Proportion valve / brake system

[tard01]

So trying to get my hands on the proportion valve for the brake system. trying to work out a pressure problem im bhavbing. i have already replaced teh master cylinder calipers brake pads and the rotors and teh rear drums and shoes and a wheel cylinder.


oreilly's telling me they dont carry these cause they are dealer parts, but the dealer is telling me they're no longer produced and hence are not carried in stock.

while doing work on the truck, the constanbt troubleshooting has worn out the nuts/bolts on the brake lines and i've been debating rebuilding the brake line system frmo scratch. they're all the original parts - 1975 c10.

anyone know or can recommend where i can get a new proportion valve -- or, are they entire necessary? can i find an alternate means of splitting them?




for background on issue,
originally felt like major air in lines.
bled brakes, improved, but still lacking stopping significantly.
replaced rotor/pads/caliper/master cylinder/drum/shoes/wheel cylinder(1)
not much improvement.
still had to pump, and still had to exert a large amount of force to get any pressure. it never felt like the front brakes were ever biting. felt like almost all my stopping power was from rear.

so i was working on replacing the 2 wheel cylinders in the rear cause i noticed they were bleeding spo i decided to replace abnd in the process, i striipped the bolt on the brake line. i was going to cut it off and re-place it, but the splitter for the brake line that goes onto the axle was also so rusted it was stripping.

so my options... i can either cut the rear line and replace that rear segment... but that doesnt solve my front end biting problem... or i can replace the proportion valve in the front.

my concern is that its clogged up and that is whyt i am having to exert so much pressure on the brake just to be abloe to get any form of bite from the front. when i initially bled the system the first timew, there was a lot of small metal chunks as well.


the entire front braking system has been replaced minus the lines themselves and the proportion valve.

[Keith Seymore]

1) What about the brake booster? Could it be that you are not getting any power assist?

2) You can buy an adjustable proportioning valve through most supply stores like Jegs, Summit, or specialty race brake shops.

http://www.jegs.com/c/Brakes-Drivetr...10165/10002/-1

K

[tard01]

There is no brake booster on this truck. I have a functional 69 same style brake system to compare to and rhey are miles apart
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[75chev4x4]

Why do you think its the proportioning valve? What is your bleed process? What are you using to bleed?

[tard01]

thinking prop valve because i've replaced the entire front end braking system, minus the valve and flex line.

calipers, rotors, pads, master cyl.

bleed process i've done many many times a few different ways.
bought a hand vacuum,
had a 2nd person press down while i open/closed
bled into an acquarium hose with a rubber fitting into a water bottle with a small resevoir of brake fluid in it.

even when i felt the bleeding was perfect (best result was with 2 ppl), it still felt like hte frnot wasnt biting.

on first bleed, i saw crud coming out of the brake line on the first bleed.

since hte only thing i havent replaced is the prop valve, thinking it might be clogged with crud.


i have to press with an almighty force to get any firm braking power when it works. fairly ridiculous.

we have a 69 c10 with the same set up and it is a dramatic difference.


side note, i have cleaned hte banjo bolt thoroughly.


not sure what else could be the problem for the front brakes not biting than the prop valve itself.

[dogpound]

You r on the right trac. I do this for a liveing. The proportion valve does just that. Distribute brake fluide in differnt presser between front and rear brakes for your nose dive effect. You can buy any ajustable proportion valve through after market, this will correct your problem.

[tard01]

having trouble identifying what kind of proportioning valve to buy.

seems most of what i find refer to disc conversions.

i am running discs in front, and 11" rear drums.

also, is there any reason (fluid dynamics) that i have to keep the kit in the original location, or can i create a new mounting position for it closer to the master cylinder?

i'm hesitant to buy anything because i know the front/rear tubes are different size connectors.


eventually when i am prepared to buy, i will yank the existing lines/prop valve off and inspect everything diameter/length, but trying to get to that phase first.



this is the list "specific" to my truck. 75 c10 rwd v8.
anyone able to shed some light?
http://www.jegs.com/webapp/wcs/store...Id=10002&Nty=0

[tard01]

also, i havent seen, but can you get the end screw/bolts for the hard lines seperately? ie, if i want to buy a roll of tubing, can i cut it and buy extra bolts? does the diameter of hte line itself automatically mean a certain size bolt?

[cmyc5575]

Originally Posted by tard01

also, i havent seen, but can you get the end screw/bolts for the hard lines seperately? ie, if i want to buy a roll of tubing, can i cut it and buy extra bolts? does the diameter of hte line itself automatically mean a certain size bolt?

I kinda went threw the same issue with mine come to find out it was my brake lines hoses were collapsing on the front so all i had was rear brakes for awhile.

[tard01]

Originally Posted by cmyc5575

I kinda went threw the same issue with mine come to find out it was my brake lines hoses were collapsing on the front so all i had was rear brakes for awhile.

interesting. ill try to get a 2nd person to stomp the brake while i check the flex lines. the hard lines looked satisfactory as best as i could tell.

i was budgeting for 2x flex lines, plus the rear flex if i needed, and then the entire hard line system - though ill have to do some work confirming the sizes and such. i'm nervous ordering an entire spool when i dont have the most optimum way of gauging it. i'll likely cut off a line, take it up to oreilly's and just replace that 1 piece, then order the rest as needed.

[hatzie]

You used to be able to buy fittings and a coil of line.

New Combination/Proportioning valve. http://www.ebay.com/itm/73-77-Chevy-...-/190540606447

Test Combination/Proportioning Valve from a detailed writeup on troubleshooting brakes. http://www.classicperform.com/TechBo...t.htm#testprop

Use a test light by attaching a clip to a positive contact on the vehicle and touch the point of the tester to the electrical connection of the combination valve. If the the light does not come on, the valve system is operating correctly and no further testing is required.
If the light does come on, this indicates that the pressure differential valve is stuck in the front or rear position.
Bleed the brake system to determine if the front or rear lines are blocked off. Set up one front wheel and one rear wheel for bleeding at the same time. Crack both bleeder screws and gently pump the pedal a few times.
The blocked side will trickle fluid out when the bleeder screw is cracked and the pedal pressed. An unblocked line will squirt fluid out the bleeder.
The lines that are clear must be left open and the blocked lines should have the bleeder screws tight to cause pressure to build up on that side. Be sure to use the standard bleeding procedures to prevent air from entering the system.
Slowly press the pedal with steady pressure a number of times until the light goes out; this will center the differential valve. You may also hear a pop come from the proportioning valve. This is the metering valve returning to its equalized position. When the light goes out, close the bleeder screw. (See fig. below)

[76C10Stepside]

I've had brake hoses collapse on the INSIDE and look fine outside (not even any cracks), but only one one at a time per car, so far.

You said you replaced the master cylinder. IF you've already replaced the front calipers (you said in a later post that you have front discs, even tho it's a 69), then it's down to blockage somewhere. You can put the front on jack stands and test each of the front brakes separately. Have someone step on the brakes while you are turning the left wheel, repeat for the right wheel. If ONE of your front brakes works and the other one does not, it's probably a collapsed brake hose. If BOTH of them do not work, it's probably the proportioning valve (could also be blockage in the hard line, but I doubt it).

Just to make sure it's not an air bleed issue: When you step on the brake pedal and hold it down, does it a) only go down part way and STAY there, or b) sink to the floor? If "b", you have a leak in the system or a bad master cylinder.
I've had wheel cylinders look ok (no fluid leak), and bled the brakes for hours. Finally, after hours of re-bleeding and re-checking for leaks, one wheel cylinder started leaking. CAUSE: It was letting air in, but not letting any fluid out! That's a borderline situation that can happen once in a blue moon!

[75chev4x4]

You bench bled that master out before you put it on the truck right?

[tard01]

i think i got a clue whats going on now thanks to my girl giving me a hand.

1) one of hte wheel cylinders is still old and leaking. I was triyng to replace but the bolt stripped almost instantly for the brake line. i'll need to cut beyond it and replace that segment to restore it and have it useable.
2) we bled them normal, got back to the pressure htey had been at before. then, unlike other times, 5mins later, i decided to bleed one of the rear lines again. instantly i had air back in the line. a small amount, but enough to fully validate that i think the old wheel cylinder is letting air in.
3) while driving around town testing, i started to notice a pattern. the front brakes did lock in, but it didnt seem like they were since i had to pump for pressure and then i had to apply a large amount of force to get them applied. i started jamming harder and harder on them and noticed more and more bite.


so... that being said, i think if i replace the old wheel cylinder (already have replacement, just have to do the lines), and add a brake booster, i think my truck will seem normal.



and for reference to 76C10Stepside - i have a 75. i referenced i had access to a 69 to compare to. the 69 is my buddy's truck i've helped on. you're probably right though - his probably doesnt have discs in the front to compare with.


I did some of the proportion valve test mentioned above. i did feel like i was getting adequate pressure with both lines open, and i did not get a voltage reading on the switch indicating it had an error when i probed it.

this all being said.. i think my lines/flex lines/calipers/master cylinder are fine. i think the crappy pedal i'm getting is a combination of hte driver rear wheel cylinder taking in air and the lacking of a brake booster.

i bet my buddy's 69 feels better on the pedal without a brake booster cause he likely has drums all around. I think replacing the wheel cylinder and adding a brake booster should give me much more of a 'modern' feel to the brake system.

sincerely appreciate all the help and wisdom provided by you guys. even the ability of kicking around possibilities is a huge help.

[earnhardtgm3]

I bought a proportional valve a few weeks ago from here for my 77 C10

http://inlinetube.com/Prop%20Valves/VCT104.htm