Bleeding Brakes - This is stumping me.

[WB72]

Back story...
Everything is new except proportioning valve, which the piston moves freely.

I can’t get firm pedal on rear. The piston continues to trip and not allow the brakes to bleed the rear. I know there is a tool to install where the sensor is located to stop it from tripping.


There are posts mentioning to use a clamp or hold the pin on the front to reset the piston, but this only works if the front brakes have low pressure.

These tools are just a few bucks, but is there a way to block the piston without the specific tool as I would like to get this done without ordering this specialty tool.

[KQQL IT]

I have to gravity bleed my square it trips the proportioning valve if you look at it funny.

[Rickysnickers]

I have one of those centering tools that i bought and dont need. Pay for shipping and you can have it.

[randy500]

The pin in the front of the prop valve opens the front “proportioning valve” so there is a free path for fluid to flow to the front, only needed if pressure bleeding.

As you have found out when the centering valve moves it cuts off fluid flow...
You could open a front bleeder to equalize the pressure to get fluid flowing to the rear without tripping the valve. When you begin to build pressure in the rear close the front bleeder.

[ncpetersc]

Originally Posted by Rickysnickers

I have one of those centering tools that i bought and dont need. Pay for shipping and you can have it.

If he doesn't take you up on that offer, can I? I have a power brake upgrade kit on the way, I hope to install soon.

[Rickysnickers]

Originally Posted by ncpetersc

If he doesn't take you up on that offer, can I? I have a power brake upgrade kit on the way, I hope to install soon.

Yes you may, just give him a chance to reply first

[WB72]

Rickysnickers,
I would like to take you up on your offer, let me know the cost to send it to Canada, Ill send you the $$

I will PM you with exact address.

KQQL IT,
While gravity bleeding, I only get a few drips and then it stops, I am too impatient and usually wonder away to do other things and then forget. I don't want to come back to an empty MC as then I would have to start all over.


I do have an 8" channel in my frame that takes the brake lines 8" higher than a normal frame. is this what is causing me my issues?

[AussieinNC]

Pull the trip switch out of the proportioning valve....then bleed the back brakes first....

Try and use a pressure bleeder and not the old pump the pedal etc....

Replace the trip switch once you are done....

The prop valve wont leak when you pull the switch...

[typerr]

Originally Posted by WB72

Back story...
Everything is new except proportioning valve, which the piston moves freely.

I can’t get firm pedal on rear. The piston continues to trip and not allow the brakes to bleed the rear. I know there is a tool to install where the sensor is located to stop it from tripping.


There are posts mentioning to use a clamp or hold the pin on the front to reset the piston, but this only works if the front brakes have low pressure.

These tools are just a few bucks, but is there a way to block the piston without the specific tool as I would like to get this done without ordering this specialty tool.

I chased a soft pedal for weeks when I changed to front discs and also did the master and prop valve. I had bench bled the master twice but finally pulled it off for the third time and slowly bench bled it just a bit at a time and pulled tiny little bubbles out of it. Kept this up until no more tiny bubbles and finally got my firm pedal. I also used one of the prop valve tools to keep the valve centered.

[KQQL IT]

KQQL IT,[/B][/U]
While gravity bleeding, I only get a few drips and then it stops, I am too impatient and usually wonder away to do other things and then forget. I don't want to come back to an empty MC as then I would have to start all over.


I do have an 8" channel in my frame that takes the brake lines 8" higher than a normal frame. is this what is causing me my issues?[/QUOTE]

I don't know about the channel. But mine drips then a burp of air and runs pretty steady.

I chased the bleed on the back brakes forever.
And gravity was finally the answer

[randy500]

A pressure bleeder is about $65 on amazon, no need for bench bleeding etc with a pressure bleeder, save yourself the hassle and buy one. They are great for flushing your brake system and adapters are available for most all vehicles.

Taking the switch out wont help, the valve moves and cuts off flow to the end that its tripped to.

[WB72]

Originally Posted by randy500

A pressure bleeder is about $65 on amazon, no need for bench bleeding etc with a pressure bleeder, save yourself the hassle and buy one. They are great for flushing your brake system and adapters are available for most all vehicles.

Taking the switch out wont help, the valve moves and cuts off flow to the end that its tripped to.

I have used a vacuum bleeder. What is the difference between a vacuum bleeder and pressure bleeder?

[typerr]

Originally Posted by randy500

A pressure bleeder is about $65 on amazon, no need for bench bleeding etc with a pressure bleeder,

That has not been my experience. Pressure bleeding worked great at my calipers and wheel cylinders but did not clear the air out of my master cylinder, which required very careful bench bleeding.

[rpmerf]

Originally Posted by WB72

I have used a vacuum bleeder. What is the difference between a vacuum bleeder and pressure bleeder?

Vacuum bleeder you connect at the bleeder valve to PULL fluid through.

Pressure bleeder you connect at the master to pressurize the reservoir and PUSH fluid through. This works better than pushing the pedal as you can get one continuous stream through.

Another interesting one is reverse bleeding. Pushing fluid in from the bleeder. Only do this once the system is bled of all old dirty fluid. I've done this with an old sauce jar, some hose, and a regulator set to a couple PSI. Really seemed to help on my 97 with ABS. I always thought this made sense, as it is pushing the bubbles up toward the master, where they can bubble out through the reservoir, instead of down.

[BigBird05]

Food for thought, At the factory they vacuum bleed.

[randy500]

I have changed probably a 100 gm master cylinders and never bench bled one, 50 percent vacuum bled and 50 percent pressure....there is no need to bench bleed it if you have bleeding tools.

Vacuum bleeding is not nearly as effective as pressure as you can't tell when your free of air because air gets introduced to the fluid stream from around the bleeder screw threads.
Also vacuum can let air in around wheel and caliper seals.

When pressure bleeding you can press the brake pedal if you feel there is air in the master cylinder.

With pressure bleeding you have pressurized fluid entering the master cylinder so it never runs empty, you can see the bubbles coming out of the bleeder (use a hose with fitting on the bleeder to capture the fluid and see the stream). Let each bleeder run a couple seconds after the bubbles stop and your all bled.

[68 P.O.S.]

https://www.brakebleeder.com/

[toolboxchev]

I have not ever had to go through all that. You most likely have a defective piece or some other problem.

I have bled my unit over 5 times in the last 10 years.

[RichardJ]

P.O.S. is linking to the Phoenix Systems Reverse flow bleeder as was mentioned by rpmerf in post #14.
I have one of their low end plastic bleeders and it works as advertised. It can also be used as a vacuum bleeder hand pump. IT IS NOT A ONE-MAN BLEEDER. IT CAN BE USED TO FLUSH THE COMPLETE SYSTEM, BUY AGAIN REQUIRES TWO MEN.

TWO MEN ARE REQUIRED, BECAUSE YOU MUST CONSTANTLY REMOVE THE OLD EXCESS FLUID FROM THE RESERVOURS OR RISK FLUID OVERFLOWING IN THE ENGINE BAY. Vacuum bleeding is safer with one man, because emptying the reservoir is a nuisance, but not a disaster.

Post #16
>>I have changed probably a 100 gm master cylinders and never bench bled one, 50 percent vacuum bled and 50 percent pressure....there is no need to bench bleed it if you have bleeding tools.
Vacuum bleeding is not nearly as effective as pressure as you can't tell when your free of air because air gets introduced to the fluid stream from around the bleeder screw threads.<<

Air from the bleeder threads can be eliminated by removing the bleeders and wrapping the threads with cheap thread sealer tape. This is also necessary with the reverse flow pressure bleeder. In this case, fluid is pushed out around the threads. Usually, very little fluid escapes while you are wrapping the threads.

I agree with bench bleeding not required on horizontally mounted MC's. Bench bleeding was first introduced in the '70s when they started mounting the MC, nose high at an angle, trapping air in the front. When mounted horizontally, most of the air will escape on its own as you pour the fluid in. A couple of raps with a screw driver handle will shake loose most of the remaining bubbles.
After you bench bleed and remove your bleeding apparatus, you are allowing air to enter the fittings anyway. You're fooling yourself if you think that multiple bench bleedings actually fixed anything.

The pin on the end of the combination valve is not part of the pressure differential switch nor is it connected to it in any way to the Proportioning Valve. The pin is part of the Metering Valve. The Metering Valve functions completely independent of the functions of the Pressure differential Switch as well as the Proportioning Valve.
These three valves function completely independent of each other. They share and are COMBINED into the same housing to save space and plumbing.

[Overdriven]

A little bench bleeding story. Was helping install a disc conversion kit on a Nova and a bench bleeding kit was included that was all plastic. My buddy is there at his bench vise pushing and releasing the piston of the master for a couple minutes and I’m wondering what’s taking so long? He says he’s still seeing bubbles, so I go over, give it a few pumps and sure enough there’s no shortage of bubbles. Because on my next few pumps I noticed the included plastic fittings were letting air get sucked past them when releasing the piston preventing any progress.

You can point out whether bench bleeding is needed or not, but it’s kinda funny that a task that shouldn’t slow you down more than 5min was stymied by the included plastic fittings.

[AussieinNC]

I havent bench bled a Master cylinder in 20 years....

Have a collection of adapters for my pressure bleeder...full truck bleed takes less than 15 minutes....including the ABS system on my 2006 Sliverado...