1980 – 1986 2wd 3.03 to NP435 transmission Swap

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By Evan MacDonald

I did this swap on a 1980 F100, and it should be applicable to any 80-86 with a 3.03, and likely any column shifted truck. Also, any floor shift 4 speed could be substituted for the NP 435. I can’t guarantee that the details such as the speedometer gear will be the same though.

To do this swap, you will need

  • The 4 speed of your choice, complete with shifter
  • Speedometer cable and gear to fit the 4 speed, the 3.03’s cable won’t fit a NP435, and the gear is cut the opposite way, so if you are removing the transmission from a donor truck, grab it’s gear
  • Floor plate from a truck that was equipped with your 4 speed
  • Transmission yoke for drive shaft (NP 435 unit is larger, if you have a slip yoke style NP435)
  • Backup light wiring from a NP435 equipped truck, including both plugs
  • A new transmission mount (optional)
  • Possibly a drive shaft, custom or from a donor truck (I had a donor truck, but I can’t remember which shaft I ended up using) definitely if you are using a flange style Transmission

  • To start, chock the wheels, unhook the battery, etc. You know the safety drill.
    I was able to get away without jacking the 80 up, I put the 31×10.50s off my 82 on it, and I had plenty of room to work.

    Once you have that done, start by draining the transmission. I thought I could get away without draining it like I could with a 4 speed, but when you remove the speedometer cable from the transmission you end up with a large hole in the side of the trans below the oil level.

    While you are waiting for the oil to drain, remove the floor mat/carpet. You may be lucky enough to find the build sheet taped to the passenger’s side of the floor pan if the mat hasn’t been removed previously. I found the 80’s under there…

    To start the disassembly, unplug the back up light wiring from the transmission and chassis harness. Disconnect the transmission shift linkage at the transmission, and pop it out of the grommets in the end of the steering column.

    Then unhook the drive shaft at the rear axle (the nuts on the U-Joint U-Bolts are �") slide the slip yoke out of the transmission, and, remove the speedometer cable. If you haven’t already drained the transmission, you had better have something handy to catch the oil that will leak out.

    Once you have that done, support the engine and transmission separately, remove the bolts holding the transmission support to the transmission crossmember (a transmission jack or transmission adapter for a floor jack would come in handy here, although the 3.03 is manageable by hand) and remove the transmission crossmember (you only have to loosen bolts on the triangulation braces bolted to the top of the frame enough that you can get the crossmember out.) Once you have the crossmember out of the way, remove the transmission support, and then remove the 4 bolts (5/8th IIRC) holding the transmission to the bellhousing, move the transmission back so that the input shaft is clear of the bellhousing, lower it and slide it out from underneath the truck.

    This would be a good opportunity to check and or change your clutch, but I won’t cover that here.

    Take the floor plate, sit it in the dimple in the floor, (the 80-86 trucks have the floor stamped where the plate goes) and mark the boltholes with a marker. Once you have that done, drill the holes to suit the fasteners you are going to use to hold the plate down. Now comes the real fun part, mark out the floor about �" inside of the bolt holes, and, cut it out (I prefer my Sawz-All for this J) Once you have this completed, it’s time to start wrangling the NP 435; I really hope you have a tranny jack…

    Once you get the transmission under the truck, line it up with the bellhousing, slide the input shaft into the release bearing, the clutch (you may want to put the transmission into 4th so that you can easily turn the input shaft to engage the clutch, a long standard screwdriver is good for shifting it without the shifter) and then into the pilot bushing/bearing, which can be by far the most time consuming part of a transmission installation. Once the transmission is in place, install the 4 bolts that hold it to the bellhousing (with the NP 435 you will need an open-end wrench, in my experience, there is insufficient clearance to use a ratchet and socket) and remove the support under the engine.

    Installation of the transmission crossmember can be done in 2 ways, the first of which I find a bit easier, install the transmission mount onto the transmission, jack the transmission up as high as it will go, and slide the crossmember in underneath. Then line up the boltholes, lower the transmission into place, and bolt it down.
    The second way is to install the support after you install the crossmember, but it’s easier to bolt it to the transmission before you get the crossmember in the way.

    Now, if you have a driveshaft from a donor truck, skip this step, but, if you do not, take the slip yoke for the NP435 and install it onto the transmission output shaft to about the mid point of it’s travel. Then, take a measuring tape and measure between the U-joint seat and the Yoke. This will give you an approximate measurement to compare to your existing driveshaft. It will likely be close enough to have a custom shaft made, but I recommend you use the method of measuring recommended by the builder.

    If you have a flange style NP 435, the proper measurement for a slip shaft style driveshaft is quite simple, just measure the distance between the flanges, but again, do NOT take my word for it, check with the person who is going to build the shaft for you. Once you have your driveshaft ready to install, go ahead and do so.

    Now, go ahead and fill the transmission with oil, install the shifter (it will have to be in neutral for this,) unclip the speedometer cable from the clip on the bottom of the cab and bring it up into the engine compartment.

    Next, remove the dash cap and instrument cluster trim panel, then reach in from the top and disconnect the speedometer cable (press the flat part of the plastic ring in and pull the cable away, this may be easier if you remove the 4 screws holding the instrument cluster so you can move it,) then pull it along with it’s grommet out of the truck… Install the new one that fits the transmission, connect it to the cluster, and re-assemble the dash. Then install it into the transmission. If you were lucky enough to have found a donor truck with the same gear ratio as yours use, it’s speedometer gear permanently, if you weren’t so fortunate, make a trip to your Friendly Ford Parts guy with the gear out of your 3.03 and see if he can get the proper one to work with the NP435.

    Once you get it all together fire up the truck and take it for a test drive, and enjoy your 4 speed. If your truck is quiet enough to hear the gear whine, enjoy!!

    On the 80, I went a bit overboard and swapped out the steering column for one from a floor shift truck for the sake of originality, the truck only has 57,000 miles, and, is almost show worthy, so, I figured I may as well make it look like it’s supposed to be like that…


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