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Thread: Dual brake system upgrade.

  1. #1

    Default Dual brake system upgrade.

    Has anyone done a step by step job discription on doing a dual master system brake upgrade? It would seem to me that somewhere, someone has written it down and with pictures so that someone, even like me, would be able to follow and understand.

    Thanks

    Carmen
    Last edited by bump_r; January 18th, 2007 at 04:02 PM.

  2. #2
    Join Date
    Dec 2003
    Location
    Lone Pine, CA
    Posts
    451

    Default

    In a nutshell, using the Gladiator MC:

    You need the master cylinder, two line adaptors, one brake line plug, one brake line union and about 2' of 3/16" brake line with flares and fittings.

    Find the junction block at the frame below the stock master cylinder. Remove either the line going forward or the line going rearward.

    Using a 3/8-16 IFM (inverted flare, male) plug - plug up the now open hole in the junction block.

    Using a 3/8-16 IFF (inverted flare, female) union, join your new 24" (or whatever is necessary) 3/16" brake line to the existing line that you just removed from the junction. Point the other end of this line up near where the master cylinder will go. You can bend the line by hand if you don't bend it too tightly.

    Install two brake line adaptors into your new master cylinder. The female end of both will be 3/8-16 IFF. The male end will be 9/16 or 1/2 IFM (most likely). Chances are that they will not be the same front to back. Have your parts guy fit the adaptors to the MC. There was very recently a picture on the zone of what the adaptors look like.

    Remove your original master cylinder and do with it as you please. Leave the pushrod attached to the brake pedal.

    Bench bleed the new master cylinder. Cover the two outlet holes to prevent fluid from dripping on your paint and making a mess.

    Install the new master cylinder, same as original. Make sure the pushrod goes where it belongs.

    Install your two (one old, one new) brake lines into the adaptors at the master cylinder. Typically the line going to the front brakes goes to the MC port closest to the firewall, the line going to the rear brakes goes to the port farthest from the firewall.

    Bleed your brakes as normal. It's also a good time to adjust your brake shoes (and that's a good habit to get in to at least with every oil change).

    Chris

  3. #3
    Join Date
    Sep 1998
    Location
    North Central Wisconsin
    Posts
    11,521

    Default

    From the archives....using the Jeep dual master cylinders is not recommended in the M715:

    Caution to all who are considering installing dual piston
    master cylinders: the 60's and 70's vintage civilian
    Jeep master cylinders are NOT suitable for use in an
    M715. Warning is straight from a Wagner Brake Engineer.
    Those Jeeps used different diameter wheel cylinders on
    front than on rear. M715's have 1-1/16" diameter units
    front and rear.
    The member who posted that, Mozarkid, did extensive research with the Wagner folks and came up with this as the acceptable setup:

    Source of master cylinder part number: Wagner, Alabama Plant 205-593-7260, product engineering.
    Master Cylinder Application: Chevy/GMC pre 1972 P30/P35 series
    vans. If memory serves correctly, the best match is 1971 P30.
    Part number: Wagner #F66857
    Same unit by other manufacturers: Raybestos #36246, A1 Cardone #A-1-10-1331.
    At fire wall: bolts right on, no modifications necessary, use stock brake pedal and push rod.
    Outlets are threaded for 1/2-20 and 9/16-18.
    Steel nuts for 1/4" brake line are Edelmann #121045 and Edelmann #121049. You will need a double flare tool to make up 1/4" brake lines for them.
    In the front brake circuit don't terminate 3/16" line at the master cylinder, the brass flair cone is too big. Use 1/4" line and convert to 3/16" line down at the tee fitting you'll need to install down at the frame where the two front lines are near each other.
    The primary circuit is the rear brake circuit.
    The secondary circuit, nearest firewall, is the front brake circuit. A proportioning valve isn't necessary.
    You have several options from here, but you MUST split the lines between front and rear. I replaced all the lines with 1/4", removed the hydraulic brake switch and installed a mechanical switch at the brake pedal (JB welded a limit switch on the steering column directly between it and the brake pedal, a standard cylinder type brake switch can be installed on the existing braket). The wiring from the old switch will reach these locations. The tee located at the left front wheel flex hose connection will need to be changed to one with 1/4" connections. If you choose to keep the 3/16" brake lines and the hydraulic brake switch: Put the brake switch in the rear brake circuit. Put plugs in the two outlets that went to the front circuit.

    CAUTION: If you can't position the hydraulic switch in a manner that will not trap air in the plugged section or the switch section, don't use it.

    If you want to use DOT 5 brake fluid, be sure to get a new brake switch to avoid the possibility of melting the seals.
    If you want to use DOT 5 brake fluid, be sure to get new flex hoses, 2 on front, one at rear axle.
    Wheel cylinder rebuild kit is Wagner #F3609, this kit has upgraded boots, seals and springs - others mfgs do not. Get new bleeder screws Wagner #F11579, these have BIG wrench flats and stick out farther so you can reach them.

  4. #4
    Join Date
    Sep 1998
    Location
    North Central Wisconsin
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    This is the info on the Corvette master cylinder swap that many have used:

    From Barrman:

    Many people want to get rid of the stock single line master cylinder. Either for better braking or to replace a worn out stock one. Many have done this already. This post is not about arguing what might fit or power or non power. This is a swap that I have done to my truck using the following parts. The part numbers are NAPA and the prices are what I paid for them last week.

    1976 Corvette non power disc/disc master cylinder: #10-1371 $23.99

    30" 3/16" brake line: #813-1205 $2.49

    3/16" line plug: #131 x 3 $.29

    3/16" line butt connector splice: #302 X 2 $1.99

    1/4" reducer from mc to 1/4 line: #7913

    3/16" reducer from mc to 3/16 line: #7914


    The swap involved pulling the stock master cylinder off. Bolting the Corvette one on using the stock mount and pedal push rod. (I think adding 1/2 to 1 inch to the stock rod would make the pedal have instant pressure from its rest height. Instead of the 2-3 inch travel I get now. I will add power brakes later and see no need to mess with it twice.) I used the reducer and connected the stock brake line to the port closest to the firewall on the new master cylinder.

    I then disconnected the line going to the rear brakes from the distribution block that includes the brake light pressure switch. I put the plug in the block. Put the splice on the line and connect the new 30" line to it. Slightly bend it so it goes toward the master cylinder. I now had a new line sticking about 10 inches above the master cylinder. I put a loop in it the diameter of my fist and it came out right at the master cylinder. I connected it and the reducer to the master cylinder. That is it.

    I did pull the lines off of the master to "bench bleed" it on the truck using the pedal. I just hooked the lines back up and had firm brakes right away. I vacuum bled the right rear wheel cylinder to get the air the 30" line contained out of the system. I can now here the brake shoe springs working when I hit the brakes with the engine off. Not so before.

    The 1976 Corvette had the option of a non power brake system with disc front and rear. That means the master cylinder had to push a lot of fluid to stop the car. They have the biggest pistons of the same size front and rear without any proportioning valve that can be found nationwide. That makes them a perfect swap into our drum front and rear trucks. Spicergear figured this out years ago and the rest of us are just using his research for our benifit. Thanks Tom.
    From Spicergear...aka Tom:
    Thanks Tim. When I did my conversion I wanted the largest piston I could find that was on a cheap part and plenty of fluid. The '76 'Vette non power had that. At like $22, it a nice part. Let me add, I ran one for years and had great brakes 'til I tore up the pads in mud. Now...all that being said, we cannot discredit or ignore mechanical theory or proven facts that our own Luckypabst/Chris has brought up time and time again.

  5. #5
    Join Date
    Sep 1998
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    North Central Wisconsin
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    The last line of the above post, and the variety of options listed above, shows that there are several opinions on what to do with the brakes.
    Whatever is done, the brakes are extremely important, CUT NO CORNERS!

    Personally, I still like Mozarkids approach as it was thoroughly researched and given the nod by a brake systems engineer...you can download the old Yahoo board archive document from the Manuals link above, down at the bottom of that page...search on "Wagner" and you will see many posts concerning the details of Mozarkids research and what all he did putting it in the truck. He graciously answered questions for a couple years about that setup. He put it in an M725 and didnt have any troubles with it.

    Remember, that is my personal choice, I am definitely not saying it is the only way to go...others trucks I have seen and ridden in prove that.

  6. #6
    Join Date
    Dec 2003
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    Lone Pine, CA
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    Good info Jon - too bad the cardfile was never updated to reflect this.

    Did Mozarkid offer any reasoning behind this? I'm not about to argue with the engineer but my understanding is the reason for different sized wheel cylinders is to offer a very basic from of brake proportioning - something that's not a feature on our trucks to begin with. MC bore should be constant, no? And therefore provide equal pressures front to rear?

    Chris

  7. #7

    Default

    Typically the wheel cylinders are different sized because most vehicles have larger front brakes than they do on the rear. In the M715s case, the brakes are all the same and therefore so are the wheel cylinders. Bore and stroke of the master cylinder are matched to the wheel cylinders to provide equal application of the brakes. Most modern vehicles also have a proportioning/safety valve to balance the brakes further and to to shut off a complete circuit in the event of a failure. Drum brakes to me are a pain anyway because it is almost impossible to get them all adjusted the same and even then changes in the 40 year old drums can throw all that careful adjusting out of whack causing them to apply differently. I have found drum brakes to be an imperfect science at best, lol. Just my .02
    -What We Have, We Hold-

  8. #8
    Join Date
    Sep 1998
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    North Central Wisconsin
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    I gave up on the card file when I went from Windows 98 to Xp...that was a few computers ago...it hasnt been available for download in many years and it wasnt updated because I could no longer open it or edit it.

    If you search the old Yahoo forum, the answers may be in there...

  9. #9
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    Dec 2003
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    Lone Pine, CA
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    So basically the different sized wheel cylinders are used to balance out (or further refine) the amount of work that each brake is capable of - same as proportioning the brake pressure.

    I've never had issue with keeping drum brakes equally adjusted and the inherent self-equalizing properties in the hydraulic system make up for any slight differences side to side (or all around for a single circuit system).

    As long as the brakes are correctly adjusted, you won't see near the end of MC stroke and assuming MC bore is the same you should have the same rate of fluid/pressure transfer.

    I still see no compelling reason why the Jeep MC is not a good match to our trucks. From 6 years of driving mine - daily at times - the only problems I've ever had are trying to keep on the ball with adjustments.

    I still stand by my feelings that the 'vette MC has an appealing bling factor that's hard to pass up. But if the Jeep MC isn't sufficient based on a few things, the 'vette MC is less suitable since it's engineered for transfer rates of a disc brake system. Either way, both MC's seem to operate correctly on our trucks.

    Jon - at the time I came into M715's, the cardfile was the go-to for part numbers. I still have a copy of it on disc somewhere that's certainly obsolete by the standards of the current zone.

    Ramble off
    Chris

  10. #10
    Join Date
    Sep 1998
    Location
    North Central Wisconsin
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    The multitude of people that couldnt open the card file was the impetus for the online version in both html and pdf fromat that I made from the card file. I also could no longer edit the card file in Windows 98, I could view but not edit....with XP I couldnt even view...and there were many people both on the board and through email that were having the same problems. It was therefore abandoned in that format.

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