strange brake pedal behavior

[fenixus]

2000 Solara I4 2.2L

Front brake pads are about worn leaving around 6-6.5mm (Wagner Thermo Quiet). they were replaced about 20k miles ago.

After checking on front caliper pins I discovered one (top sliding pin on driver side) sticking, so I re-greased it. brakes were working OK for a few days and they still are when driving ... however ...

today I noticed the brake pedal going deep when car standing in parking lot (no matter what gear) or at full stop. brake fluid level is around half way between FULL and MIN. strange thing is that when car is driving (even locally) then the brake pedal reacts normally being hard half way through.

does it mean the master cylinder is failing or it is something else?
as a summary i can say:
1) it behaves normally when driving
2) at full stop or in parking lot it requires more pressure on brake pedal to keep car stopped (pedal goes deeper).

any thoughts?
thanks.

[tankf2008]

your pads are really low so the brake fluid that is in the system is getting spread thin because the amount of fluid is for the brakes when they have new pads

so... change those brake pads and turn the rotors and you wont have that problem anymore

[fenixus]

really? as simple as new brake pads? I already have new Hawk HPS (front pad set) waiting for install. Planning also on getting calipers/rotors cleaned and sliding pins replaced along with rubber anchor boots.

so no worries about other parts failing (master cylinder, booster, etc.)?

why does it behave different when driving vs at full stop?

[JohnGD]

The puzzling part is the difference between stopped vs driving.

The problem of low pedal could be excessive pad/rotor clearance, air in the system, or a faulty master cylinder.

But you don't seem to have a problem while driving, right? And you didn't open up the hydraulics or touch the master cylinder, right?

I wouldn't want to be changing stuff just yet, but would focus on the parts you touched recently. Probably something in the front calipers area.

Originally Posted by fenixus

really? as simple as new brake pads? I already have new Hawk HPS (front pad set) waiting for install. Planning also on getting calipers/rotors cleaned and sliding pins replaced along with rubber anchor boots.

so no worries about other parts failing (master cylinder, booster, etc.)?

why does it behave different when driving vs at full stop?

[fenixus]

yeah, i was thinking about what i touched. that means no hydraulics at all, nothing baout brake fluid tank, nor master cylinder.
All i touched was calipers and pins. i didn't even touch pistons, also i made sure they are sitting on pads by pumping brakes a few times after re-installation. I wanted to keep current pads for a while, maybe 2-3 weeks more before i attempt messing with brakes again.

what is strange is that i've got this strange problem since some time now, never bothered me a lot, but today i noticed that brake pedal goes quite deep at full stop (e.g. at stop lights on D gear, or on Park before pulling out of the parking lot) and i have to keep it deep to avoid car moving.
also i can feel that brakes are holding from let's say half way pedal depressed, but also i can easily press it almost down to the floor (but not touching it) with no struggle (no hardness feeling) - that is at full stop only.

perhaps my engine low idling revs have anything to do with it?

I'm sick atm (damn sinus infection and a great headache), but once i get over this I will attempt to replace the PCV valve and clean the TB, hoping for idling revs quick fix. not sure if master cylinder compression depends on engine revs or not though (brake booster does maybe?).

[JohnGD]

Check for brake pads binding (crooked even slightly) in brackets. Check for loose caliper bolts (so allowing the caliper actually push itself away).

The only thing with low speed idling is that you may have more engine vacuum than open throttle operation. But I'm not sure this fully explains it or should even make a difference.

However, it may be a coincidence with a master cylinder cups failing just now. But given that's a major safety risk, do check it: while stopped, use up the booster vacuum by repeatedly applying brakes. Then apply light pressure to see if the pedal drifts towards the floor. If so you probably have a faulty MC. If you apply heavy pressure it may seal the imperfections in the cup, sealing the leak. I wonder if this was the difference whey applying brakes while stopped and while driving?

[fenixus]

not sure what you mean by brake pads binding, last time i looked at them all looked normal to me, pads sitting in brackets, both looking like nothing was warped, pads were flat.
caliper bolts all are moving freely with 2 fingers (except one which i had to re-grease), but i think this is how it's supposed to be?

i just returned home from car. i started engine cold, so it was running on "auto-suction" (term my dad used when talking about old diesel cars, not sure if it applies here) and engine revs were around 1500.

I tested brakes as suggested. first give them a few (a dozen) pump ups, then pressed brake pedal slightly. it feels like becoming hard half way down (and i can feel brakes applying), but it doesn't stay firm. its more like i becoming soft again, so i can still push it down.

to better picture it, I have put my left foot (wearing sports shoes) behind the brake pedal and started putting pressure onto it. half way through it becomes hard (there is space between my shoe and pedal), then like a second later it becomes softer so applying slightly more force i can still press it deeper and it goes until i can feel hurting my toes in left foot.

so pumping didn't change anything, engine revs make no difference (tested twice at 1500 rpms and around 600 rpms). tested on P gear, however i tried shifting to D or R while brake pedal was pressed down and it didn't make any difference.

you know, i feel it differently while driving, because i never stomp on brakes like i do in the parking lot (or when standing at stop lights). what i mean is that brakes apply, but perhaps they do not apply as hard as they should then?

not sure what to think about it... should i just wait 2-3 more weeks and replace brake pads and see how it goes? or maybe it's a critical problem and i should be visiting mechanic soon?

EDIT:
was i supposed to pump up the brakes with engine off or on? i did it when engine was running, wrong?

[fenixus]

also i'd like to make sure about correct order of things. i guess i should replace pads first (plus caliper pins which i want to do as well) before messing further with anything, right?

I just hope it all clears up after simple brake project (clean brakes, replace caliper pins and boots, install new pads, top up with fresh brake fluid).

I did some digging and there are few more options (except for pad wear causing the low fluid level and lower pressure) i can see:
-i got air (somehow, quite hard to believe, but maybe) in brake system, if this is the case then i had it for some time as no one touched it for a long time (prev owner never mentioned bleeding brakes or changing fluid it, he even never replaced the pads!)
-brake fluid is old and filled with moisture (never touched it, highly likely) and getting worse with every month
-master cylinder is poor and will have to take it to shop for replacement (and flushing brake fluid)
-brake booster unit failing (?), on this website it says when booster fails the pedal will go deep:
http://autorepair.about.com/od/troub.../ts_brakes.htm
http://autorepair.about.com/od/troub...s_brakes_4.htm


I understand that i could flush/bleed brakes myself, etc. but i just can't picture doing it ... would need to buy 4 jack stands (and take all wheels off), brake bleeding kit (hoses), hire my wife for the job and spend a wonderful weekend afternoon with her while working on brakes (priceless)

[JohnGD]

I don't recommend changing parts right now. That just adds more uncertainty for you. Let's resolve the soft pedal issue first.

1. Sure, if pads and calipers bolts, etc, are as they were, with the now lubed anchor pin, then all is well. Because if your caliper bolts (the ones holding the caliper to the bracket) are loose, some piston travel will be used to compensate for those. I mentioned these because these were the last parts touched, as we always do in all diagnostics is all. And if all this is well, then this rules out excessive brake/rotor clearance that can cause low pedals.

2. I don't expect your power booster to be a problem. Because otherwise you'll have a hard brake pedal instead of a soft pedal.

3. We were talking about checking the master cylinder. It would be easier to modulate the pedal without power assist. So you can leave the engine off. Use very light pedal pressure and see if the pedal continues to sink, as mentioned earlier. If so, the primary circuit may have leaks if you don't have brake action with a short pedal travel (but you said you did while driving??).

4. Then there's always the possibility of air in the system.
4a) You can just bleed it and see. I recommend Castrol GT LMA (Low Moisture Activity) or Valvoline Synthetic. Brake fluid should be replaced every 2 years. I do it roughly every year. It's ~$8-9/qt for material.

4b) Another method is to check for the squirting action in the reservoir. It's kind of hard with the translucent plastic. You pump a few times. Hold. And then release. You should see some squirting action from the vent port (or compensating port) in each chamber. If you have a heavy squirt (sort of like the Yellowstone's Old Faithful), then that circuit has air.

Originally Posted by fenixus

not sure what you mean by brake pads binding, last time i looked at them all looked normal to me, pads sitting in brackets, both looking like nothing was warped, pads were flat.
caliper bolts all are moving freely with 2 fingers (except one which i had to re-grease), but i think this is how it's supposed to be?

i just returned home from car. i started engine cold, so it was running on "auto-suction" (term my dad used when talking about old diesel cars, not sure if it applies here) and engine revs were around 1500.

I tested brakes as suggested. first give them a few (a dozen) pump ups, then pressed brake pedal slightly. it feels like becoming hard half way down (and i can feel brakes applying), but it doesn't stay firm. its more like i becoming soft again, so i can still push it down.

to better picture it, I have put my left foot (wearing sports shoes) behind the brake pedal and started putting pressure onto it. half way through it becomes hard (there is space between my shoe and pedal), then like a second later it becomes softer so applying slightly more force i can still press it deeper and it goes until i can feel hurting my toes in left foot.

so pumping didn't change anything, engine revs make no difference (tested twice at 1500 rpms and around 600 rpms). tested on P gear, however i tried shifting to D or R while brake pedal was pressed down and it didn't make any difference.

you know, i feel it differently while driving, because i never stomp on brakes like i do in the parking lot (or when standing at stop lights). what i mean is that brakes apply, but perhaps they do not apply as hard as they should then?

not sure what to think about it... should i just wait 2-3 more weeks and replace brake pads and see how it goes? or maybe it's a critical problem and i should be visiting mechanic soon?

EDIT:
was i supposed to pump up the brakes with engine off or on? i did it when engine was running, wrong?

[JohnGD]

Again, let's try to identify air in the system or MC fault. You may decide to take it to a knowledgeable mechanic as well if there is difficulty in pointing to the air or MC given the safety issue. Let's not touch other parts at this time and introduce more uncertainties.

Properly maintained disc brakes are self adjusting. You can wear the friction nearly down to the metal and essentially feel like you have new pads. (The pad's ability to dissipate heat decreases however, but that's another story)

Brake fluid level between Max and Min has no play on the pedal in a properly adjusted system. You wouldn't know the difference that's why we have the brake fluid level warning light.

No, a non-boosting power booster will cause a hard pedal problem, like you don't have power brakes. Unless the push rod is out of adjustment (nobody touched it, right?), you won't have a soft pedal problem.

Originally Posted by fenixus

also i'd like to make sure about correct order of things. i guess i should replace pads first (plus caliper pins which i want to do as well) before messing further with anything, right?

I just hope it all clears up after simple brake project (clean brakes, replace caliper pins and boots, install new pads, top up with fresh brake fluid).

I did some digging and there are few more options (except for pad wear causing the low fluid level and lower pressure) i can see:
-i got air (somehow, quite hard to believe, but maybe) in brake system, if this is the case then i had it for some time as no one touched it for a long time (prev owner never mentioned bleeding brakes or changing fluid it, he even never replaced the pads!)
-brake fluid is old and filled with moisture (never touched it, highly likely) and getting worse with every month
-master cylinder is poor and will have to take it to shop for replacement (and flushing brake fluid)
-brake booster unit failing (?), on this website it says when booster fails the pedal will go deep:
http://autorepair.about.com/od/troub.../ts_brakes.htm
http://autorepair.about.com/od/troub...s_brakes_4.htm


I understand that i could flush/bleed brakes myself, etc. but i just can't picture doing it ... would need to buy 4 jack stands (and take all wheels off), brake bleeding kit (hoses), hire my wife for the job and spend a wonderful weekend afternoon with her while working on brakes (priceless)

[JohnGD]

And right! It's normally a 30 minute job, a Harbor Freight 1/2" torque wrench for lug nuts (maybe a 1/4"-drive inch-pound torque wrench for the bleeder plug), a plastic tube and bottle, and one scissor jack from the trunk.

But if you haven't done this before, it would be better to get a shop to diagnose the problem. I suppose you can get the fluid flushed first, about $100 at the dealer, because the MC replacement would be about $350 ($200 MC+labor?).

Originally Posted by fenixus

I understand that i could flush/bleed brakes myself, etc. but i just can't picture doing it ... would need to buy 4 jack stands (and take all wheels off), brake bleeding kit (hoses), hire my wife for the job and spend a wonderful weekend afternoon with her while working on brakes (priceless)

[SexieWASD]

Originally Posted by JohnGD

Properly maintained disc brakes are self adjusting. You can wear the friction nearly down to the metal and essentially feel like you have new pads. (The pad's ability to dissipate heat decreases however, but that's another story)

Sure does, I've seen someone wear completely through the pad. They only noticed something was wrong when the piston started dragging on the cooling fins in the rotor, even then they said that they only wanted new pads put on, not rotors.

[JohnGD]

Also, you adjusted the transmission throttle linkage, right?

Try adjusting it back to where it was before, which should be with the little silver cable stopper showing 1mm out of the rubber tube tip.

Now does the brake feel return to what it was like? If so, just go ahead and have the brake fluid flushed and see how it works out.

Originally Posted by fenixus

also i'd like to make sure about correct order of things

[fenixus]

Originally Posted by JohnGD

Also, you adjusted the transmission throttle linkage, right?

Try adjusting it back to where it was before, which should be with the little silver cable stopper showing 1mm out of the rubber tube tip.

Now does the brake feel return to what it was like? If so, just go ahead and have the brake fluid flushed and see how it works out.

hmmm, yeah i did adjust it a little when in my noobness trying to compensate for lower than expected idling RPMS (forgot that ECU actually controls idling revs). but how can this have anything to do with brakes system, i don't understand ?
i also adjusted the kick back cable (this can stay right?), it's the one with no rubber tip.

will reverse the throttle adjustment as the first thing and re-test brakes on engine off.
you know I have had soft brake pedal problem from a long time (since i bought it), but since i had new pads I could hardly notice that. it becomes more visible (i know it shouldn't) with more pads wear somehow.

Today I have some spare time today, so will try some suggestions soon.

[JohnGD]

Are you idling at about 700 rpm/ If you're higher then it's like you're trying to accelerate from a stop. You're going to need more brake.

Ok. The top cable, which pulls on the throttle lever as you step on the gas. That's the accelerator cable. It should have about 3/8-1/2" deflection from a straight line.

Verify that the pedal can open the throttle valve all the way and releasing it will close it.

After this is set, the lower cable, which is the throttle linkage. This is one with the rubber tube over the silver cable stopper that comes out of the metal tube's threaded end. This is the 1mm out thingy I mentioned.

The throttle linkage should be adjusted back to where it was before. It raises the line pressure in the transmission.

I mean, you can change them later on (but hopefully not by much). But for diagnostics we should try to get everything back to the "factory default setting" as possible so we're not working against other variables.

If these will bring you back to what it was before, then I think we can proceed to have the system flushed with new fluid and see if the soft pedal goes away. That way you can eliminate one more thing when diagnosing the master cylinder.

Originally Posted by fenixus

hmmm, yeah i did adjust it a little when in my noobness trying to compensate for lower than expected idling RPMS (forgot that ECU actually controls idling revs). but how can this have anything to do with brakes system, i don't understand ?
i also adjusted the kick back cable (this can stay right?), it's the one with no rubber tip.