PT81PlymouthPickup

I concur! 3:73 ratio is the way to go. The 4:10 was not great for speeds over 50 in my opinion.

Yeah! I remember installing the inner seals on mine. I believe the inner seal could be installed backwards if not paying attention to the lip design which could make it leak. Also, I too have seen axles with grooves worn in so deep that even a new seal won't keep the oil back. Been too long for me to remember for sure on mine, but if the axle is grooved, you might be able to reposition the inner seal a tad to a good surface on the shaft. It is possible to overfill a differential which could cause problems. The oil level should be just below the threaded drain plug hole.

Not sure if the ones I have are Mopar or aftermarket, but they screw right in to the underside of the windshield defroster vents in my dash on the 39. I'm relatively certain it should be the same for all cabs up to 47?

Likely not worth much. ? I have a complete one in perfect condition that I know will fit 39-47 Dodge and Plymouth pickups which I've been trying to sell. Can't even give it away. I suspect the one I have will fit other car and truck applications as well? They are robust rear ends, but with tapered axles and rarity of good drums along with no emergency brake provisions not very popular. If you find someone that really needed one for a restoration you might have a chance at getting a few bucks?

Sure! I plumbed between vacuum port on intake and where the downdraft tube used to be. That was fairly easy using available parts. Pretty sure Vintage Power Wagons sell them? I got mine off a 60s vintage 230 engine. Bolted right on. I purchased an oil fill tube with 1/4 npt fitting from VPW. Making the connection for filtered air from the oil fill tube to the the carburetor was more of a challenge. I machined an adapter out of brass and bent up some steel tubing.

https://www.ebay.com/itm/235223352508

I agree with Los_Control. It's why I have a stock differential and housing along with brakes and drums sitting under a shelf in my garage. This original housing with a 3.90 ratio low mileage differential had the ball & trunion u-joints. I installed a Jeep Cherokee posi-traction rear end in my truck. Very happy with it. Easier to service and get parts, better ratio choices. 3:73 being the best in my opinion, and emergency brake that works much better. That said, for those that are not experienced in such transplant endeavors or not having access to fabrication equipment would be frustrating and if having a pro do it, cost prohibitive. I spent many hours doing this conversion. Cut off spring perches, weld new perches at correct angle, fabricate custom bracketry for parking brake cables. Custom length brake cables. Custom drive shaft. Just pointing out that some often touted easy projects can be a can of worms especially if not accustomed to doing such things. Anyhow, the original differential I have would be a bolt in for any 39-47 Mopar unmodified 1/2 ton trucks. Not sure about 48 up? I know the Yoke could be changed for later model u-joints, but not sure the housing and perches would be correct? Perhaps someone here knows? I'm hoping to see this original rear put to good use again. If you (jdrader2) were close I'd give it to you if it fit. Until I find a good home for it, I won't scrap it.

Anyone know if the 39-47 truck rears (differential and housings) were the same used in the 48 and up trucks? Or are they different? I have a complete (39-47) rear with brakes and drums in perfect condition. Hoping to see it go to a worthy project.

Jim, Any flat-head 6 engine from late 30s up to 1960s with 23 inch blocks will go in if you have the original type bell housing. Likely be smart to try to get an engine from a 39-47 era truck or car because there are some differences in the later engines that might cause some install aggravation. I doubt the trans out of a P8 would be compatible? Should be others on here who would know. The original gear box in my 39 was not synchronized (which I still have in my attic) I adapted a Borg Warner T5 five speed. I'm not certain, but perhaps the later trucks by 47 were synchronized? If that's the case, and you need one, try to get a synchronized box. Much easier to drive.

I retrofitted a PCV system from a NOS 1960s 230 cubic inch military engine. The first photo shows how it came from the factory. AC CV-698C was the valve used. The valve has 1/4" NPT male and female on opposite ends. Plumbing from where my downdraft tube was using the same fitting in your photo to the intake was a fairly easy job, but I had to fabricate an adapter for the clean air intake and bend up a tube. I Purchased an oil fill tube with threaded boss from Vintage Power Wagons. I think I have an extra one if anybody wants it? The project was a little challenging, but has worked perfectly. No more stinking oil fumes and less oil seepage around seals. I believe the oil stays cleaner as well? To do something like this you'll need access to a tube bender and a flaring tool and some fittings. There may be an easier way to connect to your air cleaner, but I couldn't figure a way I liked, so being a machinist, I made the adapter from a piece of heavy-wall brass tube.

Yeah, I'm running BF Goodrich LT 215/85 R16 Commercial front tires which can be inflated to 80psi. I run 60psi in them which it steers remarkably easier than with the light duty tires which I used to have with 35psi. I do feel the potholes a bit more. I think it was a good tradeoff on my 39. Steers much easier.

I'm guessing to adjust caster on our straight axle trucks is to use wedged shims between the leaf springs and the axle? My 39 does not have any such wedges. Did most of our era trucks use wedges for caster or were they manufactured well enough to not need them? I remember having a professional alignment done by a good shop in my area back in the early 80s. They had to bend the axle a bit to achieve proper camber. No easy task for a shade-tree mechanic! Perhaps they could adjust the caster by bending as well? I think they did it using hydraulic equipment? Not sure if they had to heat them? Seems to me heat would be a bad thing for metallurgy?

I'm wondering if electrical connections on our vehicles were soldered originally? Seems to me on my original harness they were not? Like Sniper, I soldered all mine and then shrink tubed. It was a bit tricky not to have the solder wick up the wire, which might make it rigid and more susceptible to breaking from vibration? Any thoughts on this? Oh yeah! Be careful to not use any acid flux. Ask me how I know. Lols! As always, "the devil is in the details"

Quality looking repair on that frame! It's not often to see someone going back to original after those kinds of hacker modifications. Too bad you're not close. I have a perfect complete rear end 3.9 ratio that I'll give to you or anyone that would actually use it. I won't ship it however. Too much hassle. I'm curious how the truck steered with that rack and pinion in there?

No rush! It's been sitting in my garage for almost 20 years. Lols!

Others here might have a more definitive answer on which differential ratios were available when our trucks were first built, but I'm thinking most of the 39-47 Dodge / Plymouth 1/2 ton trucks most likely had 4.1 ratios. When I first rebuilt my truck in the late 1970s I found a low mileage 3.9 ratio pumpkin which I took out of a circa 1950 Mopar car. Other than the ratio, it was the exact same carrier (pumpkin). It worked well with tall tires. Plenty of pull on hills and lower revs on the highway as compared to the 4.1. I ended up taking it out when I installed a T5 transmission because I no longer had an emergency brake on the trans. I installed a 3.55 ratio rear out of a jeep Cherokee. It works OK, but struggles on long hills. If I were to do it over I would select a 3.73 ratio. I think several others on here might agree with 3.73 ratio as being a good choice for our trucks? Anyhow, if you want a perfect bolt in condition complete rear end with a 3.9 ratio it's free to you or anyone else that might want it. Drums and brakes are all like new as well. I won't ship it, but I'd be happy to see someone come get it that might use it.

My opinion is get a 3.73 differential! I'm running a 3.55 behind my .040 over bored 201 block in my 39 PT81 with a T5 trans. It will go up big hills but requires much shifting and I sometimes get a line of modern vehicles lining up behind me. It will cruise wonderfully at 65mph or better on a relatively flat roads. When I had my original trans with a 3.90 differential It would climb a mountain but at 55mph sounded like she would blow up from high revs. I have mixed feelings on dual anythings. Really sweet to look at, but the little extra performance we get comes along with more things to give me aggravation. Twice the carbs and twice the exhaust means twice the things to fail. I must admit I'm jealous of those cool looking dual installs. I started to go the dual route by accumulating some parts, but decided if I do anything more to the old girl, I'll install a 3.73 differential. I still have original rear end with a 3.90 gear in perfect condition if anybody wants it? (Free)

Yeah! And even with upgrades to brakes, gear ratios, and tires, which I've done, it's still a bit risky driving these old trucks at modern highway speeds. Like Young Ed indicated; how much nerve do you have? Lols! I suspect also that my truck might be easily rolled over in a high speed mishap? My 39 has the earlier design door latches which were noted for flinging open in accidents where the driver is thrown out, usually under the wreck. I try to stay off the major roads as much as possible. On the other hand, at my age, it might be a better way to go than ending up in some nursing home. Lols!

Tall 16" tires and a 3.90 differential with standard trans I had her up to 70 mph. The flathead six sounded like she was ready to blow up. Stay off the interstates! Lols!

My 39 PT81 did not have a relay when new. Perhaps by 47 they may have? But, I believe Young Ed is correct. No relay. A wiring diagram specific to your truck would be most useful. On my truck, power it's routed via the amp gauge through the harness to the horn and then back into the harness to a connector which connects to the ground wire that goes up through the steering column to the horn button. I kept mine wired this way without a relay. I converted to 12 volt many years ago. I'm still using the oem 6 volt horn and it works flawlessly. However, it rarely gets used. If I were to use it daily, a relay might make sense. I doubt you'll be using it much in a 1947 truck? The neat thing is; my 6v horn will scare the bejesus out of anyone I honk at. ? By installing a relay, the load will be carried through the contacts in the relay, that protects the horn button contact from arcing and as Ken suggests could shorten the life of the horn button switch. More importantly, whatever you decide, make sure there's a fuse in the circuit. When you start making changes like I did (12v conversion, stereo, halogen headlights, signals, alternator, electronic ignition) it got really challenging for me. Altering the harness and routing wires correctly and making it look right was no easy task. Did I mention, I had little idea of what I was doing. For me, it was the most frustrating thing of the entire build. But that's just me.

Jay Leno knows a thing about fire. ? Anybody know about these Element extinguishers? Sure looks like a good alternative to those bulky ones.

According to this Hemmings article, not until 1946? https://www.hemmings.com/stories/article/1939-1947-dodge-trucks

If you're worried about scratching up your paint job, it's advisable to have someone help you lift the windshield out. It's a bit awkward to do by yourself.

Yes, it telescopes from about 8-3/4 to 11-1/4 in length.

Thanks Ed! Yeah, I have a blade that looks like that, but it's 7-1/4" long. Does not work well at all. The one in my photos works better, but it overlaps the windshield frame which will damage the paint if I keep using it. I'm thinking there is an arm / blade combination that will work better than the original on our trucks, but sure hard to find any info on what that might be?