<VV> Dual or Single Master Cylinder

[Chris & Bill Strickland]

> > Yes, I know [the Fiero] has a seperate plastic reservoir, but I don't think the guts work materially differently from a Corvair dual MC < <

John --

There is a difference! Maybe not in the basic idea that they are all hydraulic brake cylinders, but the Fiero, like many other GM's of the era has a bit of a twist on the design. I cannot at the moment remember their 'name' for this feature, but GM redesigned their disc brakes for a lower rolling resistance or drag by giving the piston seal a bit of an angle, causing the piston to retract further providing more clearance between the pads and rotor.

This 'feature' required more hydraulic fluid volume to activate the brakes, so GM designed their 'stepped master cylinder' with an internal compensating valve. There is a website that goes into great detail about this system, some of the problems it causes, and some of the cures. This site is bookmarked on a different hard drive that is not in use, so I am sorry I can't reference it. Anyway, the Fiero, with four wheel discs brakes, all of which are of this design, barely has enough pedal travel to adequately service the brakes when all is in good repair, and is barely marginal (which is a whole lot better than nothing) with a partial failure.

You want to be VERY familiar with all of this if you want to adapt one of the stepped master cylinders and its pre-pressurizing feature to any use other than what was intended, but for the low drag brakes found on many 80's GM vehicles, they are the oem design.

I believe that the owners manual for most dual baking system cars (Volvo does, or used to do, it a bit differently) does say that it offers reduced braking performance under conditions of partial brake failure. So, "Blow a circuit, and you really don't have much left," is the normal modus operandi. I sincerely hope that I never again have the personal experience from which I speak.

Perhaps one would want to consider a true dual master cylinder setup, ala:
   http://www.stoptech.com/tech_info/PedalSetup-DualMaster-Guide.pdf,
also perhaps considering professional installation.

Drive On!

Bill Strickland