[accordinGB]

My wife's 03 has always had a low brake pedal. I took the car to a shop, they bled it, and could not get it any higher.

Now, at 150K, I just did the annual maintenance on the brakes, replaced the brake fluid, and replaced the rear pads.

Not running, the pedal pumps up high and hard. After starting, the pedal now drops even more. There are no leaks on calipers or master. They work, but near the floor.

I am at a loss. What are your thoughts?

 

[visionguru]

Classical symptom of air in the brake lines. If you are sure all the air is out, then it's the master cylinder.

 

[accordinGB]

We bled with the boss pumping and holding, and I did get a bubble or two, but not much else.

Any thoughts on the ABS possibly being involved? I have heard of having to bleed it on my bikes.

I will get an MC on order, and keep you posted.

 

[WDHewson]

Have an assistant wrap their hands around the rubber lines when you press the pedal.

The lines should stiffen a bit, but not expand or bulge.

 

[neil hostetler]

Temporarily block all brake hoses with a brake line block off tool (basically a clamp that wont damage the brake line). Brake fluid cannot flow to the wheels, so they are currently taken out of the system. If pedal height is restored, the problem of low pedal is with one of the wheels. This simple test eliminates the master cylinder and ABS unit as possible causes.

 

[accordinGB]

Wouldn't I have a leak if this was the cause?

 

[neil hostetler]

if you had a leak youll see brake fluid on the ground right below the line thats leaking. maybe a rubber brake hose is swelling up

 

[Shrimpy]

Check out this video, it may help.

 

[accordinGB]

Thanks Shrimpy. When I do brake service, pulling the pins, cleaning them, and re-lubing with silicone paste is part of the procedure.

Interestingly, the rears were more gooed up than I would have expected (Wisconsin winters, you know) so I even cleaned out the tube where the pin goes with cotton swabs, ran the top of the pins (where the ridge is that the boot seals around) on the wire wheel, and applied a generous serving of the good stuff.

So that's not it (I did however find that the slider pin on the rear of my BMW bike was rusted tight this fall - shame on me ), so it can happen!

 

[Shrimpy]

Oh well, it was a long shot accordinGB . Another long shot that you may look into is if the rubber portions of the brake lines are faulty. Everywhere there is rubber brake line, have someone pump the brakes as if you were bleeding them. Grab the lines tightly with your hand and see if you can feel the line swell from the pressure. This would indicate that the rubber portion is breaking down internally. Long shot, but a possibility. I had it happen on two different trucks years ago (mid 90's). Good luck.

In Edit: I missed WDHewson and neil hostetler responses above, they were on it before me!!

 

[t-rd]

You need to take the car out and brake extremely hard until you trigger and pulse ABS, this pushes air bubbles out of the ABS modulator. Then you bleed it a couple times after that, it will be good. Speaking from personal experience.

 

[accordinGB]

Thanks T - that should not be too hard to do with the weather we are having right now!

BTW - I took the car to local shop because I saw one of the boots in the rear was torn, and I did not want to fight the rust back there. They ended up saying that those boots are not that important, and to not worry about it. The significant part is that when we picked it up, my wife said the brakes had come back up to where they normally are (still lower than my '07). So, I am returning the MC that I was going to put in it.

 

[WDHewson]

You need to take the car out and brake extremely hard until you trigger and pulse ABS, this pushes air bubbles out of the ABS modulator. Then you bleed it a couple times after that, it will be good. Speaking from personal experience.

Interesting idea.

In snowy weather I often lock 'em up to circulate fluid within the ABS module.

But I admit that I'm unsure of how the flow is handled in the module when it's not engaged.

 

[t-rd]

In fact, you can trigger ABS way easier if you have snow around. It'll pulse like crazy. This is the way to do it, without using an expensive scanner to pulse the ABS modulator.

When I replaced rear calipers years ago, I had the same problem and could not bleed air out, until I went out and braked hard. Then I had air bubbles literally right by the bleeder screws after a few 'hot laps'.

 

[accordinGB]

 

[WDHewson]

In fact, you can trigger ABS way easier if you have snow around. It'll pulse like crazy. This is the way to do it, without using an expensive scanner to pulse the ABS modulator.

When I replaced rear calipers years ago, I had the same problem and could not bleed air out, until I went out and braked hard. Then I had air bubbles literally right by the bleeder screws after a few 'hot laps'.

More than sufficient snow today to give the ABS module a good workout. So I did.