brake pedal sometimes goes mushy

[Good351]

Hello everyone!
I've recently had the brake pedal on my 03 Runner sometimes go mushy.. Like it takes a lot of travel to start engaging the brakes. It's probably 50/50 now working correctly or requiring extra travel. Also, if it does require extra travel, I can then "pump up" the pedal and force it to act normal.

I've read a few posts on checking the brake booster pump.. How does one check this or listen if it is working?

Rear brakes are 2 years old, fronts just over a year (all new parts).

 

[That_Titanium_4RNR]

Hello everyone!
I've recently had the brake pedal on my 03 Runner sometimes go mushy.. Like it takes a lot of travel to start engaging the brakes. It's probably 50/50 now working correctly or requiring extra travel. Also, if it does require extra travel, I can then "pump up" the pedal and force it to act normal.

I've read a few posts on checking the brake booster pump.. How does one check this or listen if it is working?

Rear brakes are 2 years old, fronts just over a year (all new parts).

Start by getting your brake fluid flushed and bled

 

[Good351]

Start by getting your brake fluid flushed and bled

Oh, I should have stated that the brakes were bled about 2 months ago when a faulty caliper was replaced under warranty.

 

[That_Titanium_4RNR]

Oh, I should have stated that the brakes were bled about 2 months ago when a faulty caliper was replaced under warranty.

Next step is turn the car on and then open the hood. Have someone get close to the master cylinder while you press the brakes. They should hear an electric buzzing type sound when you depress the brakes. It should happen every time the brakes are depressed I believe.

 

[95supra]

could be a stuck caliper or possibly a front wheel bearing. check both front wheel bearings for excessive play. this with cause the brake pedal to have too much travel at times.

 

[AuSeeker]

Next step is turn the car on and then open the hood. Have someone get close to the master cylinder while you press the brakes. They should hear an electric buzzing type sound when you depress the brakes. It should happen every time the brakes are depressed I believe.

If everything is working correctly, the electric motor will come on when you first start the engine and then about every 3 depressions of the brake pedal and stay on for 5 to 15 seconds, if it comes on every time you press the brake pedal or the motor runs too long the accumulator is not holding pressure and should be replaced, the motor should be relatively quiet but you should be able to slightly hear it from the driver's seat, if it's really loud and noticeable the motor maybe worn and either needs to be rebuilt or replaced or it could stop working all together.

 

[A70BoosTFienD]

Hello everyone!
I've recently had the brake pedal on my 03 Runner sometimes go mushy.. Like it takes a lot of travel to start engaging the brakes. It's probably 50/50 now working correctly or requiring extra travel. Also, if it does require extra travel, I can then "pump up" the pedal and force it to act normal.

I've read a few posts on checking the brake booster pump.. How does one check this or listen if it is working?

Rear brakes are 2 years old, fronts just over a year (all new parts).

Im having the same issues as you OP. Mine however when it does have a low pedal i hear this fluid squish sound which concerns me... I bled them but no bubbles were found which concerns me further.

If everything is working correctly, the electric motor will come on when you first start the engine and then about every 3 depressions of the brake pedal and stay on for 5 to 15 seconds, if it comes on every time you press the brake pedal or the motor runs too long the accumulator is not holding pressure and should be replaced, the motor should be relatively quiet but you should be able to slightly hear it from the driver's seat, if it's really loud and noticeable the motor maybe worn and either needs to be rebuilt or replaced or it could stop working all together.

Is rebuilding the unit easy enough to do on a bench with standard tools or does it require some extra steps?

 

[AuSeeker]

Im having the same issues as you OP. Mine however when it does have a low pedal i hear this fluid squish sound which concerns me... I bled them but no bubbles were found which concerns me further.



Is rebuilding the unit easy enough to do on a bench with standard tools or does it require some extra steps?

The complete master cylinder assembly is quite complicated and very expensive because of the ABS system, the electric motor/pump/accumulator brake booster portion, etc. and of course the actual master cylinder portion.

The actual master cylinder portion is not too different from old school master cylinders and can be rebuilt...BUT the portions mentioned above aren't that easy to rebuild if at all...and if the actual master cylinder portion isn't showing signs of leaking where the push rod from the brake pedal enters into it, it shouldn't need to be rebuilt.

That all being said Toyota does sell a kit for the actual master cylinder portion and there is a section in the Toyota shop manual on doing the rebuild.

I can't give you a part number for the kit or a link to the shop manual section for doing the rebuild but both have been posted at least once if not more on this forum.

 

[Good351]

could be a stuck caliper or possibly a front wheel bearing. check both front wheel bearings for excessive play. this with cause the brake pedal to have too much travel at times.

Well, I checked my wheel bearings and the right front is toast.

I also listened for the electric motor on the master cylinder. Every 3 pedal pushes I could hear the motor turn on for a few seconds, then shut off. So I'm thinking it is ok..

I'll have the wheel bearing replaced and see how the brakes respond.

 

[95supra]

Well, I checked my wheel bearings and the right front is toast.

I also listened for the electric motor on the master cylinder. Every 3 pedal pushes I could hear the motor turn on for a few seconds, then shut off. So I'm thinking it is ok..

I'll have the wheel bearing replaced and see how the brakes respond.

Im pretty sure the bad wheel bearing is the issue. I had the same problem/symptoms you have and the wheel bearing fixed all the issues with my brake pedal travel and also the pump motor coming on too much.

 

[Good351]

Well i finally got the wheel bearing replaced, and I'm happy to report that the brakes are back to normal!

Thanks everyone for your suggestions!

 

[earthrealm]

Well i finally got the wheel bearing replaced, and I'm happy to report that the brakes are back to normal!

Thanks everyone for your suggestions!

wow, wouldnt have believed a faulty wheel bearing could throw off the brakes like that.making the pedal mushy:toilet:

could someone care to explain the physics behind that??

 

[That_Titanium_4RNR]

wow, wouldnt have believed a faulty wheel bearing could throw off the brakes like that.making the pedal mushy:toilet:

could someone care to explain the physics behind that??

my theory is that when a wheel bearing fails sometimes it will start to bow out a bit. Sort of like a car with a lot of negative camber. When this happens the disc is on the same axis as the wheel hub and the pads and caliper are on the axis as the spindle (the correct axis with little to no camber). Because of this difference in axises (sp?) the brake pads are only slightly engaging and causing slippage and soft pedal issues. My buddy has a ram with wide wheels and spacers and had the same type of thing going on with his until we fixed the wheel hub. Once we did that, the 2 axis were brought back into alignment and the brake calipers and pads were meshed perfectly again allowing for a nice full contact patch

 

[95supra]

my theory is that when a wheel bearing fails sometimes it will start to bow out a bit. Sort of like a car with a lot of negative camber. When this happens the disc is on the same axis as the wheel hub and the pads and caliper are on the axis as the spindle (the correct axis with little to no camber). Because of this difference in axises (sp?) the brake pads are only slightly engaging and causing slippage and soft pedal issues. My buddy has a ram with wide wheels and spacers and had the same type of thing going on with his until we fixed the wheel hub. Once we did that, the 2 axis were brought back into alignment and the brake calipers and pads were meshed perfectly again allowing for a nice full contact patch

wow very good description of whats going on when the wheel bearing has excessive play. the only thing I will add is, the reason the brake pedal gets mushy or has more travel is because the rotor being on the wrong cambered angle causes the brake pads to push the caliper pistons back in the caliper way more than they should be pushed in.