Highboy p/s conversion with a 78/79 F150 box

[69Highboy]

Since I've heard about putting a late model F150 box under a Highboy but never seen a good how-to guide, I figure I'll share my experience and mistakes.

This first post will just be the spec sheets of what I'm dealing with and what I used. Unless I give a manufacturer name the part numbers will be Napa part numbers.

The truck:

1970 F250 4x4, 360FE, NP435, with a 1976 Dana 44HD Low Pinion open knuckle disc brake front axle instead of the original 44 closed knuckle drum brake setup. Everything else is original/stock. No a/c, dual pulley alt/fan setup.

The parts list:

3-groove engine pulleys: Ford C8AE-8509-B and C9TE-6312-A

Alt/fan belts for those pulleys: Bando 2450

P/S pump belt: 25-9463

Pump: 38-1032N (38-1032 if reman)

Pressure line: 7-1470

Return line: 7-1202

In-line filter: 35-1004

Box shell: Couldn’t find suitable a/m, got a used one off eBay

Box guts: From 39-1012 box

Pitman arm: Moog K440026

Drag link at pitman: Moog ES2147R

Sleeve: Moog ES362S

Drag link at steering arm: Moog ES2027L

Steering arm is off 70’s 1/2 ton Chevy D44

[69Highboy]

Now on to the process!

Pull off the hood and driver's side inner/outer fender, and remove the driver's side core support mounting bolt. Next, remove the old manual steering box and drag link. You won't need any parts from them later, so don't worry about that. At this point the engine bay should look like this:



I didn't document this next bit, but you'll need to install the new 3-groove pulleys on the motor. Also, you'll need to source a power steering pump pulley, dipstick/cap and mounting bracket. My neighbor who helped with this had all those laying in his parts stash, so I just used them. They're all factory parts off a 1971 F250 360FE 2wd p/s equipped truck, as well as the hoses and pump. This is what the bracket I used looked like:



You can install all the pump and other bits before or after you retrofit the box, I chose to do it before. I'll split the conversion into multiple posts for ease of reading and download speeds.

[69Highboy]

Now onto the box. You NEED an oem box for this. I bought a new aftermarket box for this only to discover that the genuine Ford guts don't fit in an a/m box, the bore diameters are different. Anyways, on the frame you'll notice a flared "lip", circled below:



When I set my box on that lip the pitman arm read at dead level at center, max left, and max right. Might've been a fluke, but that's what I used to align the box and mark out the mounting holes. Here's how the box leveled out just resting on the frame:



Somewhere I think I heard that you can use one of the original holes egged out a bit, the flared areas near the brake line and shock tower kept me from doing that so I just drilled all new holes. Here's the measurements I wound up using. Ignore the tracings and tiny hole in the background, I didn't do a good job of checking my layout the first time so I had to reposition the box and I just left the old marks.

Upper rear:




Lower rear, the right hand hole is the one you want to pay attention to, ignore the one on the left:




I mounted the box using those two holes and used the box to locate the 3rd hole. You will have to use the hole in the underside of the crossmember to put the nuts on the backside of the mounting bolts as the holes are in the crossmember. It is possible to fit wrenches, ratchets, etc on the nuts through the hole, but having small hands is a major plus.

[69Highboy]

Now for a pair of problems I encountered that may be unique to the axle. Since the original shock mounts had been torched off new ones had to be fabbed up. In order for the drag link, etc to clear the drivers side shock I had to use a steering arm off a mid-70's open knuckle disc brake GM 1/2 ton front axle that was in my neighbor's parts pile, like so:



I also had to move the shock towers, there is a set of mounting holes ~3" behind the original holes so I just moved them onto those. Crossover steering would eliminate both of those issues and another one I'll encounter later, but I don't want to go to all that effort, lift the truck that much, etc. In the pic the original mounting points are on the left, the ones I used are where the shock tower is sitting.



That's all for tonight, tomorrow I'll post up the rest. Full disclaimer, this took me two weeks or so between the actual work, figuring out parts weren't right, ordering/waiting for new ones, seeing if they'll fit, etc. This isn't real-time.

[69Highboy]

And we're back! At this point the truck should look something like this:



The next phase is cutting down the steering shaft. I didn't log how much was cut off because it was cut a few times. The flex joint is welded to the shaft, but a quick pass on a neighbor's lathe got rid of the welds and freed it up. If you don't have a lathe, just carefully attack it with a grinder. Once the length was figured out the joint was welded up and the shaft was test-fitted on the box.



At this point I took a step backwards, dismounted the box, and discovered I needed an oem box when I went to swap the guts. Remove the two bolts that hold the output shaft and cover plate on, and remove the 4 bolts that hold the input shaft cover on. As I recall, center the teeth on the output shaft and the output shaft should lift out. Once it's out, pull out the input unit. Repeat that on the other box and voila! You'll have 2 of these on your bench!



Swap them out and re-assemble the box, re-install it, and put yourself on the back for a job well done. You'll need to trim the inner fender a bit too in order for the box to fit.



Once that's done, if you're running a later axle there's still one other thing you'll need to do. Get the pitman arm nice and hot, and bend it to match the outline traced out in red or it won't clear the tires at full steer.

[69Highboy]

Here's a few pics of the drag link angles with a set of 2" blocks on the front end.

Full extension:



And almost on the bump stops:

[69Highboy]

Further update, my steering has been kinda cranky and the truck does not want to turn unless you're rolling. I called the tech support line for Napa power steering pumps on an slightly related question and learned that a dentside 4x4 steering pump produces several hundred psi more than the bumpside 2x4 pump I'm using. Ergo, I believe the box is not receiving enough pressure which causes the hard steering. I do not know of a fix other than building brackets for the dentside pump, but in my case the pump that will be on the 24v diesel I'm swapping into the truck will produce almost the exact same psi as the dentside pump. Once I get the swap completed and the steering figured out again I'll report back on whether that fixed my issue.