Possible Hydo Boost problem??

[bowhuntrrl]

Ok, I'm pretty new to my 2005 Avalanche, bought it back in August in Atlanta and drove it home to the Northeast. In total, I've put about 12K miles on it since then so I know it pretty well. Always when I start the car, I have my foot on the brake, and got used to it "kicking" me in the foot when the engine started. Also, when stabbing the brake hard, it would kick me back, I loved the rock hard pedal and fantastic breaking power. This past weekend, I took a 600 mile trip up through the Adirondack mountains, and noticed that I was using a lot of pedal travel and that my braking power seems diminished a bit. How can I tell if it's a hydro boost problem and how common are problems with that system?? The power steering reservoir is full and the tell tale window on the unit shows fluid. It no longer "kicks" me when I start it. I appreciate any help on this. Thanks.

[maxwedge]

Is the brake fluid full and clean, how is the brake system in general, remember the hydroboost is just an assist. To check it the pressure would have to be tested.

[GMCustomerService]

As the hydro-boost is a part of the anti-lock brake system, I just had a quick question. Are you seeing your ABS light come on when you power up your Avalanche? It should do so and stay up for a few seconds before turning off under normal operation.

Best,
Sarah
GM Customer Service

[j cAT]

Originally Posted by bowhuntrrl

Ok, I'm pretty new to my 2005 Avalanche, bought it back in August in Atlanta and drove it home to the Northeast. In total, I've put about 12K miles on it since then so I know it pretty well. Always when I start the car, I have my foot on the brake, and got used to it "kicking" me in the foot when the engine started. Also, when stabbing the brake hard, it would kick me back, I loved the rock hard pedal and fantastic breaking power. This past weekend, I took a 600 mile trip up through the Adirondack mountains, and noticed that I was using a lot of pedal travel and that my braking power seems diminished a bit. How can I tell if it's a hydro boost problem and how common are problems with that system?? The power steering reservoir is full and the tell tale window on the unit shows fluid. It no longer "kicks" me when I start it. I appreciate any help on this. Thanks.

the power steering pump is the power generator. these gm pumps have a very common defect where the pump pulley shaft breaks internal to the pump. when this occurs you loose braking and steering.

In your case the brake pedal pulses. this would be the ABS. remove the abs fuse and see if this changes. have vehicle ABS codes checked. if any found post here .

normally the ABS will only pulse when the vehicle is moving , not on first starting the engine.

[bowhuntrrl]

Originally Posted by GMCustomerService

As the hydro-boost is a part of the anti-lock brake system, I just had a quick question. Are you seeing your ABS light come on when you power up your Avalanche? It should do so and stay up for a few seconds before turning off under normal operation.

Best,
Sarah
GM Customer Service

All self tests on ignition start up are good. No warning lights are showing.

[bowhuntrrl]

Originally Posted by j cAT

the power steering pump is the power generator. these gm pumps have a very common defect where the pump pulley shaft breaks internal to the pump. when this occurs you loose braking and steering.

In your case the brake pedal pulses. this would be the ABS. remove the abs fuse and see if this changes. have vehicle ABS codes checked. if any found post here .

normally the ABS will only pulse when the vehicle is moving , not on first starting the engine.

Maybe I haven't communicated properly. I'm not really getting any pulsations in the pedal, I really don't think it's an ABS problem. I always was in the habit of putting my foot on the brake as I start the vehicle, a carry over of starting procedure from a past vehicle that I owned that required that sequence. So when i would start the engine, with foot on the brake, I would get one quick "stab" in the foot as the pedal got very hard. I always thought this was normal. Also, when driving, if i hit the brake pedal fast and hard, I would also feel that hard resistance kick me back, giving me a wonderful, hard brake pedal and fantastic braking with little pedal effort. Now, it feels like a normal brake pedal without that rock hard feel, and it also requires higher pedal pressure and I have noticed that with repeated pushing, the pedal goes down. I just don't know how the Hydro boost is supposed to work. I took it to a tech yesterday who owns a 2004 Yukon and he thought the pedal felt good to him. What I do know is that something is different. Today looking at it, I noticed some oiliness on the bracket below the master cylinder. There also appears to be an oily mist on the firewall at the rear of the Hydo B unit. I would guess that's significant in some way.

[gmtech1]

The boosters leak p/s fluid out of the rear seal, thats probably what you are seeing. Its possible there is a slight pressure loss in the booster because of that leak, resulting in added brake pedal pressure needed. jcAT is right about the pump shaft breaking, but if you have p/s assist, it's ok. Its also possible that the p/s pump has lost some pressure, but most of the problems I have seen with the hydro-boost system is the unit itself.

[j cAT]

when you STAB THE BRAKE PEDAL this is creating a large surge in pressure as was mentioned your pedal travel is now increased, due to a possible air/leak in the system.

before you thought a pulse on the brake pedal was normal when starting the engine, now it does not do this. I would say you should not feel any pulse when starting engine ,with your foot on the pedal.

with the age of this vehicle the brake lines are in need of inspection as well.

[GMCustomerService]

If you decide to work with a dealership on this at any point, please let me know as I would like to be available to assist in any way that I can. I am unable to really diagnose over the internet, and I realize that this isn't always the preferred venue for diagnosis.

Take care,
Sarah
GM Customer Service

[bowhuntrrl]

Thanks all for the replies. I was in the business myself for 35 years, I'm just not familiar with some of the newer GM features having mostly been in foreign , Chrysler, Ford, and Harley dealerships. I just picked up the Avalanche in Atlanta in September, it's a real solid southern vehicle. The paint on the frame is still shiny! I will check the brake lines out though. One of my buds recently spent about $1200 getting the lines replaced on his 2004 Silverado, but it was a Northeast truck with rust showing on the body. Gotta love that salt!!! From what I understand, there is a certain year range of GM trucks that have brake lines subject to rust. Can anyone verify that??

[maxwedge]

Any truck /car up in here north country has brake and gas line issues regardless of year, unless they have the poly coated lines.