it could just be due to the additional pressure applied causing it to bypass when it is marginally holding pressure without the booster assist.

extending the rod won't hurt the brake system but if it is extended under normal conditions it can cause the brakes to drag.

you could try jacking the car up at all 4 corners and begin applying the brake until the wheels lock and note which do first, the front brakes should begin locking before the rears do.

if the pedal is sinking nearly to the floor i suspect your problem is solely with the front brakes still or the front brake port/rod/seal inside the master. the hydraulic pressure between the 2 pistons is what actually applies the rear brakes, if the fluid is bypassing inside the master(or has a massive air pocket) it will sink until the spring forces the rear brakes to apply as a backup measure(like a failsafe so you at least have some brakes in the event of a front rod seal failure or air in only half of the system).

it sounds like you can't even do a simple brake test to see which wheels lock up first to try and divide the system aside from the unloaded test above.

i would also physically watch the calipers and make sure all 4 pistons are moving on each caliper, even if just one is seized it will cause all sorts of problems. especially focus on that RF wheel where it is having difficulty bleeding, the piston on that bleeder port may be stuck in and partially blocking the bleeder port.

 

It seem like system flows well. When I was changing the bleeders it gravity bled good. And all bleeder have a lot of pressure when opened. I will inspect pistons on front caliper tomorrow.

 

The pedal isn't going near the floor after rod adjustment. But it sinks so easy to the middle of the stroke I could do it with my pinky.

 

Today I inspected the front calipers to make the 4 pistons were moving.
The inspections left me with some questions.
This is what happened.
When checking the front driver only one piston would come out while other barely or didn't move with descent pressure applied at the pedal. I had to hold the "functioning" piston by hand and had someone apply the brakes to make the other come out. The passenger front was worse than the driver side. With the pressure applied at the pedal now being "hard and as low as itll go", the pistons did not extract at all. After pumping the brake pedal about 3 to 4 hard times one piston came out finally. I clamped that one down and slowly got the others to extract.
Im not expert and do not know if my calipers are trash or not.

Questions.
1.My pistons will obviously do not extract at the same time, what does this mean?

2. The pistons on this calipers might not slide in and out with ease, are they trash?

 

the pistons won't all move at the same rate but it does sound like they are partially seized by crap inside the calipers.

i would recommend rebuilding them or replacing them off a car that had properly functioning brakes. the GXL and GTU models had the same calipers btw.

 

i would rebuild, its very easy, and cheap

 

Your weird pedal issue could easily be the adjustment between the booster>MC.

I'll reiterate the advice I gave two weeks ago in post #12...rebuild the calipers and replace the booster/MC with a matched pair.

 

at some point, if normal stuff isn't fixing it, you need to start eliminating possibilities.

so rebuilding calipers is a cheap and easy way to take those out of the equation. adjusting the booster to pedal, and booster to master adjustments. making sure all the bleeders are clear, etc etc.

eventually you will find the culprit

 

I had rebuilt the front calipers about 3 to 4 yrs with Mazda parts. I guess it wouldnt hurt to try it again, its only like 45$ for rebuilt parts. I also have an extra set in the back shed that have been sitting in there since 05'. I dont know if they would be good after sitting for so long even though they had come of a working car. I'll order the rebuild kit tonight.


Im getting desperate. I would hate to leave her at a shop.

 

My car did all of these things including after replacing pads and MC.

The issue was my front calipers being absolutely trashed. Half the pistons were seized and teh ones that weren't were pitted so bad inside they couldn't be repaired. Buy new Calipers online for cheap and test again.

 

Also try bleeding the master cylinder itself. Have someone pump it get them to hold the pedal and crack the lines on the master all while the pedal is being held. Do it a few times.

 

I will look into replacing the front calipers or rebuilding them. I had bench bled the mc so I never did bleed it at the mc. I will try this first since I'm off tomorrow.

 

Since remain calipers are only 45$, I chose that route instead of rebuild kit. Limited lifetime. So we will see tomorrow when they get here.

 

OK so it wasn't the front calipers.

I just got done installing them and bleeding them with a helper. The brake pedal quickly sinks all the way to the bottom and has incredibly weak braking force.

 

Might be time for clokkers advice of ripping a matching pair booster and mc from the same car.

I'm curious though. Why does the front passenger brake line run thought the prop. Valve. Does it even get regulated? If a 2 port mc is used, it is correct to T off the front line?


I think tom. Is a junk yard day.

 

D'oh.
Neither front line is "regulated", they are merely a reference for the rear line which IS getting regulated.

Before you go nuts, try adjusting the booster >MC pushrod and see if your symptoms improve.

 

I extended the booster/Mc rod already. I extended it about 3 full turns. Its between 1/4 to 1/2 in. Longer. Read a couple of posts back. It fooled me at first thinking it was improving. But prooved to be same after starting the car. And feeling the pedal.

 

Are we talking about the same rod?
I'm not sure the FRONT pushrod can even be extended 1/2" out.

 

I'm trying to visualize and guesstimate how much i adjusted it.
The rod that makes contact with the mc. It was a 7mm.

 

Yeah, OK.

So, now what?

 

Idk. I haven't gone to the junkyard and picked up and matching booster and Mac yet. My friend has some sort of pressure bleeder that attaches to the mc filler cap or something. I want to try that.

 

So I had a friend come take a look. He saw no leaks. We also rebled them,we bled both bleeders on the rear calipers ; he used his technique and got a few more bubbles out of the rears. The fronts had no air bubbles coming out.

He suspects the master and proportioning valve. But again, we have no obvious signs of where the problem lies. I sat in his fc and felt the brakes... and boy.. his are 10times better. His travel like 1/4 to 1/2 inch and the begin firmness. Mine travel a couple of inches of Dead travel and then get barely stiff. When car is off I cannot bottom out the pedal, but when its on the area of dead travel seems to be way bigger and I can bottom out the pedal. I test drove it and tried to apply The brakes aggressively and the pedal just sunk with extremely poop braking power. Even the e brake works like ****; Tried to pull it when car wouldnt slow down. Also, we checked if the fronts apply brakes before the rears and this checked out OK. Also when you pull the e-brake and your foot is applied on he pedal, you can feel the foot pedal move. So that checks out, if it means anything.

 

You may have a small pinhole sucking in air. Easiest way to find that is with soapy water.

Your pedal feels like that because there is still air in the system. Bleed the master like I said, and if that doesnt work go from there. Proportioning valves almost never fail. I havent seen one go bad yet.

 

I forgot to mention that we also bleed it at the master. He bled the horizontal port on the front of the master. He said a bit of air did come out.

 

IF all hardware is fine, the brake booster pushrod is still the secret sauce. If you adjusted a 7mm nut, that's the right thing to adjust. Just to make sure you moved it enough, pull the pushrod back out (you really only need to remove the two nuts for access and not disconnect any hydraulics). Loosen the nut a significant amount until it is over-adjusted. When it's over adjusted, the brakes will drag. You will know when it's over-adjusted after you start the engine and test it.

Then adjust it the other direction until the brakes don't drag but the travel is acceptable. This is the only thing I've ever been able to do to fix the mushy/high travel feeling on FC brakes that don't have obvious mechanical failings. Adjusting the pedal, bleeding everything, etc basically does nothing.