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Re: [oletrucks] master cylinders

To: oletrucks@autox.team.net
Subject: Re: [oletrucks] master cylinders
From: "ROGER GLEASON" <rogerg@maverick.facil.uconn.edu>
Date: Tue, 9 May 2000 09:38:42 -500
Not so... The fluid you push into the lines when you hit the 
brake pedal only displaces the fluid in the lines and ultimately the 
wheel cylinder/calipers actuates....  ie: if by pushing on the brake 
pedal 5 cc of fluid is inserted into the main line, then after it 
leaves the proportioning valve 2.5 cc goes to the left side and 2.5cc 
goes to the right... the proportioning valve only equalizes the 
pressure front to rear should a difference in pressure occur... 
normally this would not occur or your idiot light "BRAKE" would come 
on... The reservoir has no effect on the amount of fluid pushed 
out thru the plunger. The chambers inside the master cylinder is 
what counts and the size of each (front & rear) are of different 
sizes in a disc/drum brake system.
The reason your front reservoir (For the rear brakes) is smaller is 
that the rear brakes are not as important as the front ones. If you 
have calipers they fill with fluid but do not have return springs to 
pull the piston back so it keeps the brake pads in slight contact 
with the rotors, thus using up more fluid as the calipers are large 
in diameter (However they use less fluid to activate them).. As the 
brake wears down the caliper piston moves outward and fills with more 
fluid (Taking more from the reservoir) until they are all the way out 
and you start hearing metal scraping sounds.... There fore you need 
more of a reserve for disc brakes. If for some reason you were low on 
fluid in the rear brake reservoir your low fluid light (if you have 
one) would come on... If you lose all your rear fluid then the 
proportioning valve would sense the difference in pressure and the 
"BRAKE" light would come on... If for some reason you lose your front 
brakes the proportioning valve would sense the difference in pressure 
and the light would come on. You would still have brakes but only the 
rears...and they will not stop you in a crisis situation. Your pedal 
will also feel low and or spongy.
I do not know what a residual pressure valve does but unless it adds 
fluid to the front brakes (Drum/Drum) system i would still use a 
drum/drum master...

> From:          jelerath@us.ibm.com
> To:            "ROGER GLEASON" <rogerg@maverick.facil.uconn.edu>
> Date:          Mon, 8 May 2000 15:02:50 -0600
> Subject:       Re: [oletrucks] master cylinders

> I have a disk/drum master cylinder in a F*&d in which the front reservoir
> is smaller than the rear, but the front reservoir is connected to the rear
> (drum) brakes.
> In Chevy products (Camaro proportioning valves) the "proportioning valve"
> also has a restrictor built in internally.  I think that will dominate in
> the flow restrictions over the line diameter.  My logic says if the line
> diameter were critical, we'd have to make sure that each brake line, to the
> left and right side, is exactly the same length....they aren't.
> Regards,
> Jon Elerath
> '53 3100 (Camaro, Bel Air, Chevelle, Chrysler, etc, etc)
> Cupertino CA
> I'm not an expert but i still disagree ... The front plunger chamber
> in the master cylinder on a disc/drum system is smaller than the
> rear, the front lines are also smaller... This will restrict the flow
> to the front wheel cylinders... When the rear brakes fill up faster
> than the front they are going to lock up causing you to spin
> out... It will take a long time to fill up the front cylinders
> because these cylinders are usually larger than the rears... When you
> push on the brake pedal the rear chamber will fill the rear cylinders
> first and thus stop the master cylinder plunger from going any
> further thus causing the proportioning valve to move but it can only
> move so far and has its own limiting capacity. If you guys that have
> made this exchange can get your front wheels to lockup before the
> back ones do then I stand corrected but if it was me I would exchange
> a drum/drum master cylinder to replace the old single line type, and
> I would stay away from those designed to work with disc/drum ones.
> rogerg
> > From:          "joe" <chevy1@jps.net>
> > To:            "ROGER GLEASON" <rogerg@maverick.facil.uconn.edu>

> > You can still use the disc/drum master cylinder on a drum/drum system but
> > that's where the proportioning valves and the added residual pressure
> valve
> > comes into play.  The added residual pressure valves takes over for the
> > added pressure needed for the drums 10 lb (disc uses a 2 lb valve).
> > The proportioning valve then fine tunes the braking system for the weight
> > characteristics of the truck to make sure all brakes apply evenly.
> > You could just buy a drum/drum master cylinder but your still going to
> need
> > the proportioning valve.

> > > I don't think you can use the master cylinder from a front disc rear
> > > drum brake system on a 4 wheel brake system due to the different line
> > > sizes being that they use small lines for the front and large for the
> > > rear... The system was designed for use with disc on front and the
> > > fluid needed to push the calipers closed is much less than the amount
> > > needed for the rear drums.. You need a master cylinder for a drum
> > > front drum rear.
> > > rogerg

> > > > From:          "Brian m" <pkupman57@hotmail.com>
> > > > To:            Passnb4U@aol.com, oletrucks@autox.team.net
> > > > Subject:       Re: [oletrucks] master cylinders
> > >
> > > > hi all
> > > > well, i went to pick-in-pulls half off day today. got a power
> booster,
> > pedal
> > > > assy. and master cylinder from an 85 camaro. but becuase the M/C is
> at
> > such
> > > > an angle, i also got a M/C from a 77 firebird. both have
> proportioning
> > > > valves (are they needed if im useing 4 drums?) ive held it all in
> place,
> > and
> > > > from the way it looks, it should fit perfectly. the pedal hangs to
> about
> > > > where the stock pedal is (but a lil more to the left, as the arm is
> on
> > the
> > > > left side of the colume) and the booster and M/C line up nice on the
> > engine
> > > > side, the lower left hand bolt on the dash support looks like it will
> be
> > > > used to hold one of 4 courners of the M/C and pedals up. is this a
> good
> > > > idea? what about this plate on the motor side? welding it up is no
> > problem,
> > > > as i have access to welders. but id rather not weld if i dont have
> to.
> > also,
> > > > i got a brake light switch that works mechanically, and it has 4
> wires
> > in
> > > > it, im assuming 2 are for the brake lights, and 2 are for cruise
> > control,
> > > > but which is which, all i remember of the colors are that one swtich
> is
> > blue
> > > > and orange, and the other two are some other colors i forget.
> > > > thanks,

51-3100 AD Huckster
Lisbon, Connecticut
oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959

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