Hello from Mt Vernon, WA where the rivers are rising fast...

I bought recently a Chinook motorhome built on a '75 F-350 chassis. I have the 390 V8 with four speed trans and what I'd like to do is to convert from 2wd to 4wd. Can someone fill me in on what this will entail beyond the obvious front axle, transfer case additions. Can an F-150 donor truck work or does it have to be an F-250 or higher? Do I have to find a donor with a manual trans like mine or can I use an donor with an auto trans?

I am already finding good donor trucks available so any advice will be greatly appreciated and thanks in advance.

 

Not knowing the "E" series vehicles of this year, I am just gonna throw out some questions and see where we can get.
In any 4wd conversion, I am partial to the remote mount transfer case. I like it because it will allow youto use the existing 2wd transmission. This eliminates some troubles taking the trans apart to replace the output shaft. The alternative is to replace the shaft and this requires the disassembly of the transmission.

Alright, as I recall, the vans had a wider frame than just about any other truck, so a donor axle will require quite a bit of fabrication. This might just eliminate the use of leaf springs and require the use of coils. Still a radius arm front suspension might be an option. I might be concerned that the tires might hit the radius arms during a lock to lock turn.
This frame dimension might make things interesting. Have you any pics of this rig? Maybe some suspension shots, and perhaps some frame dimensions?
This might help a little.

Holy smokes, where were my manners?

Welcome to the site...........

 

Thanks for the reply 75F350

My Chinook is built on a F350 truck frame. It is what is referred to as a chassis mount style as opposed to the much more common class c style which are built on the van chassis. It is possible that this is called a class b?

I'll try to find a pic somewhere of my rig if you have never seen one before and thanks for your advice and the words of welcome.

cheers

 

Ahhh, no worries, Thank you for the lesson. I learned something from this. I was not aware that this was not a van.
This sheds a whole new light on things.
How much of a concern is the heigth of the vehicle going to be? 2wd frames will have a different crossmember and this creates some clearance issues. This may require some lift, or modification to make this work.
Now we have many threads that discuss the 2wd to 4wd conversion. Some choose to use the radius arms from a half ton truck and use coils springs while others simply install some leaf springs.
I have converted a 2wd 75F350. (user name, lol) to a 4wd, and I chose to use leafs.
I did use the same spring hangers and stuff from a 4wd truck, and modified the x-member to fit the truck.
This was a painfully long process, and I will probably never do this again.

In many of the threads it has been recommended to use an existing F250 frame and modify the body mounts to accomodate.
In this application this might prove to be a slight problem, since you might be limited with your current body. You might be able to use a 77.5 to 79 4x4 frame to accomodate this swap. The frame dimensions will be similar.
So here is another idea. Use some bolt on spring hangers from a later 4wd truck, and modify the frame horns to utilize these. The 77.5 tp 79 hangers are bolt on, and are factory. Then you can acquire some pivots, and bolt them into your frame.
I still like the divorced t-case idea for the same reasons I stated above.
The rest is still just math and geometry.
You will have to look foward to modifying the steering. The 2wd trucks had a steering box that is mounted behind the front crossmember and the 4wd trucks used a mounting style that placed the box in front of the crossmember.
This will be a good time to upgrade to the later 78/9 power steering design, or other creative system.
You have your work cut out for you, and this will be quite a bit of work.

Using the donor frame will minimize a bunch of the fabrication work.

 

Can I ask, were there any 4wd F350's from the 70's? If so, would using the running gear from one of those be as intensive an effort as say using an F250?

I was basically hoping to take my Chinook and donor truck to a frame and axle shop and hiring them to swap the parts. I am personally not mechanically savvy enough to make all the mods you discuss.

Btw, here is a pic of my rig:

 

well i dont have any info to help you with, just looking for ideas for my truck.... but dont forget to join the washington chapter.... welcome to FTE... and good luck with that flooding lol... im basically stuck in one great big island right now, with the flooding of the stiligumish river, and the mud slide just past my house on highway 530, and the aditional flooding up on high way 20 GRR!!! another year!!

 

It could be done, just like anything if you throw enough money at it. Among the things that would have to be done: remove entire front suspension including steering box, remove crossmembers, box frame, remount steering box in front of axle, install leaf spring hangers & springs/axle, install transfer case, lift rear of vehicle to level with new height of front end. Yes, 4x4 F350s were available in the 70's but I've never seen one with dual rear wheels.

I'd suggest finding an existing 4x4 F350 and moving your camper onto it unless you just really want to convert your existing truck and money is no object. It would be more feasible if you could do it yourself, but cost prohibitive to have someone else do it. This would be a MAJOR change, someone would really have to know what they're doing to make it safe.

 

I wouldn't want a big lift as the cog is already high in my motorhome but know that some lift would be necessary. As far as using a donor frame to put my body on, my rig is almost factory new condition both above and below so that would not be in my desire to do.

In a 4x4 F350 vs. a 4x4 F250 would there be big differences in the front axles or other running gear between models? Would an F-350's be heavier duty due to the higher payload rating of the truck? THe reason I ask is that there are several really good 4x4 F250 donor trucks available in my area but not a whiff of a 4x4 F350.

If it ends up being a much bigger job to swap running gears to make my MH a 4x4, I wouldn't have a problem not going ahead with doing it. It was only an idea I had to make my MH into a truly one of a kind rig out there. (I have never seen a Chinook MH like mine with a 4x4 chassis)

Thanks again for the insight, info and advice.

Mike

 

There were NO 4wd F350's until 1979. Expect not to find dually 4wd's from this era either.
The dually deal is easy as pie if you can use a D60F later model dually hubs and adapters can work.
Now, as I suggested earlier, the COG could be a problem. Remember that differential has to clear the low crossmember of the 2wd. This can be a problem.
Now again as I recommended, it would probably be easier to find a 78/9 4wd xhassis, and swap the chassis and entire package over to it. Now, you can decide whether or not you keep the FE engine, or use a 335 or 385 series engine.
I suggest the 78/9 4wd because the frames and body mounts are so similar, you will minimize the labor to do so. Plus this era truck had a lower COG than any other early truck. These low boy trucks used an even different crossmember than the early trucks, and had a much lower ride heigth. This will come with a married t-case, so you will have to get creative about installing the FE engine using the existing transmission, but this is relatively easy to overcome.

Now a good fab shop can use your existing frame, and fab up a custom crossmember, and use coil springs and radius arms. This will keep the heigth down and the COG low. This will probably require the most amount of work, but will net the greatest results.

This company:
Quigley Motor Company, Inc.
Takes this approach on brand new vehicles.

I like this swap, and it really peakes my interest. I would like to take on such a conversion. I am undergoing a late 80's Jer-Dan roll off tow truck. (personal truck) and making this a 4wd. I use this truck to take one of my trucks to and from any given run, and the last run I made was to the sand dunes (Glamis) and I got the truck stuck. I had to take the truck off of the back to pull the tow truck out. Talk about comedy. I could barely use the controls to tilt the bed, but fortunately, it was stuck, and was low enough that I could drive my giant truck right off of the back. It was then I made the decision to convert this tow truck to 4wd. I can appreciate your desire..

 

I don't know much about 4wd conversions other than it seems to be a pain but possible to do, but welcome to the site. That is one cool looking camper.

 

75F350, what is the wheelbase of the Cab&Chassis' for 1975? I'm wondering if that might present an issue for the frame swap? I agree with you that the radius arm conversion with a fabbed-up crossmember is probably the best plan of attack here - keep it all lower to the ground.

 

Someone near me right now has a '93 F350 4x4 with a blown diesel so for sale pretty cheap. It has a 4speed with overdrive trans but otherwise the ad says little else. What is the feasibility of using this as a donor truck and what should I ask the seller?

1993 Ford F350 Crew Cab XLT 4x4 Pickup

 

man! that motorhome looks like it just came out of a 70's time travel machine. it looks brand new! nice find. i would leave it the way it is if i were you,but thats just my opinion.-hey chinook_dude welcome to FTE by the way.

 

thanks for the thumbs up...your right that she really is like new. one owner, 48k miles, absolutely maintained by a type A personality..he even kept the undercarriage spotless!

got a 390, 2bbl, dual headers and exhausts, 4 speed, but don't know what rear end

brakes were all new inclusing drums just before I got it to the tune of $1000

don't need to say the condition of the interior and totally 70's with harvest gold and browns but not tacky. from what I can tell these were a fairly high end rig in their day.

 

Got any interior pics?