Q: AstroVan HydroBoost Upgrade?

[Barrrf]

So Im going to upgrade my brake system from manual to power assist. Ive dont A LOT of research on this website and others talking about it. I always thought you needed a prop valve for braking systems? This article http://www.carcraft.com/techarticles/ccrp_1105_chevy_astro_van_hydroboost_salvage/ doesnt show them using one.

Should I upgrade all of my brake lines as well?

[Apogee]

Proportioning valves are something that provides a means of achieving a more ideal front to rear brake pressure relationship over the entire range of possible decceleration rates. In short, it allows for equal front and rear pressure at the calipers below the "knee point" at low deceleration rates where you're not transferring much weight forward, and then above the "knee point", less pressure from that point on at a ratio as defined by the shape of the armature of the proportioning valve, typically 57% of the inlet pressure. In this way, you get progressively less rear brake torque as weight transfers from the rear axle to the front under higher deceleration rates.

If you want to optimize your overal brake performance and maximize the contribution of the rear brakes, then start out with a balanced system with respect to caliper piston areas, rotor diameters, pad CoF's, etc and use an adjustable proportioning valve for fine tuning.

As for your lines, are you referring to the hard lines or the soft lines? You should definitely upgrade the soft lines from rubber to braided stainless, or at least new rubber. The hard lines are a bit more of a judgement call depending on their condition. You can change over to all 3/16" lines with disc/disc applications if you like and you'll get slightly less compliance in the system, however probably not enough to notice at the pedal.

Tobin
KORE3

[Barrrf]

Thats the best description Ive read yet on a prop valve. Psssssh googles got nothing on Tobin.

I'll definitely replace the rubber lines as I have NO idea how old they are, what they are, ect ect. I will also concentrate on getting matched brake components before getting a prop valve. I just know that right now - manual brakes suck.

[astroracer]

Hey Tobin,
Don't want to hijack the thread but figure this will go along with the OP's initial question:
I am using a '95 disc/drum master cyl/hydroboost on the van. Should I be looking at a disc/disc master cylinder? Or will the Wilwood prop valve I am using be enough of a fix?
Thanks
Mark

[Apogee]

...I am using a '95 disc/drum master cyl/hydroboost on the van. Should I be looking at a disc/disc master cylinder? Or will the Wilwood prop valve I am using be enough of a fix?

As with anything, there are always exceptions, however many disc/drum master cylinders work fine in a disc/disc application so long as they either don't have a residual pressure valve in the drum outlet port, or if they do, you remove it. You can determine whether their is an RPV relatively quickly with a paperclip...stick the end into the hole and if it feels like it hits something rubbery right away, it has one. Remove the conincal brass disc from the outlet port with a sheetrock screw or something comparable, shake out the check valve components, and reinstall the seating surface...voila! Disc/disc MC. The proportioning valve won't do anything to effect the residual pressure in the system one way or the other.

Tobin
KORE3

[astroracer]

Okay, cool. I'll check it out.
Thank You Sir.
Mark