Cab replacement: now, later, or even at all?

[Jon M]

So I'll start by saying that I don't *want* to do a frame off restoration. It would be fun but it would take an eternity with all the demands on my time. However it's becoming clear that the roof of my cab is an issue that will need to be addressed at some point. According to the previous owner, the roof had a run-in with some fire wood and was bondo'd back together and then calked with black silicone (pictures below). During rains it leaks into the drivers side cab floor, which has rusted through such that you can see the street below - which indicates that the roof leak predates the firewood incident. He also Bondo'd the doors which I'd love to replace at some point and maybe even pretty her up with a decent pain job... dreams of course.

I would like to wait until it's road worthy but part of me is wondering if I need to disassemble everything now, get a new cab (somewhere) and install it first, and then get to attacking the rest of the vehicle. Even if I did ignore the cab roof skin I'm going to eventually have to address the drivers side floor pan and threshold which is exciting because it means I get to learn to weld. But maybe I should just consider a full cab replacement.

For context, the list of must-haves (for inspection and registration) is as follows:

- Brake system overhaul

- Suspension overhaul (all original and dangerous rust)

- Thermactor re-install (for smog requirements)

- Oil pan gasket replacement

I guess all this leads up to my question: Would you replace the cab now or later (or at all)? How much needs to be removed from the engine bay to pull the cab out? How difficult is a cab replacement? and most importantly, what would you all do in my situation?

On a completely unrelated note, does anyone out there have a good lead on a thermactor diverter valve for a 1984 4.9l 300 engine? it's one of the rare parts I can't find online.

Thanks for your help in advance!

Previous owner's Bondo and silicone calk job.

My burned out diverter valve that I need to find a replacement for...

[Gary Lewis]

Jon - Do you have emissions testing where you live? That makes a big difference.

The best way to fix all of this is with a replacement cab. And the easy way to do that is to buy a donor truck with a good cab but bad something else so it is cheap. Then you disconnect the wiring, unbolt the cab, raise it up, and roll your frame/engine/bed under it.

The wiring runs from the driver's headlight back through the cab and forward to the passenger's headlight. So you can leave everything in the cab and disconnect from the engine harness and other things under the hood. Remove the fenders and pull the 4 bolts that hold the cab on and it'll come off.

BUT! You need a cab wired like yours. And in 1980 there were differences so don't go with an '80. And from 1981 through 1985 there were trucks with gauges and trucks with idiot lights, and the wiring is different between them. And there's A/C and non-A/C. So you have to pick one like yours.

[JimJam300]

I would assess the rust damage further if you haven't already and find where that leak is before making a move. That paint could be hiding something spooky underneath and it could just be the picture but it looks like the back window isn't sitting in there just right, maybe pull it out and inspect? My Bronco was parked for a number of years with the windows down and similarly had rust damage from water intrusion. The worst spots were the driver-side floorboard like yours and the door sills on both sides.

To yank the cab you'd have to pull off the hood and front fenders and everything attached to them. Disconnect every bit of the wire harness that runs through the firewall, brake lines between master cylinder and proportioning valve or the master cylinder itself, parking brake, throttle cable, cruise control cable (if any), windshield washer lines, ground straps, A/C lines (if any), heater lines, transmission linkage if it's an auto, steering shaft or the whole column, probably more I'm forgetting but these are largely easy things. Then transfer everything over to the new cab including the dash, wire harness, etc etc.

From my experience (I didn't pull the cab off my Bronco but I have had it nearly completely disassembled) there are some extra things you would likely need to do work on. If the brake lines are seized at the flare nut you have break them off to remove and bend new lines. though I suppose you could just pull the master cylinder off the brake booster/firewall and support it without losing any juice. Body mounts are a complete pain if the bolt comes out in 2 pieces and the correct replacement parts are hard to find (and aftermarket ones are totally wrong), I've had to cut several of mine apart. I would probably drain and refill the coolant and brake fluid since you're already opening the system. I'm also thinking it might be difficult to find a cab that you're satisfied with. Not only would you have to find the correct one for your transmission and A/C or lack thereof, but one that is free from damage and heavy rust. It would be way more work than a patch and paint, and you'd probably break things in the process. I think it's only worth it if you're going to do the whole truck, but you may be a lot more focused than me. I'm already down the rabbit hole of going from getting a truck roadworthy to doing a full restoration and it was frighteningly easy transitioning into that mindset.

[81-F150-Explorer]

When I see something like that, I wonder what happened etc.

Some ideas for you.

Ford used to make patch panels for the outer and inner roof and drip rails. They sadly do not any longer, but getting a roof panel from a good cab (or one that has a good roof section at least) to put on this one might be of help? Ford didn't change the outer roof section from 1980-1996. F-100/F-900. Only difference would be cab lights or cargo lamp. The floor and lower cab corner patch panels are already reproduced etc. A heck of a lot of work to be sure, but if you can't find the correct cab, it might be an option.

If the cab is too far gone, then getting another cab, and transplanting your firewall to it might be an option as well if you can't find the right one for your truck.

One thing for sure, when it's time to seal the truck again, use a auto body sealant such as "3M's all around auto body sealant". You can use it on all the seams, and can be sanded, and is paintable. It can also be used to seal small drill holes. Silicone caulk can actually rust steel, making things worse.

Good luck to you in what you decide is best!

 

[81-F150-Explorer]

As for your thermactor valve, do you have the engineering part number on the part itself by any chance?

[Ford F834]

I can tell you from experience that cab removal is relatively easy… and a single cab is decently manageable from a weight perspective. Unless you otherwise succumb to scope creep, there is no reason to equate a cab swap with a frame off restoration. With some preparation the swap can be done in a weekend.*

*Provided the cab going on is run-ready…

**If it isn’t run-ready and you have to transfer the wiring and interior from your existing cab, allow at least another weekend 😅

Given the issues with your cab, I would say that the labor involved in fixing it is probably not worth it. I can’t speak to the prices or availability in your area, but I would only repair the one you have as a last resort. As far as now vs later, I would vote for sooner rather than later. These things are not getting any easier to find in salvage yards or online as parts trucks. This body style is taking off among hobbyists and I would grab one if you can find one. You will feel better about investing in your project if the body is solid.

Gary mentioned that the wiring is very different for 1980. There are more large differences in 1983 (when most to feedback carbs with computers). Note that that 351 HO and 460 engines were non-catalyst and tend to have simpler wiring that is more like the early models. The diesel trucks are also simple and slightly different.

The cab wiring is not to difficult to swap if you need to use yours, and is best removed in one shot attached to the dash shell. A full cab wiring removal takes me about 2 hours, and perhaps a bit longer to put it back. The catch is AC vs non AC since the firewall is different and mix matching AC and non AC wiring HVAC cables etc., gets messy very fast. When shopping for a cab, AC vs non AC is more important than the wiring. Learn to recognize dealer added AC as well, as that is a whole different can of worms and the cab should be treated as a non-AC model.

[Jon M]

As for your thermactor valve, do you have the engineering part number on the part itself by any chance?

according to the PDFs in the Documentation tab the part number "9F491" but it is definitely discontinued and I don't see aftermarket makes anywhere.

[Gary Lewis]

according to the PDFs in the Documentation tab the part number "9F491" but it is definitely discontinued and I don't see aftermarket makes anywhere.

Jon I'm not sure that Jolene is 4wd, but I think it is. And assuming it isn't a California truck and doesn't have the high-altitude calibration there are only 3 calibration parts lists that are for an '84 F150 4wd w/a 300 six: #353; 355; & 364. And all three use the same valve: E43Z 9F491-C or CX-921.

Right, Ralph?

[Jon M]

Jon - Do you have emissions testing where you live? That makes a big difference.

The best way to fix all of this is with a replacement cab. And the easy way to do that is to buy a donor truck with a good cab but bad something else so it is cheap. Then you disconnect the wiring, unbolt the cab, raise it up, and roll your frame/engine/bed under it.

The wiring runs from the driver's headlight back through the cab and forward to the passenger's headlight. So you can leave everything in the cab and disconnect from the engine harness and other things under the hood. Remove the fenders and pull the 4 bolts that hold the cab on and it'll come off.

BUT! You need a cab wired like yours. And in 1980 there were differences so don't go with an '80. And from 1981 through 1985 there were trucks with gauges and trucks with idiot lights, and the wiring is different between them. And there's A/C and non-A/C. So you have to pick one like yours.

I do have emissions testing unfortunately. So I feel like it's a risk to leave this unaddressed. Also I'll eventually be trying to register this thing in California and they are notoriously strict on emissions.

As for trading the cab out. I guess I'm going to need to get looking into a donor vehicle... and a place to put it. My truck is a manual transmission, would I have to find a donor truck with that transmission style or would I be able to cut the appropriate holes in the cab floor?

I'm quickly finding that not all cabs are created equal. This is going to take some doing.

[salans7]

I do have emissions testing unfortunately. So I feel like it's a risk to leave this unaddressed. Also I'll eventually be trying to register this thing in California and they are notoriously strict on emissions.

As for trading the cab out. I guess I'm going to need to get looking into a donor vehicle... and a place to put it. My truck is a manual transmission, would I have to find a donor truck with that transmission style or would I be able to cut the appropriate holes in the cab floor?

I'm quickly finding that not all cabs are created equal. This is going to take some doing.

As someone who is running a 1990 F350 pretending to be a 1980, don't go with a 1987-1996 cab unless you're robbing panels. The newer cabs may look the same, but they have some differences that require a welder and grinder to work around, and definitely some hours into making it all work together. Stick with a 1980-1986 cab if you can and save yourself the headache.

Also, when shopping for a new cab, pay close attention to the firewall. You're not just looking for rust, you're looking for other damage to the firewall like cracks caused by a hydraulic clutch and no reinforcement or a previous owner who lifted the cab by the weak fender mounts and cracked the firewall in the process.