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Thread: Soft-ish brake pedal after big brake job

  1. #1
    Senior Member 82DMC12's Avatar
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    Soft-ish brake pedal after big brake job

    Hey guys, as part of my front and rear suspension overhaul, I did total brake overhaul as well.


    • New master cylinder from DMCMW (DMC logo version) - this was a few years old but still in the original sealed wrap and no sign of corrosion or anything.
    • Turned front and rear rotors
    • Brake calipers plated and new bleeders
    • All piston seals replaced
    • New SS front pistons, rears were re-used as they still looked great
    • New SS crossover pipes for the rear calipers
    • Re-used my SS flex brake lines
    • Castrol GT-LMA brake fluid
    • New pads and hardware from DMCMW
    • Powder coated the booster bracket and painted the booster
    • New check valve and grommet, installed with Girling veggie-grease, replaced the hose vacuum hose from booster to hard pipe
    • New seal between the master cylinder and booster


    Anyway, first I installed the master cylinder and "bench bled" it using cut up old brake line and directing hoses into the fluid. I pumped a few times and no longer heard air pushing through, so then I hooked up the two hard lines and started to bleed the brakes in the order in the book (RR, LR, RF, LF). I tried a MityVac but didn't have a lot of confidence in the purge so later enlisted the wife to do it the old "pump pump pump HOLD" technique while I cracked the bleeder and watched the air come out with a clear tube into a jar. That was a lot better, and we went around the car twice. Then I went on a 20 minute test drive and I was stopping but the pedal felt a bit spongy. We tried again and I definitely got more air out and I feel like it's all purged now. The M/C never went below halfway during all this.

    I have gone around the car multiple times with a lamp and I'm confident there are no brake fluid leaks.

    And yet the brakes still don't feel super hard.

    Any techniques I'm missing or should I bed the brakes first and then try bleeding again? I'm not doing any hard braking until I do a brake bedding sequence.
    VIN 11596 Jan 1982 build - owned since Nov. 2000!

    Photography and Backpacking is life.

    Was Fargo, ND
    Now Olathe, KS

  2. #2
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    Yes, sometimes there is still air trapped somewhere in the system, especially when a lot of brake parts were renewed/drained. Usually I drive around a bit and then bleed again. And again if necessary. It is astonishing, sometimes it is o.k the first time bleeding, on some cars it took me a few bleedings. Good luck!
    '81 DeLorean, 20.000 mls, second owner, automatic gearbox

  3. #3
    Senior Member
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    You could still have some air trapped in the system or you could have a bad hose. A bad hose will swell up under pressure making the pedal feel soft. The S/S braided hoses do give a stiffer pedal.
    David Teitelbaum

  4. #4
    Senior Member Citizen's Avatar
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    My 2 cents (and I’m certainly no expert, but…)

    A spongy pedal means air is still in the system.

    The old “pump pump pump hold” technique should actually be “pump, hold, bleed, close, repeat, repeat, repeat, repeat. Did I mention repeat? Oh yes, and then repeat.

    That is to say your helper should not release the pedal off the floor each time until you’ve had time to crack open the bleeder and let the air/fluid exit, then reclose. Only then should the pedal be released. This is because when the pedal is released, air will be reintroduced into the line if the bleeder is the least bit open.

    Why so many repeats? I had done a clutch M/S job one time, and even started with a bench bleed. Still, I had to pump bleed so many times I got frustrated and was convinced something was wrong. But no, it just took lots of bleeding. Now that’s a clutch, with only one line from M to S, and only a short distance at that (master cylinder to slave, which is mounted on the transmission). Now imagine a brake system with 4 lines, each way longer in distance than a single clutch line.

    And there you have it.

    And just one more thing. Bleed again. Fluid is cheap.

    Good luck.

    Last edited by Citizen; 11-15-2021 at 10:35 AM.
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  5. #5
    Senior Member 82DMC12's Avatar
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    Quote Originally Posted by Citizen View Post
    My 2 cents (and I’m certainly no expert, but…)

    A spongy pedal means air is still in the system.

    The old “pump pump pump hold” technique should actually be “pump, hold, bleed, close, repeat, repeat, repeat, repeat. Did I mention repeat? Oh yes, and then repeat.

    That is to say your helper should not release the pedal off the floor each time until you’ve had time to crack open the bleeder and let the air/fluid exit, then reclose. Only then should the pedal be released. This is because when the pedal is released, air will be reintroduced into the line if the bleeder is the least bit open.

    Why so many repeats? I had done a clutch M/S job one time, and even started with a bench bleed. Still, I had to pump bleed so many times I got frustrated and was convinced something was wrong. But no, it just took lots of bleeding. Now that’s a clutch, with only one line from M to S, and only a short distance at that (master cylinder to slave, which is mounted on the transmission). Now imagine a brake system with 4 lines, each way longer in distance than a single clutch line.

    And there you have it.

    And just one more thing. Bleed again. Fluid is cheap.

    Good luck.

    That was my fault on the clarity. It was more like "pump pump pump HOLD" and then I cracked the bleeder, watched bubbles fluid go out momentarily, then closed the bleeder, then signaled to her she can left off the pedal. We did this maybe 5 to 8 times per wheel.
    VIN 11596 Jan 1982 build - owned since Nov. 2000!

    Photography and Backpacking is life.

    Was Fargo, ND
    Now Olathe, KS

  6. #6
    Senior Member 82DMC12's Avatar
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    I have the Midstate DMC Goodridge stainless flex lines which I installed maybe 15 years ago. The are stainless braided with a clear vinyl sleeve over them. The only thing I can think of that might be a problem there is the tip of my propane torch flame swiped the front driver side line briefly and melted a tiny spot the size of a lemon seed so the SS braid is exposed under the vinyl. I can't believe that would make a difference since most SS lines don't even have the clear sheath on it and the current lines sold by Goodridge don't have a clear sheath. The line never got "hot", the flame just briefly side-swiped it while re-positioning torch. I assume there is some kind of flexible hose under the stainless braid and the braid is what keeps the rigidity? The sheath just keeps the stainless clean.

    I could change the SS lines for the hell of it but I'd rather not if it's probably just air.

    Maybe bring it to a shop who can use a power bleeder? Anyone ever use one of those?
    VIN 11596 Jan 1982 build - owned since Nov. 2000!

    Photography and Backpacking is life.

    Was Fargo, ND
    Now Olathe, KS

  7. #7
    Senior Member
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    My procedure for bleeding brakes goes like this.

    1. Open the bleeder valve
    2. Install clear Tyson hose on the nipple and the other end in a cup
    3. Pump multiple times till you have clean fluid coming out the hose

    You can do all this by yourself. At this point, you should have the hose end under the the fluid surface so if there’s any back flow, it sucks up fluid. You can pump as much fluid as you want through it like this as long as you keep filling the reservoir. (Wash out the lines) The only problem at this point is every time you let off the pedal, a little air can suck through the threads on the bleeder. If you snug the bleeder slightly by finger, you may stop most of the air getting by, but it really is time to get help.

    4. Now have a helper (wife) pump the brakes a couple more times. But these times, you have a end-wrench on the nipple. As she pushes slowly on the pedal, have her call out when she is nearly to the floor. Tighten the bleeder. She can let off then. As she applies slight pressure, crack the bleeder again and tighten again when she calls out. You can repeat this several times, but it normally doesn’t take but twice.

    The idea is, what ever leaking at the threads is leaking out as she pushes the pedal. No air can leak in as she lets off because you have it tight.

    This system has worked for me for years. It’s nice because I don’t need my wife but for a few seconds.
    Last edited by Helirich; 11-15-2021 at 01:09 PM.

  8. #8
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    hi andy

    you can drive it to my house this weekend and we can finish bleeding it out if you like.... its supposed to be nice outside i think..

  9. #9
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    When you split the front calipers to rebuild, it's easy to get air in the outside caliper. This air is not easily removed because the bleeder and brake line are both connected to the inside caliper. Opening the bleeder allows flow (and air) thru the inside caliper. But there is no flow thru the outside and air will stay trapped there. Normally the trick is to fill the outside caliper with brake fluid and push the air out by depressing the piston during assembly. If the front brakes are installed and air is stuck in the outside calipers, the best option is to open the bleeder and depress the outside piston with a clamp or channel locks to push as much air out as possible. Reassemble and then continue with your normal bleed procedure.

    Ron

  10. #10
    Senior Member 82DMC12's Avatar
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    Quote Originally Posted by DMC-Ron View Post
    When you split the front calipers to rebuild, it's easy to get air in the outside caliper. This air is not easily removed because the bleeder and brake line are both connected to the inside caliper. Opening the bleeder allows flow (and air) thru the inside caliper. But there is no flow thru the outside and air will stay trapped there. Normally the trick is to fill the outside caliper with brake fluid and push the air out by depressing the piston during assembly. If the front brakes are installed and air is stuck in the outside calipers, the best option is to open the bleeder and depress the outside piston with a clamp or channel locks to push as much air out as possible. Reassemble and then continue with your normal bleed procedure.

    Ron
    No way, really? I think that's actually my problem because when I got my rotors turned, I got them zinc dipped to protect them until I install them. After driving around for a bit and taking the front wheels off again, I see the zinc is totally removed from the surface that the pad touches in the rear, but not much disturbed in the front, at least on the outside, I did not check the inside. I better have an air pocket at the piston.

    I ordered new stainless steel flex lines so when I installed them this weekend I think I'm just going to split my calipers again and fill them on the bench like you suggested.

    Sent from my Pixel 3a using Tapatalk
    VIN 11596 Jan 1982 build - owned since Nov. 2000!

    Photography and Backpacking is life.

    Was Fargo, ND
    Now Olathe, KS

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