Hydroboost Master cylinder

[zerostar2410]

I’m finally getting some rear disc brakes. Only problem is I’m not sure what master cylinder to go with. I used the search function and only found suggestions for the corvette master. I don’t like the look and inability to see fluid inside. I currently have hydroboost from a 95 Astro Van and use the 95 master cylinder that was with it. I like the clear plastic and leak free design but it’s only used for disc/drum applications.

Is there any master cylinders out there that will fit my 94-95 Astro van hydroboost unit with the clear plastic design?

Do I even need a new master cylinder or can I use the disc/drum one that I currently have?

 

[Hazegray]

Is there a residual valve in the Astro van master cylinder for the rear brakes? I "believe" the Astro Vans had them downstream in the ABS braking system. If so, run it and see if it works, but more than likely you will need some type of adjustable proportioning valve.

See: https://www.powerbrakeservice.net/chasvan1hyma.html

 

[zerostar2410]

Is there a residual valve in the Astro van master cylinder for the rear brakes? I "believe" the Astro Vans had them downstream in the ABS braking system. If so, run it and see if it works, but more than likely you will need some type of adjustable proportioning valve.

See: https://www.powerbrakeservice.net/chasvan1hyma.html

Residual valve? I’m not sure.

That is the current mast cylinder I have though. I bought the proportioning valve for disc/disc. Would I be able to run this master cylinder with that prop valve or does it need to me adjustable type?

 

[68ford]

Just run the Astro. Take it for a drive. Find a long road where you can travel about 10min without touching the brakes. Coast to a stop. Measure rotor temp. If rears a noticeably hotter, like 100 degrees there's likely a residual valve retaining pressure designed for drum brakes. As stated, since it was intended for use with abs, residual valve was likely downstream

 

[zerostar2410]

Just run the Astro. Take it for a drive. Find a long road where you can travel about 10min without touching the brakes. Coast to a stop. Measure rotor temp. If rears a noticeably hotter, like 100 degrees there's likely a residual valve retaining pressure designed for drum brakes. As stated, since it was intended for use with abs, residual valve was likely downstream

A residual valve located in the master cylinder? Where would this be located? I was reading that the Astro van master cylinder may not have enough fluid to compress pads because of the smaller front reservoir on that master cylinder.

 

[toddz69]

A residual valve located in the master cylinder? Where would this be located? I was reading that the Astro van master cylinder may not have enough fluid to compress pads because of the smaller front reservoir on that master cylinder.

If it was in the master cylinder, it would be located behind one of the conical brass seats where the brake line threads in (like the Bronco master cylinders).

Todd Z.

 

[68ford]

A residual valve located in the master cylinder? Where would this be located? I was reading that the Astro van master cylinder may not have enough fluid to compress pads because of the smaller front reservoir on that master cylinder.

The different side reservoirs just means your fluid levels in each reservoir will not go down evenly as pads wear. fluid in the reservoir is only to compensate for pad wear and piston moving in the calipers accordingly from wear. Each time you press on the pedal, the supply port gets blocked off, so technically the fluid level doesn't move when you depress the brake pedal.

 

[zerostar2410]

The different side reservoirs just means your fluid levels in each reservoir will not go down evenly as pads wear. fluid in the reservoir is only to compensate for pad wear and piston moving in the calipers accordingly from wear. Each time you press on the pedal, the supply port gets blocked off, so technically the fluid level doesn't move when you depress the brake pedal.

So why have different size reservoirs? Why not just have one large one or both equal in size?



So I should be fine with my original master cylinder?

 

[toddz69]

So why have different size reservoirs? Why not just have one large one or both equal in size?



So I should be fine with my original master cylinder?

Re: your first question, you need enough capacity for the discs as the pads wear. That takes up more volume than the wheel cylinder needs as the shoes wear.

Todd Z.