[LATECH]

So your point of fact checking is...What? To completely miss the point you cant always trust everything as it's told?

Just stating what I have seen firsthand

Or

I dont understand your point

 

[LATECH]

On a 4 disc system, you could disable the prop valve for the rear and the metering valve(hold off valve) for the front and run the block as just a safety valve.
Or summit has this which would work nicely:

https://www.summitracing.com/parts/rsd-pv72b/make/chevrolet/model/monte-carlo/year/1972

It would take all the guess work out of it for you
They are calling it a proportioning valve, but it will not have a proportioning valve setup inside as it isnt needed ,nor will it have the hold off for the front
It is a distribution block, it also still has the safety function inside ,in case one set of brakes loses pressure

 

[LATECH]

Leaving the disc/drum assembly in it wouldnt hurt though
It would prevent the rear brakes from locking up, useful in snow/skids/rain(proportioning part)
It also would "hold off" the application of the front brakes untill the rears had some pressure to activate. (Metering/hold off valve)

 

[jpalmer1717]

Ok, well after reading all of that, I do think I SHOULD replace the combination valve to a disc disc...with probably a C5 valve since I have huge C5 brakes on the front (And the small Summit OE type on the back). QUESTION - the brake lines running to my current stock combo valve are in good condition. I've been soaking them for days as well. Is it possible I could extend those lines with male to male fittings to get them up to a nice location under the master? Currently it sits tightly between a header and the frame. I know it's POSSIBLE to extend the lines but I guess I'm asking if you folks think it could be done successfully...?

 

[LATECH]

well you may still have issues. Remember the part about piston to piston area master vs slave
large fronts and tiny rears may equal a huge stopping problem. The tiny ones in the back may lock the wheels and skid before the fronts actuate well enough to perform a safe stop. If the pressure is maxed at the rear the pedal wont go any farther ,it wont apply any more pressure to the front. That is why bore size is VERY important
the piston area of the front vs rear on a disc disc system should be 60/40 or close to it

I would relocate your valve and lines as you are thinking very well there. Keep the heat away
brakes get hot as it is. no need to add heat - cause trouble

Post the specs of the master cylinder bore
the # of pistons in the front caliper and their diameter
the number of pistons in each rear caliper and the diameter

you may need some dual piston or quad pistons on the rear to get a good balance

 

[Unstable]

Post the specs of the master cylinder bore
the # of pistons in the front caliper and their diameter
the number of pistons in each rear caliper and the diameter

This ^^^ yes.

For the average guy, we see “disc brake conversion kit” and think “oh cool…let me buy that and improve my car” - without ever thinking that a company could or WOULD sell a single kit like this that wasn’t all inclusive…If it doesn’t have a master cylinder or proportioning valve…If must mean I don’t need to worry about that…right?

The best thing you can do from a safety and longevity perspective in my humble opinion is pull that into together and determine what optimal master would be.

Also please forgive me for my earlier posts—I’ve been through a similar exercise myself recently and brakes are something to take seriously.

 

[LATECH]

Brakes are important. when they dont work, strong underwear are important

 

[2old2fast]

Something to keep in mind is aftermarket brake companies are in business to sell parts , whether you need them or not . Some m/c have residual pressure valves in them , some do not, there's no point in doubling valves . There are proportioning valves , metering valves , safety valves some are separate some are different combinations of the three types . The popular " Corvette m/c comes in different flavors , just like combo valves . Unless you are using a factory ( OEM) combination of parts or are a brake " professor" , you've no idea of what works , works correctly or works so/ so. I'll side with OEM engineering , they have a better track record . Do you feel confident in aftermarket " sales techs" ? I don't . Keep in mind you're engineering for the street , not a closed circuit race course

 

[jpalmer1717]

well you may still have issues. Remember the part about piston to piston area master vs slave
large fronts and tiny rears may equal a huge stopping problem. The tiny ones in the back may lock the wheels and skid before the fronts actuate well enough to perform a safe stop. If the pressure is maxed at the rear the pedal wont go any farther ,it wont apply any more pressure to the front. That is why bore size is VERY important
the piston area of the front vs rear on a disc disc system should be 60/40 or close to it

I would relocate your valve and lines as you are thinking very well there. Keep the heat away
brakes get hot as it is. no need to add heat - cause trouble

Post the specs of the master cylinder bore
the # of pistons in the front caliper and their diameter
the number of pistons in each rear caliper and the diameter

you may need some dual piston or quad pistons on the rear to get a good balance

I'm going to start a new thread and post my brake specs and see what people recommend for a combination valve.

 

[joe_padavano]

The first thing to understand is that nearly all of the disc brake kits sold are poorly engineered. You should note that GM used a wide variety of combo valves that were tuned for specific car weights and weight distributions, yet the aftermarket only sells the single imported PV2 valve (for disc/drum) and PV4 (for disc/disc). The function of the metering valve is to delay operation of the FRONT disc brakes to give the rear drums time to take up all the slop in the linkages. Yes, you can remove the metering valve function. The problem is, do you think the proportioning valve part of that combo valve is correctly calibrated for rear disc brakes? Keep in mind that the function of the prop valve is to REDUCE the effectiveness of the rear brakes to avoid premature rear wheel lockup and resulting loss of control. I've found it humorous that people spend thousands of dollars on rear discs then use a prop valve that reduces their effectiveness down to what you had with the drums.

 

[LATECH]

I'm going to start a new thread and post my brake specs and see what people recommend for a combination valve.

That would be like putting shoes on a dead horse.
A combo valve will not fix the inherent problem.Period

 

[LATECH]

The valve I posted at summit is ideal.
A new prop/safety/combo valve is not going to fix the problems with the system as assembled
Your biggest need is to do the math for the ratios between the front and rear calipers.
Lots of good advice and tech in this thread .It would serve you well to use it to your advantage
Post your caliper piston diameters for the front and rear as asked for in previous posts.
The math is not that hard , and will ultimately be what you need to solve this problem

 

[jpalmer1717]

The valve I posted at summit is ideal.
A new prop/safety/combo valve is not going to fix the problems with the system as assembled
Your biggest need is to do the math for the ratios between the front and rear calipers.
Lots of good advice and tech in this thread .It would serve you well to use it to your advantage
Post your caliper piston diameters for the front and rear as asked for in previous posts.
The math is not that hard , and will ultimately be what you need to solve this problem

That's exactly why I'm here and asking questions...to use this thread to my advantage.

 

[jpalmer1717]

Here are the specs:

Disc/disc master with 1" bore

Dual piston on front (1 9/16" diameter piston, 13" rotor)

Single piston on rear (2.75" piston diameter, 11" rotor)

18" wheels

What else?

 

[LATECH]

OK so rears have 5.9 square inches each in piston area
fronts are at 4.01 each side (counting both pistons in one caliper)
rear will apply roughly 50% more pressure to the pads than the front
rear pads being smaller than front means the rears may lock up quickly
So fronts are dual piston ?or 4 piston? per side
now ,bigger rotors give more stopping power as the force to stop applied is farther from the center of rotation than an 11 inch caliper. But only if the force on the pads between the systems is equal. which it is not . at the very least the front is too small or the rear is too large
Pad size also figures in here too as it is important ot keep the PSI on the front and the rears
Can you also provide a rough measurment of the pad sizes?

 

[LATECH]

The rotors being 13 front and 11 rear sounds pretty good . Equal pressure applied to the pads at all wheels would be balnced pretty well
the front rotor has a radius of 6.5 inches
the radius of the rear is 5.5 inches
close to the 60/ 40 split you want in braking force if comparing the amount of torque it can control. The larger rotor will have more stopping power due to the simple fact it has a larger radius. so the rotor sizes IMHO are pretty much perfect
as long as you can get the caliper piston sized correctly

post up pad sizes .Thanks

 

[jpalmer1717]

On a 4 disc system, you could disable the prop valve for the rear and the metering valve(hold off valve) for the front and run the block as just a safety valve.
Or summit has this which would work nicely:

https://www.summitracing.com/parts/rsd-pv72b/make/chevrolet/model/monte-carlo/year/1972

It would take all the guess work out of it for you
They are calling it a proportioning valve, but it will not have a proportioning valve setup inside as it isnt needed ,nor will it have the hold off for the front
It is a distribution block, it also still has the safety function inside ,in case one set of brakes loses pressure

That valve is almost perfect. I found basically the same thing, but it's adjustable. Check it out...

CPP Adjustable Proportioning Prop Valve with Brake Lines Light Switch + Wire | Classic Performance Products CPP | Private Label

This new CPP adjustable proportioning valve block is what CPP is all about. This is a must have item! CPP Adjustable Proportioning Valve. New CPP adjustable proportioning valve block. 1/8" pipe connection at the brake light switch(included!).

www.ebay.com

 

[jpalmer1717]

The rotors being 13 front and 11 rear sounds pretty good . Equal pressure applied to the pads at all wheels would be balnced pretty well
the front rotor has a radius of 6.5 inches
the radius of the rear is 5.5 inches
close to the 60/ 40 split you want in braking force if comparing the amount of torque it can control. The larger rotor will have more stopping power due to the simple fact it has a larger radius. so the rotor sizes IMHO are pretty much perfect
as long as you can get the caliper piston sized correctly

post up pad sizes .Thanks

I'm not sure exactly how to measure a brake pad while on the car, but the dual piston fronts are 7" x 2".....the single piston rears are 5.5" x 1.75".

 

[LATECH]

7x2 is 14 sq inches
5.5 x 1,75 is 9.6 sq inches
14 x 60% = 8.6
so your rears are actually real good pad and caliper wise
The front only need the calipers I isted as the pistons need to be around 2" diameter (pair) to be good to go as far as square inch area and they would make the front and rear very well balanced size wise.The front you have are not going to work well IMHO
That valve does look good and if the rears are justa little to agressive it would allow you to dial them back a tad
Perfect

 

[55_327]

Here's my understanding: A proportioning valve only affects rear brake pressure during panic stops. There is absolutely no reduction in pressure to the rear brakes -- ever! It's only a reduction of the rate of pressure increase to the rear. So during normal driving, rear brake pressure will be the same as having no proportioning valve.

For disc/disc, I'd start with no valves. And if the nose of the car tends to dive, you could try a 2-lb valve in the front circuit. Remember that a metering valve compensates for front disc brakes activating before the rear DRUMS.

As for a proportioning valve, if the rear discs do lock up before the fronts during a full-on panic stop, then an adjustable proportioning valve would help. I'm not a big fan of the one-size-fits-all valves that most vendors sell. What works on an unloaded long wheelbase pickup with 31" tires, may not work on a Camaro with 26" tires.

On a factory engineered brake system, the rear disc brakes are smaller than the fronts -- rotor diameter, pad size, and even piston area. IMO that pretty much negates the need for a proportioning valve. But with an aftermarket system, who knows?

**Edit: I just noticed that LATECH addressed sizing above.