'07 LBZ Soft Brake Pedal

[BradL07]

Before I go back to the dealer a 4th time.....

Since new, I've had a soft brake pedal on my '07 LBZ - pedal travel before you get any brake feel, then more pedal travel to actually stop the truck.

Dealer bled the brakes once, and I bled the brakes once, and pedal firms up for a week or more, and then fades to soft again. This is really frustrating in comparison to my '01 LB7, which always had a firm pedal.

I've also noticed that I can depress the pedal all the way to the floor when stopped without too much more effort than a normal stop - said another way, it seems like there is no "bottom" to the soft pedal feel.

Anybody out there seen this before?

BradL07

[cowboywildbill]

I'm guessing but it sounds like it might have a bad master cylinder. Sometimes the vavles in the piston assembly on them screw up or bleed back somehow.Or a bad cup or O-ring inside. I have had this problem on other vehicles, and even had a new replacement one do that. Also saw one that wasn't machined properly, had a bad scratch inside and wouldn't hold a good pedal.
Do you get a brake light warning? I think the brake system is a lemon law saftey issue in most states. If they can't fix it in so many visits they may have to replace the truck.

[SoTxPollock]

I think Cowboywildbill, is right. You have leak by at the master cylinder. Just tell them about the Limon Law and after 5 times if its not fixed they get to give you a new truck, that will probably prompt them to replace the master cylinder.

[BradL07]

Thanks for the replies guys.

I'll definitely alert the dealer, with whom I normally get very good service, that this will now be the 4th service for brake service, meaning one more and she's yours! Although I really would hate to give up on the truck, it's been a good one so far, other than the brakes.

BradL07

[BradL07]

Well, a fourth trip to the dealer yesterday resulted in the standard "nothing wrong, normal operation, it's the hydro boost" explanation for my soft pedal. The shop foreman even advised it's normal to be able to push the brake pedal to the floor in these trucks...I couldn't believe it. He called GM and got a case # assigned - I of course called b.s. on it being "normal" to be able to depress the brake pedal all the way to the floorboard in these trucks.

Anyone else have this same situation? Can you push the pedal all the way to the floor with only a little more effort than what's required to stop the truck?

BradL07

[DmaxMaverick]

You can push the pedal all the way to the floor on these trucks. The hydroboost will do it with enough pedal pressure. The boosting force available is significantly higher than vacuum systems. The PS pump should be growling a little when you do this. Hydroboost has been this way since it was first used. However, if you are pushing the pedal all the way to the floor and still rolling, that's a problem.

Try this test:
Start engine, E-brake off, and enough space in front of the vehicle to allow for some roll. Press brake pedal enough to prevent rolling, and put in D. Depress the brake pedal about 1/3, and pump it between 1/3 and 1/2, never doing more or less. Do not let up more than 1/3 pedal (if you do, you'll have to start over). If the pedal gets softer after a minute or so, or you start to roll, the MC is shot. You can do the same test between 1/3 and barely any pressure (light pedal pressure), but the key is to keep enough pressure on the pedal to prevent the pedal-off venting of fluid, which makes it start over. Try it at varying pedal travels. If it never changes or lets loose (lets vehicle roll), it is normal. A leaky MC will allow the same pedal pressure to gradually work more into the pedal throw, and at some point, may leave you w/o enough pedal travel to hold the vehicle.

[BradL07]

Thanks for the tip DMaxMaverick!

I performed the test you described this evening, and slowly but surely the pedal travel did increase while cycling the pedal, and it got softer and softer at the bottom - it never let the truck go, but it did get softer and softer at the bottom of the pedal travel.

I think I'll try another dealer here in Houston, and explain the whole thing again, and hopefully get them to check the master cylinder.

You would think they explaining that the brakes are losing "pressure" after being bled twice would be enough to get the tech's to check the master cylinder, but they never do, they just road test and say nothing wrong with it.

BradL07

[BradL07]

On the fifth trip to the dealer I finally got them to replace the master cylinder, and all seems well at the moment - nice firm pedal. I'll drive it for a while and see if it holds up.

This has been a tough one to get corrected - no codes, no warning lights, no obvious leaks.

Thanks for the tip DmaxMaverick on cycling the pedal - I actually demonstrated that with the technician Friday morning and it proved helpful.

BradL07