Hi all,

I’m new to this forum but new to car forums, I’ve had a lot good experience with forum folk and look forward getting involved with FTE.

This first post is really about getting the advice/opinion on my next project from people who know a lot more about f-trucks than me so please feel free to contribute. I am in Australia so some of my car terms and models may be slightly different so bear with me.

For a while now I’ve been after a ’73-80 LWB 4WD F100 with a factory diesel engine (Perkins 6.247) and manual tranny. In Australia such a combo is extremely rare (there were only 200 factory diesel F100s of that era brought/made here), the only one that I have seen was out of my price range by 10K.

Recently a ‘78 2WD LWB diesel 4sp f100 came up for not much and is in great original condition (factory logbook, hubcaps, etc), and I have access to a ’77 LWB 4WD minus engine (351 petrol) that has been written off at the rear end.

So I’m thinking of buying both trucks and putting the front 4wd gear (complete front diff assembly, transfer case, brakes etc) into the 2wd truck. There doesn’t seem to be much info on how interchangeable the part/chassis are on the internet, or maybe I’m not looking hard enough.

It’d be great if people could let me know how realistic this is and what sort of difficulties I might encounter.

I suspect that the diff ratio in the petrol front diff would be different to the diesel rear diff, is this correct?

Would the transfer case be different between diesel & petrol engines?

Are the chassis-suspension anchor points different?

Just for some background I’ve got ~10 years spinning spanners on all manner of cars as a hobbyist mechanic; from making spastically powerful Gt-R skylines to restoring older Mercedes diesel s and running them on veggie oil.
I feel comfortable with challenges but I just would like to know how much is ‘bolt-on’ work and how much would be custom /welding work territory with this potential project.

Thanks in advance for your contribution, it’d also really help if you could post links that may be useful, and remember that some things relating to F-trucks may not be obvious to me because the closest thing I’ve owed to one was a 351 ford falcon coupe.

Cheers,

James

 

Hey James welcome to FTE

A perkins diesel ? Nice! Sounds worth while .. One potential problem may be the oil pan .. A rear sump oil pan would be a requirement unless lifted enough .. Just a thought a 2wd with a rear locker will perform just as good as a 4wd 97% of the time in most cases is my experience .. So drive it most of the time .. Restore the 4wd petrol for the other 2% of your driving ..

 

Most guys on this forum will tell you that you're wasting your time, that it's a huge undertaking, and to just go buy a 4x4.

Things that will need to be done.

-Frame will need to be boxed and the steering box will have to be changed for a 4x4 unit and relocated to the front of the axle. The 2wd box is mounted to the rear of the axle.
-You will have to run some lift and/or modify the original 2wd front crossmember to clear the axle.
-Swap axle gears to match
-Swap your trans tailshaft for one from a 4x4, or on the easier side, just swap trans and transfer case as a unit from a 4x4 truck
-Fab up and mount a Track bar mount to your frame.
-I would swap to coil buckets and spring mounts from a 4x4
-Miscellaneous things such as brake lines, transfer case linkage, steering column, trans crossmember etc..

If you're in Aus. I assume your trucks are RHD? May prove difficult to source some parts, but I have no knowledge of RHD units.

If you have a full parts truck you have a good start, I have been throwing around the idea of swapping my 2wd F100 over to a 4x4 after I'm done the rebuild. I could find an axle and parts donor easy enough. Solid 4x4 dentsides pull a premium around here, or are they are rusted out heaps.

Since I can't buy the truck I want, why not build it?

 

There is nothing nuts and bolts about a 4wd conversion, there is not a thing that is bolt on or swappable. The engine cross members are entirely different, and this means that if an un molested truck is what you are after, it will be impossible to create one with a 2wd platform.
The 2wd will have to be lifted quite a way to clear the front diff. 2wd trucks are coil sprung and most F250 4wd's are leaf sprung. None of the suspension items are even close to the same, so you will be fabricating or modifying some original 4wd stuff to work.
Steering systems are entirely different as well, so you will be upgrading that too.
My last conversion with leafs ran me several thousand dollars, and that was with the work that I performed for free. The difference in sale values between a 4wd and 2wd are minimal, and the 4wd conversion is hardly justifiable.
Well the frames are similar, with a few exceptions. The frame horns are slightly different, and the frame widths aft of the cab are different from 73 to 77 trucks. The frame rise is also slightly different, but this is not a show stopper and does not make much difference one the fabrication begins.
Now the important question is whether or not you will be using a coils springs or a leaf spring. It is possible to install a 78/9 radius arm and suspension. Not a big deal really, and with a standard cab this is reasonable. Not quite as easy with a super cab and or crew cab.
The 2wd frames are not cut for the shackle pivot, and they do not have the provisions for a spring hanger, but again, this is not a deal breaker. Installing a pivot is just a tedious process, accuracy is key.
Ok, so next is the transfer case. You have two choices, install a married case, and this requires the proper transmission. Might find some difficulty making or modifying an output shaft to accommodate the early C6 and a married transfer case. So then the next option is to find a divorced transfer case, and install this. You will have to make up a cross member, but then you will have to get creative with the shifter linkage. See the 4wd trans will have an adapter or tailshaft with a pivot for a typical 205 shifter. Fabrication is the only limiting factor here.
Next and final factor will be the speedo. See your speedo works from the trans, so that being the case, you will have to get a speed reference from the t-case. If you do not, the speedo will read twice as fast when you put the case in low range. But you will be in 4 low so who cares how fast you are going.

As mentioned the steering box will have to be relocated, and the truck will require some lift. That engine crossmember has limited clearance so you will be looking at some lift to even clear it. The other option would be to remove it and replace it with a tubular unit.

Shane?? "I would swap to coil buckets and spring mounts from a 4x4"... F150 coil buckets and radius arms or F250 front leaf springs but (read above info )....both are not needed. Also trac bar is a F150 set up only. just saying.

 

Pardon me if this is a stupid question (and please don't anyone say there are no stupid questions...we all know that isn't true), but why not just straighten the rear of the 4X4 frame and do a body-engine swap onto it? I'm sure there would be issues with engine mounts and the oil pan, but a heck of a lot easier than turning a 2X4 frame into a 4X4 frame.

David

 

"I have access to a ’77 LWB 4WD minus engine (351 petrol) that has been written off at the rear end".

Written off by who, DMV or insurance company? It is fixable, fix it and just do a engine swap. If its not, so what a rear frame from the 2wd swap a fish plate frame joint and you are rocking.

So what rougerriver said.

 

Thanks guys, that's exactly the kind of info that I've struggled to find.

"Written off by who, DMV or insurance company? It is fixable, fix it and just do a engine swap. If its not, so what a rear frame from the 2wd swap a fish plate frame joint and you are rocking."

Yeah I had thought of making an easier hybrid of the two but the 4WD donor has seriously bent chassis rails where the rear was struck by small truck so it's really only for parts.

I'm negotiating with the seller for the 2WD diesel truck and if that works out I'll pick up the 4WD then put the project on the hold until I have a lift kit and a clearer idea of what's required.

It wont be my daily driver so it'd be ok to leave it jacked up and in bits for a while.

Thanks again, I'll post pictures when/if I get the truck.