Bronco Forum - Full Size Ford Bronco Forum banner

1978 Bronco Plus 1991 12 Valve Cummins

27K views 122 replies 16 participants last post by  SHR3DD3R 09 
#1 ·
So I have been working on this project for just over a year now, and the whole drivetrain swap is complete. The project has now moved more into the “get the rig on the road safely and reliably” stage, which will then be followed by the “cosmetic improvement” stage.

I picked up a running/driving 1978 Bronco last August (2020) and also sourced a complete intercooled 12 valve Cummins from a 1991 Dodge truck at around the same time. Once I got them both home I started tearing into the project.

The plan was to use a 12 valve Cummins and ZF5 manual transmission and retain the NP205 transfer case, which is exactly what I did. The goal here is to share what I have done so far and to provide updates on the restoration as I continue it.

Here is what the truck and engine looked like when I bought them….

Automotive parking light Wheel Tire Automotive side marker light Vehicle


Automotive tire Motor vehicle Automotive design Rim Automotive exterior


And, as a teaser for what’s to come, this is what they look like now… stay tuned everyone!

Motor vehicle Vehicle Auto part Machine Engineering


Wheel Automotive parking light Tire Land vehicle Vehicle
 
See less See more
4
#5 ·
Thanks! It's original paint was medium copper and raven black, only 36 made with the same paint codes and only 6 made with the same paint AND trim codes. The "copper" on the exterior was re-sprayed a lighter orange by the PO, but I am going back to original, which is why you can see the engine bay has been sprayed with the original medium copper, which is darker.
 
#4 ·
I like it! Please let us know what fuel mileage it gets please
 
#7 ·
Looks awesome. Any chance you can do me a favor and let me know the length of the rear driveshaft. And the angles
I appreciate it.


Sent from my iPhone using Tapatalk
Right now the rear driveshaft is factory! Or at least whatever shaft was used by the PO in conjunction with the 4" lift. The transfer case ended up in roughly the same spot as factory, so the original shaft bolted right in. I think it could be just a tad shorter, though to be perfect. Regardless I will be replacing it with something beefier down the road.
 
#8 ·
Where else is this posted I’ve seen this build before?
 
#11 ·
I really like it! Post away show us how you did it please.
 
  • Like
Reactions: SHR3DD3R 09
#14 ·
A bit later on I discovered the track bar mount on the axle was egged out, allowing the axle to have some movement. Also the frame was cracked around the steering gear mounting points, the steering shaft rag joint was shot, and the steering gear bolts were all hand tight, so the whole steering gear would visibly shift while turning!... And I drove it 190 miles home. All these issues have since been fixed, and I will detail them later on... I am just amazed it drove straight on the way home. It just seemed like it had a lot of steering play and a lot of body roll, but no wobble. Am I lucky to be alive? Haha.
 
#15 ·
Knew I had seen this and had been following it, this is an Awesome build. You have a talent. Sent you a PM
 
#18 ·
To really kick off the project I had to remove the factory drivetrain which included the old 400, C6 auto, and NP205. I also removed the front end including the bumper, grille/grille shell, and core support. It all came off fairly easily. I did have to cut one of the bumper bolts with a cutoff wheel. Pics below.

Wheel Tire Automotive tire Hood Vehicle


Wheel Tire Automotive parking light Car Vehicle


The old 400 next to the Cummins.
Automotive tire Motor vehicle Automotive exterior Tire Tread


Dirty engine bay! To fit the Cummins I ended up removing the original engine perches from the frame as well.
Automotive tire Motor vehicle Vehicle Art Automotive exterior


With the drivetrain removed I decided to suspend the engine in place in the engine bay to confirm what I thought I already knew….that I would have to modify the front crossmember for crank pulley and oil pan clearance, and get rid of the original low mount AC bracket on the Cummins. No room for it. Later on I removed the factory AC box and plumbing for turbo clearance, and made a block-off plate for the firewall. I plan to run an aftermarket heat/AC system eventually. But we’ll get there...

Also, notice the extra crossmember across the frame horns. At some point in the past someone must have had a winch on this bad boy.

Automotive tire Wood Motor vehicle Wheel Rim
 
#21 ·
I then notched the front crossmember and sat the engine in the frame again using engine mounts I purchased from Diesel Conversion Specialists. In hindsight I should have just made my own, but these will work just fine. Don't worry, the crossmember wasn't left like this. Later on I re-plated it to strengthen it back up. I'll show that in due time.

I ended up taking even more material out of it later, but the general shape of the cut is the same as what is shown here.

Automotive tire Motor vehicle Wood Bumper Automotive exterior



Engine bolted in place. Notice the engine mounts utilizing polyurethane bushings. I used the exhaust manifold from DCS as well. Later on I sold it and switched back to the factory manifold once I decided to delete the factory AC box. I also got an adapter plate to use a ZF5 from a mid 90s Powerstroke.

Motor vehicle Automotive tire Automotive exterior Automotive design Rim



Once I was satisfied with the engine placement I pulled it out and disassembled the rest of the front end for more cleaning.

Tire Wheel Car Vehicle Automotive tire



More pressure washing...and I wire wheeled the entire underbody and frame. What a job! At this point I had also installed 1" body spacers. I figured it would give more room for the ZF5 and also make maintenance easier. One inch isn't much, and I can easily move the bumpers up later if it looks off visually.

Wheel Tire Car Land vehicle Vehicle
 
#23 ·
The next order of business was fixing the cracked frame at the steering gear mounting point...

Tire Automotive tire Wheel Synthetic rubber Chair


I ground v shaped grooves along all the cracks and drilled holes in the ends to hopefully stop them from spreading. After that I welded it all up and then ground the welds flat.

Automotive tire Automotive exterior Wood Bumper Snout


I purchased a 1/4" reinforcement plate from a fellow member on FSB. I also made an additional piece out of angle iron because the first plate did not cover all the cracks. Once I had it secured as shown below I welded it all the way around.

Automotive tire Motor vehicle Automotive design Metalworking Wood



This pic is waaaay later down the road after I had painted the whole frame and underbody, but you can see the finished product complete with a new bluetop steering gear.

Automotive tire Motor vehicle Vehicle Bumper Automotive exterior
 
#24 ·
This is a really cool build, you have some talent!
 
  • Like
Reactions: SHR3DD3R 09
#25 ·
Next I moved on to reinforcing the front crossmember to add some strength back to it. The picture below is me standing in the engine bay facing the front of the truck. You can see how much material I removed.

Wood Automotive tire Bumper Automotive exterior Gas



First round of welding everything up using 3/16" plate.

Automotive tire Automotive exterior Motor vehicle Wood Bumper



Once that was done I added additional 90 degree curved pieces in each corner on top of the first plates I welded on. These were made out of some old bumper brackets I had laying around. I figure having those extra supports in the corners, and the fact that they have a smooth curve at the 90 degree bend and not a corner, will add a good bit of strength. It looks a little rough in this pic due to lighting...but mostly because I went a little too nuts with the grinder.
Automotive tire Bicycle tire Wood Tread Bumper



Months later....finished product below all cleaned up and painted. This gives about an inch or two of clearance for the crank pulley and oil pan. That little extra piece in the center of the crossmemeber I added later. It's just an extra stiffening plate that wraps over the trapezoidal plate I welded in first...it probably wasn't necessary.

Tire Wheel Land vehicle Vehicle Motor vehicle
 
#26 ·
With all the frame repair now complete I moved on to the next project...installing the entire drivetrain for transmission and transfer case crossmember fabrication. But first I had to notch the ZF5 tailhousing in order to fit the shift linkage for the NP205. I also had to shorten the "rod" that connects to the linkage on the transfer case. I don't have a picture of that, but I ended up taking roughly an inch out of it for it to work correctly. Not too bad of a project just a lot of grinding, test fitting, and then grinding some more.

Automotive tire Motor vehicle Bumper Automotive exterior Rim


Wheel Crankset Tire Automotive tire Tread
 
#27 ·
Man I’m enjoying this build makes me want to do one
 
#28 ·
It's definitely a lot of work! But I'm also restoring things as I go along, so that has added a lot of extra time to the whole process. I was inspired to do this swap after I put a Cummins 4bt in my old 2000 Ford Ranger, which I sold last summer to fund this project. It was an awesome truck as well, but not big enough for the family. The Bronco should solve that problem. It really hurt to sell it, but I really wanted to build something older and more capable. In a perfect world I would have kept it and also built a bronco.

Motor vehicle Automotive fuel system Automotive tire Automotive air manifold Automotive design


Tire Wheel Automotive parking light Vehicle Motor vehicle
 
#29 ·
Now on to the drivetrain installation! First I mounted the engine in place using the engine mounts I purchased, then bolted on the ZF5 and NP205.

Motor vehicle Automotive tire Tire Hood Tread


I actually was able to bolt the factory rear driveshaft in place. The transfer case is in almost the exact same spot as it was from the factory, so later on I was able to use the original side mount by turning it upside down and adding a spacer or two. Once I had the angle right (engine angled back about 6 degrees, which lowered the transfer case down a few inches from it’s factory location) I moved on to measuring for the crossmembers.

Check out the shifter locations! Pretty good! I did have to cut a slot in the trans tunnel cover to move the NP205 shifter back a bit. Since then I cut and welded the shifter because it ended up interfering with the seat and the ZF5 shifter slightly when going from 1st to 2nd gear. We'll get to that...

Automotive tire Motor vehicle Automotive fuel system Automotive exterior Automotive design
 
#30 ·
My Bronco came equipped with a factory skid plate under the transfer case, so my genius idea was to split it roughly in half lengthwise and use the two sections as skeletons to reinforce and turn into load bearing supports for the transmission and transfer case.


Automotive tire Wood Road surface Plant Asphalt



So let’s focus on the transmission crossmember first. I took the Bronco’s factory trans perch and sat it in the center of the crossmember skeleton I made. After determining where it needed to go on the frame I drilled holes and bolted it in place under the ZF5. I slid the trans perch around just a bit and lowered the ZF5 onto it so that it lined up correctly with the trans mount. With all the weight resting on it I tack welded the perch in place. The result is below.


Wood Gas Composite material Hardwood Plank



Next I added reinforcement to the crossmember by using some 3/16” thick square tube. I also took some angle iron and added L shaped pieces on the ends to be able to bolt the crossmember to the frame from the side as well as the bottom. I also cut a notch in the driver side for slightly better front driveshaft clearance. I then drilled a few drainage holes in the bottom so the enclosed portions can't retain water. The finished product is below....minus a bit of grinding, degreasing, and paint work.


Wood Table Road surface Bumper Gas
 
#31 ·
On to the transfer case support! For this one I purchased a mounting kit specifically for the NP205 from TMR Customs. It utilizes a bracket that bolts to the NP205 tailhousing and connects to a bushing with a built in grease fitting. The process for this was similar, I just had to test fit many times and slowly cut material off of the TMR bracket until I had it just right. I don’t have tons of progress pics for this one, but here is how it turned out. Notice the nifty bracket that bolts to the NP205 tail housing. You can’t see it in this pic, but that bracket is isolated from the rest of the crossmember by a polyurethane bushing. Here’s a link to the TMR kit if you want to understand how it works. This should take a ton of stress off the ZF5 tail housing.


Wheel Tire Automotive tire Motor vehicle Hood
 
#32 ·
At this point I really wanted to add a support back across the radius arms. What I decided to do was use the original transmission/radius arm crossmember and cut a ton of height out of the center of it for better clearance with the ZF, and then reinforce it afterward. Here are some pics of that process.

Original crossmember shape...

Composite material Bumper Automotive exterior Wood Auto part



Material removed....super strong looking huh? Haha.

Gesture Hand tool Pliers Bumper Tool


Here is the almost finished product. I re-plated all the "holes" with 3/16" plate and added gussets on either side, leaving plenty of room for the ZF5 housing and front driveshaft. It's not shown here, but I actually welded an additional flat stiffening plate to the bottom to add a little rigidity to the center section. It bolts right back in to the factory location!

Automotive tire Asphalt Road surface Bumper Automotive exterior
 
Top