A few months ago I picked up a 1981 F150 and I’m starting to do some work on it. The idea is get it mechanically decent on a budget so I have a truck to use while I am taking my time with my 4-door diesel build. It is a permanent addition to the diesel, and I plan to keep it and rebuild/restore both trucks eventually. The 1981 fits most of my light duty truck criteria but not all. It is a straight six, manual transmission, pre-computer truck with factory AC. However it is 2wd, and I need 4x4, so I picked up a non-running 1982 F150 4x4 donor truck for the swap. The straight six in the 1981 was recently rebuilt and is strong. I have a lot of extra bullnose parts that I have collected over the years so let’s see what I can make of this truck without wrecking the budget…



First order of business is the 4x4 swap. I want the cab and frame VIN’s to match, so I am switching axles. I have read that the “correct” way to do this is to switch the spring brackets and keep the wider 3” 4x4 rear leaf springs. Why? The 4x2 has five 2.5” leaf springs and is rated for 6,100 lbs. GVW. The 4x4 has four 3” leaf springs and is rated for 5,700 lbs. GVW. I don’t know why Ford used wider, fewer leaves on 4x4’s, but unless someone can give me a solid logical answer as to why I should switch to the 3” springs I’m not doing it. It is a lot of work to drill out 32 factory frame rivets and replace them with bolts.





Next order of business is the rear axle itself. The 4x4 axle is leaking a lot of oil into the passenger side brake drum. Should I switch axles and fix the leak, or should I perhaps just trade out the center section? Both are Ford 9” rear ends. The 4x2 has 2.75 gears, the 4x4 is 3.00 ratio. The 2.75 center section has a lip extending over the u-joint and the 3.00 center section does not. My understanding is that they will still interchange.







Third question/decision I have to make is regarding the transfer case. The donor truck has a BW 1345. I also have a BW 1356 laying around. Both were ridden hard and put away wet, I believe. I have been told I should open them and check the case to ensure that the triangular oil pump flange is not wearing through the anchor notch, and perhaps weld a piece of rod to it so that does not happen in the future. What else should I look for when deciding which unit to use? Chain stretch is the only other thing I can think of besides general appearance. Is one model of transfer case better than the other? My 1356 is the type with the speedometer gear so I’m okay there. The 1356 has a slip yoke, whereas the 1345 is fixed. Since the rear drive shaft has some spline play I am anticipating the need for a new rear shaft either way.


BW1345/1356 oil pump flange modification

The donor truck has a NP435 transmission. However, I think I am going to shelve that one and use the BW T19 that came out of my diesel. The close ratio transmission will be a better fit with the straight six’s narrow power band. Driving it like a true 4-speed with 1st gear starts (in my opinion) is a near-perfect match with the 3.00 gears and 31” tires. It gives you a strong, clutch-friendly synchronized 1st gear, and 3rd gear is only 4.26:1 if you need to drop out of direct drive to pull a grade without making the engine scream for mercy. The straight six has a torque peak and power band that is almost identical to the 6.9 IDI so the shoe fits.


4.02 x 3.00 = 12.06
2.41 x 3.00 = 7.23
1.41 x 3.00 = 4.26
1.00 x 3.00 = 3.00

I have many other points to discuss, but for now I think I will keep the focus on the three main drive train questions mentioned above. That is what I need to tackle first, and I need answers. I’m happy to have a 1981 again, it is my favorite year of [gas engine] bullnose!

 

I'm along for the ride.

As for the rear spring question, don't bother to change. Rusty was originally a 2wd truck and had the narrower springs, and they didn't change that when they converted it to 4wd. It worked well for many years, so I see no reason to change.

On the rear axles, just swap out the center sections if the 2wd axle isn't leaking.

The 1356 I have uses a different shift lever arrangement than the NP208. And I think the 1345 uses the same arrangement as the 208. If so, you need to think about the linkage arrangement. And I think you are right about the pump. But other that, I'd change out the change.

 

Thanks Gary! I hadn't thought about the transfer case linkageneeding to be modified. As you can probably tell I'm trying to keep this project simple so as not to subtract too much effort from the diesel. Unless the 1345 is a basket case I'll just swap that in.

Good to know about the springs. That is kind of what I thought.

On the 3rd member swap, I recall reading that you need to replace some copper crush washers? Anything else I should do while I'm in there?

 

Yes, I replaced the washers using copper washers with ones I got from the parts store for brake connections. Beyond that, I think you are good.

 

I would go through the whole complete rearend. Not necessarily replacing everything, but you will be pretty much taking it apart anyway to pull the pumpkin. I think I would go ahead and check/replace the brake shoes, go ahead and replace the rear wheel cylinders unless they look brand new, and replace the rear parking brake cables unless they look new. The wheel cylinders will eventually fail so you might as well replace them now and they are cheap. While you are doing that go ahead and replace the metal brake lines with the copper nickel lines if your lines look pitted and rusty. And the parking brake cables rusting and getting stuck is a very common problem, and they are not expensive either.

Try to clean the frame up as good as you can and put some sort of paint on it. These frames are known to get rusty. I would also drop the fuel tank down, make sure it's not rusted out on top where it sits against the crossmember.

When you swap the frontend in place, check the condition of all the bushings and the steering joints. You might want to wait to check the balljoints unless you can check them now on the donor truck.

All these things are common problems with these trucks. Fix them now or fix them later.

P.S. I never replaced the copper washers, a little rtv where it goes together and re-use the washers has always worked for me. The rtv will ooze in around the studs and seal it up.

 

Thanks for the tips Franklin. I am definitely in favor of replacing all the common, small ticket wear items that I can. This may be a budget project for now, but it certainly isn't zero budget. I need to get it dependable.

I am in Arizona so rust isn't a huge problem, but they are starting to use salt now in the north end of the state. The 1981 actually needs cab corners, and I want to see to it that it never goes beyond that. Members here gave me some good advice concerning rust prevention in my diesel build thread.

Sounds like switching the 3rd member is the easiest route. Unfortunately I still need to do the U bolts and lift blocks, but it should still be less work than wrestling the axles around. The 9" might not be as bad, but Sterling 10.25 swap I did was exhausting.

 

I'm hoping to do the 3rd member swap this weekend. I bought the copper washers for brake hoses as Gary suggested. Now I have two more quick questions:

Paper gasket or ultra-grey RTV to seal the 3rd member to the housing? I've read both will work, but if anyone has any experience to share I'd appreciate it.

The certification label on the donor truck says the axle code is H4. This should mean limited slip. However, I can't imagine that the clutches are still working. Do I still need to use the gear oil with friction modifier, or will any gear oil do? Since the truck has 4x4 I may or may not ever repair the limited slip, and if I do I will probably go with a Detroit tru-trac, not wearable clutches. But that is another day.

 

Ultra-Gray. That's what I used and it worked very well.

On the rear axle, Dad's had the clutches and they were worn so badly that I had to go to 4wd to get out of a pasture. If yours are that worn the LS additive isn't needed. But I agree - if I had Dad's to do over it would be Tru-trac and not the Kevlar clutches. That's what Big Blue has and I don't get the twitchyness that Dad's had on a bit of sand in a corner.

 

I know this is an extreme long shot, but it does not hurt to ask...

Does anyone here have, or know of, some available Ford 5 on 5.5" x16" wheels? My dad had these on his 1966 F100, and evidently they were used from 1950-1966. So as you can imagine this isn't the kind of thing you can just go grab at the junkyard.



The reason I want them is because I would like to run the 235/85-R16 tires that I've always used on my F250's and F350. I want the diameter (31.75") because I don't have an overdrive transmission. I need the narrow tread for traction. I can't stand wide tires. The only thing close to that tall and skinny for a 15" rim is bias ply super swampers and that is not a very good general purpose tire. To get the diameter in a regular 15" tire you have to go wide...

I did find one aftermarket rim option, but the rim width is 8". I know it is sometimes done, but 235/85 manufacturers recommend no wider than 7" rims. The wheels I found are also pricey and not really to my taste.

Alternately, David has made me a proposition on his argent spoke wheels with chrome beauty rings. They are 15"x7". I am open to tire recommendations that I may be overlooking. Both trucks currently have 31x10.5's. They are too wide for my liking, and they are not a full 31" in diameter (more like 30" new, 29" when used up a bit).

 

Get on Summit Racing's site and search for wheels. They give you lots of options in the left column when searching. They have these, I picked 6 inches wide. They have 7 inch wide and you are right, lots of 8 inch wide.

https://www.summitracing.com/parts/w...0504/overview/

 

Thanks Franklin! Those look very promising. I would actually prefer 6" to 7" width. I need to understand the 4" backspace and see how that compares to stock wheels, and check the pilot hole diameter for the D44 hubs. It's a minor detail, but I wonder if stock dog-dish hub caps will fit?

 

Looking at the picture I would say no to the stock hub caps. If you look at your picture above, it has 3 nubs on the od of the center that the hub cap snaps over. The wheel vintiques at summit is smooth. I bet it's made for a very old Ford hub cap like on a 1940 that clips on the inside.

 

Thanks. That's what I was thinking about the hub caps. Not a deal breaker, but unfortunate. Had I only known to hold on to the wheels from my dad's 1966. It had terminal rust cancer and it went to the recyclers almost 20 years ago.

 

Jonathan, here is an idea... sometime, around 2005 - 2008, Ford offered a 16" rim [alloy] for the E150. It is 7.0" wide, has the correct offset and utilizes the 5 X 5 1/2" bolt pattern, I am relatively sure. I am going to include a link, for illustrative purposes, but perhaps you can find some @ the junk yard. The description says 6 bolt, but is incorrect.

https://www.wheelsandcaps.com/p-2040...16x7-3552.aspx

 

Hmmmm, good info David! I did not know the 5.5" bolt circle was used that late... I thought everything was metric by the 2000's. I will have to check out some Econoline vans at the junkyard. I wonder if by chance they came with a steel rim spare? One almost never finds a full set of alloys at the JY... but I might be lucky and get a matching set if it is a common enough wheel.