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Bwingate |
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#1
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Newbie ![]() Group: Members Posts: 19 Joined: 30-March 24 From: New York Member No.: 28,029 Region Association: North East States ![]() |
I have been fighting mushy brakes since I got my 914. They are better but not great. I suspect there is a lot more bleeding to do, including finding the proportioning valve to bleed.
The PO said that they had the master cylinder changed by a local "Porsche expert" I suspect it was replaced with the 17 mm master cylinder. Can I confirm with an external inspection whether it is a 17 mm or 19 mm MC? So my plan is: 1) Bleed MC 2) Bleed proportioning valve 3) Possible replace soft lines 4) Bleed each wheel again. I saw something on this site that made sense, but I had never seen it before: Clamp off all the soft lines and test the pedal. If the pedal is solid, then the problem is at the wheels; if the pedal is soft, then it is the MC. Then unclamp each wheel one at a time - the "bad" wheel will be soft, the "good" wheels will have a firm pedal. Is this a bad idea? |
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technicalninja |
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#2
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Senior Member ![]() ![]() ![]() Group: Members Posts: 1,435 Joined: 31-January 23 From: Granbury Texas Member No.: 27,135 Region Association: Southwest Region ![]() ![]() |
It does not help to remove air bubbles from the caliper by bleeding the bottom bolts.
Bubbles rise to the top inside the calipers. Opening the bottom bleeder alone might ALLOW air to enter the caliper body. Now, if you want to actually DRAIN the caliper (like when you are flushing brakes) the bottom bleeder is instrumental. On single bleeder system (almost everything else in the world!) if you want to clear the old fluid out of the caliper you have to do one of two things. Remove caliper/pads. Open bleeder and push piston back. Close bleeder. slowly pump brake pedal to drive piston/pistons out. Open bleeder, push pistons back. Lather rinse repeat until you THINK you've got the old fluid out. You're going to do this two or three times for each caliper and there's four. Or rebuild the caliper... Those bottom bleeders should be MANDATORY on everything IMO. |
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