brake switch replacement and then bleeding issues

Kurt K

SCCoA Member
OK, I replaced the leaking brake switch on my car and then have been attempting to bleed the brakes. I'm still seeing very small air bubbles coming out of the bleeders. So far I have ran about 1.5 quarts of brake fluid through the rear brakes and I'm still hearing the pump run on the 2nd pump (after the bleeder has been tightened). My accumulator was fine prior to replacing the switch.

Any thoughts or suggestions?
 
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Well if the pump is running every other press while the bleeder is open, that sounds normal. BTW, you only need to bleed one side to clear bubbles from the switch. Shouldnt take more than a pint either. I use clear plastic tubing that fits air tight over the bleeder tip with one end submerged. Actually, what works best is one of the silicon fittings from a nebulizer. And if its new fluid that comes out clean... I pour it back into the reservoir. :eek:
After its bled, if you "feel" like its good pedal under normal use, I'd just go with it. Accumulator air should work itself out.
 
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Yeah, I know the pump will continually run while bleeding, I should have been clearer. After I tighten the bleeder screw, my ABS pump comes on during the 2nd push of the brake pedal. Before I changed the pressure switch, I would get at least 3 pushes of the pedal before the pump started.

I'll try a little more bleeding in the next few days and see if anything improves.
 
Did the master cylinder get pretty low while you were changing out the pressure switch? It can easily do so. And if it does, you have to bleed all 4 corners.

I assume you are doing the bleeding method of open the bleeder, press down the brake, hold it, close the bleeder lift up the brake? If not, that's the only way outside of pressurized bleeding that I've found successful. I also ask whoever is running the pedal to go slow, not fast.

On my 89 I found that if they go too fast it would break up the bubbles into very small bubbles, aerating the brake fluid making the task so much harder. I assume due to the structure of the master cylinder. When that happens you either wait a few days for the bubbles to coalesce or buy enough brake fluid to change out the entire system. Happened once to me and I ended up going through 5 pints of brake fluid until it flowed clear all the way around. I would get one cycle where it looked good, then do one more cycle and then 3 bubbles would show up. I swear there is a architecture in the brake system that makes it hard for bubbles to flow out.
 
Did the master cylinder get pretty low while you were changing out the pressure switch? It can easily do so. And if it does, you have to bleed all 4 corners.

The master cylinder never got very low. I was able to work fast and ensured the level never dropped that low.

I assume you are doing the bleeding method of open the bleeder, press down the brake, hold it, close the bleeder lift up the brake? If not, that's the only way outside of pressurized bleeding that I've found successful. I also ask whoever is running the pedal to go slow, not fast.

I've been doing pressurized bleeding

On my 89 I found that if they go too fast it would break up the bubbles into very small bubbles, aerating the brake fluid making the task so much harder. I assume due to the structure of the master cylinder. When that happens you either wait a few days for the bubbles to coalesce or buy enough brake fluid to change out the entire system. Happened once to me and I ended up going through 5 pints of brake fluid until it flowed clear all the way around. I would get one cycle where it looked good, then do one more cycle and then 3 bubbles would show up. I swear there is a architecture in the brake system that makes it hard for bubbles to flow out.

I definitely had times where my brake fluid was very frothy, but I think some some of the bubbles were being introduced when I opened the bleeder too far. Maybe I'll let the car sit for a day and see what happens.
 
I've been doing pressurized bleeding
Hmmm.. I don't know how well that works with the rear brakes. I've always just cracked the bleeder open and pumped the pedal. Get out and check the line for bubbles and repeat. When no bubbles, close the valve and call it done. I have had problems when the hose on the bleeder nipple is not tight enough and allows bubbles to squeeze their way in. I open the valve just barely enough to let fluid out as sometimes air squeezes past the fitting. I also keep the drain end of the line submerged so that air doesn't suck back up the line as it takes me 10-15 seconds to get out and look.

I definitely had times where my brake fluid was very frothy, but I think some some of the bubbles were being introduced when I opened the bleeder too far. Maybe I'll let the car sit for a day and see what happens.
The frothy (looks milky) stuff usually works its way out after 1/2 dozen pedal presses, or about 1 pints. Not sure why its there, but I do have a theory.
 
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