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Bleeding brake fluid really necessary?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by JC50, Mar 29, 2002.

  1. JC50

    JC50 Registered Member

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    I'm replacing the brake pads on my front disc brakes. The guy at the parts place where I got the pads advised to bleed the brake fluid. I know to remove about 2/3 of the brake fluid from the master cyl. reservoir to avoid backflow(overflow) in the reservoir when depressing the caliper piston into the bore but is bleeding all the fluid really necessary? I can see it's probably a good idea every so often but I need pads on a regular basis and don't want to do it every time I replace pads if it's not going to cause problems.
    87' K5 Blazer Silverado 350 TBI
    P.S. First time I'm doing this because I'm tired of paying somebody $100 for what seems to be a fairly simple task. I've got pads, 3/8" hex brake caliper bit, brake parts cleaner, c-clamp, am I forgetting anything? Any tips for installing pads appreciated.
     
  2. DieselDan

    DieselDan 1/2 ton status

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    If you don't open the brake system: unscrew a line or open a bleeder, you don't need to bleed the brakes.
    BUT brake fluid is hydroscopic (absorbs water) and really should be bleed/purged/changed every other year. You'ld be amazed in the difference in pedal feel from just changing old brake fluid. Old fluid can vaporize when braked hard and it rusts the calipers/master from the inside.

    Change it! It's not hard (providing the bleeder screws are rusted frozen). Takes two people, a small wrench, a foot of clear fuel line, a couple pints of brake fluid, and maybe thirty minutes.
     
  3. dyeager535

    dyeager535 1 ton status Premium Member

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    My opinions:
    If you don't open the system, you don't need to bleed it. Changing pads doesn't require bleeding.

    If you bleed the system, you run the risk of having the master cylinder fail. It's common enough that if bleeding the brakes with a master cylinder you've got your use out of, spend the money and replace it at the same time. There's nothng wrong with changing the master cylinder, just be aware that bleeding the system may result in its failure.

    Brake fluid does absorb water, and it can be a problem. Tough call. In some areas, the brake lines do rot out. Here in the NW, I've never seen any hard lines fail whether the fluid was ancient or new.
     
  4. DieselDan

    DieselDan 1/2 ton status

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    Dyeager is right on about the possibility of loosing a master cylinder during bleeding. I never lost one myself but it could happen. During the bleeding the pedal/piston travels much further than it normally would. There might be some corrosion further down the bore that tears up the piston seals, trashing the MC. Hey, I'ld much rather loose the mastercylinder in the garage than out on the road during a panick stop.

    I have had the misfortune of bursting hard brake lines. Rear ended a Neon! Thank God it was with my Isuzu Pup not the Jimmy (The rusty Isuzu just folded up like tin-foil, the Neon got scratched!) Guess we must use better salt up here in the North East.
     
  5. BigBadCad

    BigBadCad 1/2 ton status

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    How can you tell when your master cylinder is going out? Does the power assist make any addtional noise? How can you tell when you've bled enough brake fluid..aside from the lack of bubbles in the fluid? I just finished a rear disc conversion and will be doing a front end brake job in the near future, so I'd like to know.
     
  6. René

    René 1/2 ton status

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    You can see it at the colour of the brake fluid. There an indicator is in it and water colors it dark brown. If the Fluid comes out of the bleeder honey coloured, than it’s enough. I’ve replaced nearly 2 pints.

    Don’t mix however under any circumstances silikone with glycolical break fluid.
     
  7. dyeager535

    dyeager535 1 ton status Premium Member

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    After bleeding my master cylinder, I could never get a "firm" pedal feel. Drove about two months, finally sitting at a light, the pedal went to the floor, and I started to roll. I could pump it back up and get the brakes working again, but it took me exactly one time of that happening before I swapped the master cylinder.

    BTW, we don't use salt out my way, so rusted hard lines, even on 40 year old vehicles, aren't the norm.
     

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