88 master cylinder, alternatives ? (Page 2/2)
theogre APR 05, 12:29 AM
Nearly All MC Do Not setup Brake Bias. That's by others things including pistons sizes for well over 90% of vehicles world wide.
88 Fiero Has No "Natural" Bias at all. Only Bias is in the Prop Valve in the Combi valve and likely because made GM Bean Counters happy. The rest of the world hates this setup because prop valves are known failure issue and when happens the rear can spin out very easy and labeled as "Unsafe at Any Speed" (R. Nader. Wiki Page)

The 2 bores in many GM MC are for added Volume of Fluid. When brakes are at Working Pressure, the Big Rear Bore stops working.
See my Cave, Quick Take-up notes

Very likely you run out of Volume for front, rear or both w/ this "Alternate."
More so if any caliper has problems and getting too much pad clearance.
While Rears have P-brake problems causing that there are other things that do the same like wheel bearings w/ too much play, slider that doesn't work right, etc.

MC Pistons have Hard Limits so the springs never crush beyond normal range. Once you hit either or worse both then whatever Pressure for a circuit is all there is.
Max Working Pressure often is 1200+ PSI put your MC may only putout 700 - 900 PSi Max when hit the hard limit(s). Might be ok at a stop sign/light w/ plenty of room to stop but not when you panic stop because a kid ran in front of you. If that happens... Can have Civil and Criminal Problems because you hack the brakes.

QT MC could allow the OE Fronts w/ problems use up the Volume and hit the hard limit but QT section will try to makeup the extra Volume w/ Rear that have problems often showing up as "Low Pedal" when really bad.

[This message has been edited by theogre (edited 04-05-2022).]

OldGuyinaGT APR 05, 06:54 PM
When I decided to post about my new brake setup, I was quite aware that I would get response(s) like this. A couple of additional notes regarding the use of this MC:

I was aware of the quick take up issue. While I was unable to find any information as to whether or not the Trailblazer MC is in fact a QT design, I figured as likely as not that it is, because I can't see any reason that ALL newer brake systems (GM, at least) would not have calipers that draw the pads back slightly and need a QT MC to compensate, given CAFE standards, etc. Admittedly, this was part of the guess I made when I selected it. It does appear to have a check valve where a QT type MC needs one. That's one of the reasons I tested a lot before driving anywhere.


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Very likely you run out of Volume for front, rear or both w/ this "Alternate."



I'm quite sure I do not come anywhere close to running out of volume here. This MC has a listed piston bore diameter of 1.000", same as what I found for 84-87. The only MC bore diameter listing I could find for '88 is 0.937". As for travel, I lock the brakes long before end of travel. I know this because The first time I bled the brakes i got a massive amount of air in the system and found out just how far the pedal - and the MC pistons - would move. The brakes now apply when the pedal is a bit higher than before I did any work or made any changes.


quote
Can have Civil and Criminal Problems because you hack the brakes.



Of course, ANY modification can have safety and legal implications if not performed responsibly. That's why any sensible car owner exercises loads of caution, good sense, and testing when making any safety-related change. The only other alternative would be not to make any changes at all, ever, and have all service done to stock specifications by an OEM. Even then, you can be liable because you contracted the service center. This applies to every safety-related system in the vehicle, from brakes to steering to suspension to headlights and on and on. We all undertake these projects at our own risk. That's why I put my own"YMMV" disclaimer in my previous post.

Ya pays yer money and ya makes yer choice...
marc-alan APR 13, 06:29 PM
Thanks for posting the alternative master cylinder.

To close the loop on my side, I used the rebuild kit for the master cylinder and also rebuilt all the calipers. I went from brakes barely working to a car that stops nicely.

Thanks for the replies

Marc-Alan