Brake pedal is 1" off the floor (when applied)

energyhog · January 30, 2014

for 2007 Express 3500 RV....pumping pedal makes no difference in reserve heighth; operation seems normal. Booster & master cylinder check OK using shop manual as guide. Truck stops it's just that pedal is too close to the floor for me. Replaced rotors and pads; any suggestion as to what to look at next?

LeoS41280 · January 30, 2014

If the rear brakes are drums, try adjusting them.

KMGZ400 · January 30, 2014

I would re bleed the brakes and go from there

Doug_Scott · January 30, 2014

for 2007 Express 3500 RV....pumping pedal makes no difference in reserve heighth; operation seems normal. Booster & master cylinder check OK using shop manual as guide. Truck stops it's just that pedal is too close to the floor for me. Replaced rotors and pads; any suggestion as to what to look at next?

There are not many causes of a low pedal. The most common on a 4 wheel disc brake system is air in the system, If the system is using floating calipers, seized or sticking slides on the calipers can also cause a low pedal.

If the brake fluid is original, change it completely. This is not as easy as it used to be. ABS adds a complexity to the flushing and bleeding job. Reason for old brake fluid causing a low pedal is due to brake fluid being hydroscopic. That means it absorbs water/moisture. Brake fluid that is contaminated with moisture will boil at a much lower temperature, and once it boils, you end up with air in the system. Take a look at the colour of the brake fluid, the darker it is, the more moisture there is in it. Change the entire volume of brake fluid.

Something you can try is blocking off each of the 4 calipers using locking pliers on the flex hoses. Once they are all blocked off, see if the brake pedal movement has changed. If it is now very short travel, and hard, you will know the reason is after the locking pliers. Take one pair off at a time and check pedal travel after removal of each pair of pliers. The pair that creates the greatest change in pedal movement is where the issue is.

If after all flex hoses are blocked the pedal travel is still to long of travel, that pretty much tells you there is air or some contaminents in the system before the flex hoses. Usually bleeding brakes will correct it.

There is the possibility of the ABS system malfunctioning causing a low pedal, but, that should also cause the ABS light to come on.

energyhog · January 31, 2014

Thank you all for the suggestions. It looks like I have a handful of steps to check in sequence, from your feedback......

1. I did have the rotors and pads replaced but this problem occurred a few trips before that, but I will have the slides on the calipers checked for being seized or sticking.

2. I also thought that (maybe) the master cylinder is somewhat bypassing internally on the front brakes whereas I'm really stopping mostly using the rear disk brakes. Makes sense, since the rug does not stop like it use to. Therefore I will R&R the master cylinder.

3. Anyway, fluid is slightly darker than new and I thought that heat might be the source but I did not think of boiling and therefore allowing air in system; this all started after driving down a curvy mountain road for a few hours. Therefore I will change the fluid and bleed the breaks.

I live a 1/2 day from a repair facility that rig fits in (Class C RV) so dropping off is a pain and multiple trips while local mechanic figures it out then sleeps on it is a pain. Your feedback will save time and buying parts before hand is not the issue. Thanks again for your help