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Projects 1939-47 Mopar Pickup Trucks disc brake conversions

Discussion in 'Traditional Hot Rods' started by Steve Lowe, Nov 8, 2019.

  1. Steve Lowe
    Joined: Nov 8, 2019
    Posts: 13

    Steve Lowe
    Member

    I'm new here and hoping not to offend. I consider my 39 Plymouth PT81 as a resto-rod and not certain that qualifies as "traditional"?

    I'm wondering if anyone out there is driving a 1939 - 47 Dodge or Plymouth pickup with upgraded (front discs / rear drum) brakes maintaining the original front beam axle? A couple years ago I installed a Borg Warner T5 trans behind my Flathead and a 1986 Jeep Cherokee 3.55 differential along with it's drum brakes and that all went OK. I also installed a Master Cylinder from the same 86 Cherokee in my original bell housing location. It sorta worked, but too much pedal travel which I believe is due to the smaller (.9375) M.C. bore? The 1939 original M.C. had 1.375 bore. I'm now considering converting the front drum brakes to disc. The Rusty Hope setup has my attention, but I'm hoping to talk to someone that may have done this before. Probably wishful thinking, but perhaps to find the right combination of components (M.C., Combination valve, etc.) that have worked well for someone else. The more I read about brake engineering and about the myriad of issues others have had modifying brake systems, I'm hesitant to start buying any parts. I'm hoping to make it a bit safer stopping now that it goes a bit faster at lower rpm. I want to keep my original wheels as well. I've been reading for days on several sites trying to find trucks similar to mine with these brake modifications and how they perform. Not much luck so far. Perhaps I'm not searching correctly but haven't found much regarding 39-47 dodge / Plymouth pickups. Anyhow, that's how I found this place. Any advice would be much appreciated!

    Steve :)
     
  2. 41 C28
    Joined: Dec 17, 2005
    Posts: 1,761

    41 C28
    Member

    Can't help with your question but I have and love old MoPars, welcome.
     
  3. Steve Lowe
    Joined: Nov 8, 2019
    Posts: 13

    Steve Lowe
    Member

    Thanks 4l C28! Mopars are cool!
     
  4. goldmountain
    Joined: Jun 12, 2016
    Posts: 1,024

    goldmountain

    Haven't done disc brakes but have swapped the later pickup truck drum brakes. The spindles are basically the same.

    Sent from my SM-T350 using The H.A.M.B. mobile app
     
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  5. Los_Control
    Joined: Oct 7, 2016
    Posts: 601

    Los_Control
    Member
    from TX

    They sell a disk brake conversion kit for them, check out http://rustyhope.com/site/
    Scarebird also sells a kit. The difference is scarebird is a complete kit, while rustyhope is the custom brackets and bolts, and a list of parts to buy from your local parts store off the shelf..

    The rear you may be better off going with a axle swap, modern jeep cherokee or a ford explorer is the popular choice.
    Highway gears, modern brakes, plentiful in wrecking yard, pretty simple swap with welding on new spring perches.

    Good luck
     
  6. gene-koning
    Joined: Oct 28, 2016
    Posts: 1,364

    gene-koning
    Member

    I've installed a few of the Rusty Hope disc brake conversions. Well worth the effort.
    Back when I did my swaps, I nearly always used a master from an 80s rear wheel drive Chrysler 5th Ave. Those should match up pretty well with your 86 Cherokee rear brakes and the suggested parts for the Rusty Hope brake conversion.
    It is also possible that after you replace the original front wheel cylinders with the disc brake calipers, your current master cylinder will work fine. The original 39-47 front wheel cylinders have 2 large diameter single shoe units on each wheel. Gene
     
  7. Steve Lowe
    Joined: Nov 8, 2019
    Posts: 13

    Steve Lowe
    Member

    Thanks Gene! Very helpful! :) The original front brakes worked well, but are a pain to keep adjusted properly. The Fifth Avenue M.C. looks good having a 1.031 bore. Do you recall which proportioning valve you may have used? And were your conversions on the 39-47 trucks?
     
  8. gene-koning
    Joined: Oct 28, 2016
    Posts: 1,364

    gene-koning
    Member

    I used the stock 5th Ave proportioning valves. The front disc conversions used Volari rotors (and about the same diameter GM calipers) and 10" rear brakes, the same setup as the 5th Ave.
    The vehicles I used the Rusty Hope kits on were mid 50s Dodge pickups, and 40s Mopar cars. Mopar used the 2 cylinder per wheel front wheel cylinders for many years, up into the mid 50s on the trucks.
    My 39 truck has a Dakota frame. Gene
     

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