97 Chevy Lumina brakes/Master Cylinder

[Robdaparamedic]

I have had a brake situation ongoing and I finally got around to replacing the rear brakes and had a bad cylinder. I replaced it and bled the brakes. Problem is, I still have a soft pedal and my brake light and ABS light will be on at times. If I pump the brakes before I start the car, The pedal is rock hard and the lights won't come on. Once I start the car, the pedal goes soft again. If I just start the car, they will both be on. Here's the question...If I change the Master Cylinder, can I omit the ABS? Don't care for it, don't have "that tool", and this car is only going to be around a few more miles. Thanks in Advance.

Rob

[jeffcoslacker]

When you pump the brake with the motor off, you are exhausting all the reserve vacuum in the brake booster, that's why the pedal firms up, it is not because the brakes are hydraulically firmer, just you are venting booster assist. Soon as you start the car boost is restored, and the pedal drops.

You just still have some air in it someplace.

I used to work alone in the shop, so I had to come up with solo ways to do things like bleeding brakes...half the time when you use the two person method, the other person doesn't really understand how it works and ends up making it worse anyway...they relax and let the pedal up slightly and suck in a bunch of air before you close it, etc...

You realize FWD cars use a split diagonal system, right? Each side of the system works one front and one rear brake, on opposite sides of the car. So one works LF and RR, the other works LR and RF...you have to bleed front and rear, and go in this pattern, RR,LF,LR,RF...

My guess is you are trying to skid a rear wheel because the other has a big air pocket, and that side of the system isn't doing much, and the ABS kicks in.

Get the air out, you'll be fine.

[Robdaparamedic]

i"m on it, thanks for the quick response. NO..I did NOT realize that and that's why I'm a weekend mechanic and love this site. I will never be without a back-up car and that is how I have the luxuary of working on them myself. NOW if only I had a garage. THANKS AGAIN.

Rob

[jeffcoslacker]

I've had a lot of luck with gravity bleed...I just remove the bleeder screws in one circuit completely, then remove the master cyl cap and just keep refilling as it drops, sometimes you might have to push the brake pedal slightly to get it started (it will suck a little air back in when you let up, but will push it back out immediately)...when clean fluid begins running out at the bleeders tap the caliper or wheel cylinder with a wrench to dislodge any air bubbles clinging to the interior, and put the screws back in.

Many times that's all it takes. Just make sure the fluid level doesn't drop all the way in the master cyl, or you got a new problem...

If doing a two-man bleed, you want the pedal guy to push slowly and consistently, and you want to open your bleeder and close again before they bottom the pedal...too often the pusher is cramming the pedal down to the floor as hard as they can, and the bleeder guy isn't closing it until after he bottoms the pedal...

Bad for two reasons, when they hit bottom, involuntary movements will draw air back in, and it's hard on the master cylinder bore to be rammed into to overtravel spring and bottom the pistons out...

Slow and smooth is most effective...

[Robdaparamedic]

I wasn't able to get the front bleeder open but I bled it from the line. They are much better. The gravity bleed was going to be my next option. I have a new driver in the house now and feel much better about him driving. Thanks again.

Rob

[Scrapper]

my sons car we had to put brakes on it after each year mostley the rear. but yah like they you got air still in the brakes. and you can try gravity bleeding works also like he sais just keep your eye on master cylinder don't let it go dry...