Workhorse Hydro-Max Master Cylinder Repair When Dashboard ABS Brake Light Wont Go Off / Stays On

When the Dashboard ABS Brake Light Wont Go Off / Stays On your Workhorse Chassis this will help you trouble shoot the problem and possibly fix with out having to buy a new Bosch Hydro-Max Master Cylinder. The root cause is do to the Differential Pressure Switch sticking.
This applies to Workhorse Bosch Brake Master Cylinder numbers W0000036 and W8005118
2001-2007 Workhorse W20, W22 & W24 Chassis and 2007 Workhorse W62
and W8000130 - Brake Master Cylinder Pressure Switch
https://www.workhorseparts.com/W00000...
https://www.ultrarvproducts.com/W8000...

Another source for Hydro max parts https://www.powerbrakeservice.net/bos...
Ask for Matt 714-330-5286

Master Cylinder Description
The master cylinder is a split system type with separate fluid chambers, pistons and outlet ports for the front and rear brake circuits. A differential pressure switch, fluid level indicator switch, and
remote reservoir are also available

Master Cylinder Operation
In the released position actuators of both the primary and secondary pistons are in with
their respective compensating valve stems, which project into the cylinder bore. This contact tilts the valves to an open position, which allows hydraulic fluid in the reservoir sections to communicate with the primary and secondary pressure chambers. Each pressure chamber has a piston/actuator sub-assembly containing a preloaded (caged) spring and return spring.
Initial forward travel of the primary piston moves the primary actuator away from its compensating valve, permitting the valve to seat. Closure of this valve shuts off the passage between the primary pressure chamber and the reservoir section serving the primary chamber.
Further movement of the primary piston creates pressure in the primary pressure chamber, causing the secondary piston and actuator to move. As the secondary piston and actuator move, the secondary compensating valve closes, shutting off the passage between the secondary pressure chamber and the reservoir section serving the secondary chamber. Additional movement of the primary piston causes both chambers to build pressure.
When the load on the primary piston is removed, fluid pressure in each chamber, combined with return spring force, causes the primary and secondary pistons to return to their initial released positions. Each actuator opens its respective compensating valve, reopening the passage between the individual reservoir sections and its associated pressure chamber.
Should the rate of release be great enough to cause a partial vacuum in the chamber, the compensating valve will open to allow replenishment of fluid into the cylinder bore.
Any excess fluid remaining at the end of the stroke due to "pumping" and/or volume change due to temperature fluctuation is released to the reservoir as the compensating valves open.
The primary circuit is separated from the secondary hydraulic circuit. Hydraulic leakage in one circuit does not affect the function of the other circuit.
A fluid level indicator switch is available. It illuminates a light on the dash panel to warn of low brake fluid level in the master cylinder reservoir. A low fluid level can result from brake shoe lining wear, or it can occur if there is an external leak in the vehicle brake system.
A differential pressure switch is available. It illuminates a light on the dash panel to warn when there is a pressure differential between the primary and secondary brake circuits caused by a leak in one circuit. This may occur when one circuit leaks or is improperly bled.
A remote reservoir application is available where under-the-hood space constraints prohibit the use of a conventional booster and master cylinder assembly. In a remote application, the master cylinder reservoir is mounted separately from the master cylinder.