Mechanics

BLEEDING

1996 Geo Prizm

Brakes problem
1996 Geo Prizm 4 cyl Front Wheel Drive Automatic 200000 miles

I replaced the rear drum brakes and the master cylinder. The pedal is going almost to the floor and pumps up about halfway but very spongy. The brakes are working properly but I cannot get the system to bleed. All I get out is fluid and lots of air but get no further. I have tried a vac brake bleed but it just keeps up air and some fluid over and over. This goes on and on I seem to get no where. Could the brake booster be bad? I cannot find a leak anywhere. I do not understand how I cannot get fluid to flow as I have never had this problem. All the bleeder screws are working properly.
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Gasman39669
October 13, 2010.




First, do not use a Vacula, they really suck, next did you bench bleed the master? Run out of fluid while bleeding? Bleed fronts too? This is a diagonal braking system, so the left rear and right front are paired off the master and right rear and left front are paired, to successfully bleed this, bleed all four wheels AFTER bench bleeding the master, You can gravity bleed it by opening all bleeder screws, keeping the master full, and wait until fluid comes from each bleeder, you can close them as they start to drip. Now bleed by pushing the pedal no more than half a stroke and bleeding at the wheels, RR, LF, LR, RF. See how this works. Also very important for rear drums is the shoe adjustment, this controls pedal height!

Merlin2021
Oct 13, 2010.
We are still having a problem. Yes, I did bench bleed the master and yes we did run the master dry during bleeding. The problem is we can not get any pressure in the system. The pedal will not pump up at all. When I open the bleeder screws, I just a dribble of fluid. If the pedal is pumped, I still get no fluid to come out or very little. We can not find any leaks anywhere. Help!

Tiny
Gasman39669
Oct 14, 2010.
Take the master off and re bench bleed it, then follow my instruction WITHOUT running out of fluid again.

Merlin2021
Oct 14, 2010.
Okay, I bench bled the master and got all the air out. I have got to the point where fluid under pressure is coming out of all the bleeder screws and seems to be bled of air. The pedal pumps up pretty good but is spongy. All of the brakes are working. When I start the car, the pedal goes to the floor. What gives now? Thanks.

Tiny
Gasman39669
Oct 18, 2010.
Adjustment good on the drums? ABS or not? Pull up on the handbrake, does the pedal improve? If yes the rear brakes are out of adjustment, or the wheel cylinders are leaking(sucking air). If you have brake hose pliers, clAMP OFF ALL FOUR WHEEL BRAKE HOSES, THEN TEST THE PEDAL HEIGHT, IF IT'S very GOOD(NO MOVEMENT) THE MASTER AND LINES ARE AIR FREE, IF NOT KEEP BLEEDING, Now remove the clamps one at a time, while the pedal is held down, when it drops significantly, you have your bad hydraulic unit located. Seals under the caliper dust boots and under the rubber boots on the wheel cyinders need to be checked for fluid dripping.
When you bench bled the master, did you use the finger, hose or brass plug method? I use the brass plugs and gently push the plunger half way in and repeat until the piston no longer moves, this removes all doubt about air trapped in the master.
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Merlin2021
Oct 18, 2010.
I will try that but it doesn't seem there could be a leak. Couple of things----the pedal was going to the floor before I even touched the brakes. The wheel cyclinders were both replaced. If I had a leak, wound'nt there be fluid around as everything is dry as a bone and the calipers and shoes are moving out and working although the pedal is going to the floor. I bled the master by hoses going into the resevoir from the lines while still on the car. A lot of air came out and we bled it to all but fluid was coming out. Should I remove the master? Thanks for your continued help.

Tiny
Gasman39669
Oct 19, 2010.
Also, I clamped all 4 lines, the back lines do not move the preal at all. The left front moves the pedal about halfway and the right front moves the pedal to the floor. The left front appears to only been working partially as the rotor is corrroded and not shiny and clean. Do I need to replace the calipers? There is no fluid leaking anywhere at all that I can see.

Tiny
Gasman39669
Oct 19, 2010.
Have you bled the fronts? How many miles are on these calipers, if over 70,000 I would replace calipers and the flex hoses to be certain. Good pedal with front hoses clamped?

Merlin2021
Oct 19, 2010.

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