Soft brake pedal culprits?

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nthach

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Me and a friend are working on reviving a 2001 Mitsu Eclipse that had a hard time starting(IAC isn't working - it starts and idles OK when it's warm, I'll clean the idle air passages first before throwing a new IAC valve) and has a constant soft pedal.

I filled up the reservoir with DOT 3 after sucking out the old stuff and I had someone inside the car pump and hold the pedal while I cracked the fittings loose at the MC to bleed it out. The pedal did firm up and drop again - I repeated this a few times. I didn't check the rest of the brake system but my plan once I get a new gasket for my Motive Power Bleeder is to pressure bleed and flush the brake system, replace the pads and rotors and inspect the hard/soft lines and rear wheel cylinders/front calipers for leaks.

If the rest of the brake system is bled and leak free, would the master cylinder be at fault - but wouldn't a internally leaking master cylinder also result in brake booster failure and a hard pedal since brake fluid destroys the diaphragm and you can't compress a liquid?
 
You might have damaged the seals in the MC with the two-man method. Was it firm or soft before you bled the brakes?

EDIT: NM I read the post again. One of the calipers could be leaking into the dust boot but not visibly leaking.
 
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Leaking MC, leaking booster (itself or hose), leaking wheel cylinder(s), leaking caliper(s), leaking brake fittings on brake lines or even bleeders. I've come across those before and the symptom was soft pedal and difficulty stopping the vehicle. Good luck.
 
WAG but a brake hose(s) that's collapsing internally. You can buy some brakes hoses on RA that are pretty cheap yet decent(per an expert on here) esp on that car. I'd start there if isn't anything else that's obvious.

Rock Link, guessed at trim level
 
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Originally Posted by anndel
Leaking MC, leaking booster (itself or hose), leaking wheel cylinder(s), leaking caliper(s), leaking brake fittings on brake lines or even bleeders. I've come across those before and the symptom was soft pedal and difficulty stopping the vehicle. Good luck.

+1 it could be anything. If you aren't able to find it take it to a qualified person because if it gets worse you could have issues stopping when you need it the most.
 
Originally Posted by maxdustington
You might have damaged the seals in the MC with the two-man method. Was it firm or soft before you bled the brakes?

EDIT: NM I read the post again. One of the calipers could be leaking into the dust boot but not visibly leaking.

It was soft before I touched it - my friend(and neighbor) drove it back from the auction with the soft pedal and downshifting to slow the car down. He drove it to where it currently sits.

I'm going to grab some line locks from HF this weekend. I had a suspicion the PO tried to mess with the brakes - the fluid was surprisingly clean for a car that got towed for too many parking tickets and there were markings on the flare fittings. The booster itself is holding vacuum.
 
Originally Posted by SatinSilver
Has Critic looked at it yet?

Not looping him in, the car in question is a sub $1000(if even that) auction find that would be used as a beater.
 
Ok, I thought maybe thats who you were referencing in the OP.
smile.gif
 
When you depress the pedal (all bleeders shut), does it continue to sink to the floor (slowly or veeeery slowly)?
 
Originally Posted by gathermewool
When you depress the pedal (all bleeders shut), does it continue to sink to the floor (slowly or veeeery slowly)?


I would describe the feeling like squeezing a foam ball - the pedal sinks to the floor and it stops.
 
Originally Posted by nthach
Originally Posted by gathermewool
When you depress the pedal (all bleeders shut), does it continue to sink to the floor (slowly or veeeery slowly)?


I would describe the feeling like squeezing a foam ball - the pedal sinks to the floor and it stops.


Sounds like the master cylinder is toast, then. IF the system is truly bled and there are no apparent leaks (i.e., you're not losing fluid with each pump).
 
If you google it there are ways to test your master and booster by how the brake pad feels when you start the car and turn it off. It sounds like your master is toast, and if what you say is true about the bleeders having wrench marks on them then you are not the first to come to this conclusion.
 
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Originally Posted by JamesBond
Why would you even make guesses before bleeding the brakes at each wheel?
Why would you even post such a comment without thoroughly reading the first post?
 
If it's still soft after you bleed, there may not be a leak OR air in the system. Seized from caliper pins will give you a low, mushy pedal, as will mis-adjusted rear drums (if I remember right, base Eclipse's had rear drums). If you have those plastic hose-clamp pliers just pinch off all 4 brake hoses (after you bleed) and pump up the pedal gently. If it firms up, you know the issue is post-brake hose. If it DOES fade, you have a failed master (or possibly ABS hydraulic unit, if equipped).

Remove the hose clamps one corner at a time a repeat the test. When your pedal drops again, you've found your culprit. Or, at least where to further your diagnosis.
 
Originally Posted by nthach
Originally Posted by SatinSilver
Has Critic looked at it yet?

Not looping him in, the car in question is a sub $1000(if even that) auction find that would be used as a beater.

I'm too expensive....
wink.gif
 
Originally Posted by 14Accent
If it's still soft after you bleed, there may not be a leak OR air in the system. Seized from caliper pins will give you a low, mushy pedal, as will mis-adjusted rear drums (if I remember right, base Eclipse's had rear drums). If you have those plastic hose-clamp pliers just pinch off all 4 brake hoses (after you bleed) and pump up the pedal gently. If it firms up, you know the issue is post-brake hose. If it DOES fade, you have a failed master (or possibly ABS hydraulic unit, if equipped).

Remove the hose clamps one corner at a time a repeat the test. When your pedal drops again, you've found your culprit. Or, at least where to further your diagnosis.

That's what I'm going to grab this weekend - https://www.harborfreight.com/4-piece-fluid-line-clamp-set-65116.html

The car does have rear drums but no ABS - I'm dreading having to pull the drums, on Japanese setups, I've always had something fly out.
 
Originally Posted by nthach
That's what I'm going to grab this weekend - https://www.harborfreight.com/4-piece-fluid-line-clamp-set-65116.html

Maybe it's just me... but I wouldn't use fluid clamps on original 2001 hoses. Really I wouldn't use them on brake hoses at all, but really not on 17 year old hoses. Maybe I'm just being superstitious... but if I were in there doing brake work, I would just replace the hoses, and the rear brake cylinders too.
 
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