PT81PlymouthPickup

I restored a 1939 Plymouth PT81 pickup almost 40 years ago. I believe it had a 201 or 218 engine from the factory, but when I acquired the truck the engine had been replaced and the identification numbers had been milled off. I was told at the time some professional re-builders did this? Anyhow, this engine was worn out, so we rebuilt it. Bored, oversized pistons, rings, all new bearings, etc. It has performed pretty well. I've tinkered with the truck over the years and have made several upgrades including T5 trans, 12 volt conversion, Jeep posi differential, front disc brakes with split master cylinder, but never any engine modifications. Lately, I noticed the engine seemed to falter a bit at about half throttle and seems to lack the power it once had. Still Idles very smooth. The engine has less than 2,000 miles on it since rebuild and still had the same points which I had filed a few times over the years, so I figured the likely culprit of the mid rpm faltering? I pulled the distributor, installed new oem Mopar points, condenser, and rotor, set the gap and reinstalled. I still have the same issue. I misted the ignition wires with some water while running to see if the wires might be leaking at higher rpm, but they did not seem to be. I'm uncertain as what to check next? I doubt spark plugs would go bad with only a couple thousand miles on them even though they are old? I've been considering installing either Langdon's mini HEI or Pertronix ignition. But here's the weird thing! I did a little research on my distributor #IGS-4003-1 which looks like it came in early 1935 vehicles? From what I've read the truck should have had a IGS - 4103 distributor. So now I'm wondering if the engine was an earlier one? There are some casting numbers on the block. Perhaps someone knows how to identify from these? (1119729-21) I'm hoping to get some advice to resolve the faltering issue and also wondering if I were to install a Pertronix ignition, should I use the distributor I have? I'm leaning towards Langdon's HEI because it uses off the shelf components and Langdon's price is only slightly higher than the Pertronix, but seems like a much better value when you consider you're getting the entire distributor. Opinions, comments, and advice welcomed and appreciated.

While doing a disc brake conversion I decided to address a few other steering and suspension things on my list. Made a new tie rod and bought a set of front leaf spring bumpers which were missing. Anyhow, after taking off the U bolts (spring clip 564009 according to old Dodge Job Rated master parts list) I discovered the 7/16-20 threads were in less than perfect condition. They feel looser than I like and thought it a good time to replace them hopefully with NOS. These original parts are forged steel. My truck has 1-3/4 wide springs which seem to be an unusual size. I have not been able to find any NOS or aftermarket. I'm hoping someone might know where to find 4 of these? I made a drawing in case I need to have them fabricated.

@PT81PlymouthPickup did you get that tube material at classic tube? No, I bought it from rockauto.com Do a search for hydraulic line and you should find it there. AGS CNC3 {#CNC3100, CNC325, CNC350} NiCopp® Nickel/Copper Brake Line Tubing Coil, 3/16". A 25 foot roll cost me around $36. including tax and shipping. You might find it cheaper locally?

They are residual check valves. The original master cylinders had a internal valve which would hold about 10 psi on the system. Very important on vehicles with master cylinder mounted below floor. They keep the fluid from draining back. New master cylinders don't have internal residual valves. So you need to add them when converting to a newer split system mc. With disc brakes on front 10psi is too much. Typically 2psi for discs. Blue one is 2psi and red one is 10psi.

I'm all about "overkill" too. I'm not sure if it's a virtue or a curse? Lols! Thanks for posting the photo. Very helpful. Do you remember the O.D and I.D. of the DOM tube you used?

Thanks Jerry! I'm surprised there was not more postings on tie rods?

The original tie rod on my 1939 Plymouth 1/2 ton pickup truck was bent. I straightened it best as possible when I restored the truck and it works OK but it's not perfectly straight and I wonder if it might be prone to bending again during a rapid turn? Anyhow, it looks bad and I wish to replace it. I'm sure the engineers knew what they were doing, but I have to say it sure looks a bit wimpy on these trucks. It's been a long time and I can not remember if it's a tube or a solid bar? The original measures .775 diameter with 3/4-16 male threaded ends. Overall length is about 43-7/16 long. My thinking is to fabricate a slightly larger diameter new one from tubing. The original tie rod ends on these trucks had female threaded holes which seems to be different from most cars and trucks that have male threaded ends. If I change the tie rod ends, I would have to find some with the same taper. Has anyone any experience with what might be a good way to upgrade? What might be the best material? Any advice would be greatly appreciated.

I thought I'd update my disc brake and split master cylinder install progress just in case anyone is interested? Finished bending brake lines needed for the conversion today. I'm using a copper / nickel alloy called NiCopp. Never used it before. I've read it meets oem safety standards and has been used for many years on European cars. I wish I knew about this before. Wow! Is this stuff way better to work with than steel or stainless. Bends and flares like a dream. That said, fabricating brake lines is still a royal pain. Laying on the cold concrete floor wasn't much fun either. Anyhow, I wouldn't refuse any constructive criticism, if any experts out there see something I've missed? Next thing to do is get the brake hoses and mount to the calipers.

That's promising to hear Ed. I agree the DCM looks pretty good. I'm hoping I might see at least one installed before considering purchasing. I reworked the original on my truck and it looks great, but it was pretty rusty and on the occasions when I get caught in the rain rusty water leaks out and leaves streaks on my paint. I think it's a matter of time before the rust surfaces through to the outside of the frame. The oem frames are so difficult to find a good one and they usually want too much money for them. IF? the reproduction is as good as it looks, I don't think the price is unreasonable.

I see that a couple outfits are now selling reproduced windshield frames for the 39-47 Dodge and Plymouth trucks. I'm always skeptical about reproduction stuff, but from the photos they look pretty good? Seems like it would be difficult to make one that fit like the originals? Anyone have any experience with these? https://dcmclassics.com/glass-accessories/1083-gl-370-kit-windshield-frame-assembly-with-door-and-rear-glass.html?search_query=windshield&results=11 http://www.srpmstreetrods.com/srpm/1939-1947-dodge-truck-39-41-plymouth-truck-windshield-frame-painted-black-with-clear-glass-seals-40288bca4b105134014b5f820e6a1455-p.html

My 39 originally had a single circuit 1.250 dia. bore m.c. The Jeep Cherokee m.c. I just installed has a 15/16 dia. bore and the Jeep Wrangler which uses the same casting has a 1" bore. If I end up with too much pedal travel? I can easily switch to the 1" bore without changing any plumbing geometry and hope it still produces enough pressure to stop well?

Yes, I believe split systems were government mandated sometime in the late 60s early 70s for safety. Did you have a warning light? Without a warning light, you could potentially lose your rear circuit and might not even notice it. Then if later the front circuit were to fail, no brakes at all. ? That's why the pressure differential warning lights were added. Perhaps something like that happened? I've read many times that if you do not have full m.c. travel before pedal hits the floor you might not get any braking if half of your system fails. My 39 brakes failed me when a deer jumped into my path. I slammed the pedal and no brakes. I almost rolled the old girl and narrowly avoided a collision with another car. ? That's what prompted me to upgrade to front disc and a split system. I've also read that combination valves were designed to be used on specific vehicles and if weight, center of gravity, wheelbase, drum / disc and caliper / wheel cylinder sizes, etc. are not the same as the vehicle they were designed for it can make a vehicle hazardous in an emergency braking situation. Might work perfectly until a panic stop. For a customized system most of the knowledgeable street rod builders recommend adjustable proportioning valve to adjust the front / rear bias for panic stops. They test them and adjust to prevent rear wheel lockup which is extremely dangerous in a panic stop.

Thanks Brad! Yes, the cast iron m.c. in my photos is exactly 8" long from mounting surface to the front. I'm fairly certain it will fit all 1939-47 Dodge and Plymouth pickups. Sounds like it won't work in yours? I was hoping the smaller Jeep aluminum master cylinders would work in mine, but the stroke was such that my pedal hit the floor before allowing full stroke of the m.c. I learned this could negate the purpose of a split system if you lose one half of the system from a hose or line rupture in an emergency situation.

The geometry would be different on the front side depending on which master cylinder is used. I have a drawing of the one I made if anyone wants it?

Made from scratch. I wanted to be able to reinstall the rubber boot to protect the back of the m.c. from dust, so I made one out of aluminum round stock as a prototype and then another out of stainless steel round stock. The alum. would have worked fine, but being too fussy for my own good I made another that will last forever. I am a machinist by trade and have access to lathes, mills, etc. which makes it a fairly easy project. Not sure why Mopar put the mounting holes on strange angles, but once you have them figured out, it's a basic lathe part. Steve ?

Thanks Ed! I try to make things look good, but it doesn't always work out that way.

Here's a few more photos.

Wow! I started this thread a while ago, got sidetracked and have just returned. Interesting discussion! Anyhow, to answer your question; Yes, I mounted the Delco #18M957 (95-2001 Jeep Cherokee) master cylinder and No it won't work because on my truck the pedal hits the floor before achieving full travel of the m.c. That's a No - No. So, I've installed a cast iron one from earlier 84-89 Jeeps (Bendix 11896, Cardone 13-2409, Wagner MC105876). It's a little tight but adapted easily and allows full pedal travel. It has a 15/16 bore which I'm hoping will work well with my system? I chose this one because the 90 - 95 Jeep Wranglers uses a m.c. with exactly the same casting only a 1"bore. I figured it would give me the option to go to the larger bore if I have too much pedal travel and I would not have to re-plumb the lines. After much research about custom brake systems I've decided to use a adjustable proportioning valve and 10lb residual valve in rear circuit and 2lb in front. It's still in process, so I can't report yet how it will work out, but I am hopeful. I've attached some photos showing my mounting adapter which allows the rubber dust boot to be reinstalled.

Did you experience and increase in pedal travel after converting to the smaller bore toyota master cylinder?

The length of the master cylinders in my photos are exactly 6 inches from mounting flange to front of master cylinder

I'm in process of installing disc brakes on my 39 Plymouth PT81 1/2ton pickup. I did a bunch of research and concluded that Rusty Hope, Scarebird, and ECI all to be decent if installed correctly. Rusty hope uses a in - rotor hub which I liked better than the separate aluminum hubs the others use, but even having the skill, I did not want to modify my steering knuckles and steering arms. I believe also because Rustyhope's mounting plates are mounted between the steering knuckles and arms it might require changing tie rod length if there is not enough adjustment? ECI's rotors are customized (redrilled Firebird rotors for 4.5 b.c.) making it more of a pain if you ever need to replace them. Rustyhope offsets my wheels just about 1 inch out per side. ECI 1/2 inch per side and Scarebird 3/8 inch per side. Rustyhope and Scarebird claim no issue with using original wheels (16" on my truck). I ultimately chose Scarebird and a jeep master cylinder which several on p15-d24 have had good luck with the trucks. There's another kit offered by "The Ram Man" which uses all mopar parts which is cool, but on the trucks require some steering arm modifications. The Ram Man's videos are worth watching but he did not respond to some questions I sent him. I found the others decent about answering my questions. Anyhow, make sure kingpins and bushings are good first and keep posting your progress.

Might you remember the part # of the m.c. you used?

Thanks! I thought so too.

Thanks Ed! Makes me want to buy a WC to go with this engine. I imagine the later replacement engines for these trucks were all 230s? I believe the original engines in the 42-45s would have been 201s or 218s? I knew this engine would fit in my truck because it was the shorter version at 23 inch long. I think the Mopar flat heads with larger displacements up to 265hp had 25 inch long blocks? Thanks for the information

I agree Eric, the cast iron MC's look better but these more "modern" ones do take up less room. I had adapted a cast iron split master off of an earlier Jeep that I shoe horned in there but the piston diameter was too small and resulted in too much pedal travel. I've heard the 95-01 Cherokee mc's work well?