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1 ton master cylinder tech ?

Discussion in 'The Garage' started by BigMac, Oct 13, 2002.

  1. BigMac

    BigMac 1/2 ton status

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    I am in the middle of a brake upgrade thats gone cause me a bald spot.. I recently installed a 14 ff w/ disk brakes. The brakes felt like they just wernt getting enough fluid, so, I purchased a 1 ton master cylinder. I pull my master cylinder (1/2 ton) and make up some new hard lines to the praportioning valve.. I get the whole thing bench bleed and try to install the new 1 ton master cylinder to my 1/2 ton brake booster. Hmmmmm, first snag.. the plunger in the 1/2 ton master cylinder is hollowed out to allow the vacuum booster rod to ride inside of it. The one ton is solid with a small indentation. Ok.. So I fork out a 140 bucks for a 1 ton vacuum brake booster...this thing looks perfect for the master cylinder. The rod looks right ..except it wasnt adjustable like the documentation with the master cylinder ... Snag# 2 .. II have a first gen truck... you dont want to buy a first gen booster, trust me. The second gen booster, unfortunetly, will not bolt into my first gen truck without major sugery.. So I purchase a 1 ton first gen brake booster that now has the proper adjustable pushrod ... While at the part store I asked to see the master cylinder for a 1 ton 72 truck.. It is exactly the master cylinder I have.

    Now, the 1 ton booster will bolt into my truck with a minor bracket adjustment, I think..
    My measuring tape says my mounting brackeet is too tall now..

    My question is how far is the vaccum booster supposed to depress the piston in the master cylinder. When I checked the master cylinder on the booster, with the adjustment at its shortest setting, it stuffed the piston in alot.. near an inch.. from what I'm reading it is supposed to "preload" but gees an inch..

    tomarrow it looks like Im going to be sick putting my half ton setup back on while I work out the bracket issue..

    did any of that make sense?
     
  2. keith

    keith 1/2 ton status

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    Makes no sense! First stick with the same year as your truck and just walk in and get the combo for a 1 ton the same year as your truck. Then bolt it on. Thats all we did. I have a 79 so I went and got a 1 ton 79 master/booster and bolted it in. It was $115 for both out the door at Advance Auto with Lifetime warrenty. /forums/images/graemlins/grin.gif
     
  3. 72THING

    72THING 1/2 ton status

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    I'm not understanding your problem. Can you explain it some more? I put a 3/4 ton MC and booster on my '72 truck and it was a direct bolt-on except I had to fab up the prop. valve to MC lines just like you did. The booster you bought should just bolt right on. You shouldn't have to modify anything.

    Will
     
  4. Sandman

    Sandman 3/4 ton status Author

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    I ran into the same thing. The 1 ton MC had about a 1" indentation that needed a rod that stuck out of the Brake Booster that was not there on the 1/2 ton Brake Booster. the fix was to saw off about a 1" piece of smooth rod stock. Smoothed out the edges and slipped it into the end of the MC. Has been working like a champ. All this was for an '82. Got a 1 ton MC for an '82 also and it had this problem. Maybe other years would have been a better choice.
     
  5. BigMac

    BigMac 1/2 ton status

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    What pisses me off now is NOTHING is direct bolt in. The boosteer is for a 72. The rod that conncts it too the brake linkage is about two inches shorter than the half ton one was. The master cylinder has to be depressed about an inch into its travel to actually bolt to the booster... I have the adjustment rod on the booster as short as it will go..

    Although I could get it bolted to the truck by bending the stock booster bracket... the linkage wont conect.

    Oh so my question is how much should the booster depress the master cylinder just to bolt it together?
     
  6. BigMac

    BigMac 1/2 ton status

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    If I had a 79 that would have been my choice...
    Since the first gen booster is twice that I tried a different year and had to return it..
    Now with the correct year it still does not fit.

    (short version) /forums/images/graemlins/rotfl.gif
     
  7. BigMac

    BigMac 1/2 ton status

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    I have exactly the oppisite problem.. Now I have too much rod.

    I have considered just cutting the damn rod and be done with it.

    The damn 1 ton booster doesnt fit anyway.
     
  8. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    </font><blockquote><font class="small">In reply to:</font><hr />
    I have too much rod.


    [/ QUOTE ]


    Geeessh....some guys are so ungrateful! /forums/images/graemlins/rotfl.gif
     
  9. BigMac

    BigMac 1/2 ton status

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    I whish this were true... it seems my truck is a bastard..

    I broke out a tape measure and measured the bolt spacing. The distance top to bottom matched but left to right was smaller on the one ton. I played around and figured that I could just treak the bracket and bot it in, but then I could conect the linkage because the rod is too short.

    Im thinkin I need to go get a couple of parts at the junk yard and shorten a couple of half ton booster pushrods.
     
  10. BigMac

    BigMac 1/2 ton status

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    my wife will get a laugh outa that too /forums/images/graemlins/eek.gif
     
  11. 72THING

    72THING 1/2 ton status

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    I forget about tweaking the bracket on mine. It was smaller left to right spacing on the one ton, just like you said. I put the booster up to the bracket and made it go in place with a big dead-blow hammer. I don't know why your bracket would be different than mine. Maybe 'cause mine was originally 2WD?? But I don't see how that would be different. On the other hand, GM did some strange things from time to time, so you never know. I hope you get the booster to work because it will make a world of difference. My factory booster was a single diaphragm design and the 1-ton booster is a dual-diaphragm. It made the brakes easier to apply.

    Will
     
  12. BigMac

    BigMac 1/2 ton status

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    It looks like the one ton booster is going back...
    The master cylinder is going in one way or another...
    I know where there is a one tone fist gen in Modesto I need to go check out it's brakes...

    I ended up putting my half ton unit back on so I could at least drive the damn beast...

    So was your master cylinder piston cupped or dished? The booster pushed the master cylinder piston nearly an inch just to bolt the two together.. I dont think thats right..
     
  13. jstevenj

    jstevenj Registered Member

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    When you get the booster and master cylinder problems worked out there is something else you will run into. You will need to take the guts out of the pressure reducing/sequencing valve that the lines run into from the master cylinder. The fluid going to the front is sequenced or delayed just a bit to allow the rear shoes to move to the drum before the disc pads grab on. And the rear brakes have a pressure reducing valve in the block. I did the rear disc conversion with the 1 ton master cyl a while back and didn't really have better brakes until I took the guts out of my valve. Your turning it into a simple manifold by doing this. It will go back together and seal up fine. I can lock up all four 42" swampers on pavement now. Good luck.

    Steven
     
  14. BigMac

    BigMac 1/2 ton status

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    maybe I'll try that with a valve from the junk yard...

    Im pretty careful about being able to reassemble my truck..cus I dont like to ride my bicycle..
     
  15. 72THING

    72THING 1/2 ton status

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    My master cylinder had just a slight indentation where the rod pushed against it. It wasn't hollowed out deeply like my old MC was, just indented. When the MC and booster are bolted together, the booster rod shouldn't push in the MC piston ANY AT ALL. As a matter of fact, there should be a very small gap between the booster push rod and the MC with them bolted together. I don't think you have the correct booster bracket on your truck. Do me a favor and compare this measurement to yours. From the sheetmetal on the firewall to the end of the bracket where the booster mounts is 5.5" on mine. In other words, this is the length of the booster mounting bracket from the firewall to the booster mounting flange. Maybe you can change out your bracket with another one to make the 1-ton stuff work.

    Will
     
  16. MudFrog

    MudFrog 1/2 ton status

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    </font><blockquote><font class="small">In reply to:</font><hr />
    The fluid going to the front is sequenced or delayed just a bit to allow the rear shoes to move to the drum before the disc pads grab on. And the rear brakes have a pressure reducing valve in the block. I did the rear disc conversion with the 1 ton master cyl a while back and didn't really have better brakes until I took the guts out of my valve. Your turning it into a simple manifold by doing this. It will go back together and seal up fine.

    [/ QUOTE ]

    Can this be done instead of buying a new proportioning valve?
     
  17. BigMac

    BigMac 1/2 ton status

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    rather than gut my current praportioning valve I plan to remove the valve completely.
     
  18. TX Mudder

    TX Mudder 1/2 ton status

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    The proportioning valve includes a wire that is what turns your break lights on when you stomp on the brake pedal. What are you going to do about that?
    -- Mike
     
  19. HarryH3

    HarryH3 1 ton status Author

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    The wire that comes off of the proportioning valve turns on the brake warning light on the dash if there is a loss of pressure in one of the brake circuits. A switch under the dash, that's activated when the brake pedal arm moves, turns on the brake lights out back. /forums/images/graemlins/cool.gif
     
  20. BigMac

    BigMac 1/2 ton status

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    not on my truck...
     

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