Soft Brake Pedal During Reverse or Low Speed Turn

[Dubbedown]

Noticed this at NJMP while gridding, brake pedal went almost to floor. Not the greatest feeling when you're about to go out for hot laps. Pump the brakes though and pedal comes back. Took it really easy for first few laps and brakes worked fine.

Then it happened again this morning while backing into a parking space. It seems to happen when reversing or maneuvering (or coasting) at low speeds. Does this make sense to anyone? I know it's unlikely I boiled the fluids because I just did a flush the week before and I've yet to encounter fade ad NJMP.

[lmtfi]

Sounds like time to do a bleed - maybe activate ABS during the bleed to make sure you don't have some air in the system.

[ScotcH]

check your wheel bearings.

[ScotcH]

check your wheel bearings.

Also this.

[Dubbedown]

Bled all 4 corners and still the same...

Also not not sure if worth nothing but when the car is off brake pedal stops where it should and has normal resistance. Turn on the car and the pedal travel increases and feels soft.

Also this.

I'll do this next though I didn't hear any typical worn wheel bearing noises. Could you explain how worn wheel bearing would lead to soft pedal? I was thinking it was maybe the master cylinder...

[ScotcH]

Bled all 4 corners and still the same...

Also not not sure if worth nothing but when the car is off brake pedal stops where it should and has normal resistance. Turn on the car and the pedal travel increases and feels soft.



I'll do this next though I didn't hear any typical worn wheel bearing noises. Could you explain how worn wheel bearing would lead to soft pedal? I was thinking it was maybe the master cylinder...

Wheel bearing issues will cause the disc to run out, which will push the pistons in ... ie, knock back. When you then push the pedal, most of the pedal travel goes to push the pistons back to the disc. It's really obvious after paddock manouvers for us when it happens

[MemphisRob]

Sounds like time to do a bleed - maybe activate ABS during the bleed to make sure you don't have some air in the system.

how do you do this?

I thought my issue was a bad brake booster... so I bought a used part and spent all of last Saturday swapping it out. I can tell I have the same issue... albeit not as bad.. but clearly I didn't fix it by replacing the booster, master cylinder, pedal position sensor assembly. It really must be the ABS unit, some air in the lines (although I bled all 4 corners to zero bubbles), or maybe that wheel bearing thing another poster said. I am no professional, so I don't quite understand how the wheel bearing can cause that issue.

But my symptom is like the OP... brakes feel pretty good except right before the car comes to a stop it feels like the brakes let go and you have to add more pedal pressure to make up for it softening up.

[MemphisRob]

Wheel bearing issues will cause the disc to run out, which will push the pistons in ... ie, knock back. When you then push the pedal, most of the pedal travel goes to push the pistons back to the disc. It's really obvious after paddock manouvers for us when it happens

what wheel bearing failure symptoms should I look/listen for to figure out if this could be my issue?

I do have some rotor "burn spots" on my front left but I don't remember seeing any on my other rotors... I will pull the wheels off tomorrow on all 4 corners and check it out.

[ScotcH]

what wheel bearing failure symptoms should I look/listen for to figure out if this could be my issue?

I do have some rotor "burn spots" on my front left but I don't remember seeing any on my other rotors... I will pull the wheels off tomorrow on all 4 corners and check it out.

Just put it in the air, and wiggle the wheels. There should be no play. If there is, find out where ... could be ball joints or other bushings, which won't affect pedal. but if the play is in the bearing/hub, you'll get knockback and low pedal.

[PbFut]

Do you get a relatively firm pedal after pumping up? If so, Wheel Bearing or Pad Taper.

[Dubbedown]

So wasn't air, wasn't pad taper and wasn't bearings. When turning full lock the sway bar end links were pushing in against the caliper. Not sure what would cause this though...