Soft PM Pedal

gorge1087

Active Member
Joined
Apr 28, 2017
I know there are a lot of different threads on the subject, however, I’m looking for this specific issue.

My pedal became somewhat soft last time I drove the car. I looked around for leaks, none found at the moment. What concerned me was some very small air bubbles coming up into the reservoir from the rubber hose.

I recently did the brake pads on her and everything was fine earlier that day. No brake light warning either. Are these signs of a failing PM? Or just a leak? I wouldn’t mind going to vacuum if this one is done.
 
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Is the unit "leaking down" when its just sitting there? A good unit will hold it's pressure without leaking back into the supply reservoir.
2 ways to tell:
1. Key on / engine off. The unit should run only once (after you pump the pedal), and then hold it's pressure. If it's "self cycling" just sitting there without being used, then it's leaking down / leaking back.
2. Key Off after Key On. Watch the fluid levels after key off. A good unit will hold fluid level without rising. If you see the pass side reservoir level rising over a period of 5 minutes or so, the unit is leaking back. If it's leaking profusely, you could see it leak back much faster. Like a minute. A good unit will hold fluid for hours or days without any leak back.

leaking back through the supply hose indicates that the check valve is bad.
leaking back through the master cylinder booster return port indicates that the internal seals need to be replaced.
You can use your finger over each hole to detect / feel the leak back from each port. It will push your finger off the hole.

Either way, a fresh seal kit installation is recommended, and it includes everything needed to address either leak.
I always use a brand new switch for a rebuild, and use the larger / newer HYDAC accumulator ball.

Store/park the car with the system depressurized and swap in fresh fluid once per year, it will last a very long time.
 
Is the unit "leaking down" when its just sitting there? A good unit will hold it's pressure without leaking back into the supply reservoir.
2 ways to tell:
1. Key on / engine off. The unit should run only once (after you pump the pedal), and then hold it's pressure. If it's "self cycling" just sitting there without being used, then it's leaking down / leaking back.
2. Key Off after Key On. Watch the fluid levels after key off. A good unit will hold fluid level without rising. If you see the pass side reservoir level rising over a period of 5 minutes or so, the unit is leaking back. If it's leaking profusely, you could see it leak back much faster. Like a minute. A good unit will hold fluid for hours or days without any leak back.

leaking back through the supply hose indicates that the check valve is bad.
leaking back through the master cylinder booster return port indicates that the internal seals need to be replaced.
You can use your finger over each hole to detect / feel the leak back from each port. It will push your finger off the hole.

Either way, a fresh seal kit installation is recommended, and it includes everything needed to address either leak.
I always use a brand new switch for a rebuild, and use the larger / newer HYDAC accumulator ball.

Store/park the car with the system depressurized and swap in fresh fluid once per year, it will last a very long time.


It’s definitely leaking then. I remember hearing it cycle every 30 seconds or so with key On engine Off.

I’ll check the reservoir for backleack when I get home.

Where do I get the sesl kit and accumulator ball from?

Thanks for the info
 
Kirbans has it. Switch, seals, accumulator.
Kirban also has new reservoir gaskets too.
 
When rebuilding, it’s a good idea to use an ultra fine sand paper to resurface the check valve. And use compressed air to blow away any lint during reassembly
 
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