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NASA instructor
Join Date: Oct 2001
Location: San Jose, Ca
Posts: 316
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Bad master cylinder?
I was using my new Motive power bleeder on my friends car. It didn't go as planned.
I started in the RR , but when I opened up the bleeder, the fluid was slow and there seemed to be no pressure on the fluid. I made sure I had the valve as open as possible. No pressure at all. The left rear was the same. However the two front calipers bled out just fine. In addition, the brake pedel action is really mushy. Does this sound like a bad master cylinder?
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Matt Rich 1999 Porsche 911 Zeniith Blue 1999 BMW 540i 2011 BMW 535i |
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02-01-2003, 06:10 PM
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I'm guessing that the pressure was low due to the presence of ABS. I used my Motive bleeder on my 89 Mercedes 300E and had the same experience. While bleeding, have someone pump the pedal a few times to push air and fluid out. I had no problem.
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Mike 89 Carrera 3.6 V-ram #94 Livin' for Targa time! Want to make God laugh? Tell him your plans! |
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02-01-2003, 06:28 PM
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You do not have permissi
Join Date: Aug 2001
Location: midwest
Posts: 39,916
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Not sure what vehicle you're refering to but there are a couple of different valves in some systems. (This is coming from a class memory and may not pretain in your case.)
One is a hold-off valve which allows pressure to only the rear wheels for a second at first so that the car doesn't nose dive and the other is a pressure diferentiation valve which gives more pressure to the front wheels which do 2/3+ of the braking. These are on some vehicles but not sure which-check manual/friendly dealership parts guys(go on different days) for special procedures. Another thought is plugged rear lines/screws. If you want to be extra sure take the line off and run air through it. When I bled my new steel braided lines, the RR for some reason took an hour and a half until I got pressure but this was with the cr#p speed bleeders. After a certain year (no clue) it was manditory to have the 2 part brake system control FR and RL to retain control so I don't think one piston is wedged over the feed port in the MC. Oh yeah-very important- put a block of wood under the pedal if you use the pump method. If you push it all the way to the floor, the seals inside travel over the uncleaned/corroded part of the bore and can tear creating future leaks. Last edited by john70t; 02-01-2003 at 06:54 PM.. |
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02-01-2003, 06:50 PM
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NASA instructor
Join Date: Oct 2001
Location: San Jose, Ca
Posts: 316
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The car is an 84 and it doesn't have ABS. I was reluctant to have someome pump the brake, I though it might have an adverse affect on the power bleeder.
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Matt Rich 1999 Porsche 911 Zeniith Blue 1999 BMW 540i 2011 BMW 535i |
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02-01-2003, 06:50 PM
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If pressure is higher at the front brakes and low on the rears then try to bleed the master cylinder to remove any contanimants or debris.
There are two ports (lines) on the master cylinder - one for the front brakers and one for the rear brakes. You can loosen the tubing nut on the master cylinder for the rear brakes and press the pedal to bleed the cylinder of old fluid. Before you let the pedal back up, tighten the nut to pull in new fluid from the resevour. Do this several times until the new fluid is visible. Once you complete this, tighten the line and then try to bleed the rear brakes the same way and see if that doesn't help. Steve "A Porsche does more then just go fast in a straight line"
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SteveKJR Proud Owner of a 78 911 SC Targa "A Porsche does more then just go fast in a straight line" |
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02-02-2003, 02:43 PM
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1978 Porsche 911 Targa 3.0
