[68chevelleSS454]

The only difference the size of the line is going to make is how fast the brake fluid moves from the master cylinder to the wheel cylinder. the bigger the line is the faster a given volumn of fluid can move thru it.
The amount of pressure exerted at the wheel is a corralation of the sizes of the pistons in each one.A bigger master cylinder piston will exert more pressure but the time that it takes for the pressure to work on the wheel cylinder depends on the size of the brake line. The bigger the line is, the less time it takes to get pressure at the wheel.
The biggest difference the size of the line will make is the bigger the line is the less pressure loss there is from friction in the line.
I gotta take a dig at these "engineers". I am an industrial mechanic and I just have to say that there are times that they should have to work on some of the things they design. lol

[willys36@aol.com]

68; Actually, it is the opposite - you get more system pressure with a smaller diamete master cylinder piston. See my longer post earlier in this thread. And I agree, even though I am an engineer (oil business), I get very frustrated working on some of the abortions that automotive engineers come up with!

[ January 24, 2003: Message edited by: willys36@aol.com ]</p>

[Mrfixmaster]

So what you're saying is that if I can find a master cylinder with smaller pistons, I will have more braking force on the slave cylinders? The pistons on the master I have now are the same size, are there any that have different size pistons, front and rear, or would the rear slaves be easier to swap out?
MF <img src="confused.gif" border="0">

[willys36@aol.com]

Depends on the car but yes, you can generally find smaller master cylinders. Front and rear are usually the same size on the ones I have worked on. Since your front end seems to be working but the rear isn't, if you change the master cylinder you will have the same ratio problem. Proper solution is to change the rear slave cylinders to achieve system balance.

[trees]

A lot of varied thoughts on this thread. Think back to early hydraulic brakes when there was a single chamber/piston master cylinder, one outlet port to a T that sent one line front and one rear. How did we get the increased braking on the front? Done primarily by larger diameter wheel cylinders in front and different size brake shoes and drums. Now comes dual chamber master cylinders which means two fluid chambers one piston that still builds the pressure, but now there are two lines coming from the master cylinder, but still different size wheel cylinders to get the desired balance. Along comes disc brakes front and drum rears and because of the higher volume requirement of the calipers, we gotta do something different. A proportioning valve is added to reduce the volume of fluid to the rear drums, and most have a residual valve built in. Racers and street rodders have been playing with adjustable proportioning valves (volume control) for years. Some good ole boys on the dirt tracks have had the valve in reach to tweak their braks during the race as they start to fade or track conditions change. For street rods, it only takes a couple of tweeks to get them set and you could then weld it up. You have not given any feed back on what changed when you, as I understood it, had the lines crossed coming out of your master cylinder. I assume you did change them. Have you disconnected the line going to the rear brakes to see if you are in fact moving fluid? Have you re-examined your proportioning valve to make sure you have the lines in and out correct? By the way, I have always put a 2# residual valve in the drum brake line, regardless of position of master cylinder (with a manual proportioning valve)

Trees

[Mrfixmaster]

Man, you guys are a "boatload" of information!

Thanks for all the posts. I currently have the car totally dis-assembled to paint it, and wanted to make sure I had things right before I re-assemble it. I will check the local auto parts store to try to find some larger slave cylinders for the drums. I'll let everyone know how I make out in the spring!!
MF

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