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

Hey Guys,
I looked around the forums and couldn’t find the information for my specific issue. I am replacing my single chamber master cylinder with a dual chamber master on my 1953 3600. The master is under the floor but I have installed a remote fill up on the fire wall. I have 4 wheel drum brakes (original to the truck).

When I originally rebuilt the truck I replaced the entire braking system from the master to the drums. Recently I had the brilliant idea of upgrading the brakes to a dual master as i drive the truck a lot more since i retired. The old system did not have residual valves but is stopped pretty good. The new system i bought came with 10 pound residual valves (appropriate for a 4 wheeled drum system as i have read). I have been having a great deal of difficulty bleeding the system. I even tried a pneumatic vacuum bleeder. I get a lot of air out but the pedal is still soft and stopping is scary.

Is it possible to have air leak into the system when no fluid is leaking out? Do i really need the residual pressure valves with the firewall mounted remote fill reservoir? Is there another reason I keep getting air out but the pedal is still so soft?

I bled the brakes for hours and still air in the system. I put a little teflon tape on the bleeders to make sure they weren’t leaking air in as i bled. I plugged the master cylinder and the pedal is rock hard so it’s not the master.

I am in the process of re-plumbing the system to see if maybe I caused an air trap some where but I would think the pneumatic vacuum bleeder would have pulled any trapped air out.

The real question is why is there air after all the bleeding? I have essentially replaced all of the fluid at this point and still have air in the lines somewhere.
Do I need the residual Pressure valves? Could they be the culprit?

Thanks much for any advice᠁ I am pulling my hair out at this point.
Best
Rich

PS᠁ This truck spends most of its time on quiet country roads going under 50 mph. The gearing in the rear end is so low just taking your foot off of the gas is like stepping on the brakes. Not sure that matters but wanted it paint the full picture
Thanks for any help.

Make sure your residual valves are going in right direction. pressure should be held on brake side.
They are required when master is below the brake cylinders in drums or disc brakes to keep the flow from going back to the master.
It should bleed with you just opening the bleeder and no cap on the remote reservoir in the engine bay. (i have this system as well).

I found my issue to be a small leak in the lines and brake cylinder causing the leak down and air getting into system.

In theory you would not need them with the remote fill way above. But they are nice to keep the cups closed and tight on the drum cylinders to keep air from bleeding back in.

once i got air out it was big difference. Like barely push the pedal and it was tight and I could not get it to the floor. When it had air it was push more than halfway and i could pin it to the floor.

Also note did you a proportioning valve in as well? needed for drum disk combos but some guys put them in when replumbing.

hcb3200,
Thanks for the advice. I did have the residual valves with the arrows facing away from the MC. That is what the tech support guy from Performance Online confirmed for me. I do think I have a leak but for the life of me I can’t find it. I would think if air could leak in fluid would leak out so i could find it.

I did gravity bleed for about 30 minutes on each wheel. I got bubbles for a long time but they dissipated eventually. I then closed the bleeder. After all 4 wheels were done i pumped the brakes and pedal went to tower floor. If I pump up I get about 1/2 pedal but stopping is not good.

So far I have done a conventional bled with someone in the truck working the pedal. I did a gravity bleed as described and I even bought an inexpensive pneumatic vacuum and essentially power bled them᠁ all resulted in the same squishy pedal. I am going out re plumb the system and omit the residual valves to see what that does. If Im not happy i can always add therm back in.

One issue is I may have created an air trap as i had to go over my drive shaft.I didn't want to go under and I was too impatient to go around it where I should have᠁ live and learn. My haste made significant waste I believe.

Best
Rich

Did you pre-bleed/bench bleed the MC before installation?

Are the brake shoes adjusted all the way up?

Yes the shoes are adjusted to touch the drums and
yes i did bench bleed the MC

I have the brake pedal adjusted so there is no play between the pedal and the MC. I know there is supposed ot be some but i was hoping that maybe that would help᠁ it didn't.

Did you flare your brake lines or are they factory flares?

Did you double flare them?

Did you tighten each connection, then back it off and retighten it again...doing this 3-4 times and you'll see the wrench make the fitting a little tighter each time using the same amount of force. This process helps seat the flare...

I personally wouldn't run a brake line over the drive shaft. If a U-joint ever breaks the shaft will beat the heck out of everything in it's path...I'd hate to have it smash a brake line and loose my brakes at the same time.

Mike B

Some of us (including me) have had good luck with the Motive pressure bleeder system, the universal plate works on the dual masters, many of us use ‘c’clamps instead of the chains. Available at Summit Racing and other large suppliers.
First step with it is to pressurize the system for 5 minutes or more to 15psi with fluid in the res and lines but without fluid in the Motive, this is to confirm there are no leaks, then release, add fluid to the Motive tank, pressurize it again, and bleed away.

Worked great on mine with 1” bore dual master under floor, residual psi devices front and rear, and drums on all 4 corners. I too had no luck with a vacuum bleeder᠁.

Btw: Some play in the pedal adjustment is needed to confirm the master is getting to the beginning of travel to grab fluid to push᠁..

Good luck᠁.

You can also do like I did. Clean every joint and every drum cylinder in side around under etc. wrap what you can with a paper towel. Then get a book or iPad get in truck put the foot on the brake and hold pressure. Switch feet and keep pressure. Reading a book or iPad. (A nice block of wood wedged super hard between seat and pedal did same thing. ). After a good long while check every towel and location for a leak. I found one drum cylinder leaking. Since it was inside the drum I didn’t notice right away. I replace that one cylinder and it fixed my leak down and air. Also you can used process of elimination. Start caping a line or two and see if pedal gets hard. That will indicate where you may have air.

Something to try is to raise the rear axle up as high as you can and bleed each rear brake, then lower back down and raise the front, anything you can do to get the air to the highest point. Pumping the pedal should do the same, but sometimes simple gravity helps. Parking on a steep hill works too.

Vacuum bleeding from master cylinder can pull air into a system from the wheel cylinders, I've been down that road once, it made the problem much worse. I have also seem vacuum bleeders pull air around open bleeder screw threads and the fellow just kept trying to get all the air for a very long time.

I've run my truck for 23 years with no residual valves, disk/drum, master under the floor. A good working system shouldn't need them, fluid is not going to return to the master cylinder without a leak.

Thanks for all the great advice guys.

I like the tissue test idea. I realize the vacuum bleeder may be sucking in air around the bleeder. I wrapped the bases with a little teflon tape to try to prevent that.

The drive shaft where the bake lines go over is near the tranny᠁ it is a closed drive shaft at that part. I did double flare the fittings but i dint tighten and loosen and tighten again᠁ i will do that this time.

I am going to reroute my lines and put them where they should be. Then test all for leaks before i try to bleed again.

I am omitting the Residual valves and I don't have a portioning valve᠁ does that make a difference? Will I get the benefit of a dual chamber without the portioning valve?

Thanks again guys

You only really need proportion valve if you are running disk drum combo or have a habit of locking up front before rears.
I would go with residuals since you have a frame mount master.
Put them in when you redo lines. Get everything where you want it. Last thing you need is to introduce a new leak
moving things around. Ask me how I know on this one

If you were sold the correct dual master cylinder for a drum/drum system it should already have a built in residual valve.
There would be no need for more additional residual valves. That may be part of the problem.
Fred

The MC I bought came with 2 10 pound residual valves. It says it’s for a drum/drum system. I am replumbing and omitting them and trying to use as few connections as possible. I have the back done and I will work on the front after lunch.

The MC has 2 different outlets. The one towards the front (as it is oriented in the truck) is about 9/16 and the other, towards the rear is 7/16. That seemed odd to me. Do you think they sent me the wrong part? The one I have looks like the one in the catalogue and states it fits my trucks drum/drum system. I think I attached pictures of the item I have.

My local auto parts guy loves me now᠁ 4 quarts of fluid and about 20 feet of brakeline in the past 2 weeks.

Here’s a dumb question? Could the MC not be large enough for my 3600? Maybe not moving enough fluid?
How tight should the brake be adjusted. I always adjust so that I can feel drag on the shoes when I push the wheel by hand.
A hard shove gets me about 3/4 turn of the wheel. I have always done it this way with no issues. I am at my wits end.

The front lines are very difficult to lay out.

I may need to walk away from this before i put a hammer through he windshield. Im tired of broke fluid dripping on me.

The only benefit you get with a dual reservoir system is that a leak in one wheel cylinder or brake line only affects two of your brakes (both front or both rear) instead of all four.

Otto,
So I capped both outlets on the master and step on the pedal᠁ very little movement then rock hard like standing on the ground. Then i connect the rear brakes and bleed the air. Step on the pedal and it goes to the floor very easily. With the front outlet capped i would think I would have some resistance in the pedal even if the rear bake lines had some air.

Is is possible that the MC is not large enough? This is a 3600 with 8 lug wheels. I can hear and feel the brake pads moving when someone pumps the brakes. Just not enough. They are adjusted out to slightly drag on the drums. Like I always do them.

I removed the MC and bench bled it again. Once done with the outlets capped the plunger will move about 3/16 inch and stop rock hard. I do get some spurts of fluid from the bottom of the MC chambers when i do this᠁ is that normal?

I would think if i had a leak I would see fluid escaping but my fittings are all dry. How can air leak in if fluid can’t leak out?

Ps᠁ the sprouts of fluid are fluid only no air. Like a water fountain

Yes and here is why. You can see in the diagram the reservoirs have two holes. fluid is all around the piston. the second hole sends back into the master reservoirs when the primary push is moving along.
Normally you would have a separate piston as in the first is pushing the second springs. to allow for the second to keep pushing when the first is hard pressure.

Here is a video showing how it works

How It Works...

and here is a cutaway diagram

so yes totally normal and expected.
So if you block the fronts and can push the rears to the floor either you have air, a leak or not enough fluid going the the wheel cylinders (a to small of a master bore).

Secondary question.

If you pump them do they get hard and you cannot push to the floor?

Did you get a Drum/Drum master cylinder as they are different than a disc/drum? Are the bowls the same size or different is a good indicator but not always 100%

And
remember that the frame mound master the the bowls are matched to the front and rear. As in the rearward port of master goes to rear of truck and front of master goes to front of truck.


(when viewing a firewall setup it "looks" backwards because master is turned around);

Technically on a true drum/drum master it does not matter as they are bored and setup the same BUT if you decide to convert to disc/drum if you setup a frame mount with rear to rear and front to front your lines will be correct for the switch.

HCB3200
So do you mean the port at the back when mounted on the frame goes to the back and front to the front. That is how I set it up. The port closest to the push rod (which faces front) goes to the front and the one away from the push rod goes to the back.

If I pump the brake comes up some, maybe half way, but never really gets hard. I drove it and it was scary. The only thing that saved me is the low gear ratio in the read end. The truck is slow

The 2 chambers are the same size. If you see the pics I attached, the description states is is for a drum/drum system for as 47 to 54 Chevy truck,

I am bummed I drive this truck all the time and I can’t seem to see my way to getting this fixed. I spoke to the company and they said to send the MC back and they will send a new one. Im not sure that is the problem.

I am sucking air in somewhere but for the life of me I can figure it out. never had an issue like this before.

I believe you have Huck brakes on a 53 3/4 ton. The "sprout" you mentioned is caused 2 things that we already know about. Either you have air in both systems or they are not adjusted Correctly. Adjusting them till you get a "slight drag" doesn't get it. Sometimes the shoes are not centered & you get a drag before they are adjusted up enough. Adjust each adjustment till you get a heavy drag. Then back it off about 4 notches. Yes it may drag somewhat but thats OK. If it has Huck brakes you have 2 adjustments on each wheel.

George

Also, once the lines are full with no air, the master cylinder size should be plenty to operate the brakes. I've never heard of anyone saying the master cylinder was to small. What you will get with different cylinders is more or less pressure at each wheel due to the piston sizes. You have a leak or air in the rears, fronts sounds like an adjustment issue.
Till you get the air out or leaks fixed, tighten each adjustment as tight as possible so you are not chasing two problems at once. If you can get the pedal tight with very little movement, then you can back off each wheel adjustment and see how the pedal reacts.

I think your brake master is ok the fact that when you have it on the bench and you push and hold for a few min it gets hard and stops tells us that its not leaking around the piston and back to the non pressure side. you can always test it with the peddle and the ports plugged like bench test you did.

The fact that it does not pump up tells us that you either have a lot of air some where or like Joe H said way to much slack in the brake shoes. I agree with his assessment put them hard against the drums then back them off a little. even if its not turning and even if you don't drive it its a good test to see if your pedal will get hard. if it does you know it was brake shoe spacing and can adjust accordingly.

99% of the time you will never have a too small of a brake master if your wheel cylinders are close to the master bore. But i have seen where someone put a lot bigger brakes on a car with a lot bigger wheel cylinder without adjusting the very small bore and stroke length master they had. And it would stop but took a whole lot more pedal travel. Fluid volume is fluid volume if you push out and the wheel cylinder takes a ounce of fluid then a ounce has to be available put push in. Pressure does change with bore size. Match this with stroke length and you have fluid volume. And brake fluid does not compress like air does hence why they use brake fluid.

But I am guessing air. if its not the huck brake spacing.
bleed lines and cap them on end of lines it should get hard immediately. Then hook them up to the wheel one cylinder at a time (bleed the cylinder ) and see what happens.

And your plumbing is correct on master and ports based on your post above.

Joe H
Thanks to the advice. I will try adjusting the brakes out tight to see what happens.They are not huck brakes. I am sure they are bendix. I replaced everything when i rebuilt the truck. New MC all mew lines and wheel cylinders. Had the drums machined.

I spoke to the company tech support sand they want me to send it back to them and they will send a replacement MC. I am not sure the MC is the issue but I have never had a brake bleed issue like this. I have tried almost everything suggested here and as well as everything else I can think of

One issue I measured out this morning is that the travel in the MC is about 1 7/16”, so just under 1.5 inches. The travel on the push rod on the truck as it is connected to the tab on the pedal is only 1 1/4”. That is with the push rod adjusted to touch the little bullet in the MC, essentially no play but it does allow the MC to return all the way. In other words I cannot get anymore travel out of the push rod as it is. I can’t adjust it any further out or the MC will not recover all the way and I can’t push the pedal any further as it hits the floor.

Would that missing less than a 1/4 inch of travel create this issue? ᠁ if so᠁ How can I correct it?

I think it should get hard way before that travel length. Once I got mine done and all the air out and all cylinders bled I cant go more than 1/2 to 3/4 pedal travel if I am standing on it.
and that 1/4 could be spring load in master as well and any little bit of play.
If they ware willing to ship you a new master why not will at least eliminate that maybe.

If I read correctly you said you replaced the whole system on the build
Wheel cylinders, brakes shoes , drums, lines and master all 4 all the way around.
Was this a kit or did you pick and choose items? Can you load up some pictures and maybe part numbers.

hcb3200
The original build started in 2005 with a frame off restoration. The first system to be restored after the disassembly and clean up was the brake system. I got most of the parts from LMC Truck or Classic Parts (Formerly Chevy Duty). I reused the blocks for the rear end and the Tees for the split from front to rear. Everything else was new. I bought straight brake lines from Nappa and bent up and flared my own. If memory serves, it bled out fine with no leaks and I really have had no issues with the brakes. They worked fine (I regret ever deciding to upgrade at this point!!)

The current master replacement was a kit from Performance Online. I bought the MC, mounting bracket, push rod, remote fill and a bench bleed kit. It also came with 2 10 pound RSV valves. (See below). The 2 rsv valves are no name. I have ordered 2 new wilwood valves.

Today, I had a buddy over and I showed him the MC. It is on the bench and drained of fluid getting ready to go back. He thought that due to the fact I plugged both outlets and had a hard pedal but when I unplugged the rear and connected the brake line (and bled the back brakes) I had no pedal even with he front still plugged. He suggested the chambers may be leaking into each other. I think this seems reasonable since I would expect some resistance from the plugged front outlet. This test tells me if i lose a line front or rear, I can’t rely on the other chamber to work the other brakes. It also may be why I can’t get the air out of the system if the chambers are trading air back and forth. I can’t get enough pressure in the lines to see a leak but they could be sucking air when the brake is released.

I’m going to send the MC back and see what the new one brings. I hope it solves this issue but I will be [censored] I spent this much time and money only to have a bad brand new part.

I had a similar issue when I converted to 12 volt. Everything worked great᠁ I let the truck sit for a few weeks and the battery was dead. I checked everything and found out the brand new alternator was drawing 12 volts with the key off. They sent me a new alternator and the truck worked fine. I can’t believe my luck at getting the 1 out of 1000 parts that are bad right out of the box!!!

From what I understand the odds are much greater then 1000 to 1 for getting defective parts nowadays.

George

OK keeping fingers crossed that new master fixes your issue.

Probably more like 1 out of 100

Thanks for all the help᠁ I will post and update when the new master arrives and is installed

So the saga continues. I was away for a while and left the truck alone. (Trying to keep from putting a hammer throughout the windshield) I am so frustrated with this brake system. I bench bled and installed the new master with 2 new wilwood RSV valves. I had a small leak at one of the valves that sealed with a little more tension. I have no pedal. I bled and bled and bled and got a ton of air.

Finally had enough pedal to put pressure in the system. Pumped up and held for a minute or 2 and realized i had a leaking wheel cylinder. I replaced that yesterday and bled the brakes. Still no pedal. I re bled this am and no air comes out of the bleeders but the pedal is still soft. first push goes to the floor. If I pump it up I get about a 1/2 pedal on the 3rd or 4th pump. Hold for a minute or 2 and no leaks. I drive the truck and can’t stop it speeds over 15MPH.

I am ready to sell at this point. I have never had any issue with this truck I couldn’t solve (with your help of course) I don’t know what to do. Does anyone have any suggestions? I am filling the fluid from a remote reservoir so I don't think I have introduced any air into the system. I have put gallons of fluid through it at this point. If air was to get into the master is this what would result?

Any suggestions. My next step is to start all over and re bench bleed, redo the lines maybe omit the rsv valves (the old single chamber MC didn't have them and the truck stopped fine). I am at my wits end᠁ yesterday day I had to close the garage door so the neighbors wouldn’t hear my tirade of cuss words. I’m into this brake upgrade for a lot of time and money and now my sanity is at risk. Any advice is welcome.

I just want to drive my truck!!!!

Thanks
Rich

Rich, are you filling the system via the remote reservoir? It could be that it isn't refilling the MC as fast as you are bleeding it out. Remove it while you're bleeding and fill the MC directly with a squeeze bottle with a straw and a mirror from underneath and see if that works.

https://www.amazon.com/Economy-Bott...eze+Bottle&qid=1698167294&sr=8-9

Mike B

Mike B, The remote is right over the MC but I will try this. It can’t hurt. At this point it can’t get any worse. The more it work on this the less control i seem to have over stopping.

Thanks
Rich

How is that master cylinder actuated?
You may not have it set up to get the full stroke of the cylinder. It's either that, or you have a bad master cylinder. Take the master cylinder apart and see if there is a cut in the rubber inside. Pretty common occurrence with the the kind of help available these days who assembles them.

52Carl.
This is the second master cylinder. If I block both ports I can’t move the piston after the bench bleed. So I think it’s ok. My brother told me i have leak somewhere and air is being sucked in. I can’t believe that much air can come in and no fluid leaks out. I have gravity bled the system until no air comes out then pump the brakes. Still no pedal until the 3rd or 4th pump᠁ then I gravity bleed and great more air. This has happened for several cycles.

I guess i could still have air in the master but not that much. The master is perfectly level in the truck so i would think the air would be purged when i pump the brakes. Im not an expert on brakes but I have bled many systems and never seen this.

I think the piston is traveling the entire distance with the pedal. I have it adjusted so that there is no play when the pedal is up. I had some play in there but adjusted it out to see if that would help. I will disconnect the rod and see if the cylinder is bottoming out at the other end. It’s worth a try.

Thanks
Rich

So i adjusted the push rod to make sure I was getting a full stroke and when I pressed hard on the brake i bent the rod᠁ so i think it’s bottoming out in the cylinder where i had it. I know it some all the way out as there is just a but of play in the rod when the brake pedal is up.

I hope I dint mess up the MC doing this but It’s not working anyway so᠁

Any other suggestions> I am all ears.
Rich