Didn't bench bleed brake master cylinder... Now what?

[mk2davis]

My brakes are not working right. It started after sitting for a few days, and my brakes would randomly go most the way to the floor. But then they would work correctly most the time. There did seem to be a correlation with downhills and soft pedal feel.

So I decided to swap out the master, as it is at least 10 years old and possibly the original unit.

I did NOT bench bleed the master.

Bled the lines in the funky diagonal pattern and I have no bubbles coming out. Brake is hard with the car off. Turn the car on, and each time I press on the pedal, it's different. Driveable, but certainly not confidence inspiring. The idle changes slightly when the brakes are pumped, too.

So the question is, is there anything I should check before taking the lines off the master and doing the bench bleed?

The changing idle when the brakes are pumped made me consider the booster and or check valve, but I understand that would make braking harder and not softer.

Thanks in advance.

 

[fuel]

still have ABS?

 

[mk2davis]

I do.

 

[FlyingEagle]

Try this to start:

brake booster function test

If the master wasn't bled properly, you can crack the line fittings and have someone depress the pedal to the floor and reconnect while the pedal is still depressed. Tapping on the housing can help migrates air bubbles "upwards" in the system, to help facilitate a bleed.

You could have air somewhere in the system, but most don't post about having air trapped in the ABS module, but most cars nowadays have an electrical function bleed operation setup for their abs pumps; mainly for component replacement of the abs pump but can help move air regardless.

You can do a bleed with the engine running, pump once and hold, crack bleeder, close, allow slow pedal rise/stablilize at the top and repeat - to help get fluid moving more quickly than a gravity or non assisted bleed, but this may not be necessary.

They do make pressure bleeder machines and vacuum setups that can push or pull air out of a system. The cost does add up though.

Assuming you do not have any issues with your base mechanical brake setup, air in the system will give less than desirable results once pressurized.

 

[mk2davis]

It's bloody hot outside, haven't tested the booster yet, but I did take a drive and learned something. It appears that after boost I have less brakes. If I just baby it, brakes seem solid. So at this point, I suspect the check valve. Not definitive, but we will see. Tomorrow's cooler, I'll post more then.

 

[mk2davis]

Anyone know the ID of the brake booster hose? My understanding is that oem isn't available, thinking if making a line using a check valve from another booster application.

 

[mk2davis]

Just to wrap this up, I ended up getting a Evo 8 check valve from jnztuning.com . I had to trim it down some, but it slipped right on.

I have another brake bleed in my future (I'll probably wait until new pads come in), but things are feeling much better.

 

[boostme]

It's not exactly clear if you did it, but do you know there's a bleeder valve on the ABS unit??

 

[mk2davis]

I've read that, but either I'm not looking at the ABS unit or what the FSM calls the hydraulic unit doesn't have bleed nipples.


I see bleed nipples on 91's, but not 92's?

If someone can point me in the right direction, I'd be much obliged.