 4L85 Long to Short
 

frame work

Re: 4BT Cummins 4L85 Long to Short
 

Why buy when you can build!? C notch, 1/4" plate, Universal bump stop from Speedway. Sand blast, primer, undercoat, and paint suspension parts

Re: 4BT Cummins 4L85 Long to Short
 

Front end came out of a 71 GMC 1/2 ton giving me front disc brakes. McGaughys drop spindles up front, 4 inch CPP drop springs in the rear. New 3.08 Eaton Limited slip.

Re: 4BT Cummins 4L85 Long to Short
 

Weld on disc brake kit from Speedway. First, the axle must be turned down to allow the rotor hat to slide over it. Next, the inner circle of the hat must have material removed to slide over the axle.

Re: 4BT Cummins 4L85 Long to Short
 

Install the caliper, making sure there are lug nuts keeping pressure on the rotor, push it towards the "pumpkin" and put some tack welds on the bracket. I was able to get good welds on both sides of the caliper bracket, around axle tube and axle flange.

Re: 4BT Cummins 4L85 Long to Short
 

Cab Bath.

Re: 4BT Cummins 4L85 Long to Short
 

Smoothed out the firewall. Body work, primer, hosed it down with under coating (my favorite product so far has been Titeseal.) Dries fast, lays down nice, and it's paintable. Last, I got the factory green paint color and put a few coats on. You will find this undercoating every place I could get to- inside and out. I did whatever I could to keep the rust away and help with noise- because this engine makes a racket.

Re: 4BT Cummins 4L85 Long to Short
 

cab corner

Re: 4BT Cummins 4L85 Long to Short
 

cut out the old, make new pieces, seam sealer, primer, paint you know the drill...

Re: 4BT Cummins 4L85 Long to Short
 

Wasn't very impressed with the fitment of this patch panel. I had to cut off about a 1/2 inch where the panel meets the rocker for it to be straight on the backside of the cab

Re: 4BT Cummins 4L85 Long to Short
 

corner

Re: 4BT Cummins 4L85 Long to Short
 

I will explain the process when I get to the bed chop.

Re: 4BT Cummins 4L85 Long to Short
 

paint

Re: 4BT Cummins 4L85 Long to Short
 

Cleaned the metal with purple power first, then spray on the PHIX

Re: 4BT Cummins 4L85 Long to Short
 

undercoat

Re: 4BT Cummins 4L85 Long to Short
 

Seam Sealer, Dynamat, Dynaliner

Re: 4BT Cummins 4L85 Long to Short
 

con't

Re: 4BT Cummins 4L85 Long to Short
 

Dynapad, under the hood- dynamat and dyna hoodliner

Re: 4BT Cummins 4L85 Long to Short
 

Brace up the bed, measure it all out

Re: 4BT Cummins 4L85 Long to Short
 

Make sure to cut on the correct side of the tape. I used a 4 1/2 in cut off wheel. Clamp it back together, making sure it is straight with a straight edge and glue it back together.

Re: 4BT Cummins 4L85 Long to Short
 

This is where things got hairy for me. I started on the right side, could not for the life of me keep the panel straight after tacking where the old fuel fill door was. Tried and tried to weld on pieces of metal to pull out the low spots (don't have a dent puller) and use the hammer dolley for and extensive period of time with no luck. I went over to the Left side where I found a pile of bondo. I decided to cut it out and weld a different piece in from my trusty donor truck. In doing so I rid myself of the dreaded fuel door section. Got the panel in place and welded in with no issues in about 45 min. Since that went so well I cut out the abortion I had going on on the right side. Again, it took about 30 min- lifesaver! I'm not afraid to admit and show my failures, that's how we all learn. If you are cutting down a box I highly recommend doing one that does not have the fuel doors. Straight cuts and welds go much faster!

Re: 4BT Cummins 4L85 Long to Short
 

The bumper came into contact with the bedside a few too many times. As you can see, the original piece had lost its body line. Cut it out and start over. I refuse to "fix" things with bondo.

Re: 4BT Cummins 4L85 Long to Short
 

This is my redneck dent puller mentioned previously. Weld on pieces of scrap metal and use them as leverage to pull the dent out.