4 disc master cylinder - Team Camaro Tech
Brakes, Suspension & Steering Conversion questions, Steering & Handling

 
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post #1 of 7 (permalink) Old Jan 16th, 02, 05:03 PM Thread Starter
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I am presently planning a front brake drum to disc conversion and was wondering if i could use a master cylinder from a car with 4 disc brakes in case I decide to put rear discs on at a later time? If so, what cars would be good donors? Im trying to think ahead a little.
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post #2 of 7 (permalink) Old Jan 16th, 02, 07:58 PM
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i don't think you can do that. the amount of fluid the rear discs needs is more than what drums need.
..BUT...
i seem to remember seeing an older truck master recommended for a 4 wheel disc setup, and they never had rear discs til 99. maybe with a prop valve in the rear you can get by. but a disc/drum master is like $35 at NAPA, so you aren't out much if you have to swap it out later.
maybe you should do a search and see what pops up. this has been covered in great detail.

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post #3 of 7 (permalink) Old Jan 17th, 02, 03:05 AM Thread Starter
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This may be the subject of another post, but can anyone tell me if there is noticeable difference between a stock front disc set-up and using the larger vette set-up?
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post #4 of 7 (permalink) Old Jan 17th, 02, 03:53 AM
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drum brake masters have check valves in them so they can maintain pressure in the system at all times enabling them to have instant pedal response when the brakes are applied.you need a disc\drum now. then you could remove the check valve and spring when you go with 4 wheel.the 74,75 20 and 30 series chevy truck masters have larger resevoirs and a 1 and 1/4 inch diameter piston.
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post #5 of 7 (permalink) Old Jan 17th, 02, 04:20 AM
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Southwnr.
You could go with the disk/disk master cylinder, but you need to things: an adjustable prop valve in the rear line, and also a 2 lb residual pressure valve in the rear line. This will allow you to fine tune the brakes with the adjust valve, and keep the pressure in the line like fig said.

As far as noticing a difference, that depends on a bunch of things. First, why would you think you need the larger front brakes or the rear disks? For a cruising car, they are not necessary and you will not notice any difference. Not until you get into some pretty aggresive cornering and repeated stopping will you see any difference. Then, it also depends on how the car is set up. One thing about rear disks is that you can lock them up pretty easily, so in a normal car, you will have to adjust the bias down to a point where they don't provide any additional stopping power. If you have tightened the suspension and are keeping weight transfer during braking minimized, you can get more bias in the rear brakes and then you will notice a difference.
I have done quite a bit of work on rear disks for my Chevelle, so I can offer additional info if you want, but they simply are not a simple bolt on and go type solution. Plus, the rear calipers tend to be a PITA.

One option you might consider for some additional rear braking power is to use some 11" rear drum off a 76 or 77 Monte instead of the 9 1/2" stock ones. This lets you keep all your existing disk/drum hardware like MC, prop valve, lines, etc. and get better braking for cheap! A lot less than rear disks!

Good luck,
Bill C.


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post #6 of 7 (permalink) Old Jan 17th, 02, 10:07 AM Thread Starter
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BC,
Thank you (all of you actually) for answering my questions! I dont think I will need disc brakes all the way around. This is just a daily driver and I got carried away. Two is good, four is better!!
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post #7 of 7 (permalink) Old Jan 17th, 02, 01:09 PM
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The drum and disc master cyls are supposedly different in three ways.
1. larger reservoir on disc MC.
2. Longer stroke on disc MC
3. No residual pressure valve on the disc side of the disc MC.

I'm not so sure the Camaro system actually uses residual pressure valves. Most books saya they are needed or used on drum systems.
I have looked in some master cyls and not found them. I have heard there is one in the proportioning valve outlet to the rear brakes.

I have played with residual pressure valves and they do increase the pedal height slightly. I guess slightly less fluid needs to be pumped by the MC when they are used.

You can have pretty darn good braking with only front discs, especially if you have drums now.
The rear discs DO have less tendency to lock up or grab, so you can adjust more rear braking to them and gain some performance from that.
David

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