79 brake problem
Thread Starter
Cruising
Joined: Aug 2017
Posts: 10
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79 brake problem
My pedal was hard but very low, car stopped good. I replaced all caliphers because i found some leaky seals, and rotors, lines all good, brake pads had very little wear but some fluid on some, cleaned with cleaner looked good, bled the system in order several times till no air. No loss of fluid but pedal still the same. Started to come up a little but no significant change., pedal still near floor. Could master be going bad..I would assume mc and I m going to change it because car sits a lot and is older but any other ideas would be appreciated.
Race Director
Joined: May 2006
Posts: 18,598
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If you open the master cylinder cover and with the fender and cowl covered with something to prevent brake fluid hitting the paint, step on the pedal and you should see two spots of fluid coming up from both the front and rear half's of the master.
Le Mans Master
Joined: Aug 2006
Posts: 7,411
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From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
To test the master cylinder go to the 'help' section of your auto parts store and get a plastic 'bleeder kit'.
Remove the front M/C line and plug it, the brake pedal should be rock hard.
Replace the front line and remove the rear line and plug it, if the pedal is not rock hard both ways the M/C is bad.
Remove the front M/C line and plug it, the brake pedal should be rock hard.
Replace the front line and remove the rear line and plug it, if the pedal is not rock hard both ways the M/C is bad.
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,809
From: Cool Northern Michigan
Peterbuilt has the right idea for isolating the Master from the rest of the brake system. If the MC can't pass this test then you know which part to buy next.
Unfortunately, this MC test also introduces air into the ENTIRE system again. When the brake line is removed from the MC a small air bubble is now in the lines.
So a complete bleeding will be needed (again).
Also, those plastic bench bleed kits are fine for what they are intended to do: bench bleed. However, used when the MC is mounted on the car, I found the plastic fittings and hoses blew off and sprayed brake fluid. I believe the MC is putting out 400 lb of pressure at the ports when the brake pedal is activated. So, I made a better, two STEEL line MC test kit with the correct brass fitting on one end from NAPA. I closed off the other end with brass hardware.
(Each port on the MC is different dia & TPI)
Unfortunately, this MC test also introduces air into the ENTIRE system again. When the brake line is removed from the MC a small air bubble is now in the lines.
So a complete bleeding will be needed (again).
Also, those plastic bench bleed kits are fine for what they are intended to do: bench bleed. However, used when the MC is mounted on the car, I found the plastic fittings and hoses blew off and sprayed brake fluid. I believe the MC is putting out 400 lb of pressure at the ports when the brake pedal is activated. So, I made a better, two STEEL line MC test kit with the correct brass fitting on one end from NAPA. I closed off the other end with brass hardware.
(Each port on the MC is different dia & TPI)
Last edited by HeadsU.P.; Aug 23, 2019 at 03:56 PM.
