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Suzuki Disk Brake Conversion Mc

Discussion in 'Early CJ5 and CJ6 Tech' started by 1967 CJ5A, Sep 3, 2019.

  1. Sep 3, 2019
    1967 CJ5A

    1967 CJ5A Mike

    Raleigh, NC
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    For those that have successfully converted to Samurai disks, what size master cylinder bore are you using? I have been disappointed with the braking performance of this setup, and I think it may be the result of a MC bore that is too large. I am using a 1" dual MC mounted under the floor with a 2lb residual valve. The pedal is very hard. I am using organic pads and I did follow the break in procedure.

    Braking ability with front disks and rear 10" drums is definitely less than I had with 11" front and 10" rear drums.

    To complicate the matter further, I took the Jeep off road for the first time since I installed the conversion. Since then, the brakes have been almost totally non-functional. I can barely stop with the pedal pressed as hard as I can. If I feel the hubs after driving, they are cool. Normally they heat up significantly from the brakes. The pedal is still very hard.

    Any thoughts?
     
  2. Sep 3, 2019
    Muzikp

    Muzikp Sponsor Sponsor

    Sacramento Ca.
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    Are we talking thru the floor pedal or did you go to a hanging pedal setup?
     
  3. Sep 3, 2019
    Howard Eisenhauer

    Howard Eisenhauer Super Moderator Staff Member Sponsor

    Tantallon, Nova...
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    There's a number of variables here, for power brakes 1" is about right, if non-power 7'8" would be more suitable but there's also a dependency on the mechanical advantage referred to as "pedal ratio".

    We need more details on your setup.
     
  4. Sep 3, 2019
    Oldriginal86

    Oldriginal86 Member

    Pasadena, Md.
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    Smaller master cylinder would be an improvement. Is there a proportioning valve in the system?
     
  5. Sep 3, 2019
    1967 CJ5A

    1967 CJ5A Mike

    Raleigh, NC
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    It is a Crown replacement stock style MC under the floor with stock pedals.

    No proportioning valve, but I was under the impression that that would only be necessary if the rear was locking up before the front, which they didn't when I first installed the disks. Now that they are acting up, I can't even come close to locking the front or rear, even on gravel.
     
  6. Sep 4, 2019
    jeepstar

    jeepstar Sponsor Sponsor

    Sheboygan
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    Dual master cylinder?
     
    Last edited: Sep 4, 2019
  7. Sep 4, 2019
    47v6

    47v6 junk wrecker! Sponsor

    Washington DC.
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    When I went to disks on my present jeep they gave me fits. I tried different master cylinders, bleeding every thing you could think of. No good pedal, always pumping the brakes a couple times to stop...

    I used all GM stuff, backers, calipers and jeep disks with frame mounted master... What I came to find is that the rear disk setup on tapered axles does not quite line up centered for the calipers over the disk, or so I hypothesize.. You may want to check that..

    My solution was to build a full float axle that uses the same setup as the front D30 for brakes, install hanging pedals and a YJ booster and master. Now my brakes are awesome even with 35's..

    I can't speak to the samurai conversion, but I can empathize with your situation. It really gave me fits and wasn't really as safe as I needed it to be. Good luck.

    Oh, and crown may or may not be a quality product. Might want to take that master out and check the bore and orings.
     
    Last edited: Sep 4, 2019
  8. Sep 4, 2019
    givemethewillys

    givemethewillys Sponsor Sponsor

    New Kent, VA
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    I have all of the parts for the samurai conversion sitting in my garage right now, so I'm curious to see what you end up figuring out. I would think that something is definitely wrong though.

    Out of curiosity, what did you use for brake hoses?
     
  9. Sep 6, 2019
    1967 CJ5A

    1967 CJ5A Mike

    Raleigh, NC
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    This is the MC in question. Crown Brake Master Cylinder | Morris 4x4

    The brake hoses I used were for an 85 Honda Accord. Uses the same fitting on the frame side as stock, but you will need to source banjo bolts.

    I tried opening the bleeders for the front. I was able to pump fluid through like normal. Once I closed them up, I got about two normal feeling presses, each increasing in height, until the pedal became rock solid again with almost no free play. I test drove it a bit and I still have almost zero brakes. The brake lights also don't come on unless I press very hard (they used to take very little pressure). So it seems like somehow the MC is not building pressure despite the hard pedal.
     
  10. Sep 7, 2019
    1967 CJ5A

    1967 CJ5A Mike

    Raleigh, NC
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    It's looking like a bad MC to me. After a little more bleeding in the front, the pedal stopped wanting to come back up (without the return spring it just fell back to the bottom). A while later i tried again with the rear and couldnt get much fluid out, it the pedal didn't always want to return. I tried plugging the front port at the MC and it still doesnt want to push out much fluid.

    So the question is, which MC do I replace it with? Again it is under the floor, no booster, etc. Samaurai front disks and 10" rear drums, though I would like to swap those for 11" drums in the near future.
     
  11. Sep 7, 2019
    47v6

    47v6 junk wrecker! Sponsor

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  12. Sep 9, 2019
    1967 CJ5A

    1967 CJ5A Mike

    Raleigh, NC
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    I think I would like to get a smaller bore MC. Even before this 1" master stopped working, the performance wasn't great. I did some calculations and I think that a 3/4" bore would be my first choice, and a 7/8" bore would be my second choice. I am having trouble finding a source though. Does anyone know what OE application would have used such an MC?

    Am I correct in thinking that GM cars from the 70's have the correct bolt pattern? It seems like the MC from a 75 Monza would work except for the ports being on the wrong side.

    Edit: Centric 130.63008 might be a 7/8" bore? Original application seems to be a Scout 800?
     
    Last edited: Sep 9, 2019
  13. Sep 9, 2019
    givemethewillys

    givemethewillys Sponsor Sponsor

    New Kent, VA
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    I was just about to say, didn't Brennan use the MC from a monza on rango, when he first did the conversion?
     
  14. Sep 10, 2019
    1967 CJ5A

    1967 CJ5A Mike

    Raleigh, NC
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    Yes, that is what gave me the idea. But unfortunately that MC has ports on the drivers side, which is very close to the frame for an under floor setup. He has swinging pedals so it's not an issue for him.
     
  15. Sep 16, 2019
    red61cj5

    red61cj5 Just fell off the turnip truck!

    wv
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  16. Sep 16, 2019
    47v6

    47v6 junk wrecker! Sponsor

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    Its a 1970 to 1975 cj5 dual master cylinder. Also is for many other models. If you dont have the mount to upgrade your single circuit master to the dual version, you can buy it here CJ Kits | Herm The Overdrive Guy amongst other providers as well. Its a simple and easy upgrade that adds a lot more safety to the braking system for a minimal amount of effort.
     
  17. Sep 17, 2019
    1967 CJ5A

    1967 CJ5A Mike

    Raleigh, NC
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    Mystery solved about the sudden extra hard pedal and loss of braking. The primary and secondary pistons have a spring between them and a screw that holds them together and limits the spring extension. This screw backed out and got jammed between the two pistons, holding them apart and preventing the primary from building pressure and the secondary from returning enough to draw in fluid. Pictures coming soon...

    Anyway I am still going to try out the Monza MC. I should be able to get it plumbed in this weekend. It's a tight fit with the ports on the driver's side but it will work.
     
  18. Sep 17, 2019
    givemethewillys

    givemethewillys Sponsor Sponsor

    New Kent, VA
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    I'm glad it was a simple solution!
     
  19. Sep 17, 2019
    1967 CJ5A

    1967 CJ5A Mike

    Raleigh, NC
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    Primary piston is at the bottom of this picture. The screw should be connected to it, compressing the spring. The secondary piston contacts the spacer that the screw goes through.
    [​IMG]

    You can see where the screw was contacting. It broke off one of the ears
    [​IMG]

    The screw
    [​IMG]
     
  20. Sep 18, 2019
    jeepstar

    jeepstar Sponsor Sponsor

    Sheboygan
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    well shoot! at least you know what it was. this is all good info for others.
     

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