1985 Dodge D150 Brake Problem
check this out; The pink fluid is the rear brakes in a Mopar.
The two pistons are hydraulically coupled, shown by the green fluid between them. If that fluid escapes, into an adjacent reservoir, or into an adjacent power chamber; you lose the front brakes, AND the pedal drops nearly to the floor, but does then mechanically engage the rear brakes using the extended post on the front of it.
Piston #2 has a post on it as well, so that when it bottoms, it leaves enough chamber behind it that the front brakes can still work, allbeit with the pedal very low.
This picture shows the hydraulic coupling is intact between the pistons, but shows a rear brake failure because piston #2 is fully bottomed out.
There are return springs (not shown) that are supposed to return the pistons to their designated parking positions after each brake application, which will then open the Compensating ports , refilling the power chambers. If the C-ports are rusted closed then the pedal will drop a little each time the pads or shoes wear, and eventually be very low. But don't miss that as the pedal falls, it is telling you that the power pistons are running out of working range.
It has happened that rust accumulates in the bores especially when sitting for years, and the piston seals no longer work after they leave their parking spots. The only cure is a rebuild to get the rust out, or replacement.
BTW
I have rebuilt many many M/Cs some of which had pretty rusty bores. But the seals were very often still usable. After honing out the rust, the seals worked again; any leakage due to pitting is rarely felt. The C-port takes care of business.
Happy HotRodding
check this out; The pink fluid is the rear brakes in a Mopar.
The two pistons are hydraulically coupled, shown by the green fluid between them. If that fluid escapes, into an adjacent reservoir, or into an adjacent power chamber; you lose the front brakes, AND the pedal drops nearly to the floor, but does then mechanically engage the rear brakes using the extended post on the front of it.
Piston #2 has a post on it as well, so that when it bottoms, it leaves enough chamber behind it that the front brakes can still work, allbeit with the pedal very low.
This picture shows the hydraulic coupling is intact between the pistons, but shows a rear brake failure because piston #2 is fully bottomed out.
There are return springs (not shown) that are supposed to return the pistons to their designated parking positions after each brake application, which will then open the Compensating ports , refilling the power chambers. If the C-ports are rusted closed then the pedal will drop a little each time the pads or shoes wear, and eventually be very low. But don't miss that as the pedal falls, it is telling you that the power pistons are running out of working range.
It has happened that rust accumulates in the bores especially when sitting for years, and the piston seals no longer work after they leave their parking spots. The only cure is a rebuild to get the rust out, or replacement.
BTW
I have rebuilt many many M/Cs some of which had pretty rusty bores. But the seals were very often still usable. After honing out the rust, the seals worked again; any leakage due to pitting is rarely felt. The C-port takes care of business.
Happy HotRodding