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master cylinder upgrade (?)

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by dyeager535, Apr 23, 2001.

  1. dyeager535

    dyeager535 1 ton status Premium Member

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    Went and bought Master Cylinder...the one they brought out for an '82 was the plastic "new" style. Then they brought out one for a '78, and it was the style that i have on my truck now.

    He took the "new" style one in the back, so I couldn't compare side by side, but it appears that the "new" style has a much larger piston, which would increase braking noticeably. I will go to another store probably tomorrow and compare the two side by side for piston diameter. There should be no compatability issues, since the pedals interchange and so do the brake boosters.

    I can post the info on here if anyone cares. Should be a good upgrade for towing and just all around driving.

    Dorian
    My K5 and Chev/Olds tech/links page: <A target="_blank" HREF=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</A>
     
  2. Goose

    Goose 1/2 ton status

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    Interesting idea. I'm not real fond of plastic, and would prefer cast if all things are equal. If the plastic type gives better braking, that would be cool. Keep us posted.

    [​IMG]
     
  3. prjt_blzr

    prjt_blzr 1/2 ton status

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    Most of the "new" style master cylinders have a quick take up feature. This moves a lot of fluid at low pressure and then reverts to high pressure with low fluid flow when the brakes are starting to apply. This is similar to the floor jacks that don't require twenty pumps to get the jack high enough to lift the vehicle. The benifit of this is a firmer pedal. I'm not aware of any other differences.
     
  4. dyeager535

    dyeager535 1 ton status Premium Member

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    Yes, although the '82 manual shows 3 master cylinder types, it does not make any differentiation when it mentions the take up feature.

    The '82 plastic reservoir unit is much larger than the cast unit reservoir wise, and I have to say that the piston looked to be a good 1/8=1/4" larger, which is a substantial difference when you are only dealing with 1" or so in the first place. I shall know tonight.

    Dorian
    My K5 and Chev/Olds tech/links page: <A target="_blank" HREF=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</A>
     
  5. K5 NUTT

    K5 NUTT 1/2 ton status

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    One it will bolt in....all you do is bench bleed the master and you have to swap the lines fore and aft. 2ND....the booster's are not interchangeable!!! Due to the larger piston bore....and yes the late model has a quick take up valve feature. I have done the swap in both the 79 and my Chalet....i can stop in a shorter distance and with halve the pedal effort. My two cents.

    Azblazer

    1979 K5
    1976 K5 Chalet
    1972 K10 Suburban
     
  6. prjt_blzr

    prjt_blzr 1/2 ton status

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    When did GM swap the funtion of the front and rear ports on the master????? That could be a real oopppss to find.
     
  7. k5kraze

    k5kraze Registered Member

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    So one would have to change both the master AND the booster to get improved braking?

    thanks
    k5kraze
     
  8. dyeager535

    dyeager535 1 ton status Premium Member

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    AZBLAZER is right. I can see where the booster might not interchange. You can use the "smaller" MC on a new booster, but not the other way around.

    Actually went to the store again to compare. So insterad of bringing the plastic reservoir one out that they did the day before (for the same listing? How??) they brought out a cast one. This was listed as a 1982 K5, 350, and I checked all the way up to 1989, same MC, in Checker, Schucks, Kragen's computer.

    The bore difference between old (1978 K5) and new is 1/8". Old is 1 1/4", new is 1 3/8" Thats a major size difference when you are at that small of a bore. My frames an '81,as are the brake lines. The booster definitely looked old though, but in any case, it was large enough to accept the new MC, so it must be a newer booster, or one off a 3/4 ton or something. The brake lines changed over from the old MC to the new one with no problems, front to front, rear to rear. It SHOULD be pretty obvious if the brake line location changed, as the reservoir in the back would then have to be the large one....both the '78 and '82 MC's had the large (front brakes I believe) reservoir in front.

    Price difference was hefty, $60 for the larger bore MC, $25 for the older. Definitely no spongy pedal, but perhaps because of the 33's, it acts like ABS...from 35mph on dry pavement, I get no lockup of the wheels. More the ABS type rapid "skid, roll, skid, roll" until I come to a stop. It's very quick though, I am impressed at the distance I can stop in now.

    Interesting bleeding procedures, I always thought when you cracked the lines at the MC you had to bleed all the wheel cylinders, according to the Service Manual, thats not true...so I didn't. Mount dry master cylinder, install the "bleeder plugs" that it comes with, fill at least half way with fluid, pump pedal in very short strokes slowly (no more than 1" they say), until you feel some pedal pressure, then bleed with the plugs, and install lines. I assume you don't have to bleed at each wheel because the air actually goes harmlessly back into the MC (never gets close to the wheels) and into the reservoir. Not sure how that works for sure, but it does.

    Can't say its a "must do" upgrade for the price, maybe something to consider when the older style fails, and if your booster will accept it. Towing heavier loads would probably make it worthwhile as well.

    Dorian
    My K5 and Chev/Olds tech/links page: <A target="_blank" HREF=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</A>
     
  9. dyeager535

    dyeager535 1 ton status Premium Member

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    Only if the master cylinder won't accept the larger diameter MC bore...mine would, because I believe I have a "newer" booster.

    Dorian
    My K5 and Chev/Olds tech/links page: <A target="_blank" HREF=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</A>
     

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