Thread: Brake troubles

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Roger Thanks----I knew it was a cpp valve, issue with it is that it doesn't apply pressure to the rears first before the fronts-------OEM combo valves have a feature where initial pressure is applied to rears before the fronts. Without this I don't believe that the oem rear calipers will work properly which will inhibit them from auto adjusting the parking parts------

That valve is strictly a junction block to include the stop lite switch and the rear prop valve-does not satisfy the requirements for a street system.

Navy-I noticed in your pics that you ran a rod from your shifter to a pivot toward the rear of trans and then another forward to the shift arm-----good thinking to keep the geometry correct for trans/shifter notches-I did that on a car I built for a customer and the paint shop outfit left if off when putting body/frame back together---and then--------Also they sent out the polished stainless exhaust headers/side pipes(Cobra type) and had the powder coated a lite grey------------


Also I noticed on the pic of your brake pedal that you not only had an arm at a wierd angle and length but that you had shortened the foot arm by 4 or 5 inches?????? Both of those effect your leverage tremendously but also both arms are on the same side of pivot and would have extreme geometric moment of force ---------

Originally Posted by jerry clayton

Roger Thanks----I knew it was a cpp valve, issue with it is that it doesn't apply pressure to the rears first before the fronts-------OEM combo valves have a feature where initial pressure is applied to rears before the fronts. Without this I don't believe that the oem rear calipers will work properly which will inhibit them from auto adjusting the parking parts------

That valve is strictly a junction block to include the stop lite switch and the rear prop valve-does not satisfy the requirements for a street system.

Navy-I noticed in your pics that you ran a rod from your shifter to a pivot toward the rear of trans and then another forward to the shift arm-----good thinking to keep the geometry correct for trans/shifter notches-I did that on a car I built for a customer and the paint shop outfit left if off when putting body/frame back together---and then--------Also they sent out the polished stainless exhaust headers/side pipes(Cobra type) and had the powder coated a lite grey------------


Also I noticed on the pic of your brake pedal that you not only had an arm at a wierd angle and length but that you had shortened the foot arm by 4 or 5 inches?????? Both of those effect your leverage tremendously but also both arms are on the same side of pivot and would have extreme geometric moment of force ---------

I had originally shortened the foot pedal for fitting in the cab, I have returned it to its original length and lowered the pivot point to allow its use as such . The arm angles are due to the firewall/toeboard angle.
I'm going to the junk yard and get a combo valve and see what effect it has. I'm going to call the brake co. and see what they say or don't say.
Thanks to all that are giving me input.

at the junk yard see if they have Mustang hydro boost(power steering) brake system. don't know what all years but 2000-04 for sure-------since you have power steering------

Originally Posted by jerry clayton

OEM combo valves have a feature where initial pressure is applied to rears before the fronts.

That valve is available in a stand alone version called a hold off valve. It plumbs into the front brake circuit and prevents any pressure from getting to the front calipers until a preset pressure is reached. I've seen 100 psi listed.

Here are some links

ECI Hot Rod Brakes and Brackets Brake Facts

Brake Metering-Hold-Off Valve

I have one on my T-bucket, but not on my 46.

too many mods and stand alone parts being used-------use a OEM type combo valve with a master that has residual valves build into ports and problems will go away-assuming that leverage ratio / geometry is correct on pedal.

Jerry, I would agree, but most disc master cylinders intended to be mounted on the firewall don't have residual valves in the ports. They aren't needed when the MC is mounted above the axles.

If the MC has removable seats in the ports you may be able to add them, though. The hard part would be locating the individual residual valves. I can remember when they were sold in parts houses.

A factory style combo valve would be great if it didn't have a proportioning valve in it. Finding a factory valve with a fixed prop valve that would work in a custom installation would be a crap shoot at best.

I think you have a couple ideas backwards------disc brakes need 2 lb valve to keep pads near disc-and masters have them----combo valves don't have proportion valves -they have the front delay valve-OEM systems are designed as needed to be without proportion valves-hotrodders and racers create that need with either race braking needs or in the case of street rodders the big/little tire deal crated imbalance the system wasn't designed for


Somehow whole thing didn't post---------With a OEM type combo valve ( for street/road driving/braking) you shouldn't need a separate additional proportioning valve unless your caliper size/ disc diameters are why out of balanced size--again the big/little tire sizes really compound area for improper components.

Sorry Jerry, some may not have one, but the classic definition of a combo valve is that it has a prop. valve.



https://www.mpbrakes.com/techtalk/co...-brake-systems

The Combination Valve - How Master Cylinders and Combination Valves Work | HowStuffWorks

Brake Combination Valve Function

All I know is that when this is done and over we'll all be a bit smarter about putting 4 wheel disc brakes on a street rod. Here's a pic of my pedal after changes.

thanks again for the post !

Just curious, and I may be wrong, but could you have changed the point of attachment at the travis rod and added the leverage needed without modifying the pedal arm?

Originally Posted by 36 sedan

Just curious, and I may be wrong, but could you have changed the point of attachment at the travis rod and added the leverage needed without modifying the pedal arm?

Already did, the point of attachment is now over 1 inch higher/shorter, arm has been cut off to its shorter version I think there's a pic back in post 34 that shows it before I modified it. Ratio was way to small.

Today I called Power Master Brakes, here's what the tech had to say
Don't need any kind of proportioning valve
Power brakes should have a pedal ratio of 4 to 1
Manual brakes should be 6 to 1
My calipers will always be a problem, and who ever sold them to me was incompetent.
IMHO the only one who is incompetent is the tech at PMB.

Originally Posted by Hotrod46

Navy, My front calipers have a 2.358 bore and the rears have a 1.886 bore. That alone may contribute to my success. They just aren't that different in size. .

They are a bit different than is seems. It's the area of the bore that counts, not the diameter for comparison purposes.

The areas are: Front 4.37 sq. in., Rear 2.79 sq. in. The fronts will also have larger brake pad area.

and a larger diameter disc

In my case the discs are very close to the same size, so no advantage. The point I was trying to make is that in many cases, street rods are built using what parts are available or will fit. That doesn't mean they are going to work together.

In the case of GM metric calipers, typically they have a 2.496 bore in the front. The rears can range from about 1.88 to over 2". Choose the wrong bore and you can wind up with a situation that has the front brakes stopping the car, while the rears never do much of anything. If the fronts are too much larger than the rears, the line pressure required to allow the fronts to stop the car will be too low to allow the rears to offer much clamping force. In most cases, you're never going to want more braking on the rear that the front, but you do want a relationship that allows complimentary action. Bore size, for me, is just a convenient way to compare.

My Ford calipers are actually closer in bore size than some combinations of GM parts. I agree that area is a probably a better description, but bore size will work as long as you understand that bore size will determine area.