Need help with master cylinder theory/operation, please.

[YerDugliness]

Thanks, Tom....about the fluid....I was unaware it was leaking out, and not long ago I noticed a slight deterioration in brake function so I pulled the cap and found the large reservoir completely dry. I filled it, then realized through more frequent checking that it was leaking out somewhere, so I got a turkey baster and emptied the old fluid, wiped out the sediment from the reservoir, and put in new brake fluid. It gets cloudy like that pretty quickly....I don't think it is humidity, I think it is rust from the inside of the reservoir that is staining it. I did empty the smaller reservoir once but have not paid the attention to it that I do to the larger reservoir. I suspect that a flush of the system will reveal that there is significant air in the lines...and, if as I suspect, the larger reservoir supplies the front brakes, that might be the reason that the rotor looks the way it does. I can lock up the front brakes, in fact do so frequently as I am backing out of the garage as the driveway slopes down at a good angle and the weight is transferred to the back wheels.

I am pretty comfortable with brake work, have done my own on my Fords and Hondas for years, just don't understand the theories behind the mechanicals. I hope to reach Wilwood today with the numbers I got off the calipers and find out about rebuild kits...supposedly the rebuild involves a new O-ring on the pistons and little more, we'll see. I agree that the front brakes might not be working at maximum efficiency, the verbal history on the car indicates it was built in 1994 and these would be the brakes used in the build as there is slightly over 8K miles on the odometer. Almost twenty years since it has been built....and no brake work since then....sounds like it is time! I can replace the MC and rebuild the calipers in a weekend, that's doable

For now the MC will get replaced, the calipers rebuilt, and the system flushed, but once the car is up on jackstands for the winter, a totally different braking system might well be in its future, a dual cylinder one like Bob C pictured in his first reply.

Thanks to Tommy for spending time with me on the phone last night, I now understand better the impact of changing the bore size of the MC....will replace the MC with a similar size bore (or, pehaps, smaller as recommended by Jerry) rather than increasing the bore size. Sometimes things involved with hydraulic theory seem counter-intuitive!

Cheers!

Dugly

[mickmate]

Hey Dugly excellent report and even better results. Thanks for the update. Does your new master cylinder have two pistons the same size in one cylinder? They call that a tandem master cylinder. That would have two line coming out of it for the fronts and the rears.
You talk about the rears locking first, that's not good. In a panic stop at speed it causes the rear to lock up and try to pass the front end. What you want is a tad less braking on the rear to get what's called a good brake balance. In brake systems with dual master cylinders you can simply change a cylinder size by a 1/16th to increase or reduce the braking on one end as required. That may not be practical with your master cylinder set up so if you simply plumb in an adjustable brake bias valve like this on the rear brake line http://www.summitracing.com/parts/sum-g3905/overview/
Your set up is good for this fix as if the fronts were locking up early you would want to change sizes on masters. You do not want to adjust bias or balance with less braking on the front or put a valve in the front line as they do about 70% of the work stopping due to weight transfer and a gaggle of other considerations. Plumb one of those proportioning or bias valves in to the rear line, have the knob pointing in or up out of harms way and have fun playing with your optimum brake balance.

[RallySnake]

Dugly,

Do not wait, buy that proportioning valve as Mickmate suggested and install it in your rear line quickly. Take it from me, going off the road sideways at high speed is not much fun.

You will need a tubing cutter and flaring tool to do the install. It must be a double flare. If you don't have the tools, a good shop can probably do this for you in an hour.

A better alternative might be to buy an exact replacement master cylinder of the original with stepped bores. You could have your old one rebuilt. A lot of engineering went into that design to get proper brake balance.

Test your car by braking hard in a large parking lot (see my original post). This is important. I lived in Houston many years and the traffic there is very frustrating and requires excellent brakes.

RS

[YerDugliness]

I live in the Huntsville area now...but I am familiar with Houston as I own a home southwest of Houston about 30 miles in Rosenberg. My car is AWFUL in the rain, those huge back tires cause the back end to float and brakes that lock up easy will make it even worse. The valve gets ordered tomorrow and soon as it arrives I'll go out to the "rod shop" outside of town and have it installed as you and MickMate have recommended...without it I can see the writing on the wall! He says he has the tools to do the install and I don't want to invest in a double-flare set.....yet, that is!

Cheers!

Dugly