brake proportioning valve

[doug428]

I installed disc brake conversion on front
original all drums.
I purchased an adjustable proportioning valve and installed it on the rear brake line directly after master cylinder and before the distribution block.
after reading helpful advice from this forum I found out that this valve should be after the distribution block.

its been like this for a year

my brake warning light is on.

do you think this is reason or it should be relocated.

hate to change it if I dont need to, made a nice little bracket for it hidden under MC

 

[Propwash]

I would guess that is why your light is on, being there is a pressure switch on the block and if you have the brakes dialed down past that factory preset pressure signal of that switch, that would give it a good reason to light up the dash light. That is if you remembered to connect the black wire for that switch back up to your distribution block. Also, the variance in pressure with disc vs. the old drum set up could be confusing that switch as well. As far as installing it before the distribution block, there would be no difference in functionality between that and after the block. Being the rear brake circuit doesn't split inside the block, all it is doing is channeling the rear line to a different location on the block itself. Do your brakes work well? If so, I wouldn't change a thing. What good does that little red "Brakes" light do for you when all it does is light up when your brakes have already reached the point of failing. Good reason to call them idiot light...lol Pull the little 194 bulb out of the socket and call it fixed.

 

[doug428]

I would guess that is why your light is on, being there is a pressure switch on the block and if you have the brakes dialed down past that factory preset pressure signal of that switch, that would give it a good reason to light up the dash light. That is if you remembered to connect the black wire for that switch back up to your distribution block. Also, the variance in pressure with disc vs. the old drum set up could be confusing that switch as well. As far as installing it before the distribution block, there would be no difference in functionality between that and after the block. Being the rear brake circuit doesn't split inside the block, all it is doing is channeling the rear line to a different location on the block itself. Do your brakes work well? If so, I wouldn't change a thing. What good does that little red "Brakes" light do for you when all it does is light up when your brakes have already reached the point of failing. Good reason to call them idiot light...lol Pull the little 194 bulb out of the socket and call it fixed.

thanks, thats what I assumed.
I disconnected the wire from the block, so the E brake would still work the light if left on.

 

[bm02tj]

I would reset the plunger and move the proportioning valve after the block because when the light is on you are restricting the brake flow and will not know when it is closed and you have no rear brakes
that might be after you hit some thing or scare yourself

 

[doug428]

I would reset the plunger and move the proportioning valve after the block because when the light is on you are restricting the brake flow and will not know when it is closed and you have no rear brakes
that might be after you hit some thing or scare yourself

funny I was thinking this the other night, I thought I read that the distribution block would restrict the flow of brake fluid if the light was on, to keep fluid from running out of master cylinder and running your master cylinder dry. then I read other post that say it only trips the light and nothing more.

but your right, better save then sorry, uuhg back on the hoist

thansk for help

 

[Propwash]

It's just a pressure switch, and does not actuate. But hey...that would have been a good idea. As far as replumbing for the switch (my own opinion here), that brake light does not come on till your foot has hit the floor and you're already going "oh sh*t". I wouldn't waste a few hours worth of work over it, like cutting lines, reflaring and bleeding brakes if it was already installed north of the block, but is a good point. Just my opinion though.

 

[bm02tj]

when you have a brake line failure that shuttle that turns the light on also blocks the brake port in the body to help you maintain brakes on the opposite end of your car so I would fix the cause but that is only my opinion

 

[Propwash]

Hehehehehe....I'm sorry to say bm, but you're incorrect on this. There is no sort of "Brake Isolation Valve" located inside the little black switch mounted on their distribution block that will save the day by blocking and isolating a good circuit vs. bad. That switch is a simple differential type pressure switch, just like GM and Ford used back in the day. There is no actuating isolation valve/plunger that is able to differentiate between circuits and then separately isolate one of the circuits if at fault. In the pic below, you can see all the switch does is thread into the block and works off mechanical signal (hydraulic pressure). The front and rear circuits inside the block are isolated from each other anyways. If you loose one, it wont effect the other either way. It is a "brake warning switch", not a "brake isolation valve" or "differential pressure valve".

 

[PUNKN8R]

Here is a brake FAQ I stumbled upon when I was have a brake issue hope it helps !


Pedal Ratio & Master Cylinder

Mounting the master cylinder to a frame rail or roll bar is recommended to ensure a solid mount. With the correct master cylinder in place, the pedal ratio must be great enough to produce 1200 psi system pressure under severe braking conditions. A pedal ratio versus line pressure calculator is available below. We recommend using a pressure gauge connected to the system to verify the maximum available pressure before running the car. If the desired pressure can not be easily attained the pedal ratio must be increased until the minimum pressure of 1000 psi is easily reached.

Master Cylinder Sele

A common problem in many applications is a spongy pedal. Brake systems inherently have slack in the system that must be taken up before work can be done by the pads. Slack comes from two factors: retracted pistons must be moved back out, and misalignment caused by deflection in the axle and housing mis-alignment. One of the most common misconceptions is that a larger master cylinder will create more pressure. While a larger master cylinder creates a larger displacement, it takes more force to create the same pressure as a smaller bore. While a larger master cylinder will take up system slack with less pedal stroke, it will take more force to create the same system pressure. The result after adding the larger master cylinder is a harder pedal which needs much more pedal pressure to create the same amount of braking force. For instance, moving from a 3/4" master cylinder to a 1" requires 77.7% more force on the push rod.

The goal then is to balance the entire system. Pedal force, system pressure and lever travel all need to be taken into account.
A balanced system includes the following things:
1) A lever that moves the entire stroke of the master cylinder
2) A Lever that moves comfortably in the confines of a car
3) Uses a reasonable amount of force to reach the desired system pressure
4) Is aligned well enough to minimize lever travel


Below is a calculator to help you find the correct ratios. First find the correct caliper combination from the chart, then find the correct ratio for your master cylinder size.

Caliper Combination: Area of Piston
(sq. in.) Reccomended Master Cylinder Size Master Cylinder Displacement (1.25" Stroke)


Two 83100 2-Piston Calipers 4.8 sq. in. 3/4" Bore 0.55 cubic in.
Two 81100/82100 4-Piston Calipers 9.6 sq. in. 7/8" Bore 0.75 cubic in.
Four 81100/82100 4-Piston Calipers 19.2 sq. in. 1-1/8" Bore 1.24 cubic in.
Two 81100/82100 4-Piston Calipers and two 83100 2-Piston Calipers 14.4 sq. in. 1" Bore 0.98 cubic in.
Two 81100/82100 4-Piston Calipers and two 73002 2-Piston Billet Calipers 13.7 sq. in. 1" Bore 0.98 cubic in.


Caliper Alignment Clearance and Position

Axle stand out controls the alignment of the brake system and as a result is extremely critical. To check stand out, first verify that the housing ends are square to the tube and axles. Install the axles and check axle standout (face of axle flange to face of housing end) as accurately as possible. See the chart below for stand out dimensions for MW brake kits. Stand out should be + .015 of the dimension listed. Shims are available to correct the alignment moving the disc outward .015” (MW catalog page 62 or online P/N 71009). Misalignment can cause caliper mount deflection which is one of the causes of a “spongy” pedal. Install your wheels to make sure the caliper to wheel clearance is adequate both radially and from outer face of the caliper to the inner face of the wheel. To bleed the system, the calipers must be positioned at 3 or 9 o’clock. This allows the bleeder to be highest point, ensuring that all air is removed from system.

Common Standouts

Symmetrical Ends - 2.834" Large Ford Ends 2.500"
Olds Ends - 2.834" Small Ford Ends 2.500"
Mopar Ends - 2.500" GM 10-12 bolt Ends - 2.812"


Proportioning (Pressure Reducing) Valve

The front brake kits with the integral hub and adaptor are designed for Drag Race applications. The main advantage is the reduction of weight compared to the stock braking system they are designed to replace. Several considerations must be taken into account when installing these kits. When any four piston caliper is used with drum brakes on the rear, a pressure reducing valve must be installed for front pressure control. Because of the small front tire contact area compared to the rear large slick contact area, the rear brakes must absorb more of the stopping energy than the front (contrary to a normal street car). A starting point would be 70% of the rear line pressure to the front brakes. This is especially important when using drum brakes on the rear. With discs on both the front and rear the percentage could be higher depending on the weight distribution and tire size but should still use the pressure reducing valve. We have a pressure reducing valve, P/N 260-2200, and we recommend its installation with front brakes. The pressure bias should be adjusted with gauges, MW P/N 81105, in the front and rear to confirm the pressure differential and then do a stop test. When doing a stop test, for a drag race car, the front tires should skid equally or slightly after the rear tires. This test can be simulated at a very low speed (approximately 5 mph) by using a wet surface or gravel and observing the lock up sequence.

Brake Lines and Fluid

Aircraft AN-3 brake lines and fittings are recommended. Only stainless steel braided teflon hose, stainless or seamless steel tubing (3/16” x .028”) should be used for brake lines. MW has available swaged Teflon Stainless flexible braided line that can be fabricated on a same day basis. The are available on line P/N 0300-X-X. Lines should be secured to chassis rails to resist vibration and routed in such a way to avoid possible contact with wheels, tires and other moving parts. Joining hard line and braided line or “T”s should be done using a bulkhead fitting and a small tab welded to the chassis. Long runs should be done with hard tubing to avoid expansion of flexible line. The amount of flexible braided hose in the system should be kept to a minimum. See page 63 or the online store for AN -3 fittings and brake line. Use of DOT 4 or 5.1 fluid with a high boiling point and lubrication for seals and pistons is recommended. Do not use (DOT 5) silicone fluids .

Troubleshooting Your Brake system

Spongy Pedal:

1) Air in system. Bleed brakes, making sure that the bleed valve is the highest point.
2) Disc warped (saucer shaped). Replace or surface rotors
3) Calipers not square with disc. Check housing end alignment, both concentricity and squareness.
4) Linings worn on taper. Make sure that caliper is centered over the rotor and the caliper bracket is not deflecting.
5) Master cylinder bore too small creating excessive high line pressure. Match master cylinder to system.
6) Master cylinder deflection. Stiffen master cylinder mounts

Brakes are locked up after run:

The piston in the master cylinder is not being allowed to return to the full retract location, when released. This condition will maintains line pressure and prevents the car from moving. Re-adjust the linkage so that the piston completely returns to the retract location.

Excessive pad wear, disc shows excess heat:

1) Lining too thin causing rapid heat transfer to calipers, boiling the fluid. Install new linings and re-bleed system.
2) Fluid contaminated with moisture causing boiling of fluid in caliper. Flush old fluid and replace with DOT 5.1 Fluid re-bleed system.

Maintenance:

Annual disassembly and cleaning of brake system recommended. Carefully inspect pistons and piston bores. Re-assemble with new “O” rings.