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Hi - thanks for reading this. I've got brake issues, here goes:

 

'91 Legacy Wagon AWD ABS. Changed all of the pads, and the rotors on the front. Bled the brakes per instruction for ABS brakes in the Chilton's book I have.

 

In the event I'm driving for awhile without touching the brakes, upon first application of the pedal, brakes engage about 1.5" from the floor. After that initial use they'll stay 'pumped' to an almost normal but not quite comfortable position, only to recede again after I'm going for a little while.

 

This is, of course, a dangerous condition requiring immediate and accurate attention. Any suggestions on which component I should check next, and how I check it...would be greatly appreciated.

 

Sh-

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No leaks on or near it, what other physical symptoms could I look for?

 

Certainly was the reason I bled 'em. I needed the other stuff anyway. But beside the noise & shake I had before new pads/rotors, this was a big indicator i needed to get off my rump roast and fix the brakes before someone gets seriously hurt.

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Sounds there is still air in the brake lines. This is DANGEROUS!

 

Bleed them again, run at least one litre of fresh fluid though the pipes. The order I have learned is FR, RL, FL, RR.

 

There could be air in the master cylinder, but start by bleeding the pipes as normal.

 

If the seal is worn in the master cylinder piston then the pedal will be hard initially, but slowly fall to the floor under constant pressure.

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The Master Cylinder has never run dry on my watch, when I got this car 2 years ago it had 195k on it...

 

Let me run down my one-man bleed method...you guys tell me if/how I'm doing something wrong. The following steps have been carried out 6-7 times in the past week or two:

 

Open MC cap, attach vinyl hose to front right bleeder screw, place other end of hose in jar of fluid. Open screw, depress brake pedal, hold pedal down (I use a board wedged behind the clutch pedal), check for bubbles in tube...if bubbles are present release and depress again. With pedal down, close bleeder. Proceed and repeat... left rear, left front, then right rear.

 

On the last wheels I've actually tried closing the screw with the pedal depressed and upright with similar results. I don't fear changing the master cylinder, did it on my '73 pontiac about 10 years ago. If it comes to that, I'll ask you guys the bench-bleed method as obviously my chiltons book is not helping me much.

 

Thanks again.

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One thing that can happen when bleeding brakes is you will push the brake pedal down to the floor as part of the process. This will run the master cylinder piston into unexplored territory. The bottom recess of the bore may be fine, but there also may be a buildup of dirt or a rough surface resulting from moisture corrosion. I have seen master cylinders that worked great that were ruined by one full bottom stroke. There doesn't need to be any air in the system to have the low pedal condition occur, because the rubber cups are now damaged and will take a bit longer to catch a full load of fluid. It would be normal to have the second stroke feel better if this was the case. I would not give up on bleeding, because this is the only simple solution left to you. If it ends up needing a master cylinder, this is probably what happened.

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Agree with Nomad. That would be the other possibility.

 

 

Air in the system could still cause a low "first pedal". Once you have compressed the air bubble, it will take a while for it to expand again.

 

Get someone you trust to help you out. Have them press the brake pedal, and tell them not to bottom it out!

 

Open the screw and watch the fluid on the lines.

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Sounds there is still air in the brake lines. This is DANGEROUS!

 

Bleed them again, run at least one litre of fresh fluid though the pipes. The order I have learned is FR, RL, FL, RR.

 

There could be air in the master cylinder, but start by bleeding the pipes as normal.

 

If the seal is worn in the master cylinder piston then the pedal will be hard initially, but slowly fall to the floor under constant pressure.

I learned the reverse order.

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Thank you very much, that makes a lot of sense. There would also not be any kind of indication (rust, leaks) of a problem with the master cylinder from the outside.

 

So, would you suggest at this point I go ahead and bench bleed the MC? (method help?) Sounds like that's the only way to know for sure it is shot, and at that point replace it.

 

It does sound like I've been bleeding incorrectly. When moving the pedal during the bleed I thought it was supposed to go as far as possible. Should it only be pressed to where I feel it should land? That could be a fundamental I'm missing...as well as a trusted, reliable friend to help with this.

 

I definitely appreciate the guidance you guys are giving me here.

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