Technical Brake? No fluid to rear brakes

New purchase Ride that sat for 20+ yrs. disc front bled & worked fine. Tried to bleed rears ( drums) seems blocked. Pedal still high from bleeding fronts even w rear bleeder opened can’t push any fluid thru? FYI Dual master.

 

The combination valve has blocked flow to the rear brakes and must be re-centered.

 

how do you reset a proportioning valve? | The H.A.M.B. - The ...

 

I've always bled the furthest wheel (brake line wise from the master cylinder first as that was what I was taught and taught every student I taught when I taught the same class. That is usually the right rear.
That said start looking for the "why" you aren't getting fluid to the rear cylinders.
If you loosen the fitting at the master cylinder do you get even a dribble of fluid there?
If you have one of those plastic bench bleeder lines or can make up a line I think one thing I would try is pulling the line from the rear brake port on the cylinder and bleeding it at the master cylinder first, same as bench bleeding but on the car.
It's an odd shot but could the push rod from the pedal to the cylinder be so tight that it is pushing the piston and not allowing fluid to flow though the port from the reservoir to the cylinder on the rear brake side? We always seem to see it happen th other way where it won't let fluid flow back but this time it might be covering the port and not letting fluid flow in.
If all of that is squared away start checking for obstructions in the line that may or may not be a kink in the line, something like a rivet placed in a line to block fluid flow because there was a problem years ago, A line that got flattened (I saw a 4x4 where the guy put the U bolts over the brake lines and clamped them down when he put a lift kit on it squashing the lines). the hose from the line on the frame to the line on the axle being damaged or gone bad inside, plugged bleeder screws or ?
At any rate I'd trace every inch of the rear brake lines to both wheels looking for anything that doesn't look right.

 

I forgot about that Proportioning valve sticking but on this one there is a serous chance that it did if it has one. I fought that on one of the first disk brake jobs I did back in the early 70's.

 

Good info, both sound like a way 2 reset p valve. Question about using elect tester. I bled fronts ( opposite indicated) didn’t have battery connected so no V’s going to POV brake switch. Could that be the issue?

 

or the hard line was crushed on the rear end, seen that happen many times

 

Check the brake hose in the rear it could be collapsed after 20 years. Take it off and try to blow through it, if you can't buy a new one.

 

Yeah,The rubber hoses can break down from inside and prevent the brakes from working and you need to bled the wheel cylinder furthest from the master cylinder first. HRP

 

One thing though, even though the brake parts were installed new and never used until now they are still 20 year old brake parts and not new parts. There may be rust in the cylinders or other issues due to sitting for 20 years.

 

If I had a car that sat for 20 years... in fact my Ford may have sat longer than that... I'd have the car on 4 jackstands and the brake system would be 100% gutted. Try to bleed a 20-year old master? I'd never even think of it. It would be replaced along with every wheel cylinder and soft hose. Hard lines would be inspected and replaced as needed.

 

Thx, will tackle after Laborday. Too much going on til then. Started on it last week. Thought 2 or 3 days would do it & id get some playtime with it over Labor Day wk-end. Getting engine fired up was fun too. Murphy visited a lot

 

Thx & will report back

 

yes, those hooks the tow truck guys use are a problem.

 

I just gut the entire brake system like a fish, I don't waste time on old parts.

 

You would know if it was this, but I had one once that cracked the fitting where the hose meets the lines on the rear axle. It only leaked under hard pressure, so it never left a puddle under it when parked.

Either way, new hose is cheap insurance. The lines, if there's no rust visible might be okay, but they're not expensive either. And you're guaranteed to wreck some of them pulling the hose anyhow.

I can only ever bleed a disc-drum system with a prop valve via gravity, and it's tough to do on cars and pickups, it works best on my vans. A pressure bleeder is better.

 

Pressure bleeders are great. One shop I worked at had an old Ammco that worked well. I borrowed a vacuum bleeder when I first bled my Ford 2.5 years ago. I still like the 2-person method.

I had replaced a line between my master and proportioning valve last week and had a friend (owns a good repair shop) helping the bleeding. he was at the pedal... I never saw someone do so many weird things for bleeding, like pumping the pedal when I still had the bleeder open. Somehow I wound up with a decent pedal.

 

The combination valve cannot block fluid from going in any direction any more than setting a battery on concrete will suck the voltage from it. That little slug moves one way or the other according to pressure and makes ground to set off the warning light. That is all it does. You can see the slug in the cutaway picture, it cannot stop fluid from going anywhere.

 

This is just WRONG!!! The purpose of the combination valve is to block off the fluid to the side with the leak, then it also turns the brake light on to let you know there is a problem.

 

The dual master cylinder is what deals with a circuit leak, not the combination valve.

 

i have heard people say that it does not shut off fluid but from my experience it does. maybe there are different styles? more than once a truck was brought into my shop that blew a brake line the night before while plowing snow. because they could not get it fixed in the dark they just kept plowing using half the brake. after i fixed the line it would be hard to get the system to bleed until the valve would center. i could bleed the valve where the line went in but get nothing on the out ward port until i would open a front bleeder to equalize the pressure.
your results may vary.
it is actually noted at 231 of that video.

 

seem like you got good advice one thing no one answered your question on not having battery hooked up when bleeding it would not affect anything.the battery only supplies power to dash light when you lose fluid.it does not affect bleeding

 

Great discussion! Learned a lot. Will report back.
Thx to all for inputs.

 

Figure out what a whole new brake system costs. If the car is worth more than that replace it because if the brake system fails you might be replacing the car ,hopefully nobody gets injured. Good luck with your custom,enjoy it

 

We've had this discussion on here many times and proved that one of the functions of the combination valve is to block the flow to the side that allows too much travel. Watch the video. It is from the company that makes that particular valve. They supply a solid plug to put in the valve to prevent the piston from traveling while bleeding. Some valves have a plunger to push to recenter.

The quickest way to find out is to loosen the line that comes from the master cylinder at the combination valve to see if fluid flows when the pedal is pushed down. Tighten the line before releasing the pedal. If there is fluid there, loosen the line that goes to the rear brakes and try the same thing. If there is no fluid pressure there, the valve is blocked.

 

This highly depends on the type of valve. You could be 100% wrong or 100% right depending on what valve your looking at.

 

Pull the bleeders right out of the wheel cylinders
Could be rusty or dirty
Did they have the rubbers over the ends ?

 

This has been a subject of controversy when it shouldn't be. I'll see if I can't scan the appropriate sections from my 'Automotive Brake Systems' text book for the NIASE certification, I loaned the manual to an employee so it might be a week or so before I get it back.

 

There's no controversy,
Some valves do and some don't. That's a fact not a controversy. Without knowing what the donor was it's hard to say, but the most recent valve I've had here that blocked flow was 1985 Chevy truck- and that's a popular valve used on wide spread of years and applications. I can 100% verify that it blocks flow.
Here's how that goes,,,
Hey man, WTF is going on here? I've got all new parts, and hours and still can't get flow to the rears?
Me:
Did you re enter the valve?
- What valve?
This one here,, (pop)
Try it now,
Gee thanks, I've been doing this my whole life and never knew that.
Me:
You'll probably never forget it now.

The first time you encounter one of these things will be an eye opener. It's quite apparent many haven't. The controversy and confusion enters when someone who hasn't encountered one claims they don't exist and calls BS on someone who has.