Master cylinder

What master and prop valve do I use?

  • Stock factory set up

    Votes: 0 0.0%

  • What set up would u use?

    Votes: 0 0.0%
  • Total voters
    0
-
340 demon 72

340 demon 72

Well-Known Member
Joined
Feb 21, 2015
Messages
2,055
Reaction score
121
Location
Wisconsin
I have a 72 Dodge Demon I Converted the front to an after market disk brake for the for the better stopping put 10 × 2 1/2 from a 79 Plymouth volare can I still use the stock master cylinder and portioning valve. The car originally had drum all 4 corners. Can I use the original master that was for the 4 wheel drum?
 
Last edited:
I had front disc / rear drum on my 73 Dart Sport. I went to four wheel disc and didn't change the master or proportioning valve. Works great.
 
Mopar to ya said:
I had front disc / rear drum on my 73 Dart Sport. I went to four wheel disc and didn't change the master or proportioning valve. Works great.
Click to expand...
We're ur chambers the hold the brake fluid the same size or different mine are the same size? The factory one anyways
 
The larger chamber supplies the discs, making checking the fluid less frequent. That is the advantage to those.
In your drum/drum;You need to remove the Residual valve from the port that supplies the front brakes. Other wise, they interchange.
 
AJ/FormS said:
The larger chamber supplies the discs, making checking the fluid less frequent. That is the advantage to those.
In your drum/drum;You need to remove the Residual valve from the port that supplies the front brakes. Other wise, they interchange.
Click to expand...
There was just a proportioning valve nothing else
 
The Rvalves are right in the outlet ports, behind the tube seats. They are one way valves designed to keep about 8 psi in the lines to keep the wheel cylinder cups in firm contact with the bores. Almost Obviously you wouldn't want to keep 8 psi in the calipers, keeping the pads dragging on the rotors.
Some guys just drill them out. Others pull the tube seats out, and remove the valves, then reinstall the seats. You only get one shot at it tho, so if you wreck the tube seat, you wreck the M/C.
 
Last edited:
AJ/FormS said:
The Rvalves are right in the outlet ports, behind the tube seats. They are one way valves designed to keep about 8 psi in the lines to keep the wheel cylinder cups in firm contact with the bores. Almost Obviously you wouldn't want to keep 8 psi in the calipers, keeping the pads dragging on the rotors.
Some guys just drill them out. Others pull the tube seats out, and remove the valves, then reinstall the seats. You only get one shot at it tho, so if you wreck the tube seat, you wreck the M/C.
Click to expand...
so an after market M/C with porp valve would b the easiest way to remedy this??
 
Not for me; I have a drill and a box of bits. If you wreck it, thennnnn it would be easiest to remedy it, by replacing it..
I haven't seen a drum/drum car with a Proportioning valve. A Junction block?yes. Or a junction block with a Safety switch? yes. Those I have seen.
If you are running 295s out back, you probably don't need a P-valve. Even with 275s my 68 Barracuda didn't need it. I still have a brand new valve here that I bought for the car, in the planning stage. After the roadtest, I decided she didn't need it so I am running without one.It stops real nice.
 
AJ/FormS said:
Not for me; I have a drill and a box of bits. If you wreck it, thennnnn it would be easiest to remedy it, by replacing it..
I haven't seen a drum/drum car with a Proportioning valve. A Junction block?yes. Or a junction block with a Safety switch? yes. Those I have seen.
If you are running 295s out back, you probably don't need a P-valve. Even with 275s my 68 Barracuda didn't need it. I still have a brand new valve here that I bought for the car, in the planning stage. After the roadtest, I decided she didn't need it so I am running without one.It stops real nice.
Click to expand...
is this not a porp valve??
Resized_20160615_164537[1].jpeg
 
There are all sorts of things you CAN do, but the way you SHOULD run with disk brakes is with a disk brake master cylinder and with a proportioning valve. The PV was built-in to the junction block/safety switch on factory disk brake cars starting in 70, so you could just buy a replacement unit -- pure bolt on. This unit is non-adjustable, but it is likely to work OK so long as your weight distribution is not radically different than stock. Or, it was a separate part, inline in the rear brake line, on factory disk brake cars 67-69, but this unit is is not repopped AFAIK. It would be the hard way to go, anyway, since it requires splicing a brake line, and although it was theoretically adjustable, it didn't have much of a range (it was usually all the way in or out). Or, you could buy an aftermarket proportioning valve, but again, it would require messing with your brake lines. However, it would actually give you a wide range of adjustment if that is an issue.

BTW, the proportioning valve doesn't adjust the AMOUNT of braking force on the rear, it adjusts HOW QUICKLY it comes in, to avoid lockup. If you need to adjust the amount of rear braking, that requires changing the rear wheel cylinder diameter.
 
The factory valve reduces rear pressure to about 75% of the front;so says the 1969 FSM.I bet a huge percentage of time the rear brakes are doing very little more than keeping the drums shiny. Which is why I threw that Pvalve away. I figured if I had 295s or 325s back there, I might as well use them. Now they do most of the work, for me.I wear out rear shoes probably 2 or3 times as often as the fronts. 295/325s stick pretty good with about 48% rear weight bias. And with 295s back there, they work in the sideways direction too!When I hit the brakes hard, the whole car just kinda gets sucked down.No drama.
With 10" slicks I would try the system without a Pvalve. If the rear locks prematurely, just go down one wheel cylinder size.That's what I would do.
And if it's a track car,or a weekend warrior,the lack of reservoir size to the calipers,IMO, is no big thing.Just top it up more often.
295s have about 10 inches of tread; about the same as what you are gonna run. You can spend a $100 on an aftermarket valve, and spend a bunch of time plumbing it in there, and in the end it will be running wide open, so you might as well just start with wide open.The shake down run will tell you everything you need to know, and changing w/cs is easy/peasy.
My 2 cents
 
Last edited:
OK, I looked and they don't give the caliper piston size. I was just wondering as some conversions are for the 80's metric GM 1 piston calipers with 2-3/8" piston bore, and those are so small as to not give adequate front brake force. The pix the POL shosws LOOK like Mopar 1-piston calipers but it is really hard to tell.
 
nm9stheham said:
OK, I looked and they don't give the caliper piston size. I was just wondering as some conversions are for the 80's metric GM 1 piston calipers with 2-3/8" piston bore, and those are so small as to not give adequate front brake force. The pix the POL shosws LOOK like Mopar 1-piston calipers but it is really hard to tell.
Click to expand...
Pol calipers are mopar ones gm would have a Allen blot that attaches it the mopar ones have the sliders top amd bottom
 
For comparison sake
A 2.375 bore has 4.43 inches sq.
500 psi line pressure is easily achievable with even a small 15/16 M/C. With a tiny bit more legpower, the 33/32 M/C can make 600psi. Doing the math with 600psi line pressure; 2.375 x 600=1425 pounds of brakeforce.

The KH 4-piston set-ups have 1.625 pistons @ 2.074 each x 4 =8.295 total. These stop very well, with minimum foot pressure. At just 500psi x 8.3 sq inches = an awful lot of brakeforce. I get 4150, which is nearly 3 times as much....
I don't think I would want too much less on my 3650 pound tank(me in it)
 
In the above calcs, keep in mind that the single piston calipers get a 'free' force on the back side pad equal to the force from the single piston. So you either compare the single piston to only 2 of the K-H pistons, or compare 2x the single piston force against all 4 of the K-H pistons's total.

With the latter, you end up with 2950 versus 4150 lbs force....which is the point on the small GM caliper bore being a problem... it'll be under braked up front.

But the OP has the Mopar ones....so no problemo. I just wuz checkin'.
 
You must log in or register to reply here.
-

Back
Top