1. Registration trouble? Please use the "Contact Us" link at the bottom right corner of the page and your issue will be resolved.
    Dismiss Notice

Adding Power Brakes

Discussion in 'Intermediate CJ-5/6/7/8' started by earlswrench, Apr 1, 2021.

  1. Apr 1, 2021
    earlswrench

    earlswrench Member

    Atlanta, GA
    Joined:
    Apr 14, 2009
    Messages:
    135
    I put Scout axles under my 72 and now have disc on the front and drum in the rear. I'm looking at master cylinders and boosters.

    I'm thinking of going with the 91-95 YJ master cylinder. I know the proportioning valve requires me to do a little bit of brake line work so the front right and front left brake lines hook up separately. I know the master cylinder rod has to have the right size hole to fit onto the pedal stud (seems easy enough to work around if it doesn't). After that, I get a little stupid on this.

    The Scout master cylinders are 1-1/8" bore -- as is the YJ. I assume this needs to be the same?

    Is there anything else I need to worry about? Do I have to do anything to make sure the brake pedal has a certain throw distance?

    Any advice, as always, is much appreciate. Stopping is something I plan to do often.
     
  2. Apr 1, 2021
    Mr Vaughan

    Mr Vaughan

    brakes are overrated
     
  3. Apr 1, 2021
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

    Medford Mass USA
    Joined:
    Aug 10, 2003
    Messages:
    23,596
    I suspect anything you do will be new work. The power brake hardware and booster from a '72 is not readily available, and I believe you won't be able to duplicate the factory power brake setup.

    Assuming you have the Scout brakes at the wheels, I would suggest you look to duplicate the original Scout mater cylinder configuration.
     
  4. Apr 1, 2021
    earlswrench

    earlswrench Member

    Atlanta, GA
    Joined:
    Apr 14, 2009
    Messages:
    135
    All Scout stuff at the wheels.

    As far as duplicating the Scout set up, what am I looking for specifically? If I just throw a Scout master cylinder/booster on there, am I set or do I have to worry about my '72 pedals?

    I'm trying to figure out if I should abandon the YJ idea and just go all Scout or if there are enough similarities that I could use the cheaper and more readily available YJ stuff.

    Anyone else have the Scout axle swap?
     
  5. Apr 1, 2021
    47v6

    47v6 junk wrecker! 2023 Sponsor 2022 Sponsor

    USA
    Joined:
    Oct 25, 2006
    Messages:
    5,798
    I used a YJ assembly 87-95 with the included brake light switch. I have a 2a, so there was a lot of fab work to make it right. I didn't need a proportioning valve, but you might. They are available aftermarket and adjustable.
     
  6. Apr 1, 2021
    earlswrench

    earlswrench Member

    Atlanta, GA
    Joined:
    Apr 14, 2009
    Messages:
    135
    Just looked up a 2a brake pedal assembly. Took me a few minutes to figure out the geometry. My head hurts now.

    Mine should be easier than that.
     
  7. Apr 2, 2021
    47v6

    47v6 junk wrecker! 2023 Sponsor 2022 Sponsor

    USA
    Joined:
    Oct 25, 2006
    Messages:
    5,798
    I had to significantly modify the toe board, firewall and the pedal assembly to get it to fit right. Was a lot of effort and is worth it for the power brakes. If I could have figured out an economical and simple as the YJ booster/pedal assembly for through the floor PB, I would have done it. The off the shelf stuff is cheaper and reliable. Replacement parts are easy. A cj5 should be close to bolt on with the higher cowl.
     
  8. Apr 6, 2021
    earlswrench

    earlswrench Member

    Atlanta, GA
    Joined:
    Apr 14, 2009
    Messages:
    135
    Apparently, I was wrong about the bore sizes. The master cylinders on the Scouts are 1-1/8" bore the YJ is 1" bore and the 72 CJ is 1" bore.

    From what I gather, the bore size and the pedal throw work together to get the correct geometry. If I go with a 1" bore master cylinder, I think the pedals will engage the brakes with a shorter stroke since the Scout parts are expecting a 1-1/8" bore (although I could have this backwards). The converse would be true if I use a 1-1/8" bore master cylinder.

    If anyone has any opinions on this thinking, please let me know.

    If anyone has a Scout axle set up, I'd love to hear what you did.
     
  9. Apr 6, 2021
    45es

    45es Active Member 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Naches, WA
    Joined:
    Mar 31, 2007
    Messages:
    1,103
    You do have it backwards. With the smaller diameter master cylinder, it will require a longer stroke of the master cylinder to move an equal amount of fluid as that of the larger master cylinder. The smaller master cylinder will give you greater leverage however.
     
    Fireball likes this.
  10. Apr 6, 2021
    Warloch

    Warloch Did you say Flattie??? Staff Member

    Falcon, CO
    Joined:
    Mar 4, 2003
    Messages:
    5,466
    Couple items that have to be figured.
    1. The MC MUST be same or larger than the wheel cyl size. If you don't, more pedal than what you have room for will be required.
    2. Swing of the pedals and compression of the MC piston. The MC must press the piston as much with a different pedal setup as it did with stock - looking for full stroke if you can, even with aftermarket pedals and cyls. Swing matters as the longer the swing arm of the pedal, the less work your leg will have to do to generate the same power. I don't use power brakes on my rigs, so there is that.
    3. In the end - which is cheaper, changing the MC or the Calipers to make them work together. Look at aftermarket like Wilwood for different size of MC that might work for you.
     
  11. Apr 6, 2021
    earlswrench

    earlswrench Member

    Atlanta, GA
    Joined:
    Apr 14, 2009
    Messages:
    135
    45es and Warloch, thanks for the info. Very helpful.

    I was thinking leverage vs. fluid movement. I think my original idea of a YJ master and booster would have put me out a few buck and nothing to show for the effort.

    I'll check out Wildwood while I make a decision.
     
New Posts