Does anyone understand Master Clyinders???

[427v8]

They seem so simple, but I can't find a good technical explaination of how they work and why.

All I really want to know actually is what difference does it really make if I hook the front brakes to the front output of the MC or the rear of the MC?

This is using the standard '69 Corvette MC.

[CoryM]

http://auto.howstuffworks.com/master-brake1.htm

69 vette is disc/drum right? If so there are two issues, first off there is a residual pressure valve for the drum brakes underneath the sealing cone that holds pressure on the rear brakes so that your rear brakes apply quickly. Then secondly, the front calipers require a larger reservoir because the pistons on the calipers are much larger than the wheel cylinders. Otherwise as your pads wear out, you will run out of fluid in the reservoir and introduce air into the system. Also your combo valve or proportioning valve have to be hooked up correct as well. Do some reading at that site, some good info for basic stuff.
Cheers.

[427v8]

Thanks, I'll check it out but I think I need a more technical discusion. BTW,The Vette is disk disk...

[smooth]

See if this helps. First rule is dont over complicate things. Almost all c3 vettes had disc/disc. If you are running very large tires an adj. valve is a good idea on the rear line in addition to regular combination valve. TIM

[427v8]

Thanks Smooth, MP Brakes is always a good source.

What I am trying to figure out tho is do the brakes act significantly different depending on how you plumb the brakes? i.e. front of the MC to the front brakes, rear of the mc to the rear brakes or the other way round.

MP brakes and Wilwood say opposite things but they do seem to agree that the brakes on the MC's rear ( primary ) circuit will get pressure before the brakes on the secondary circuit due to the fluid coupling between the MC's pistons.

That tells me that the front brakes should be on the primary circuit to prevent rear brake lockup. But then why do the cars come from the factory the other way round?

ack! maybe I AM too much of a perfectionist

[smooth]

It wouldnt be too hard to make 2 sets of lines to the combo valve to try it. Rear brakes usualy lock from weight transfer. That is why adj. valve on rear to lower pressure. remember when you were a kid and grabbed the front brake on your bike? If you drive on the street it is possible to lock up the front if you hit water if the front react first. Race cars are a more controled environment. You have to decide where you spend more time , street or track. TIM

[CoryM]

How much more technical does it get? MC are pretty simple units. So long as the bores are the same size on the primary and secondary pistons and the reservoirs are the same size it does not matter what one goes to the front. As soon as the primary piston moves over the compensating port the link between primary and secondary piston is direct. The piston only needs to move a small amount, maybe .010" to cover the comp port so the difference between front and rear reaction time (assuming bores are the same size) is very finite. I doubt you would notice it. If you want to see how much pedal travel it takes to cover up the comp port, remove the cap and press the pedal slowly. As soon as the fluid stops moving in the reservoir the comp port is covered.

As for the rear wheels applying first, think of a metering valve on a disc/drum setup. The metering valve slows down the front brakes reaction time because drum brakes apply slower. The reason for this is reduce the chances of the car swapping ends. Applying just rear brakes will pull the vehicle to a stop, applying just the fronts means the mass of the car will be pushing against the front wheels and try to go around it. Would hate to be in a curve and dab the brakes like that.

[Rick Dorion]

I'm using a C3 MC in a hydroboost setup and it uses the rear port for the rear brakes and the front port for the front brakes - opposite of most but it is correct. The larger volume goes to the front brakes

[427v8]

OK I found a book on brakes it's called 'Brake systems' or something. they also recommend using the rear port for the front brakes.

So I'll go with the consensus and logic.

Makes me wonder why the Vette comes the other way tho...

[fuzzyonion]

The pistons inside the master appear to be designed with a specific car and brake system in mind. GM used several different secondary pistons inside the same master castings. The secondary piston pin length and diameter differs on the Corvette style and 67-69 GM style fat body castings. The primary pistons and both springs did not change except for pushrod style.

The primary piston spring is stronger than the secondary in all iron masters I have disassembled or seen. It looks like the secondary circuit would begin to build pressure first, as the primary will still be using spring tension to push the secondary piston forward until secondary hydraulic pressure overcomes primary spring pressure. No real pressure will build in either circuit until fluid movement stops (slave pistons quit moving outward). It looks like fluid movement may begin in the secondary circuit first though. The weak secondary spring begins to compress immediately, the resulting smaller area forces fluid downstream to the slaves, while the primary circuit fluid is just along for the ride until its spring begins to compress.

The secondary piston design and overall stroke of the master appear to determine the front to rear fluid displacement ratio. The secondary pin length will at least determine where the secondary circuit will bottom out if there is a failure.
Most 67-80 GMs use the secondary circuit for the front brakes. Most Ford and Mopar did the opposite. Some Ford and Mopar did not appear to use a metering valve, while most if not all of the disc/drum GMs did.

What does all this mean? I haven't a clue as of yet.
But I would use the circuit with the larger resivoir for the front brakes. On a GM, this is usually the front (secondary) circuit.

edit:
The C3 also had much smaller brakes in the rear, requiring less fluid to move the pistons outward... if that might have something to do with anything.

[Rick Dorion]

The MC port sizes on my C3 MC also are appropriately sized for front-to-front and back-to-back connection.

[427v8]

Fuzzy,
Good analysis!
I'm really starting to think it doesn't matter al that much on a disc / disc car, but I think I need to find an old master to tear apart...