Technical Brake bleeding problem on my 41

My 41 Chevy was sitting in a garage for 10ish years, of course the brakes need some attention after that time.

The front cylinders leaked badly, so I replaced them. After that I disassembled the master cylinder, cleaned everything, did a proper bench bleeding and started bleeding the wheel cylinders - rear/driver side.

Nothing. I tried the passenger side - only a few drops. Than I disconnected the hard line just before the hose that goes to the rear end. I was able to pump some amount out of the line, but it took a lot of vacuum - like something is blocking the line.

Is it possible that the residual valves I got in there are somehow stuck?



I also have a proportioning valve going to the rear end.

 

First, that is not a proportioning valve. It is a flow control valve that meters flow like a needle valve in one direction and allows free flow in the opposite direction. It has no place in a brake system. Remove it. It also appears to be closed down tight. Nothing will flow through it in the metered direction if it is closed. Did I mention you should remove it? Good luck.

 

Open the metering valve then bleed.
The valve's purpose is to meter the pressure rise time to the rear brakes. In most cases, the valve will end up set nearly all the way open. Good luck!

 

What's the difference - isn't that what a proportioning valve does?

 

No. This is a FLOW control device. A proportioning valve is a pressure control device. Not even close. Take it out of the system. This is for controlling the speed of an air or hydraulic cylinder. It has no place in a brake system and is not approved for that.

 

Wow - thanks. I was driving for years with that thing and never gave it a thought.

Frank

 

might consider the adjustable proportioning type. You can decide how much rear stopping power you want/need. Had one on my 40, (discs, drums) and it worked great.

 

Not to start a big discussion about proportioning valves but, I always ended up eventually opening them up all the way in every build I did over the last 30+ years so a couple of years ago I stopped using them. This was always on disc-drum setups. Brakes have always worked fine without them.

 

Sooooo.... I eliminated that proportioning valve and the residual valves - still no dice with bleeding.
Worked my way forward to the MC and tried to bleed direct at the MC wit a short brake line attached -nothing. It worked fine when I did the bench bleeding though. When I press the pedal, there is fluid coming.

Looks like the residual valves where not the problem - well.. except I just destroyed one by taking it apart and poking in there with a screw driver.

Why does it work when pushing the pedal, but not with a vacuum bleeder? I'm out of ideas.

Frank

 

Well Frank, I ask, because you said it worked before, yet you now removed parts and it don't work,
Might it be that you should reevaluate your work again.

What does all that mean exactly. You hone the bore, install a new seal kit? Maybe it was take it apart and after a cleaning put it back together? We don't know and you are not saying.

I think you need to rethink this.

 

Okay - try to be more clear this time.
1 - The car sat for years, the front cylinders where shot so I replaces them.
2 - rear cylinders looked good (at least not leaking like the fronts).
3. Did a test drive, but was not happy with the brake performance.
4. Took the MC out - disassembled it, no rust/crude/slush, rubber looked good - I just blew it out and cleaned everything.
6. Refilled with fresh fluid, bench bleeding - worked like a charm, everything seemed fine with the MC.
7. Put it back in the car, started bleeding the rear with a vacuum bleeder - no fluid coming.
8. Asked HAMB for help - as recommended I removed the proportioning valve and also the Wilwood residual valves, since everybody here thinks they are carp.
9- New vacuum bleeding attempt at the rear wheels - no fluid coming no dice.
10- Tried the vacuum directly at the MC to out-rule everything else - no fluid coming.

Frank

 

8. Nothing wrong with the wildwood residual valves. They help preventing air entering the system threw the cups on the wheel cylinders.

 

If the master cylinder piston/cups are not moving all the way to the "relaxed" position in the master cylinder, the cups might be covering the holes that allow fluid from the reservoir to pass into the cylinder chamber of the master cylinder. That would make it difficult to draw fluid from the reservoir into the cylinder and out to the brake lines and the rest of the system. When the brake pedal is in it's normal position is there any looseness at all of the rod from the pedal to the master? You need to have just a bit of looseness in order to let the piston and cups in the cylinder fully retract.

 

Every time my attempts at vacuum bleeding failed, it has been due to a leak. Hose connection to bleeder, bleeder screw leaking at threads or ? I asume you have a gauge on the vacuum bleed kit you are using. Do you see a vacuum on the gauge? If not there is a leak. If so check the bleed screw to be sure it is open. Otherwise, I got nothin'.

edit: one other very slim possibility. If you don't have cup expanders in the wheel cylinders and you pull a vacuum air could enter the system, but I'd expect to see fluid anyway, at least a bit.

 

Well Frank, this seems to be the start, middle and end to your trouble. Between you and me, I wouldn't have taken it apart and not rebuilt it with a kit or replaced it and those other two wheel cylinders. Knowing I'm a cheap screw, knowing I'd probably try to save a buck and get away cheaply as possible, I'd have learned that hard lesson myself, you just have to spend it sometimes.

I agree with Ken, something is leaking if you can't generate a vacuum without pumping franticly to keep up a suction.

I'd also suggest that in the future, don't just blindly trust the experts to have all the answers. They are after all, guys like you and me.
Do some study, research, ask dumb questions, challenge them for smart explanations and answers.

It could be pulling air in from the back of the master cylinder. Wouldn't that be a bugger eh. Any signs of fluid leakage?

Pedal pump the crap out of it, will it hold pressure?

 

If it worked great when you bench bled it, but wont vacuum blead, then it may be one of two things. It could be pedal adjustment, so check to ensure it's got a little free play at the pushrod from the pedal. Another cause can be right at the outlet fittings where air can be trapped and just wont pull through the system because it's so close to the master. Had this happen a couple times and had to have a 2nd person hold pressure at the pedal as I broke each fitting to let the air escape. After doing that the system bled fine, and everything was good.
Proportioning valves have a certain built in restriction in them, even when fully open. So it isn't unusual to install one on a disc/drum setup, and end up leaving it wide open as you'll still have some proportioning effect.

 

The valve shown above in the photo is an ADJUSTABLE PROPORTIONING VALVE (PPV).

If the car set that long, most likely the brake fluid crudded up at some point(s) in the system. You say the rear wheel cylinders don't leak? How about free movement of the pistons? Are they frozen (they should have gotten kits regardless)?

Brake fluid is hygroscopic and draws outside water vapor. It wicks within the fluid system and settles to the lowest point(s). As the fluid absorbs as much as it was designed to (why it needs to be changed on a regular basis), that extra moisture falls out of suspension within the fluid and collects at the lowest point(s) in the system. Corrosion results.

When you attempt to vacuum bleed, the bleeders themselves are a tapered thread. Depending on how far you turn them out, a large air leakage can occur there. You need either a pressure bleeder, a reverse pressure bleeder or speed bleeders.

Anything and everything needs to be verifies for no blockage(s). The car must have a PPV and 10# METERING VALVE(s) on the drum circuit(s).

FORGOT - Whenever there is an ADJ PPV in the system, you open the valve fully to bleed and then return it to the correct setting afterwards.

Does you system have a PRESSURE DIFFERENTIAL VALVE (warning lamp switch)?

And don't jump me because of the capital letters. I made an oversight.

 

Try bleeding it with an assistant using the pedal. The pedal will develop 500 PSI or more. The vacuum bleeder is limited to approximately 14 PSI of negative pressure in the system. Sometimes that makes a difference.

 

Taking a step sideways for a minute...is it possible that your vacuum bleeder is the problem (yours wouldn't be the first)? What happens if you pump the brake pedal to generate the fluid flow?

 

Thanks guys - since the return spring of the pedal may be a bit on the weak side, first thing I check wehen back in the shop is if the pedal is in full return position.

Frank

 

Single or dual piston master cylinder. With drum brakes and a single piston original style master cylinder you wouldn't need the residual valves as one should be inside the master cylinder.

Dual cylinders have a small check valve with a light spring behind the seats for the brake lines.
This kit showing the check valves

They work ok on a Firewall mounted master cylinder but won't hold pressure on an under the floor master cylinder more than a few days. At least that is my experience with my 48 with the dual master cylinder.

As far as a vacuum pump bleader, I'd make damned sure that the vacuum pump is working right and my hoses and the fluid cup are hooked up right. I had an older mighty vac for years that worked great until my boss ran over it a few years ago. The new one I replaced it with didn't work and the cheaper plastic one didn't work (actually broke) The red metal one from HF seems to work ok.

Brake bleeder screws don't have tapered threads at least none of the hundreds of them I have seen over the years haven't. The tip of the bleeder screw seals against the seat in the cylinder. Still there are a lot of them that the threads don't seem to seal good on.

The biggest problem most people have when bleeding brakes is frigging doing it wrong in the first place. Usually by not knowing how to do it correctly or by listening to some bullshit artist about their off the wall methods that won't work in the first place.
You can't pump bleed a system by yourself, you have to have a helper who FOLLOWS directions.
Full master cylinder, pump the pedal SLOWLY, HOLD THE PEDAL until you are told to pump it again. Slowly means delibertly slow. You have to give the fluid time to flow into the bore of the master cylinder.
As far as you go, All bleeders closed, start with the cylinder the furtherest brake line wise away from the master cylinder. Have them pump and hold, open the bleeder, close the bleeder, tell them to pump again. Check and fill the fluid in the reservoir regularly. You may not get all the air the first time but when you have a reasonable fluid flow go to the next wheel and work your way around.

You do have the tube going down into the cup on the inlet side that gets covered with fluid so as to not let air go back in the line while you are pumping.

 

Most likely the problem is within the MC (and/or push-rod adjustment). You took it apart, cleaned it and did not use a fresh kit?

This car is manual drum/drum, single reservoir MC under the floor?

You need both a PROPORTIONING VALVE on the rear circuit and a #10 RESIDUAL PRESSURE VALVE on the drum circuit(s) whether a SGL RSVR or DUAL RSVR MC (usually a SGL RVR MC will have a RPV internally).

The use of a PPV on drum/drum is not usually necessary if the car has OEM brakes that were matched front to rear from the factory. If you have a modification/mismatch, you will need a PPV.

If using a MITY-VAC vacuum pump (with a gauge preferably), you draw the vacuum first, crack the bleeder slightly and then watch for bubbles in the clear line. It the bubbles won't stop after a few tries, the bleeder screw is bad or loosened too much (or you have an air leak somewhere). Make sure the bleeding hose is tight on the pump and bleeder screw.

Maybe remove the MC push-rod from the brake pedal and try to bleed again. If it does draw, the push-rod is not adjusted correctly. If sill no draw, it is most likely in the MC.

 

The MC is what is often called a "Corvette style cylinder" - 1" dual cylinder, both reservoirs same size. And yes it's under floor, that's why I had the 10lb residual valves. I also had the proportioning valve for the rear, since it is a truck rear end that can use some dampening, especially with those bias ply tires on a wet road.

Frank

 

Pressure is pressure and Volume is Volume. [Don't confuse the two]

There is a huge difference between a pressure activated valve [Prop valve] and a volume flow restrictor.

 

OK ... It sounds to me the MC PUSH-ROD is not adjusted correctly. There should be a .020" clearance between the rod end and MC piston at rest.

Do you have an adjustable push-rod on the setup?

Try loosening the MC enough to allow it to move forward slightly and see if the vacuum pump will now draw.

Can you show a photo of the MC install? Is there any line and/or valve in the install that is above the MC piston center-line? No booster, correct?

 

Have you checked the brake line isn't blocked?

 

I think he said he disconnected the rear line @ the rear hose and tried @ one point.

But here is the cincher -

 

I guess it's the pedal/weak return spring. At least it makes the most sense for now.
I will try it, the next time I'm in the garage.

Frank

 

I changed a Buick to a 2 compartment m/c from a single (jam jar) and replaced all the steel and rubber lines throughout. The vacuum pump
works fine to get air out and fluid to the bleeders but you must bleed them in the method described above with one person on the pedal and one at the bleeders, starting with the furthest one from the m/c.