disk brake proportioning valve help - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Custom 68 · 10-30-2005, 09:06 PM

ok here is the problem. I did a disk swap on my 68 all new parts from GMC Paul except the master cylinder and prop valve. I got a used prop valve off here. My rear brakes seemed "grabby" (is that a word?) anyway I was never happy with my remufactured master cylinder since it leaked I thought I would start there and replaced it, I bench bled it and installed it. I went to bleed the rears and did that just fine went to the front and no fluid and no brakes I checked the button on the front of the valve and pressed it in while my helper was pushing the brakes that helped but was very intermintent some times it worked and others no fluid. when I had fluid I had lots. after letting it set for a minute or 2 it was back to the same no front brakes...I havent driven it but I am sure it is the same as before.
Do I just need a new prop valve?
thanks
Dave

*FormerMember* · 10-30-2005, 09:08 PM

Quote:

Originally Posted by Custom 68

ok here is the problem. I did a disk swap on my 68 all new parts from GMC Paul except the master cylinder and prop valve. I got a used prop valve off here. My rear brakes seemed "grabby" (is that a word?) anyway I was never happy with my remufactured master cylinder since it leaked I thought I would start there and replaced it, I bench bled it and installed it. I went to bleed the rears and did that just fine went to the front and no fluid and no brakes I checked the button on the front of the valve and pressed it in while my helper was pushing the brakes that helped but was very intermintent some times it worked and others no fluid. when I had fluid I had lots. after letting it set for a minute or 2 it was back to the same no front brakes...I havent driven it but I am sure it is the same as before.
Do I just need a new prop valve?
thanks
Dave

Yes, if you had 4 wheel drums before, you need to swap to a disk/drum prop valve.

There's a check valve in the drum circuit that keeps residual pressure for the shoes. You don't want that in a disk set up, as it will not allow the caliper to float, which will boil your fluid and lock the brakes.

Although I am not sure on the "just a prop valve" part, but it's where I would start.

Custom 68 · 10-30-2005, 09:21 PM

Thanks for the quick reply but to clarify I have a used disk/drum prop valve. This is the one with the button on the front. I am not sure it worked correct from the start...
sometimes I have front brakes others I dont...
Dave

*FormerMember* · 10-30-2005, 09:23 PM

Quote:

Originally Posted by Custom 68

Thanks for the quick reply but to clarify I have a used disk/drum prop valve. This is the one with the button on the front. I am not sure it worked correct from the start...
sometimes I have front brakes others I dont...
Dave

Sorry, I didn't catch that first time around.

Do you happen to have them hooked to the right circuit? Sounds like they're reversed? (grabby rears and fronts not working...)

Did you bleed the heck out of the system? (I usually fill the MC and crack all four bleeders for a bit, after bleeding the MC and prop valve).

*FormerMember* · 10-30-2005, 09:28 PM

Quote:

Originally Posted by Custom 68

well to confirm the hookup I have the fronts coming off the front of the prop valve this is also the front of the master cylinder.
I may go out and let them drip for a while that was what I initially thought but my helper pushing on the brake I crack them open and just a slight drip and the pedal didnt go down any more
Dave

That's really very strange. Something is wrong there.

Did you bleed the MC?

Custom 68 · 10-30-2005, 09:31 PM

well to confirm the hookup I have the fronts coming off the front of the prop valve this is also the front of the master cylinder.
I may go out and let them drip for a while that was what I initially thought but my helper pushing on the brake I crack them open and just a slight drip and the pedal didnt go down any more
Dave

jhow66 · 10-30-2005, 10:09 PM

Prop is not centered. To test take test light and touch one probe to hot post of battery and other to the post on prop valve. If it lights the valve is grounded to one side-which would be the front in your case because you cannot get any fluid from them. Leave test light hooked up (if brake light on dash does not work) and close off the front bleeders. Open a rear bleeder (run a line from bleeder to a jar with fluid in it so as not to suck air back into system) and press pedal slowly until light goes out (hopefuly).Close bleeder. Now you should be able to bleed front disc. The above advice carries no written warranty.

Americanrider · 10-31-2005, 03:20 AM

Quote:

Originally Posted by Custom 68

well to confirm the hookup I have the fronts coming off the front of the prop valve this is also the front of the master cylinder.
I may go out and let them drip for a while that was what I initially thought but my helper pushing on the brake I crack them open and just a slight drip and the pedal didnt go down any more
Dave

I posted this a few weeks back for a member. You say you have the fronts coming from the front of the MC??? I think that is wrong> Here is a stock 71 2wd setup.

The LL (RED)= Large line The Large line feeds the rear brakes.
The SL (green) = Small Line, it splits and feeds the fronts.

The smaller the line the higher the pressure.
The larger the line the higher the Volume.

jlmtrout · 10-31-2005, 05:03 AM

Did you pressure bleed the master cylinder? This is different than bench bleeding. Take the line loose from the front brakes, place your thumb over the hole and have someone slowly press the brake pedal. Keep your thumb in place and repeat until you don't feel any more air bubbles, then hook the line back up. The button on the front of the proportiong valve is supposed to move back and forth as the brake pedal is pressed, pushing on it does nothing. Good luck and keep on truckin'...................Jerry

Custom 68 · 10-31-2005, 10:14 AM

thanks Americanrider however that is opposite of what I was told last week posted here http://67-72chevytrucks.com/vboard/s...d.php?t=178437 again I dont want to order a new valve if it is not necessary so any body else with a picture the way their is hooked up? I will be swaping this tonight and try this new way out...

Oh yes I did bench bleed the master cylinder I put it in a vise with the 2 hoses from the port into the resovor and stroked it till there were no more bubbles.
thanks again all.
Dave

Custom 68 · 10-31-2005, 05:44 PM

anybody else, I will be checking tonight... after we go trick or treating.

A.P. · 10-31-2005, 06:00 PM

There is some information on brakes site:

http://www.classicperform.com/TechBo...tm#tshootbleed

Custom 68 · 10-31-2005, 06:40 PM

Thanks AP that helps I had fogotten about that site I had seen it before.

10-30-2005, 09:06 PM	#1
Custom 68 Registered User Join Date: Nov 2001 Location: Springfield, MO Posts: 2,930	disk brake proportioning valve help ok here is the problem. I did a disk swap on my 68 all new parts from GMC Paul except the master cylinder and prop valve. I got a used prop valve off here. My rear brakes seemed "grabby" (is that a word?) anyway I was never happy with my remufactured master cylinder since it leaked I thought I would start there and replaced it, I bench bled it and installed it. I went to bleed the rears and did that just fine went to the front and no fluid and no brakes I checked the button on the front of the valve and pressed it in while my helper was pushing the brakes that helped but was very intermintent some times it worked and others no fluid. when I had fluid I had lots. after letting it set for a minute or 2 it was back to the same no front brakes...I havent driven it but I am sure it is the same as before. Do I just need a new prop valve? thanks Dave __________________ Dave 1968 Custom Chevy with turbo charged 5.3 gen III 4l80e swap 1967-71 GMC 3/4 ton long step 4x4 (not sure what year exactly?) "A good friend will bail you out of jail...but a true friend will be sitting next to you saying "that was frekin awesome". "If it doesn't fit force it...If it breaks then it needed to be replaced anyway!"

10-30-2005, 09:21 PM	#3
Custom 68 Registered User Join Date: Nov 2001 Location: Springfield, MO Posts: 2,930	Re: disk brake proportioning valve help Thanks for the quick reply but to clarify I have a used disk/drum prop valve. This is the one with the button on the front. I am not sure it worked correct from the start... sometimes I have front brakes others I dont... Dave __________________ Dave 1968 Custom Chevy with turbo charged 5.3 gen III 4l80e swap 1967-71 GMC 3/4 ton long step 4x4 (not sure what year exactly?) "A good friend will bail you out of jail...but a true friend will be sitting next to you saying "that was frekin awesome". "If it doesn't fit force it...If it breaks then it needed to be replaced anyway!"

10-30-2005, 09:31 PM	#6
Custom 68 Registered User Join Date: Nov 2001 Location: Springfield, MO Posts: 2,930	Re: disk brake proportioning valve help well to confirm the hookup I have the fronts coming off the front of the prop valve this is also the front of the master cylinder. I may go out and let them drip for a while that was what I initially thought but my helper pushing on the brake I crack them open and just a slight drip and the pedal didnt go down any more Dave __________________ Dave 1968 Custom Chevy with turbo charged 5.3 gen III 4l80e swap 1967-71 GMC 3/4 ton long step 4x4 (not sure what year exactly?) "A good friend will bail you out of jail...but a true friend will be sitting next to you saying "that was frekin awesome". "If it doesn't fit force it...If it breaks then it needed to be replaced anyway!"

10-30-2005, 10:09 PM	#7
jhow66 Registered User Join Date: Jun 2002 Location: Knoxville Tenn. Posts: 3,058	Re: disk brake proportioning valve help Prop is not centered. To test take test light and touch one probe to hot post of battery and other to the post on prop valve. If it lights the valve is grounded to one side-which would be the front in your case because you cannot get any fluid from them. Leave test light hooked up (if brake light on dash does not work) and close off the front bleeders. Open a rear bleeder (run a line from bleeder to a jar with fluid in it so as not to suck air back into system) and press pedal slowly until light goes out (hopefuly).Close bleeder. Now you should be able to bleed front disc. The above advice carries no written warranty. __________________ 56 Chevy Bel-Air 2dr. HT (purchased new) 71 Chevy Cheyenne SWB PU (502HO) 65 GMC short bed step--work in progress and my gofer

10-31-2005, 05:03 AM	#9
jlmtrout Registered User Join Date: Jul 2002 Location: Memphis, Tn Posts: 194	Re: disk brake proportioning valve help Did you pressure bleed the master cylinder? This is different than bench bleeding. Take the line loose from the front brakes, place your thumb over the hole and have someone slowly press the brake pedal. Keep your thumb in place and repeat until you don't feel any more air bubbles, then hook the line back up. The button on the front of the proportiong valve is supposed to move back and forth as the brake pedal is pressed, pushing on it does nothing. Good luck and keep on truckin'...................Jerry __________________ '68 c-10 long wheelbase fleetside, been in family since new, originally 250 3 speed Now (389) 350 .060 over 3.75 stroke,Edelbrock Performer RPM 70cc heads and Intake 600 cfm Edelbrock,Small Comp Cams retro-roller cam and roller rockers,9:1 cr, headers, HEI,Old Air a/c, 72 power disc brakes w/stainless lines, 3.42 gear,T-56 6-speed, original paint(what's left of it). Dakota Digital Dash

10-31-2005, 10:14 AM	#10
Custom 68 Registered User Join Date: Nov 2001 Location: Springfield, MO Posts: 2,930	Re: disk brake proportioning valve help thanks Americanrider however that is opposite of what I was told last week posted here http://67-72chevytrucks.com/vboard/s...d.php?t=178437 again I dont want to order a new valve if it is not necessary so any body else with a picture the way their is hooked up? I will be swaping this tonight and try this new way out... Oh yes I did bench bleed the master cylinder I put it in a vise with the 2 hoses from the port into the resovor and stroked it till there were no more bubbles. thanks again all. Dave __________________ Dave 1968 Custom Chevy with turbo charged 5.3 gen III 4l80e swap 1967-71 GMC 3/4 ton long step 4x4 (not sure what year exactly?) "A good friend will bail you out of jail...but a true friend will be sitting next to you saying "that was frekin awesome". "If it doesn't fit force it...If it breaks then it needed to be replaced anyway!"

10-31-2005, 05:44 PM	#11
Custom 68 Registered User Join Date: Nov 2001 Location: Springfield, MO Posts: 2,930	Re: disk brake proportioning valve help anybody else, I will be checking tonight... after we go trick or treating. __________________ Dave 1968 Custom Chevy with turbo charged 5.3 gen III 4l80e swap 1967-71 GMC 3/4 ton long step 4x4 (not sure what year exactly?) "A good friend will bail you out of jail...but a true friend will be sitting next to you saying "that was frekin awesome". "If it doesn't fit force it...If it breaks then it needed to be replaced anyway!"

10-31-2005, 06:00 PM	#12
A.P. Black 72 Chevy Join Date: May 2002 Location: Los Angeles, California Posts: 662	Re: disk brake proportioning valve help There is some information on brakes site: http://www.classicperform.com/TechBo...tm#tshootbleed

10-31-2005, 06:40 PM	#13
Custom 68 Registered User Join Date: Nov 2001 Location: Springfield, MO Posts: 2,930	Re: disk brake proportioning valve help Thanks AP that helps I had fogotten about that site I had seen it before. __________________ Dave 1968 Custom Chevy with turbo charged 5.3 gen III 4l80e swap 1967-71 GMC 3/4 ton long step 4x4 (not sure what year exactly?) "A good friend will bail you out of jail...but a true friend will be sitting next to you saying "that was frekin awesome". "If it doesn't fit force it...If it breaks then it needed to be replaced anyway!"



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