My motorhome has a Hydro-Max system (apparently from Bosch), which is hydraulically boosted braking with a backup electric pump mounted on the booster assembly to provide boost if the engine-driven pump is not providing flow (as indicated by a flow switch)... which happens if the driver pushes on the brake pedal before starting the engine, and is really loud. Fortunately, the GM system to be used apparently doesn't have that feature.
I note in online remarks about the Hydro-Max system that in at least some cases the booster does not tolerate any back pressure, and apparently separate pumps are used for steering and braking... although I have not confirmed that on my motorhome. So it's just a heads-up: you might need two pumps, as already mentioned. But you might not, because apparently some systems (both no-backup Hydro-Boost and Hydro-Max) does tolerate routing the flow from one pump in series through two loads (steering and brakes).
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Power steering hydraulics are weird: the pump is controlled as a pressure source; instead, the pump speed determines volumetric flow rate, and the control valve (at the steering rack of box) controls a bypass to determine effective pressure. Having both steering and braking assists working in parallel should work (since both systems tolerate widely varying flow rate due to engine speed changes), but the interactions could be a challenge.
The backup pump on the Hydro-Max system might initially seem tempting to use full-time, instead of a separate pump. Unfortunately the backup only produces a fraction of the full assist force... and it is so loud that the first time I heard it I was seriously concerned about what might be broken.
I note in online remarks about the Hydro-Max system that in at least some cases the booster does not tolerate any back pressure, and apparently separate pumps are used for steering and braking... although I have not confirmed that on my motorhome. So it's just a heads-up: you might need two pumps, as already mentioned. But you might not, because apparently some systems (both no-backup Hydro-Boost and Hydro-Max) does tolerate routing the flow from one pump in series through two loads (steering and brakes).
Power steering hydraulics are weird: the pump is controlled as a pressure source; instead, the pump speed determines volumetric flow rate, and the control valve (at the steering rack of box) controls a bypass to determine effective pressure. Having both steering and braking assists working in parallel should work (since both systems tolerate widely varying flow rate due to engine speed changes), but the interactions could be a challenge.
The backup pump on the Hydro-Max system might initially seem tempting to use full-time, instead of a separate pump. Unfortunately the backup only produces a fraction of the full assist force... and it is so loud that the first time I heard it I was seriously concerned about what might be broken.
