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Master Cylinder/disk Brakes

Discussion in 'Early CJ5 and CJ6 Tech' started by RedWing, May 19, 2020.

  1. May 19, 2020
    RedWing

    RedWing Member

    Sutton Bay
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    I finally am getting the D30 Conversion done on my 1971 CJ5 retromod! The axle is finally rebuilt (by a shop) and now under my frame. I'm getting ready to replumb the brake systems and have some questions that I'm hoping you guys can help me with.

    I bought a new replacement master cylinder and it matches the original one that came with the Jeep. Unfortunately, last summer when I took this all apart I didn't take enough pictures of the import spots, one of which was the Master Cylinder.

    As you can see from the pictures, both chambers are the same size and volume. Does it matter which one is plumb to the front and which one to the rear?

    equal chambers.jpg overall.jpg
     
  2. May 19, 2020
    Focker

    Focker That's a terrible idea...What time? Staff Member 2019 Sponsor

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  3. May 19, 2020
    RedWing

    RedWing Member

    Sutton Bay
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    Beautiful, Thank you! I got a 2# residual valve for the disk brakes as well. I'm trying a proportional valve from a 1978 Jeep CJ 5 which is the year of the Dana 30 I'm putting in.

    Apparently, that year Jeep was also disk in front and drums in the rear (11" I think). So I'm hoping that adding it will adequately proportion the front and rear brakes. I ordered it from In Line Tube.
     
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  4. May 20, 2020
    BadGoat

    BadGoat How High Can You Climb?

    St Croix, USVI
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    If your master cylinder is mounted to the firewall, then you do not need a residual pressure valve for the disc brakes. You will need it if the master cylinder is frame mounted.

    Mike
     
  5. May 20, 2020
    RedWing

    RedWing Member

    Sutton Bay
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    Thanks, I’m going with the frame mount so I also ordered the residual valve. Hoping that the proportioning valve for the 1978 model works out
     
  6. May 21, 2020
    Rick Whitson

    Rick Whitson Detroit Area 2020 Sponsor 2019 Sponsor

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    Do you need the proportioning valve with 11" front and 10" rear drums??? I am gathering the parts to put a duel Master cylinder, and 11" front brakes on my Jeep.
     
  7. May 21, 2020
    BadGoat

    BadGoat How High Can You Climb?

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    MBM Brakes does recommend a metering valve that goes in the front brake circuit for drum/drum brakes with dual circuits.

    From their site....

    DRUM BRAKES FRONT AND REAR WITH MASTER ON FIREWALL OR UNDER FLOOR
    • drum/drum, firewall or under floor

    [​IMG]

    Drum brakes require a 10 lb. residual pressure (RPV10) to counteract the spring tension in the drum system which tends to pull the shoes away from the drums. This will give you a longer pedal travel and "spongy" brakes. The residual valve holds a pressure keeping the shoes near the drums giving a higher firmer pedal. Also required a metering valve (PVM) to the front (the metering valve prevents nose dive).



    Here's the link to their metering valve.

    PVM - Universal Metering Valve


    I would think you could use an adjustable valve to set the front to rear bias where you want it. Something like this.

    APV1 - Adjustable Proportioning Valve - Black


    Mike
     
  8. May 21, 2020
    Focker

    Focker That's a terrible idea...What time? Staff Member 2019 Sponsor

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    This can be confusing to the OP, he's running disc/drum like me. You want the most fluid volume to the front brakes. If the chambers are the same, it probably doesn't matter, but most have the large chamber in the back and smaller up front. It's good practice IMO to plumb as if they weren't the same.
     
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  9. May 21, 2020
    BadGoat

    BadGoat How High Can You Climb?

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    Yes, my post is a reply to Rick Whitson who is running drums/drums.

    For the OP running disc/drums, the rear chamber is usually the larger and should control the Discs as they require more fluid volume to operate.

    Mike
     
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  10. May 22, 2020
    RedWing

    RedWing Member

    Sutton Bay
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    My understanding is that the MC has the 10# valves internal? My plan was to take the valve out of the rear chamber (to front disks) And leave the 10# valve intact for the rear drums?

    the proportioning valve I’m using has two front chambers, one for each disk brake, do I need a residual valve for each or can I put the 2# valve inline to between the MC and the brake line that is going to the disk brake side of the proportioning valve?
     
  11. May 22, 2020
    Focker

    Focker That's a terrible idea...What time? Staff Member 2019 Sponsor

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  12. May 22, 2020
    BadGoat

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    Removing the valve will work fine if you can get it out. Focker's link shows what he went through.

    You can install the 2 lb valve between the master cylinder and the proportioning valve, or you can install one on each front brake line, after the proportioning valve.

    Mike
     
  13. May 23, 2020
    Rick Whitson

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    Thank You, Mike, I want to do this right the first time, so I am getting it all together before I take my Jeep apart. Ken B is doing the upgrade right now too, so he is keeping me up to dated on what he is learning. Thanks Everyone with your help I will get it done right. Rick
     
  14. May 24, 2020
    RedWing

    RedWing Member

    Sutton Bay
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    Is it ok to leave the valve in and install the 2# downstream?
     
  15. May 24, 2020
    BadGoat

    BadGoat How High Can You Climb?

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    No, a 10lb valve will keep to much pressure on the disc brakes and cause them to drag.

    Mike
     
  16. May 24, 2020
    RedWing

    RedWing Member

    Sutton Bay
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    I thought so, I’ll work on getting it out today, thanks for confirming.
     
  17. May 27, 2020
    RedWing

    RedWing Member

    Sutton Bay
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    One more question if you don’t mind. Did you use the stock master cylinder or upgrade? Did you add a proportioning valve.
     
  18. May 27, 2020
    Focker

    Focker That's a terrible idea...What time? Staff Member 2019 Sponsor

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    I tried to rebuild the stock MC and it didn't feel good when stopping. I bought a new one that did not come with check valves. I added WilwoodRPV's to both ports, 10lb rear and 2lb front. No proportioning valve.

    That journey is documented here...

    Brake Conversions
     
  19. May 28, 2020
    RedWing

    RedWing Member

    Sutton Bay
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    Thanks, sorry, I should have searched first
     
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  20. May 28, 2020
    Focker

    Focker That's a terrible idea...What time? Staff Member 2019 Sponsor

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    No problem... The info isn't always easy to find. I only searched for the thread because I couldn't remember. :D
     
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