Doosan (& Daewoo) GC25E-3:
wet brakes ( no pedal)

I changed the friction discs and axle bearings it was pretty straight up and after reassembly I have no pedal. I did lose about 5 quarts of oil while changing and topped the differential. I tried bleeding it through the bleeders and don't seem to have any air but I'm not even sure where the fluid flows from as I'm not familiar with wet brakes. one side while drive wheels are lifted applies the brakes a little as in gear it stops spinning but with minor throttle increase it goes. only thing else I noticed was the operator that brought the lift to me left the parking brake set and it was set the entire time I changed everything. but I don't see how that would effect it? any help would be greatly appreciated. The reason for the job was making a chattering noise when applied under heavy load.
  • Posted 26 Jul 2022 06:05
  • Modified 26 Jul 2022 06:06 by poster
  • Discussion started by Douglas_Wright
  • Florida, United States
Showing items 1 - 1 of 1 results.
If i remember right, this model is equipped with a brake valve;
Pressure comes from the engine driven pump, fluid comes from hydraulic tank.
therefore engine must run during bleeding.
After the brake valve it's just 2 pressure lines going to the brakes, identical to a regular brake system with brake fluid reservoir, master cylinder and slave cylinders.

Also, the squeeking/chatering brakes could (in most cases) be solved by changing the front-axle oil.
When bleeding is done and no pressure on the brake pedal it could be that the large diameter quad seal from the brake piston (inside the brake plates housing) is leaking> oil level in front will rise.

The brake valve assembly provides two modes of
braking :
the power braking mode, and the two stage manual
braking mode.
The power braking system is load sensing which
incorporates a shuttle sensing check valve to connect
the sensing lines of the brake valve with the
steering unit and priority valve.
Power mode :
When vehicle is running, the pump provides signal
pressure to the pilot operated check in the large piston(
6) to reduce the large piston feedback pressure.
When spool(7) is pulled out, the large piston cavity(
1) closed except for the pilot operated check flow
path, and inlet cavity(2) opens to the work port(3)
and metering begins between transfer sleeve(4) and
small piston(5).
The transfer sleeve seats against the small piston
which creates maximum inlet and work ports pressure.
Manual Mode :
The manual braking mode allows braking to occur
even if inlet oil is not available to the brake valve.
The two piston design enables the operator to remove the dead-band in the brake actuator as well
as build adequate braking pressure. The function of
the large piston (6) is to remove the dead-band
between the disk materials in the actuator with a relatively
large volume of oil at low pressure with minimum
spool travel. With the brake actuator ÒprimedÓ
the small piston creates the higher pressure required
for braking while the large piston is relieved of pressure
to keep the input forces at a reasonable level.
When the engine is not running, there is no signal
pressure from the pump to open the pilot operated
check. Therefore, it remains closed. As the spool is
pulled out, the large piston cavity(1) closes, the inlet
cavity(2) opens to work port(3) and the transfer
sleeve(4) seats against small piston(5). After large
piston flow primes the actuator, it relieves and small
piston creates high pressure
  • Posted 27 Jul 2022 21:43
  • Reply by Speedfreak
  • Niederlande, Netherlands
.

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