Mushy Brakes

[hpmaxim]

I posted about this before but I'm at my wit's end. Car is a 5 speed 2003 model with 4 wheel disc brakes and ABS (I assume they are all like that, but not sure).

Car sat for a year and a half. Prior to sitting, I think the brakes were working fine. After sitting, the brake pedal is mushy and almost goes to the floor before it engages. Pumping the brake makes some difference. I went to do a bleed and broke off one of the bleed screws in the front caliper. Replaced both front calipers. Bled the brakes. After the bleed, the brakes felt pretty much the same as right before the bleed. After bleeding for a while and restoring it to pre-bleed level, I let the fluid level get too low and lost what little brakes I had. Re-bled the brakes and the brakes are back to where they were before I started again...

I can't see anything obviously wrong. Bleed was done with a helper at the wheels. He reported that fluid coming out was clear and without bubbles for 5 pumps in a row. I also tried adjusting the parking brake by turning the adjuster screw, and then hitting the brakes while repeatedly pulling on the e-brake handle. This did not make any difference. I have no reason to suspect a leak in the brake system, I don't appear to be losing fluid nor can I see any fluid where it shouldn't be.

What the heck do I do? The only obvious things I can think to try at this point are to replace the master cylinder and/or rear calipers, and possibly do something to the ABS system (a friend with no particular knowledge of this car suggested there might be air in the ABS system that I could only get out by first cycling the ABS a few times and then bleeding it out -- he suggested deliberately engaging the ABS repeatedly and then bleeding -- not even sure if I have enough braking power to do that).

 

[JazzySP20]

Yes, you definitely have air trapped inside the ABS module.

Long story short, you need a scan tool that can cycle the ABS solenoids to release the trapped air. So unless you have access to such a tool, and you know how to use it in the correct manner, the car has to be taken to a mechanical workshop, or a brake specialist, or to a Mazda service centre.

Also, the old 'push on the brake pedal' method is not recommended for ABS equipped vehicles. The 'vacuum pump' method is the better method for bleeding brakes.

 

[hpmaxim]

Jazzy, the thing is I can't find ANY reference to such a tool (at least specific to our vehicles) ANYWHERE. The service manual as well as everything else I can find seems to indicate that the bleed procedure is identical for ABS equipped cars as non-equipped vehicles and I'm shocked I can't find a tool anywhere, which is odd, because I presume its just sending a few commands through the OBD2 port, which means even the $100 HF scanners or a program like Torque should be capable of doing it without much difficulty.

I did see someone mention elsewhere that they had put a Miata up on jackstands, accelerated the rear wheels and then hit the brakes to engage the ABS pump. This sort of makes sense to me, but I'd think it'd only actuate the rear brake channels and not the front. Maybe it doesn't matter, but I'd think it does.

Here are some threads:
http://forum.miata.net/vb/showthread.php?t=429317
http://www.mazda-speed.com/forum2/index.php?topic=26846.0

I found them confusing. Was the attempt simply to cycle the ABS or did the bleed screw have to be open at the time. I'm not clear why simply cycling the ABS would necessarily get any air out of the system since the air can only be pushed so far in a closed system. OTOH, it seems like it'd be next to impossible to engage the ABS if the bleeder screw was open unless you did it electronically. They did mention something about turning the ignition on with the brake pedal depressed and going into a diagnostic mode where you could short the TBS pin to ground on the diagnostic link connector which appears to be present on our cars. No idea if it works on our cars though.

As a general comment, I really dislike the whole concept of the "vacuum pump" method. When you vacuum you are subjecting the system to negative pressure. That means if there is any hole in the system (including around the threads of the bleed screw which is really common) you are sucking air into the system. Keeping the lines pressurized and forcing fluid out seems far safer.

 

[hpmaxim]

I called a local Mazda dealer and spoke with a technician. He initially said it sounded like I had air in the ABS system, but later admitted it was unlikely I had air in the ABS system prior to opening the system up which didn't happen until after the problem already existed. He also suggested the problem might be swelling in the brake lines. I've heard of this, but never seen this. I've replaced the brake lines of much older cars, and never felt a real difference. He said, he thought master cylinder failures themselves were pretty uncommon.

He said he didn't know of any good way to actuate the ABS system without the scan tool. I attempted to actuate it by accelerating the front wheels to 30 mph and slamming on the brakes (wheels were off the car, it was in the air), and ABS didn't activate. I tried it both in gear (which stalled the engine) and in neutral. Neither seemed to activate the ABS. It's not clear to me from the service manual that its possible to deliberately cycle the ABS without the WDS/ISD tool which is absurdly expensive. However, I did read someone else's suggestion that I remove one of the front calipers, and shove a block of wood in between the pads. So if I hit the brake one wheel stops, and the other doesn't -- triggering the ABS (although I'm not sure that would get all the air out, since the two rear wheels wouldn't be spinning at all and this might only push some of the air out one of the channels -- assuming there is air in the ABS module.

If not, I'm lost.