Bleeding new disc brake issue

[64chevmn]

During the restoration of my 64 c10 project, I added a front disc brake conversion kit with a new brake booster and master cylinder. When I tried to bleed the brakes tonight, I had brake fluid leaking out of what I think is the relief valve on the end of the proportioning valve. There appears to be a small rod in the center of the nut that moves slightly in and out when I'm pumping the brakes and fluid is dripping from it. I've bled several new brake systems with a proportioning valve in the past and I never had any leaks like this??? Do I have a bad valve or do I have another problem? The below picture shows the nut on the end of the valve that is leaking.

[64chevmn]

Apparently the issue with brake fluid leaking out of this valve is very common. I called the vendor I purchased the disc brake conversion kit from and they are sending me out a rebuild kit for the metering valve (new o-rings and washers). Hopefuly that will fix the leak........

[legotech7]

Hay, 64chevmn I have the exact same issue.. After a conversion I did to my 70 c10 I replaced everything. But when I started to bleed the brakes, witch I started from the right rear, I noticed hardly any fluid came out.. Same thing from the left rear. No fliud coming from the rear lines.. So I tried to bleed the front calipers and they seem to bleed ok But my break pedal was still to low and hardly any breaks at all. I repeated the bleeding procedure 4 times, and still no appreciable amount of breaking power... Then I noticed the PV was leaking at the same location as yours was. The valve is new, but leaking..

Did you replace the valve, and can you tell me how did you bleed your system? I've yet to replace the valve, I'm waiting for some more concrete answer's.....

[oldman3]

I'm no brake expert, but I'll tell you what little I know. This part could be bad I've seen others with this problem. What might be happening with yours leaking in the front, is because you have nothing going to the rear and continued pumping of the pedal is being to much pressure on the front of the valve. The combination valve has to be centered while bleeding brakes. Here is a pic showing a combination valve. At the top of the valve is "switch terminal" when the front or rear brake has a leak the internal valve will close off the bad section and a brake problem light will come on the dash. To correct you must reset the internal valve by pushing in on the front pin. When you want to bleed the brakes you MUST keep the internal valve centered, so fluid will flow to both the front and rear. You can do this by removing the switch terminal and installing a proportioning valve bleed tool. When you are finished bleeding removal the tool and reinstall the switch terminal. I purchased mine from POL here is their link. http://www.performanceonline.com/Com...ve-Bleed-Tool/ If you hit the little valve below the part it will show how it's installed. I had a home made one I used for years. I found this out after having the same problem you have many many years ago. Hope this helps, if you can understand how I said. I'm not the best of explaning things by typing them out...Jim

[legotech7]

Thank you Olman3, for your reply and some more incite to our problem. I'm thinking that because mine is leaking at the front as well , I might have to replace the valve? Or might I still bleed the brakes using the bleeding tool? How did you bleed your brakes? Did you use the gravity fed method or bleed them one valve at a time, and if so, did you forcefully pump the brake peddle or depress the peddle slowly, as I have read in some other post's to do? Thanks for all the information, it is very much appreciated..

[oldman3]

Originally Posted by legotech7

Thank you Olman3, for your reply and some more incite to our problem. I'm thinking that because mine is leaking at the front as well , I might have to replace the valve? Or might I still bleed the brakes using the bleeding tool? How did you bleed your brakes? Did you use the gravity fed method or bleed them one valve at a time, and if so, did you forcefully pump the brake peddle or depress the peddle slowly, as I have read in some other post's to do? Thanks for all the information, it is very much appreciated..

I've done mine both ways. Most of the time I bleed one line at a time, and pump brake pedal slowly. I normally do the longest rear line first then the second line. Up front again the longest line and then the last. Make sure before you start to bleed that the valve is centered and tool is installed. Let us know how you make out...Jim

[legotech7]

Thank you.. Will do..... 64chevmn, did you resolve your issue? And if so, please enlighten us....

[64chevmn]

The vendor I purchased the brake kit from sent me out a rebuild kit for the metering valve and it did include new O-rings and washers. Easy fix and stopped the leak. I got the impression from the sales person they ship lots of these rebuild kits out from faulty seals.

The brakes took a bit to bleed; I started by cracking the brakes lines at the master cylinder to make sure no air was left after bench bleeding, then started at the left rear, to right rear then to the front disc calipers. I used a helper to slowly pump the brakes while I cracked the bleeder screws. Took about 15 times for each brake, but eventually I got all of the air out. I did have to adjust the length of the rod from the pedal to the brake booster slightly to get the rod to fully push into the master cylinder.

I have 300 miles since and no leaks.........

Dan

[legotech7]

Good deal 64chevmn, I'm glad it worked out for you. Soon as I get a chance to work on mine I'll post results. Its just too cold in these neck of the woods these days. I still have to purchase the bleeder tool for the PV. No one hear has it locally, so I'll have to order it online. Thanks again for all the help, one and all.......