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Anyone had a Master Cylinder fail?

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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    Curious as to others experiences...on the way home last night, already braked to a stop at a light, pedal slowly went to the floor. Brake light came on as it should. Actually started to roll forward a bit. (good thing its a manual haha!) Pulled away from the light, tapped brakes again, they were back up to par, brake light went off. Seems that they work fine, as long as I don't have to hold them in position, or I can slowly push the pedal to the floor.

    Vital statistics are: cobbled together brake system. All parts (brake lines, wheel cylinders, calipers) presumed to have sat open, exposed to weather, for at least some portion of their lives.

    Within last 3 months, all brake fluid flushed, new added, brakes THOROUGHLY bled. During the flush and bleed, I noticed that the pedal now (after changing fluid) appeared to have excessive travel, but still worked fine.

    I inspected for leaks immediately after the brake light incident, and there appears to be no leaks, and the MC cylinder is topped off, and had no appearance of any lost fluid.

    Service manual suggests air in lines, or MC cylinder as being the primary causes for the "brake" light coming on associated with no braking coming to a stop. Air in lines HSOULD be out of the question, since they have worked fine for the last 3 months with no problem, besides slightly excessive (but consistent) pedal travel.


    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. HarryH3

    HarryH3 1 ton status Author

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    Sounds like fluid is getting back past the seals in the master cylinder. [​IMG] This often happens soon after bleeding the brakes with an older master cylinder. With the bleeder valves open, the master cylinder pistons travel much further down the bore than usual. There's usually some rust or other crud in that unused part of the bore that scratches the seals.

    <font color=black>HarryH3 - '75 K5</font color=black>
    <A target="_blank" HREF=http://ThunderTruck.ColoradoK5.com>http://ThunderTruck.ColoradoK5.com</A>
    It's a great day to be alive...
     
  3. Butch

    Butch 1/2 ton status

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    Yep, got to be the master cylinder. If it were air in the lines you would have to pump the brakes to make them work. When my master cylinder gave that is exactly what it did.

    I thought I was wrong once,
    but I was mistaken
     
  4. chevyfumes

    chevyfumes Court jester

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    Watch for the muzzleflash!
    I just replaced my master cylinder 2 days ago it was simple, don't forget to bench bleed it....
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    Ok, are there any worthwhile "upgrades" like a 3/4 ton unit or something?

    Funny thing, '82 service manual shows 3 different MC's, (not including hydroboost) and all the stores seem to think there is only one style. I really actually like the cast iron unit on there, something about the one piece design being a better idea than a seperate reservoir with seals.

    Rebuilt unit $35, rebuild kit $25...think it's worth $10 not to do the work, although I've never had one apart..maybe they'll get my core in pieces : )

    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>
     
  6. chevyfumes

    chevyfumes Court jester

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    Watch for the muzzleflash!
    Man, Dorian my rebuilt only cost 15 after the 4$ core. Of course mine is a 74 but you might want to shop around and from what I hear the kits kind of a pain in the keister, ya think thats how you spell that, anyway good luck!
     
  7. gokartergo

    gokartergo 3/4 ton status Staff Member Moderator

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    Spend the extra $10.00 and get a warranty. You won't get one if you do it. And I'll bet it will take you more then a hour to rebuild it. My time is worth more then $10.00 a hour. Just my .02

    [​IMG]
     
  8. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    I've actually had my brakes fail completely when the master went on my Jimmy last year [​IMG] I didn't think it was possible with dual resevoirs. I was told that it is highly uncommon but remotely possible if it bypasses internally the right way...Don't ask me more thats what i was told almost verbatim by the brake shop. I've had a few masters go and almost all do exactly what yours did. Harry pointed out the number one cause for this. The same brake shop recommended bleeding my brakes with a 2x4 block under the pedal to prevent seal damage. Takes a bit longer but saves the master.

    Rene

    [​IMG]<A target="_blank" HREF=http://jules.coloradok5.com>http://jules.coloradok5.com</A>
     
  9. DieselDan

    DieselDan 1/2 ton status

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    Just my .02 - If that crude/rust in the bore of the master (cylinder) tears up the piston seals causing a failure, isn't it best to have it crap out right after bleeding it rather than in a panic stop? I've had guys preach pressure bleeding to prevent mc damage. I believe master cylinders are dirt cheap - when in doubt replace it. Want to save money - REPLACE YOUR BRAKE FLUID ANNUALLY.
     
  10. dyeager535

    dyeager535 1 ton status Premium Member

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    Oh yes, much better to have it quit right off the bat. Unfortunately this has been a slow and lengthy process, and now that I am tied to driving this thing daily, I HAVE to fix it and not have any real down time except after work.

    Why I asked for opinions is because I know now that there is a problem, and to give myself more than ample room to maneuver, compression brake, and use the e-brake if all else fails...if I replaced the master cylinder and THOUGHT the problem was resolved, next time it happened, I would be in "secure" mode, and not anticipating a problem. That could be lethal on a freeway panic stop. Not to me, but you get the idea : )

    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>
     
  11. backlash

    backlash 1/2 ton status

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    Dorian,

    Sorry I can't help, but I sure know how that feels. The lack of confidence thing ...

    Had the dealer replace the entire works and still won't stop ... if someone cuts me off. Acts like no power assist.

    As long as the brakes are warm I'm OK, but think the fronts are dragging and the rears are not working until the pedal hits the floor. Now that the weather is getting better i'll do the leave at the dealer for a week crap and then they'll get around to it.
     
  12. HarryH3

    HarryH3 1 ton status Author

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    <blockquote><font size=1>In reply to:</font><hr>

    Acts like no power assist.

    <hr></blockquote>


    This sounds like a bad check valve in the line to the power booster. With the throttle open, there is very little vacuum available for the power booster. The check valve should close in this situation, so that some vacuum remains stored in the booster. A bad check valve will let the vacuum bleed off so the brake pedal feels very hard when suddenly pressed. A couple of seconds later, the pedal feels better because the throttle has been closed and vacuum is building up in the booster again.

    If the check valve tests OK, then it's time to look at the power booster itself. Either the diaphram or one of the internal control valves could be leaking. (Or the pedal isn't retracting all the way when released or you're lightly resting your left foot on the brake pedal, holding the internal valves open). [​IMG]

    <font color=black>HarryH3 - '75 K5</font color=black>
    <A target="_blank" HREF=http://ThunderTruck.ColoradoK5.com>http://ThunderTruck.ColoradoK5.com</A>
    It's a great day to be alive...
     
  13. backlash

    backlash 1/2 ton status

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    Hey Harry! ( Sorry Dorian ... am I stealing your thunder?

    How do you check out the check valve? The dealer replaced the M/C, booster, rebuilt calipers, relined brakes, turned rotors and drums, and bled the brakes multiple times!

    You telling me this may be a simple check valve? Is it the one about 6 or so inches from the booster? Guess it could even be the hose itself!
     
  14. dyeager535

    dyeager535 1 ton status Premium Member

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    NO worries here, my probelm was fixed by the new MC last night. Check valve test should be to start up the truck, let it idle for a few seconds, (or just after parking it) and without touching the brakes, shut it off. Come back 45 minutes or so later, and make sure you still have vacuum assist. If the one way valve or diaphram has failed, there will be no assist. Normally you should get two good vacuum assists before the reserve is depleted.

    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>
     
  15. backlash

    backlash 1/2 ton status

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    Not sure I understand ...&lt;&lt;Come back 45 minutes or so later, and make sure you still have vacuum assist&gt;&gt;

    I take it you mean with out starting it up? Just press on the pedal? Or do you have to start it up?
     
  16. backlash

    backlash 1/2 ton status

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    By the way which M/C did you go with?
     
  17. ftn96

    ftn96 1/2 ton status

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    LMFAO!!! Man I remeber when my MC went out a few years back, the funny thing was that my E-brake didn't work either. So I started down shifting adn got to around 25 but there was a beamer in front of me at a light and a Jag coming up the other lane in opposite direction. So I had to point for the ditch that had a large Tele poll. Dont know how the hell I fit through there but it did. BUT, I still had a problem, I was heading straight for the intersection where cars where waiting to turn don the street I had just escaped, so I slammed the hard right, felt like I was on 2 wheels, barley missed the rear bu,per of the car in the turning lane.
    So nowIm tripping pulse is like 300 now then I get it out on the other street and the damn brakes started working again. LMFAO!!!! I pulled over and had a cigarette.

    Will work for beer, parts and tools.
    90 Jimmy 350TBI-TCI 700R4-241-33" BFGs-10 bolts w/4.10's,
    <A target="_blank" HREF=http://www.nashvillek5.freeservers.com>http://www.nashvillek5.freeservers.com</A>
     
  18. dyeager535

    dyeager535 1 ton status Premium Member

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    Yes sorry. Since the Booster "recharges" itself when you the vehicle is running, the goal, is to let it "recharge" and turn the truck off without using the brakes. Thats easy. Come home, put park brake on, tranny in park, let run for a few seconds. Then turn off key. come back in 45 minutes without starting truck, and see if you still have assist. If not, problem. If you do, no problem.

    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>
     
  19. dyeager535

    dyeager535 1 ton status Premium Member

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    I ended up going with the '82. Check out my "Master Cylinder Upgrade" post.

    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>
     
  20. backlash

    backlash 1/2 ton status

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    F'in "A" Brandon ... think I'd want a smoke too!

    Quit a while back ... I ALWAYS WANT ONE!

    NO! I ALWAYS WANT A CARTON!

    LOL!
     

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