Originally Posted by gdirwin
Hi Thaniel - just re-read your build thread (things are more impressive now that I am facing many of the same challenges).
I know What you mean about rereading peoples threads. I've re read some of other peoples threads different things are striking me as I am in a different stage. I always glazed over wireing and instrumentation and now I really pay attention.
Originally Posted by gdirwin
It seems you removed your vacuum drive brake booster, and replaced it with a hydraulic brake booster driven from the power steering pump - I have not run across this before - it would save room in a packed engine compartment. Once you search for it though, there are lots of units...
I found this unit:
which had a backup dc pump built-in...
Do you have more details on the unit you used?
The only down-side I can see is that at high speeds, you want the power steering pump to reduce pressure to save energy (ie you do not need power steering at high speed) but this is when you need power brakes the most. I was planning to use the VSS speed sensor input from my RAV4 and input this to the signals on the MR2 PS pump... You probably would have to run the PS pump at full output all the time - this is probably not a biggy though as when you are going straight the pump should not draw any significant power...
Yes Hydroboost is more common that one would think. The unit I am using is off a '97 Mustang Cobra. I've read some Chevy Astro vans have hydroboost and numerous other vehicles. Even BMW has a hydroboost in some models Didn't go with a BMW unit as cost for one would be higher.
As far as reducing pressure or even shutting it off at times I don't think that will be a problem. The unit has a hydrolic storage vessel on it so it can hold some pressure in reserve . For example if an ICE engine shut off at high speed it would not leave the vehicle without power assist brakes. Two or 3 stabs at the pedal and still have assist are pretty typical. If I had the pump come on (or go from low to full speed) at the first press of the pedal I'm thinking the driver will not even feel the difference. Some details to work out there to be sure. In my opinion it actually seemed safer that a Vac pump and tank which could easily be depleted and takes much more space to have much storage capacity. I'll know more after I drive it around.
Realized I never posted much as far as pictures of the hydroboost. On mine I ended up remote mounting the reservior due to BMW having some weird low pressure brake fluid lines going to the ABS on my model year. Would not need to do that on most cars and could just use the reservior that came with the hydroboost.
Notice in the pic above the black round cylinder protruding toward the camera above the master cyl and below the brake fluid reservior. This is the hydrolic pressure reservior for the reserve pressure. in the other pic you can see the 1/2" aluminum spacer plate I made from some scrap to help it fit into my car. I also reworked the steel mounting plate it came with some what.