The Stovebolt Site Forums The Shop Area Driveline Brake bleeding trouble and Residual pressure valves

"(I regret ever deciding to upgrade at this point!!)" speaks volumes to me.
I have a buddy who constantly lectures me about "upgrading" my truck's brake system.
I tell him that better ain't always better.

Properly adjusted 4 wheel drums work perfectly for any normal driving situation. Stopping distance is generally shorter than front discs, too.

Are the brake shoes adjusted so there is some drag when turned the wheel by hand?

Mike B

Cut your losses... go back to stock... enjoy your truck.

The single pot master cylinders all had a pressure residual valve built into them. When dual masters came on the the market, they had these rubber duck bill pressure residual valves installed on the drum side of the master, behind a removable brass seat on the master. so one valve for a disc drum and two valves for a drum drum. These pressure residual valves kept a little pressure on the back of the cups of the wheel cylinders for sealing and operation, and also helped keep the piston itself from retracting too far into the cylinder. the rebuilders replaced these valves and the seats when rebuilding. Somewhere along the line the rebuilders stopped installing the valves. Then, the parts scene got worse with all the chineseium master cylinders coming onto the market. these new manufactured masters no longer hand a removable brass seat. the seat for the brake line was now cast integral with the main casting so now way to install the valves and no way to retro fit the valves. So, to mimic the correct residual pressure, you install inline valves.

It is possible that you have an internal leak in the master, i.e., as soon as the pedal gets so far, it loses pressure in the master around the piston part. But before we go there, can you shoot a couple of photos and show how you isolated the front and rear system and how your lines are plumbed in the master? Also, where exactly are the residual valves installed? Can you shoot a photo of your master cylinder also?

I can take some pics tomorrow. The dual cylinder has 2 ports. One for the front and one for the rear. The front line splits about a foot and an half away from the master. The rear splits at the rear axel like the stock system. The RSV valse are installed about 5 inches away from the MC.

I took the rsv valves out today and hard piped from the mC to the front and rear lines just to see if that made a difference. It is better but i am still getting air no matter how long I bleed the system.

When I was re piping I blocked off the MC and put pressure on the pedal. It was firm and did not sink at all over about 30 seconds of pressure. I have no fluid leaks but air is getting in somewhere.

I did have one bad wheel cylinder which I replaced᠁ I really thought that was the issue.

More to come.

Is is possible to have air leak in with no fluid leak out? I have seen this on a bad caliper bit never on a drum brake system.

When I replaced my original M/C with a power disc system (frame mounted), I used a vacuum bleeder, went thru over quart of fluid and still couldn’t get the air out of the system. It wasn’t until I had my wife come out to do it the old fashion way that I was able to find my leak. The vacuum only allowed air to be sucked in so there were no fluid leaks. The pressure from the M/C showed me the leak. Once I fixed that leak, the bubbles went away.

Phak 1,
Yes I tried vacuum bleeding and had the same thought. I have gone back to the 2 person pressure bleed but i get to a point where no bubbles but still a soft pedal. Then once I pump the brakes a few times I get bubbles again. I have been able to pressurize the system but pumping up the brakes and holding pressure but I still get no fluid leaks. If i gravity bleed I think I am getting bubbled from around the bleeder. Air has to be being pulled in somewhere. I just can’t find it.

Dragsix,
Here are some pics of the reservoir, MC, valves and lines. I removed the valves and hard piped to see if i had bad valves. It’s really no better so that is not the issue. I have to be sucking in air somewhere but I can’t imagine i have an air leak on both front and rear circuits. The only place the circuits are together is at the master which should isolate them internally᠁shouldn’t it?

Let me know what you think. The pics of the valves are the piping that I had from the MC to the valves. I plan to put them back in as they don't seem to be the issue. Im thinking that the bushing i have on the front line could be leaking but that doesn't explain the air in the rear.

When the truck is on the ground the MC is level so i don’t think there is air trapped there. I have put about 5 quarts of fluid through this when bleeding. When I bleed the fluid level in the reservoir drops accordingly and in real time so i don’t think there are any issues there.

Let me know what you think᠁. My brake lines are not as pretty as i would like but I don’t think that is an issue.

I admit that this is a shot in the dark...

Once I accidentally* overfilled my master cylinder and the brakes acted up; not fun. There needs to be room for the fluid to return to the reservoir. After removing some fluid, the brakes worked normally. I wonder if your remote reservoirs are causing the problem? You could try removing the top of the m/c (thereby taking the remote reservoir out of the equation) and see if it makes a difference.

* I'm using a better light when checking/topping up the master cylinder now.

Gord,
I was thinking that myself᠁ someone else mentioned removing the reservoir earlier. I haven’t tried it yet but will tomorrow. I am tied up today᠁ it’s worth a try.

If you look at my pics the lines aren’t the prettiest but i don’t think I did anything that would cause this.
Thanks
Rich

Nothing really jumps out at me. The master you have is the corvette style master. None of your wheel cylinders are leaking, none of your fittings and connections are leaking,you seem to have the rod adjusted correctly, you have bench bled the master, I was very certain it was not going to be the pressure residual valves. The only thing left is a defective master cylinder.

My remote reservoir has copper lines running to the MC...could your rubber hoses be restricting the fluid flow?

Mike B

Mike the hoses are pretty big. The only other thing I can think of is that when i was bleeding back when I first installed the Master my wife said it was getting better then all of a sudden she said it was worse. I suppose i could have sucked in a little air but the Master is dead level so i would think it would bleed out. When I first connected the remote reservoir the fluid ran right down to the master.

My next test will be to remove the remote and bleed from the master keeping an eye on the fluid with a mirror. If that doesn't solve it i may remove the master and bench bleed again.

I haven’t taken any of the other drums off to visually check the if the wheel cylinders are leaking. The drivers side front was leaking and I changed it out. It was pretty obvious when I pressurized the system that fluid was dripping from the backing plate. I would think the others would be apparent as well.

I have Ben gravity bleeding the system thinking that if air is leaking in the height of the remote would’ve prevent air infiltration and allow the contents of the lines (fluid or air) to be expelled at the bleeder. That does not seem to be working.

If all that’s fails before i revert back to the old master i may take the ruck to my local garage hand see if they can power bleed the system and sort it out.

Thanks for the suggestions I will be happy to find out if it is the remote but sad that it took me so long.
Best
Rich

Dragsix,
If I block both ports the master hold pressure at the top of the pedal. I don't know much about these masters but this is the second one. If you have a properly functioning dual cylinder brake system shouldn’t you have some pedal even if one of the circuits (front or rear) is open? I thought that was the point of the dual master. This one doesn't seem to have any resistance at all the pedal goes right to the floor and after 2 or 3 pumps i get about 1/2 a pedal but the truck wont stop at a speed over 10 or 15 miles and hour.

I am going to remove the remote fill and re bleed watching the fluid level. I am clutching as straws at this point but I am running out of ideas and patience.
Thanks
Rich

Did I read your earlier post correctly. You are gravity bleeding this system?

I started with the traditional 2 man bleed with my wife pumping the brake for me. I tried a vacuum bleed but i know that can cause more issue than it solves. Then i tried gravity bleed with a sealed canister with fluid in it and a tube from the bleeder to the canister. I tried 2 man bleed again and still no pedal.

Any suggestions᠁ I may try a pressure bleed at the local auto shop. I was going to call them tomorrow

The truth is, I do the old fashioned two man every time. Just to make sure, when you are doing the rears, you are starting with the wheel cylinder furthest from the master, in terms of brake lines? Same for the front? Rubber line on the bleeder, jar with brake fluid in it, rubber line in the jar, open the bleeder, one push to the floor, hold, close the bleeder, pedal comes up, open the bleeder, one pedal to the floor and hold, repeat until no air bubbles. Then on to the other side? Same deal, start from furthest from master.

I believe that this has already been mentioned, but it may solve all of your trouble. Even if it doesn't, it is a step one needs to make before bleeding the brakes.
1. Take all of the drums off and visually check all wheel cylinders for fluid leaks.
2. Tighten the brake shoes until you can barely move the wheels by hand. (You will need to back the shoes off as per The Book after you are done bleeding the brakes.)

If the shoes are too loose, the wheel cylinders may use up all of the volume that the master cylinder can deliver before the shoes contact the drums, thus there won't be enough pressure left to push out all of the air.

Just curious, are your residual pressure valves located as close to the master cylinder as possible, and as low to the fluid level in the master as you could get them?

Hank,
They were about 5 inches for the master and below the master as well. I have removed them to dee if the issue was with the valves᠁ it wasn’t.

Carl,
I am doing that again today to check all the wheel cylinders. I did have one that was leaking and I replaced it.

Dragsix,
I agree the 2 man is what i always used but this issue has gone on so long i was trying to spare my wife the time to repeatedly sit in the truck for hours while I cursed the bubbles in the lines.

She’s a good egg though᠁ she wants to help again to today. I will Re inspect the wheel cylinders and adjust the brakes and start form scratch.

I was thinking that if i am sucking in air on one of my connections i could put some grease or other gel on the connections and see if it moves at all when pumping the brakes. I figure if fluid can’t leak out grease wont leak in but it might show an air leak᠁. Maybe I’m crazy.

Thanks for all the help guys.
Rich

The brake fluid is thicker than air, so you can suck air in through cracks that won't leak visible fluid.

It sucks to do, but I would recommend opening each connection on the rear circuit and inspecting the flares. I can't tell what material your hardlines are, but some tend more towards cracking than others.

Carl,
I think your advice did the trick! I did as you said and inspected all the wheel cylinders. They were all fine. I adjusted the brakes so I couldn’t even move the wheel. They were as tight as i could get them. Them my wife helped me do a 2 person bleed and the pedal is solid. I adjusted the brakes in per the book and took it for a ride. The pedal is solid and I can lock up the wheels with moderate pressure and about 2 inches of pedal movement. Just like before i started this mess.

Now that the system is working properly I had my wife step on the pedal and i looks doe leaks and didn't find any. I will drive it for the next few weeks and see how it goes. I hope I am done showering in brake fluid.

Thanks to all you guys for the help!!!
Best
Rich

Fibonachu,

They are steel lines. I have used them before. I don't have the tools for stainless and I hear they the copper nickel ones are harder to get to flair properly. I always use these.

Thanks
Rich

Good to hear about your success and thanks for your update!

Only took 7 pages of posts. Brakes can drive a guy nuts, especially when we upgrade to non stock. It's easy to second guess the new stuff and neglect the basics.
That same problem which you have had is very often encountered with stock brake systems, especially Huck brakes.