[kyle_blake]

hi guys,

could use some help on my 69 gto. stock front disc, rear drums. i lost my pedal while driving months ago. there was no fluid loss that i found at any fitting and i had just replaced the master cylinder 6 years ago with new front rubber lines and new callipers.

i found the rear rubber hose appearance wise bubbled a bit and replaced that.

Went for a full re-bleed and the pedal was rock hard when not started. As soon as started felt ok for 1 pump and then by 4 pumps was back down towards floor, not literally on floor.

The wheel cylinders are a tiny bit wheepy but not a full pedal loss imo.
They drums are adjusted correctly fyi.

As we move to the examining more of the front disc system with stock prop valve and hold off valve setup found on the 69, I decided to pull the lines off the M/C and plug in some steel plugs and test M/C. I tested it without car running and pedal was hard. I forgot to test it with car running.

At a loss i pulled the m/c to find fluid there on booster seal. I figured I found the culprit, finally but that doesn't explain why plugs didn't show issue? Guess I should of started the car before removing!

Purchased a new one, bled the M/C on bench. Installed, did the bleed too with the lines gently on and a friend pushing on pedal and hold, tighten line, back off pedal. repeat and get air out of line at M/C outlets. At least try.

I decided to then bleed again all 4's yet again. Yes from the rear farthest , then other rear , then passenger than drivers.

By now , I'm like this has gotta be it. Nope, full hard pedal when not started and then same within 4 pumps running is down far. not literally on floor but you get the idea...

callipers bleeders face up and aren't installed incorrectly
no banjo fittings are leaking
no fluid leaking at prop valve.

I'm wondering what to do next aside of throwing new front rubber lines which when i test if they are a dragging a calliper , they pass.

Any thoughts? thanks PY

[25stevem]

Well the first thing is you need to stop trying to judge how the pedal feels with the motor not running!

With any front disc brake system it’s the rear brakes and there shoe clearance to the drum that set up brake pedal feel.
You had posted that your rear cylinders are weeping, well that’s not good because that’s making for a pressure loss.

If your wheel cylinders have not been replaced, then that’s the first thing I would do.

Once you get new cylinders in place that are fully bleed I would adjust the rear shoes so that the rear drums are pretty well locked up, then if you master is good you are only trouble shooting the front of the brake system.

[Formulabruce]

Front rubber hoses to calipers collapsed inside

[25stevem]

6 years ago he install new front hoses.
Could they have gone bad, I have learned that anything is possible, but those hoses going bad so soon is not something I would put money on!

[kyle_blake]

Thanks, I attached some pics of the cylinders.

You're right I really should of fired the car with the plugs in as a test.

That was my thought, just replace the rubber lines and cylinders and go from there.

Not that expensive and thanks 25stevem for idea to essentially adjust rear brakes as tight as possible when testing.

Here are the pics. I mean I consider that a weep.

Has anyone ever had a distribution block(aka prop) valve go bad?

Kyle

[Schurkey]

As said...don't bother testing when the engine isn't running. Just confuses people.

First Guess: Fluid not leaking OUT, but you've got air leaking IN.

Air can easily get into the wheel cylinders. But you should see this when bleeding--the air is also very easily pushed out again, and is very visible. If fluid can get out, air can get in. Rear cylinders should be replaced but I won't guarantee that the rear cylinders are the only problem here.

I've heard of air leaking into (aftermarket) proportioning valves, metering valves, etc. The aftermarket valves are poorly made despite being expensive. All connections--tubes, hoses, components--have to be AIR-tight, not just FLUID-tight. Under pressure, and under vacuum.

But I always question the master cylinder. It takes way more effort to properly bench-bleed a master cylinder than most folks recognize. And once installed on a vehicle, the front of the master cylinder is almost always tipped "up" in front, trapping an air bubble that will never bleed out. Often, the back end of the vehicle has to be raised so the front of the master is tipped "down" in front, to get that bubble to move rearward so it can purge though the ports between the master cylinder and the reservoir.

[mgarblik]

I have had a prickly brake problem like this one time. The problem ended up being the rear wheel cylinders. This is what happened. You have everything bled but the rear wheel cylinder pistons are stuck. You pump the brakes and get a hard pedal because the pistons are stuck and you can't generate enough pressure with your foot without the booster to get the low pedal. You start the engine and with the booster, the wheel cylinder pistons "ratchet out" a little with each pump until you have a low pedal. I would replace the wheel cylinders first. They show a little rust bleeding out around the dust seals. Then proceed with other troubleshooting as needed.

[kyle_blake]

Thanks Schurkey, always appreciate your posts. Yah that's my fear multiple things gone bad. This is stock distribution block(metering valve) and stock hold off valve. People have told me there are seals in the block but I don't know and it's like 4 weeks out to order one of those.

Yah, I made sure to bleed M/C on bench and the last one I did , I did well. So I'm hoping my skill is decent. That would suck to have to come back to that again and find out..

I'll start with cylinders and have the front hoses ready should I need to.

Thanks again everyone, picking up raybestos parts today... Sure hope this does it.

Curious does anyone think the front rubber lines are kinda short when you turn the wheel all the way? I'm like why is there such a tightness to them? the new ones are part # BH36616

[Shiny]

Sounds to me like a mess I chased for months. Symptoms were identical to yours - hard pedal that quickly degraded, yet no fluid loss.

Conclusion was air being sucked back into system through rear cylinders.

Fix was to find a different brand of rear cylinder that had "expanders" on the cups. It has been maybe 10 yrs so who knows what's being sold now but the "good" ones I bought at NAPA.

Here is a thread with the long sad story and some explanations:

http://forums.maxperformanceinc.com/...d.php?t=598515

Mike

[kyle_blake]

Thanks Shiny,

So I installed new cylinders in rear, bleed them with friend, no air. fired car, pedal goes down. Ok , not the cylinders.

Wen to front, installed new rubber lines. Bled the front, and the passenger side had no air but the drivers side, my friend said just tons of tons of air.

The "new" line he installed to prop valve last year, must be the culprit.

I have to use a crowsfoot tool just to tighten it at the block.

It's too bad I can't just buy the one line, maybe I'll just make another one or I get lucky and the tighten works.

I'll report back after I buy the new parts. again thank you py

[Ram Air IV Jack]

I rebuilt my MC years ago when you could still purchase the rebuild kit from GM. Honed the bore and it looked great. I followed the service manual and bench bled the unit without any issues. I used my vacuum pump to suck out all the old fluid at that time as well. My mechanic friend kept pouring the new fluid in the MC so it would never run dry and get air in the system. It took two of us but when done, I had a decent pedal. By the time we were done, most of the quart of fluid was used. That surprised me.

[kyle_blake]

Yah. They didn't charge a core charge up here for M/C. Yah new vs rebuilt , the world is just replace it now isn't vs rebuild.

This is what I'm saying about the rubber line being frigging tight when wheel is turned to lock... That is just BS.

Look at that stretch. Really? who wants to rally race??! not me.

[kyle_blake]

Hi,

Replaced the line to front drivers side, same thing a ton of air after a ton of 2 man brake bleeding. Ugh already replaced caliper as we know on that side. new cylinders and new front rubber lines.

I then plugged the distribution block where the "front drivers" line connects to and the pedal didn't go full hard as I expected it would.

We left last bleed session with no air on passenger side. So some how it had air now.

This leads me to believe:

Distribution block - replace? can it fail?
Line up to hold off valve - pin hole leak?
Replace hold off valve? - can it actually fail?

Unreal.

[highway star]

Are you using this when bleeding?

https://www.classicindustries.com/pr...8c9d2ffab96af7

[kyle_blake]

Hi,

No. I assumed it only came into play if M/C went dry and through out this adventure neither reservoir has...

Is this the symptom is lots of air in front's only if it has moved?

Side point: I tried testing continuity of switch to determine if it is closed, result - open circuit. Not closed.

Plugged in the switch - no brake light - confirmed 12v at wire to switch.

Plus this is a distribution block per say, not a true 1970+ prop valve, so wondering if that plug is even applicable?

[kyle_blake]

Just an update here, dropped the front of the car more level.

While the front drivers side line was off, I used a pin to push the block's internal rod inside a little bit back towards the "rear brake port". Hoping maybe it will be aligned?

I then re-bled, the back's are perfect no air.

Front's, this time I i opened bleeder valve and compressed piston back, saw some bubbles. closed valve. then continued with bleed normally. then did piston compress again less bubbles. not sure if this means anything?

some guys are saying the distribution block has that rod which has moved and that slamming on the brakes hard several times can get it back into alignment?

Anyway with moving prop valve rod back and slamming the brakes hopefully it's aligned and stupid air stops on front. along with caliper compressing.

have a good day.

[kyle_blake]

Gravity bled front's after getting no air doing single man bleed. didn't see any air.

rock hard pedal not running. running pedal not bad. I think I got it finally. pulled M/C to check behind it for leaks, none. booster is dry.

Put tires on and did a short drive and brakes are good. she stops. what a lesson.

thanks again everyone, don't know if the pushing the rod in block did it or lowering the car or pushing pistons back or all of the above but something worked.