Master Cylinder selection - GM + Hydroboost
#1050810
08/10/11 10:00 PM
08/10/11 10:00 PM
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Joined: Jan 2003
Posts: 3,078 Edmonton, Alberta, Canada
Dartman75
OP
master
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OP
master
Joined: Jan 2003
Posts: 3,078
Edmonton, Alberta, Canada
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I converted my Dart to a hydroboost setup last year I think (time flies). In that conversion I wasn't able to find a suitable dodge hydroboost and ended up with the unit from a 94 Astrovan (GM stuff). The problem is the MC that came with them have a tall plastic reservoir that wouldn't clear and a 1.25" bore. So I searched around to find one that was shorter but would have the right piston depths and specs to fit the hydroboost unit. I think what I ended up with was a 78-80 Corvette Power assisted MC. It works, but the piston diameter on this GM stuff is all 1.25". When I have no hydroboost (parked, engine off) I have almost no braking ability at all. I'd like to improve the boosted braking AND have some better potential for manual braking in case of emergency. Where can I get a 15/16 to about 1" MC that will fit (right pushrod depth and imperial brake line fittings and no dorky tall plastic reservoir. Existing unit has these markings on it: 5460346 or 5460946 hard to read these cast numbers Hy: 286 I think this is a # of the hydro unit Best pic I have at hand: http://www.telusplanet.net/public/zbhansen/temp/HydroboostMasterCylinder.jpgThanks for any help in getting a better MC selection.
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Re: Master Cylinder selection - GM + Hydroboost
[Re: ahy]
#1050812
08/10/11 11:29 PM
08/10/11 11:29 PM
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Joined: Jan 2003
Posts: 3,078 Edmonton, Alberta, Canada
Dartman75
OP
master
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OP
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Joined: Jan 2003
Posts: 3,078
Edmonton, Alberta, Canada
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For the brakes calipers I have, originally the mustang hydroboost units used a 15/16 master. There is a difference in the size of the Hydro unit the mustang used, but it's not a great % if I loosely recall the specs. The mustang brake system seems to be designed around lower fluid volumes (smaller surface areas of MC and caliper pistons) and higher line pressures. So I'm hopeful that I'm not really exceeding anything that calipers cannot handle already. Yes, I do not want to blow seals or have an unsafe over pressure condition either. I'm not even 100% sure the MC I have is 1.25" but the astrovan unit for sure was. The switch fom 1.25" to a 1" is about a 57% increase in possible line pressure. That said, before I had the hydro I had a vacuum assist with 15/16, 1-1/32" and 1-1/16" Master cylinders and I would call those borderline unsafe which is why I went to the hassel of hydroboosting it.
In general driving maximum line pressure is never reached. In emergency braking When teh wheels stop spinning the foot comes off the brakes naturally as that happens so not likely to exceed any limits and certainly not sustain them. I feel safer operating with that limit than not having enough in a more likely scenario where I lose engine power for any number of reasons, my lousy home brew electronics being one very likey reason.
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Re: Master Cylinder selection - GM + Hydroboost
[Re: Dartman75]
#1050813
08/11/11 08:26 AM
08/11/11 08:26 AM
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Joined: Oct 2003
Posts: 21,345 Marysville, O-H-I-O
70Cuda383
Too Many Posts
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Too Many Posts
Joined: Oct 2003
Posts: 21,345
Marysville, O-H-I-O
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maybe you can find a way to put a hydraulic accumulator into the system somehow, allowing you to get 1 or 2 pumps of the brakes if you do lose engine power.
I don't know if they make such a thing for any of the GM hydroboost set-ups, but aircraft use them a lot.
**Photobucket sucks**
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