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2011 Sierra 2500 Hydroboost Issues

Soft pedal and deteriorating stopping power

2011 Sierra 2500 Hydroboost Issues

Postby Soarer [OP] » Jun 30 2020, 1:43am

2011 Sierra gasser with hydroboost system. Truck is new to me with 115k on it. Used to be a plow truck. Symptoms are a squishy pedal that needs a lot of travel to get the truck to stop. The other weird thing is that if you're sitting at a stop light with your foot on the brake, after about ten or fifteen seconds, the pedal will drop a fraction of an inch in three quick pulses and then the truck will start rolling forward in gear. I am guessing that there is something going on with the ABS pump/system because there is no other reason I can think of that I'd feel three pulses in the course of a second, have the pedal drop from beneath my foot just a little bit and then lose braking power. I don't know what's been done to this truck in the past so I'd really appreciate some help in getting this diagnosed. Thanks!
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Re: 2011 Sierra 2500 Hydroboost Issues

Postby EaOutlaw1969 » Jun 30 2020, 2:39am

With the engine off and after pumping then holding the brakes 4 to 5 times how is the brake pedal, does it drop with no assist from the HPA high pressure accumulator?
Remember with Hydroboost you will have a limited reserve brake assist from the high pressure accumulator, make sure to pump the brakes long enough to relieve this pressure to see if you have a solid brake pedal when the engine is off. if you do not have a solid pedal you will have to start with a general brake inspection. if the pedal is rock solid and you have a good parking brake then we can try to help with the hydroboost diagnosis.
Here is some reading material that may help https://www.brakeandfrontend.com/operat ... t-systems/
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