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master cylinder to use?

4K views 21 replies 5 participants last post by  barnym17 
#1 ·
I have converted my malibu to rear disc using metric calipers and am trying to figure out the best master cyl. to use. These are low drag calipers needing a quick take up cyl. I think, am considering one from an 86 firebird with 4wheel disc brakes.The catch is I'm running manual brakes not power and all these were power.Can I use the manual pedal ratio and get acceptable braking?
 
#2 ·
What you are describing will give you a very hard pedal. You will either need to drastically change the pedal ratio or change to a smaller bore master cylinder to get acceptable braking. If going to a smaller bore cylinder, make sure you don't run out of pedal travel. Smaller bore means less volume per pedal application and 4 wheel disks require more volume than disc/drum applications.

Andy
 
#6 · (Edited)
This interests me also. :thumbup: I have not done this but have also begun to look into using a stepbore master in a 4 wheel disc manual application.
The step bore section of the master cylinder only works until about 100 psi system pressure is reached, as it is only designed to bring the pads up to the rotors, then the valving in the master lets the smaller bore piston take over to actually build the pressure. The pedal effort to reach 100 psi line pressure will be minimal with any pedal.

Think of the stepbore master as you would a 2 stage compressor, where you can get the necessary volume AND higher output pressure with less HP.

So I would imagine it is not a big deal as far as pedal effort is concerned, as long as you can construct the pedal so you can have a 6 or 7:1 ratio AND still have the pedal configured so that you can have the pushrod actuate the pistons through their entire available stroke.
This is not as hard to do with a swinging pedal as it is an underfloor pedal, as you can always bring the pedal up higher to get your pedal proportions right.
From my experience, if the secondary bore size is 1" or so, a 6:1 ratio will be adequate to apply enough pressure to the metric calipers, you will have a stiff pedal, and a 7:1 might be better if you are going racing and need to build some higher line pressures.

Do you know the bore size and available stroke of the stepbore master you are looking at? A couple of the step bore masters I had looked at had 1 1/4" primary bore, and 7/8 secondary bores but never investigated the stroke length.



None of the aftermarket companies I talked to had anything to tell me about stepbore masters, but I only asked a couple of them, and it's hard to get to a real brake engineer at those companies.

Later, mikey
 
#7 ·
The one I am considering has a 24 mm bore almost 1.0 it equals .996 according to a conversion chart.I already have moved the rod to the manual brake position giving more leverage but for now have a stock 79 camaro cylinder on it with 1 1/16 bore.The stock metric cylinder didn't have enough volume to activate the rears with it's 7/8 bore.Could have been a bad cyl.The main problem with the camaro master is there is a residual pressure valve in it somewhere and the back brakes stay applied somewhat after the bleeding procedure.This master is a disc drum master.After looking at the brake setup on the bird it looks like it is using metric front calipers in the front and simular sized in the rear and I figured it wouldn't have a residual valve being designed for 4 wheel disc.I have used this setup for racing but always with a dual cylinder setup with 1 inch bores.
 
#8 · (Edited)
The residual pressure valve is easily removed with an easy procedure. I went out and did one for ya in one of my mockup/visual aid master cylinders:) ..took about 5 minutes, including taking pics.
Tap the male flare seat with a 6-32 tap.


Screw a nut onto a 1" x 6-32 screw, stack up enough washers on the screw to keep the nut from falling into the port, then screw the whole stack into the tapped port.


Crank down on the nut and that seat will pop right out.


Remove the RPV valve and spring, (you will see that the RPV prevents the chips from tapping from going in the bore) clean everything with a bit of brakekleen, then reinstall the brass seat. You can seat the brass seat with a tubenut of the appropriate size.

You can probably run that 1" mc for a while, if it develps enough volume, but a 1 1/8" might be necessary. You'll have a low pedal with the 1", but you can see what the pedal effort is like.

Later, mikey
 

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#9 ·
Thanks Mikey, I will try the 1 1/16 cylinder first, was over at a buddy's we were yacking and 7/8 is the size on the dual master setup.He is using a 2lb residual valve to keep the pads from pulling so far off the rotors eliminating the need for the quick take up master one front and one rear.He uses this setup on all his hobby stocks and e-mods he builds with good success so it stands to reason we should be able to do it with a stock dual master cylinder, same difference still using two pistons one front and one rear.I will pull the residual valve like you show see how it works if the pedal is still low I'll try the 2lb valves . These setups work well on dirt but you can't use as much brake so we'll just have to experiment.If I can get it to lock up I can adjust bias from there.The best part about the bird cyl. is it is only $29.00 vs. $100.00 for a wilwood which is just a dodge truck master anyway.
 
#11 · (Edited)
I have used 10# inline RPVs on low drag fronts with no problems, it cuts the piston retraction back to about .010" from .020", so you don't have a brake drag problem with that setup. I don't know what RPV rating is in the MC you have, stockers can be as much as 16#, that extra residual line pressure is what might be making the rear brakes drag in your case, with your current setup.

You can test the RPV, the setup is simple.
Adapt a 0-30 psi gauge to the outlet. (in this case I am testing an inline wilwood)

To test an RPV in a mastercylinder, just adapt a gauge anywhere downstream from the outlet, youcan even plumb it into a bleeder on the caliper.

Apply about 20 psi, the let off the pressure...The gauge will tell you what the residual pressure rating is. :)



That is a valve that I took apart and installed a better spring, it now holds about 12 psi. I test them for pressure, as well as time it takes to leak down. It should hold indefinatly, any less than 20 minutes at the rated pressure and I would consider the valve junk.

Yes, as you can see all of my info is gotten from books. :mwink:
Later, mikey
 

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#16 ·
I thought of that but for some reason all the parts stores such as napa the zone etc. are showing the same # for the calipers from 79 to 87 like they consolidated and .Build either all low drag or all non low drag calipers to save money.Tried the s10 manual master no volume to the rear brakes.Again could have been a bad master.Switched to 79 camaro with bigger cyl and got brake pressure now.Just have to remove the residual pressure valve, this weekend project.This thing should hit 100 or more in the 1/8 so I really want to be able to stop.
 
#17 ·
barnym17 said:
I thought of that but for some reason all the parts stores such as napa the zone etc. are showing the same # for the calipers from 79 to 87 like they consolidated and .Build either all low drag or all non low drag calipers to save money.
That really sucks to hear :( I hadn't thought of that. I wonder if the aftermarket Howe or Wilwood calipers are made as non-low drag :confused: http://www.howeracing.com/p-7709-howe-metric-single-piston.aspx

barnym17 said:
Tried the s10 manual master no volume to the rear brakes.Again could have been a bad master.
Something wasn't right...and I have had bad master cylinders from the parts store before. Did you have any kind of valve (like a combination/proportioning valve) in the brake system?
 
#21 ·
I have found that the low drag calipers you get from parts stores are mixed in with the standard ones.
Example: I bought a GM metric caliper to use a a mockup in the shop, bought it from my local parts house, a small franchise that uses the Parts + brand. Even though I specified a 77 Monte Carlo..I got a low drag caliper in the box... :confused:

I made a thread about the dreaded low drag calipers a few weeks ago.
http://www.hotrodders.com/forum/test-low-drag-calipers-158523.html

The Raybestos brake technician's service manual I have says that GM started putting these on cars in 1980. It does not specify which cars they came out on initially.

I'm really interested to see how the S-10 master will work in a non boosted application.

Later, mikey
 
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