BRAKES losing presure! any ideas

[sbsisco]

Has anyone had this problem and/or have any suggestions for a fix. My 06 H3 (25k miles) looses break pedal under light breaking but not under normal to strong breaking. It normally has excellent pedal but every now and than under light presure it will quickly drop half way to the floor..? I''ve just recently discovered that at highway speed I can get it to do this by lightly holding the pedal with my left foot and with in a small amount of time it''ll drop, if i ease up just a little and reapply it''ll drop a little further and if I stay at it I can work the pedal all the way to the floor. No warning messages, no leaks, plenty of fluid and excellent pads...Of corse it won't do it when its returned to the dealer so I've got to trouble shoot this one on my own due to the lack of quality shops/mechanics in my area to trust working on my truck. I'm plannig a trip to sw colorado next month and bad breaks on black bear pass are not a good combo...any ideas, my next move is to bleed the system in the morning just to see if it could be something that simple...but i have a hard time believing this will help but i guess it could have left the factory with air in the lines???

[wpage]

From what you describe it sounds like air in the line.

[Yetti]

Ok lets start slow.

1. if you pull up on the pedal with your toe does it make any clicking noise? if so the pedal might have been held down by the brake light switch. it can and will prevent the pedal from coming to the top and letting the master cylinder refill after a brake apply.

2. if you ease the pedal down like you discribed is there a point where you feel the brakes pick up?
I suspect if the brake light switch issue doesn't fix the problem then I would put in a new master cylinder. the reason being the master applies the rear brakes first. then as it picks up load it applies the fronts. that way the systems has the default of not letting the fronts lock up first and causing an accident. I would say the master has worn out just enough to vent pressure around the seal on the apply piston under light load. if you hit it fast it applies normal because the seal is forced to stretch to meet the bore imperfections.

[sbsisco]

My thoughts as well on the master cylinder. thats my next investment if todays bleeding doesn't help. I've had a lot of master cylinders go out on classic cars I've owned and my way of testing for that was to sit stopped while pushing hard on the pedal and waite to see if it'll slowly start to sink to the floor. This won't do that..yet,,,it may later on if its is an o ring in the MC. My main reason for posting is to see if anyone has had this issue and what it ended up being. I only have my years of mechanical experience on the old cars without all the extras to the brake system. Tearing into a new hummers brake system seams a little scary to me if it could be caused by some kind of sensor or eletronic issue I don't understand...all comments or suggestions are greatly appriciated...thanks...

[sbsisco]

Bleeding helped but still has the symptoms. not the break light switch, although that was a great suggestion that I haven't thought of. It does find a stopping point about mid pedal so I'm sure your right, its a rear brake issue with the master cylinder....did discover the hard way that it has to be running to bleed the brakes. with it shut off no amount of pumping with push fluid to the calipers....with it running we bled thru each wheel 6-7 times and never really got any air in our fluid recovery line. As supprising as this is, I can find countless h2 master cylinders cheap online but nothing for h3 or colorado trucks. plenty of forums complaining of this issue on colorad truck sites I found tonight. not sure if they share the exact same master cylinder but i did find the caps have the same part no. and thats as far as i got today. the only dealer near me has seen it twice and says nothings wrong so until it has a total failure I guess warranty is out of the question......hmmm..

[Big Dad]

This is probably going to sound smartassy but it's not intended to be.

Have you ever used your e-brake?

Till you get this anomaly figured out I'd suggest that you actually use the e-brake a few times, you know, in case you ever really need to you'll know how it reacts.

A lot of people just take the e-brake for granted and never use it or never really know how to use it when the immediate need arises.

[sbsisco]

no offense at all...actually with my trip planned to colorado next month and a known break issue I can't figure out ..has got me motivated to experiment with that very thing - just incase. I'm pretty shure it would be a really low chance I'd completely loose front and rear parts of my master cyl in the same trip but it could happen. I'm taking it in to another dealer in the morning and hopefully with the explanations its going to the san juans they'll look a little closer than the others have...at the very least I'll keep my reciept to prove i tried to get it fixed incase those brakes force me to take the fast way down black bear pass..seriously, with it in 4 wheel low and the fact the pedal has yet to go all the way to the floor (ebrake as back up plan)...I'm pretty certain I can keep it on the trail but I'd feel a lot better if I can get that MS changed out. At least it won't take me by suprise, its been doing it long enough im getting used to it.

[Big Dad]

I hope you don't take this $hit the wrong way...I'd hate to hear that someone crashed while using the ebrake....

You do know that while you're driving it's best to pull the brake release handle/ lever (depending on the application) while you apply foot pressure to the ebrake, that way if you start to lock up the brakes you can ease up on the ebrake and it'll retract to it's normal position instead of locking up the brakes.

Again, sorry to imply the obvious but a lot of people don't know how to really brake using the ebrake.

As far as the problem goes, I haven't noticed anything like it with my 3. I have about 22k on it at this point. I'm sure you'll figure it out though.

[timgco]

Document every time it has failed. Since this a safety issue, and you local dealer cannot duplicate it, this is one of those times you may want to get the factory rep involved. I cannot tell from the avatar, but it looks like you might be lifted????? IF that's the case, check your added breaklines. I had a similar experience with a lifted truck last year. It turned out to be on the fitting was bad AND that same line had swelling also. It was ready to go but not obvious at first glance. ...just a thought.

[evldave]

This is exactly what happened to me at about 15-20k. It ended up being air in the brake lines - the dealer had to bleed them 3 times before they were fine. I'm still hyper-aware of the issue, and sometimes it feels like they are getting squishy. Most dealers have a fancy machine - it takes them all of 15 minutes! I'm taking mine in for some other warrantee work later this week and will ask they rebleed them.

Keep pushing your dealer. By the time I was able to get in the dealer (mine started in California and I live in Washington), I was on long grades and almost completely out of brakes...if your problem is the same as mine, it will get worse and you will likely end up out of brakes. Hope this helps

[Ryan Graham]

Brakes can't just all of the sudden "get air" in the lines. Sounds like a bad master cylinder, but older chev trucks had a problem with the abs "dump" valve doing the exact same thing. I'm with you though on not messing with the H3's system. With the traction control and abs and all the other stuff bolted to the master, you may never get it to bleed out properly if you did replace it. If a master cylinder is failing, you can get the pedal to the floor the same way you described and any shop should be able to check the same way you did. Sorry you have such lame mechanics out your way.

[pdsq99f4]

Sounds like your master cylinder. I've replaced a few and it is not fun due to the H3's electronic booster and ebcm being bolted to it. There is an bleed procedure that you need a Tech2 scan tool to perform.

[bsfh3]

2006 H3. I have been having a problem with lights coming on. I had it towed to the dealer and @11k miles. They replaced the brake switch. The light came on, at 17k, the ebcm needed to be replaced. At 25k miles, another ebcm needed, once again at 29k master was ordered. The dealership closed and I couldn't get the part installed until it happened again at the new dealer. It finally came back on and the dealer said to resurface rotors? I didn't really understand why because I had the brakes done only @10k miles back. I was told we have to follow procedure, and the service advisor told me that they found the brake problem (kinda by accident). Turns out contamination of brake fluid from factory they believe. The brakes lines were bulging, broken inside near connector. Parts have to be located now, I am just mad that I bring it in all the time, on time, for service and concerns. Now they notice this after all this time? I need this posted just to make people aware. Thank goodness nothing happened, I always have my young child in this car. I have been nervous driving it because of the concerns, now I am afraid. I was told all the parts which have plastic on it are getting replaced. The regional manager told me that they have to search for parts because they have been having this problem with the vehicles...