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Soft brake pedal after hard stop through pothole

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58K views 16 replies 7 participants last post by  Alpine-X  
M
#1 ·
Hello all,

My wife has a 2006 Mazda 3s. The other day she had to swerve to the left to avoid another car and while on the brakes hit a decent sized pothole with the left front wheel. Since then, the brake pedal is soft and goes halfway to the floor before engaging brake pressure. The brakes worked perfectly up until that point. The brakes still work and will stop the car, but the brake pedal feel and engagement is way off.

I've physically inspected all the brake lines and calipers for damage and bled the system and there are no leaks and no damage. Fluid is clear. While brakes are engaged, there is no ballooning of the rubber lines. There is ~1/4" material left on all the pads and rotors are good.

There are no Check Engine light or ABS system light on. Brake booster holds a vacuum. No leaks on the master cylinder.

I've read a couple of posts that the ABS system could be in a weird state softening the pedal and to try a few hard stops and that might reset it. It rained tonight so I did 5 or more hard ABS activated stops in a parking lot and the soft pedal remains.

I also ran across an idea of an energy absorbing brake pedal. If so, is there a disposable part that could be broken and needs replacement?

Anyone have any ideas on what could be the issue? Or anyone have a way of resetting the ABS controller without using the Mazda diagnostic tool?

Thanks,
Mizzleman
 
M
#2 ·
UPDATE - I replaced the brake master cylinder after a bench bleed today The brake pedal is slightly firmer but still not the same. When pressing the pedal there is some initial slowing of the car then softens a bit as the pedal travels and then firms up towards the end of the travel.

Not sure where to go from here. Any suggestions?

Thanks,
Mizzleman
 
#3 ·
Are you sure there is no air in the entire system. I used a pneumatic brake bleeder from PA this summer as I knew there was air in my system and it cured my problem immediately. I wish I purchased one of these 20 years ago! Was on sale for about $30-$40.
 
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A
#4 ·
What you are describing is a classic case of pad knockback, typically demonstrated by a soft pedal that when pumped, will become normal... Until the next turn. The usual cause of this behavior is a worn out or damaged wheel bearing or hub assembly... This can easily be caused by hitting a large pothole. Check both bearings on that side for looseness/runout. You may need a professional to do this check for you. Basically what is happening is the rotor is moving in a vertical axis relative to the caliper bracket which pushes the pads away from the rotors under free wheeling conditions.
 
M
#6 ·
Ashmostro,

That's an interesting take. The car did not exhibit any kind of evidence to a worn wheel bearing prior to the incident. The car wasn't driven very far after hitting the pothole and I checked the pads and the surfaces are parallel to each other. The car does have 120K miles on it, though. I'll check it out.

Lumber-jack --- I decided to pull out the master cylinder and re-bleed it again and will follow with another bleed at each wheel cylinder again to make sure there isn't any air in there somewhere.

Thanks for the help, guys!

Mizzleman
 
M
#7 ·
Hey,

After pulling out the MC, the pushrod seems to have about 1/8" of back and forth movement in it. Is it adjustable? As far as I can tell, I don't see a jam nut on it to keep it in position, so I'm assuming no. But if anyone can tell before I replace the booster, that would be great.

Thanks,

Mizzleman
 
#9 ·
master cylinder has a front and back section and there is a piston that will move and shut off compartment if you should have a pressure loss so you will at least have front or back brakes.

Personally I don't think it is a bearing but I am diagnosing over the internet and would look at the simple things first like air in system as I said before.
 
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#8 ·
A point of clarification - I'm not suggesting that a bearing might be worn, but that it (or a related part) could have been damaged by the impact.

Hopefully you are able to diagnose this soon - I can imagine this issue is quite frustrating!
 
M
#10 ·
FIXED!

All,

I purchased a remanufactured brake booster and it had the same amount of freeplay in the pushrod as the original one on the car so I skipped installing it.

I put the master cylinder back in and bled the brakes again. All good there!

Went out to test drive and the soft pedal remained.

Drove over to the gravel road I used earlier and made 10+ or so ABS activated stops. That fixed it!

When I first used the road, it was night and couldn't see the surface very well. Turned out it was hardened dirt that was about as hard as asphalt. I picked specific areas in the road where the surface was loose this time to jam the brakes on. After doing that quite a few times, the pedal hardened up.

So, it seems like fixing a soft pedal by doing ABS activated stops on a loose surface is confirmed, IF the rest of the brakes system is in order. But it seems to take 10-20 stops rather than 5-6 as I had earlier seen in other posts.

I hope this info can help someone in the future. It sure was a PITA!

Thanks for all the help!

Mizzleman
 
#12 ·
mizzleman said:
FIXED!

All,

I purchased a remanufactured brake booster and it had the same amount of freeplay in the pushrod as the original one on the car so I skipped installing it.

I put the master cylinder back in and bled the brakes again. All good there!

Went out to test drive and the soft pedal remained.

Drove over to the gravel road I used earlier and made 10+ or so ABS activated stops. That fixed it!

When I first used the road, it was night and couldn't see the surface very well. Turned out it was hardened dirt that was about as hard as asphalt. I picked specific areas in the road where the surface was loose this time to jam the brakes on. After doing that quite a few times, the pedal hardened up.

So, it seems like fixing a soft pedal by doing ABS activated stops on a loose surface is confirmed, IF the rest of the brakes system is in order. But it seems to take 10-20 stops rather than 5-6 as I had earlier seen in other posts.

I hope this info can help someone in the future. It sure was a PITA!

Thanks for all the help!

Mizzleman
Click to expand...
Did this ever happen again on your car? on my car it is re-occurring and hard braking activating the ABS does fix this but it become aggravating when it happens so often in a town where every road had pot holes and was hoping for a more permeant fix.
 
J
#15 ·
I know this is a very old thread but it's the same issue I've experienced on my 2006 Mazda5. I've had this happen 2 times and am wondering what the root cause of this is. As far as I can tell, it's not caused by worn brakes, air in the fluid, or old fluid. In my instances, the brakes have gone soft after some hard(ish) braking event. The brakes at that point stop "grabbing" on light peddle pressure and instead require the pedal to be pushed far down before the brakes engage enough to slow the vehicle. In both instances I was able to get brakes working normal again by performing a hard (ABS engaging) stop from approx 15-20 MPH on a gravel road. I've never had anything like this in any other vehicle I have owned or driven and it is a safety issue that almost seems like a defect that should be under recall. I'm curious if anyone knows the real underlying cause for this.
 
#17 ·
I had the same issue happen today on my (wifes) 2011 Mazda 5.. She hit the brakes hard just as she hit a pot hole on a dirt road, the brake pedal immediately afterwards went soft and wouldnt return to normal. It would stop the car, but only after the pedal went almost all the way to the floor. I took a quick look and everything seemed normal with the brakes, tires etc..
I read some forums and people suggested that the ABS module was in a weird state where it was basically still "on" continuously, meaning it was not allowing full pressure to build in the system.. The fix strangely enough is to activate the ABS system again by hitting the brakes hard at about 20mph on a dirt road (allowing the tires to break contact with the road).. this re-activation of the ABS system 'resets" it.. I guess you could also do it on pavement but it might be hard to get it to lock up with the pedal being so soft..
I found my closest dirt road and gave it a try, and immediately after the first hard stop (with abs activating) the brakes came back to normal with no pedal movement anymore..
Saved me a bunch of brake bleeding and who knows how much time and money..
ps, some of the forums, said it could take multiple hard stops to get it to reset..
 
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