Mr3plus1

iTrader: (5)

Okay. So I did the mazda 929 master cylinder because i thought my master cylinder was on its way out (brakes were a little sub par). Since then Ive been going nuts trying to figure out why I dont have brakes. Here's what ive done -

Bench bled master about 4 times now and took it apart to make sure nothing internaly was messed up. Master is moving fluid and seems to hold pressure.

Took off and cleaned proportioning valve. I got air to go through it, although there was a decent amount of restriction (looks to be spring loaded inside). Fluid passed through it under braking, so I figure its a-ok

Brakes are rebuilt as of a year ago so its not caliper related. And up until now Ive had no real issues.

There are no kinks or leaks in any of the lines or connections.


My problem is, my front brakes are moving fluid but kinda suck under load. My rear brakes are moving absolutely nothing. I mean nothing. When I bled them I was pulling fluid out of them with the speed bleeder, but now I get air. I thought maybe it was clogged up in the splitter thats located towards the diff. Nope, clean. So, with the lines completely disconnected, I hit the brakes. No fluid. In fact, with the back brake lines not even hooked up the pedal still gets stiff! WTF!

Now here's whats even weirder. Obviously something is preventing fluid from getting to the rear brakes. My pedal is doing all sorts of crazyness, no matter how much I bleed it. It has a small amount of resistance up until about 2 inches from the floor, then it gets ROCK HARD. Driving around like this feels like trying to stop an 18 wheeler. The brakes work, but they suck horribly. I can put pressure on the pedal and it'll start stopping, but if i put a lot of pressure the abs locks up right away and kinda pulls to the right for some reason.

My best guess is its the ABS unit thats ******* up. But there's no light on. Could it be jammed? Has anyone ever taken these apart? Should I just elminate it. Buying another one is not an option, even used. I dont have the money. At least not for this kind of problem when my alternative (removing it) is nearly free.

DaleClark

iTrader: (55)

I think you've just got air in the lines somehow. I have heard in the past to turn the car on when bleeding so the ABS pump is energized - that may help.

Brake bleeding is just a bitch. Been working on the brakes on a buddy's FC, and it's no fun.

You sure you got the 929 MC all hooked up properly?

Dale

Mr3plus1

iTrader: (5)

Yes. I know what Im doing. This should be easy. There is air in my lines. The rear brakes. Because i cant get fluid in them no matter what I do. I can try energizing the pump, but Im not sure if thats gonna help. The speed bleeder makes bleeding brakes a snap. I just need to figure out how to get fluid to the rear calipers so im not bleeding an empty line.

Mr3plus1

iTrader: (5)

What Im really confused by is the pedal feel. It springs back quickly like it should, but when you push it, it stays somewhat soft, then 2" off the floor gets real hard. I know for a fact its moving fluid. But where? Is there just a big air pocket thats caught in the frozen abs thats getting compressed when I push the pedal down?

JLee

iTrader: (1)

Bleeding brakes is a real pain in the ***, specially when you have an ABS pump. Have you considered getting a power bleeder?


http://www.motiveproducts.com

They're about $60 and you won't have to deal with opening your bleeders or having another person pump on your brake pedal.

Mr3plus1

iTrader: (5)

When I said I had a speed bleeder I was refering to an air operated bleeding device. There's nothing better that they make. Does brakes great. That is not my problem though.

Mr3plus1

iTrader: (5)

So nobody has an explination as to why my pedal feels the way it does? Has anyone ever had the ABS unit freeze on them like Im describing?

maxcooper

The brake circuits are designed so that if you have a leak in the rear, the front brakes still work (or a leak in the front, where the rear brakes will still work). I think this functionality is achieved by having a floating piston in the master cylinder on the FD (and the 929). If one circuit goes dead, the other circuit still works when the floating piston either hits the end of the cylinder or hits the main piston. I suspect your rears just don't work, and so you get some travel and then the front circuit hits.

Does the master cylinder pump fluid from both circuits when you bench-bleed it? Maybe the floating piston is stuck at one "end" of it's travel (stuck in end of cylinder, or stuck to main piston). However, based on how your pedal feels, I suspect you just have a shitload of air in the rear circuit rather than a stuck floating piston. What happens if you use the pressure bleeder to bleed one of the rear calipers? Maybe turning the car on to give the ABS pump some power is the missing element in solving this, if you didn't have the key on during bleeding before.

I was going to suggest the pressure bleeder (like the Motive Power Bleeder), too, since Speedbleeders (a brand name for bleeder screws with check valves in them, hence the confusion) don't work when there is a lot of air in the system. But it sounds like you already have a pressure bleeder. Even if you do have a pressure bleeder, make sure you DON'T have Speedbleeders on the caliper or you may not be able to pump the air out (the cracking pressure of check valve may be higher than the pressure of the pressure bleeder). You could always just remove the bleeder screw entirely until you get some fluid flowing to be certain.

-Max

Mr3plus1

iTrader: (5)

As I explained earlier, with the rear lines disconnected I get no fluid, but my pedal gets hard. So there's something BLOCKING fliud from getting to the rear. Ive already disasembeled the master. You cant get the piston stuck. Its spring loaded. The only way the master can be faulty is one of the seals is bad and you get a pedal that holds pressure, then slowely drops to the floor. Usually this can be overcome by pumping the pedal some. Mine does not do this. It also pushes fluid out of both front and rear pistons and what looks to be about the same amount of fluid.

Look, Ive already ruled its the ABS. Im not a newbie at this stuff. Im thinkin the abs unit doesnt need to be powered on for one specific reason. When I turn the car on it should (if this logic is correct) allow fluid to pass through it, sucking up a lot of fluid out of my resevoir and creating a very spongy pedal feel. My pedal does not change though. My resevoir level does not drop. And my rear lines remain empty. What if I activate the abs while Im driving. That should move fluid, right? Nope, still the same pedal. Still no fluid in the rears.

I understand that yes, it does sound like I have a lot of air in my lines. Lets ignore the rear lines since something is preventing brake fluid from getting to them. I bled the fronts over and over and over. With the air bleeder and the old fashioned way. It flows fluid through each caliper with no bubbles (and a good amount of fluid).


Okay...let me explain this so i dont get anymore people telling me its something else. If my master was in fact bad (the only real failure point would be a clog or a bad seal, since the springs on the two pistons prevent it from getting stuck at one end or the other) I would either have no fluid flowing from one of the lines (cant be this. get good fluid flow) or I would have a pedal that would slowely drop (it would move the fluid, but not hold pressure because the fluid would leak past the piston). So its not the master for sure.

Next object in the brake line is the proportioning valve. Now, Ray from Malloy told me he's never sold one of these in his life. That narrows down the chance its this, but whatever, I tested it anyways. Its spring loaded. If you put air pressure on it nothing comes out the other end. But if you created an air tight seal and give it some air pressure it'll push the spring and let air flow out the other end. This wasnt dirty. I even took the canisters off the bottom and blew through the splitters that lead into them. Nothing. I hooked the lines back up and gave it some pressure with the lines both loose on them. I got fluid leaking from both lines exiting the bottom.

Now, lets say the abs unit is good and one of those systems is bad. Neither creates enough restriction in the lines to prevent fluid from being sucked out of them. Even the proportining valve. So if I go to the back breaks and pull vaccum on them and close the bleeder screw with the air bleeder still going it should pull fluid through the whole system. Well, when I open the bleeder screw I get a hiss of it relieving the pressure. Well, maybe it didnt create enough vacuum to let fluid past the proportioning valve. Lets just try forcing it past with the lines open. I get in the car. hit the pedal. It gets hard right before it hits the floor just like i described. My god, the lines are open! Well, what could be preventing fluid from moving? I know. The ABS.

My best guess at why the pedal acts that way is there's a massive air pocket caught in the abs and im compressing it.




So back to my previous question so nobody tries to tell me its something else - has anyone ever taken apart the abs and fixed it? Is mine broken or repairable? Has anyone ever had this same situation happen to them?

efinimazda

iTrader: (29)

have you disconnected the abs elec. connections?

Buzzardsluck

this is from 2/06. his car is currently on jackstands getting its soul ripped out.

i dont remember if he ever fixed the problem or lived w/it.

Busted7

Try rotaryheads.com they have some test to help narrow down your problem!

XxMerlinxX

iTrader: (2)

I take it he's going LS1?

IRPerformance

iTrader: (41)

Bleed the abs unit lines one by one just as you would a bleeder. Once I replaced ALL the brake components and it took a whole day to get all the air out. Also make sure none of the brake booster hoses are compromised and that the check valve is there and not leaking.