Bosch Hydromax brake booster info

[CarolinaHD]

Information/discussion thread for Bosch hydroboost systems found on medium duty trucks, buses and RVs. The most common vehicle they are used on are the 2002-2009 c4500-6500 gmc and chevy top kick and kodiak. I have included all the documents, pics and websites that I have found on my search

https://www.powerbrakeservice.net/bosch-hydromax.html

http://www.powerbrake-drivetrain.com/hydromax/

Ordered my replacement pedal grommet from here, good prompt service:
https://automotivebrakeandclutch.com/?s=Grommet

Below is some info and pics from the technical manual.

Basic Operation of Hydro-MaxTM Booster Assembly and
Master Cylinder:

Reference Figure 6 for the following electrical components of the booster and master cylinder.

Backup Pump: The Hydro-Max hydraulic booster has a backup pump which will provide hydraulic boost at a reduced rate if the normal source of fluid is interrupted (refer to Figure 3). The signal for operation of the backup pump comes from the flow switch. If normal flow is interrupted, the flow switch will close and activate the relay, which will turn on the backup pump. The backup pump is available for 12 and 24-volt systems. The 12-volt backup pump can draw a steady state maximum of 55 amps at a power steering fluid temperature of 1000 F. The 24-volt backup pump can have a steady state maximum draw of 27.5 amps at 1000 F.

Relay: An optional relay is available for attachment to the booster. The relay connects to a sealed and mechanically latched wiring connector. The function of the relay is to provide current to the backup pump when triggered by the flow switch.

Flow Switch: The function of the flow switch is to activate the relay when normal hydraulic power source fluid flow is interrupted, turning on the backup pump. The flow switch has two terminals (A and B). A is positive. B is connected to the booster housing and can be used as an optional harness ground. The flow switch itself is grounded through the booster housing. A sealed and mechanically latched connector connects the flow switch to the backup pump relay circuitry.

Differential Pressure Switch: The differential pressure switch reacts to a loss of master cylinder hydraulic pressure in either side of the split hydraulic system and can illuminate a warning light at the instrument panel. When pressure is lost in either the primary or secondary circuit of the master cylinder, the switch closes. The electrical switch will remain closed until the malfunction is corrected. When both systems develop normal pressure, the switch will return to center and open the electrical switch circuit. A mechanically latched connector is attached to the switch. The switch has two tabs on a common terminal (positive) and is grounded through the master cylinder.

Fluid Level Switch: When the fluid reaches a predetermined level (low fluid level), the switch closes and can illuminate a warning light at the instrument panel. A sealed and mechanically latched connector is attached. The switch has two terminals, positive and negative, which are interchangeable.

Chassis Ground: The booster and master cylinder assembly must be provided with a ground path that will carry the maximum current of the backup pump.

Pics:
Manual cover
Flow diagram
Screenshot from manual
Parts diagram
2003-2009 c4500-c500 typical parts diagram