master cylinder/proportion valve

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The -Dools
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Joined: Mon Mar 30, 15 10:27 pm

master cylinder/proportion valve

Post by The -Dools »

hi, does any one have any links for info on master cylinder-proportion valve upgrade for front discs, car is a 68 GTX, original brakes were power drums all round, i have had a real good look for info, seems the good ole net is rapidly becoming a victim of its own success, adverts are killing finding info

any help please thanks TD
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morgan
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Location: Berkhamsted - Herts.

Re: master cylinder/proportion valve

Post by morgan »

Not sure what you are asking ? Is car already disc and you want to balance it better or is it still drum and you want to convert ?

My 68 charger i went for the wilwood conversion - its well proven and uses orig master cylinder.
Needs drum spindles which it sounds like you have. Nice n easy.

Or are you just looking to fit a proportioning valve to existing setup ?
"Cum homine de cane debeo congredi." Woof.

Current Charger status - "Working !"
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Dave999
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Location: Twickenham,London, England

Re: master cylinder/proportion valve

Post by Dave999 »

disk brake proportion valve. standard from rock auto

take residual pressure valve out of the feed to the front disks. or get a disk master cylinder

put the narrowest bore wheel cylinders you can get in the rear drums dodge dakota

servo drums to servo disks leave the pushrod in the same place on the brake peddle
servo drums to manual no servo disk

the pushrod needs to be put in the manual position on the brake peddle which may or may not be drilled.

Dave
The Greater Knapweed near the Mugwort by the Buckthorn tree is dying
The -Dools
Posts: 10
Joined: Mon Mar 30, 15 10:27 pm

Re: master cylinder/proportion valve

Post by The -Dools »

hi Dave thanks for reply, ill try to add some pics, car was power asst drums all round, my kids put together and got me a front disc kit for my B/day
new spindles, rotors , calipers the works, so got them fitted up, all went ok, fitted a new master cylinder specified for front discs and rear drums
rear brakes were lockin up so had a look and the cylinders were goosed, ordered new and they came as fronts, so reordered and currently waiting for them, so had a look at original proportion valve and thought ill replace that also, so ordered part along with a few emails explaining most of above and they sent a double valve set up, it looks like original with a extra brass assy which i assume is the pressure reduction to rear
it looks like it fits on the chassis in same place
i have been told a 87 jeep prop valve is same footprint as original and is set up ready for disc/drum

ill try to add pics from my phone to this thread

any help is appreciated tim
The -Dools
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Joined: Mon Mar 30, 15 10:27 pm

Re: master cylinder/proportion valve

Post by The -Dools »

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The -Dools
Posts: 10
Joined: Mon Mar 30, 15 10:27 pm

Re: master cylinder/proportion valve

Post by The -Dools »

i cant upload my original pics of valve on car, these are the jeep valve and the valve with extra parts on
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Dave999
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Location: Twickenham,London, England

Re: master cylinder/proportion valve

Post by Dave999 »

have a look at this it will probably help more than the valve

https://www.ebay.co.uk/itm/323796960480


when it comes to the jeep valve we will need to find a diagram of how it was fitted to the jeep

then identify which pipes go where on yours

There will be holes in it for warning light switch and potentially a port for an anti lock brake module i would think. i.e there will be some holes that you can plug as they are not relevant to the basic set up you need.

however unless the springs in your old valve have corroded away it will probably still work.

if you purchased a mopar disk brake master cylinder, all cool!
if you got a generic master cylinder that comes with some of the kits, its bore is massive, and it is more suited to a mustang
stainless steel brakes was a company that seemed to sell a 1 size fits all master cylinder of about 1 inch bore...few people had issues about 10 years ago. SSB may well have seen the error of their ways by now

if you have got the big bore master cylinder you may find the brakes feel a bit like the pads are made from nylon

i.e they work but there is absolutely no progressive effect, its nice to have an inch or more between brakes just on and brakes full on double foot standing on the peddle.

if the master cylinder bore is too large you get about 1mm travel between off and full on. it takes massive two foot effort to stop, and it is an unnerving ride.

the brakes can be described as hard or feeling a bit plastic

rule of thumb
the narrower the master cylinder the less effort it take to put the brakes on full. but the length of travel to do this may well be massive
or need more space than is available between peddle up and the bulkhead

The wider the master cylinder bore, the more effort it takes to apply the brakes, and the length of travel to do this reduces massively for a relatively small change in master cylinder bore.

coupled with that, mopar had different leverage set at the peddle linkage in different years, for brakes that had a servo and brakes and for those that did not.
the pushrod connected to a hole in a different place for each application

the position the push rod attaches to the peddle linkage within a few MM can have a similar effect.
a boosted-brakes peddle set up, into a none boosted manual brake car, will have less than optimal leverage setting (position of pushrod) at the peddle linkage
with no change to disk.

adding disks to the mix means you just have to suck it and see. 99% sure you will be fine

you will be able to get excellent brakes and excellent feel to the brakes but it might take a bit of fiddlin about initially

when it comes to wheel cylinders becasue force against the drum is created by a pressure, It is a function of area of the piston in the wheel cylinder, the smaller the bore gives less braking force at the drum, allowing more work to be done at the disks up front.
and with 10 or 11 inch duo servo rear drums you need less braking unless you tow or carry 1/4 tonne of slabs in the boot and on the rear seat.

for the rear wheel cylinders
Pressure = Force /area, so the force at the shoe = pressure x area of the piston reduce the area and the force is less so you press the shoes into the drum less

at the Master Cylinder

pressure = force/area of piston in master cylinder I.e bore you want to make pressure in the system with sensible force from your foot

increase the area of the bore and you need more force to get the same pressure in the system

if you can provide a force of 10 with ya foot and the master cylinder has a bore of 2 pressure = 5

10/2 =5

if you provide a force of 10 with ya foot (keep it the same, we don't suddenly get a stronger leg mid drive) and the master cylinder has a big bore of 5 the pressure is 2 massive reduction in pressure in the whole system for your standard leg/foot force of 10

10/5 =2

you will need your leg to provide force of 25 to get the same braking
which might not be possible, as , i say most of us don't suddenly get over double the strength in 1 leg for no reason, although being terrified by the fast approaching wall can have a positive effect in these matters

it's a balancing act but if you have a good kit someone worked all this out.

the whole issue here is swapped front wheel cylinders that are small bore for a massive disk brake piston...huge area, as big as the base of a tea mug needing higher pressure in the system to work properly, that higher pressure is easily achieved with the master cylinder you have but it is now higher than the lockup pressure for the rear cylinders, which were specified to work with front cylinders of the same of similar bore.

small rear cylinders help they lock up later allowing closer to the correct pressure for proper disk caliper function at the front in normal braking. The bias valve steps in only when you stand on the peddle with vigour. i.e worry about it second once you have a feel for how it goes.

Dave
The Greater Knapweed near the Mugwort by the Buckthorn tree is dying
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