Brake Pedal Lock Issue
 

I am having some braking problems with my 2003 H2. When I step on the brake pedal at speed (like 50 or 60mph) it will only brake so much. Once it slows to about 30-40mph it feels as if whatever limiter at the high speed releases and then I can fully brake or mash the pedal to the floor. At the higher speeds you can slam on it but it still doesn’t brake fully until your at the lower threshold. the hydraboost system has been replaced and didn't make a difference.

Something with the ABS system or maybe not bled properly when the hydro was replaced?

Thanks for the message. My mechanic has checked the abs system multiple times and bled it with each of the two hydros that were put on. The investigation continues...

Sounds like the hyrdo boost system to me. Make sure the belt is good and that you have enough fluid in the pump first. Then look at the pump.

Tim

Thanks for the message. We have replace the hydroboost system twice, replaced the belt, and confirmed enough fluid. I'll keep investigating.

Thanks again!

Higher speed failure is going to be from a bad pump or bad fluid. That's all there is to the system. It should self bleed and abs usually will not kick in at speeds above 20 mph.

Tim

I'll give the fluid another check

First have the pressure at the pump checked. If it checks out then replace the Hydroboost assembly with a GM factory unit. It will be costly! The cheap rebuilt units from the local parts stores are no good.

BTW the TRW hydroboost units on the 2007 and up GM vehicles are WORLDS better than the older units. But I don't think they are backwards compatible.

Thanks for the info! I'll give that a try.

Humdinger2: Another idea is to replace the brake fluid and flush the entire system out to each caliper, if you haven't already. Brake fluid attracts moisture from the air (even in the reservoir) and becomes contaminated with water. That will also cause a "spongey" or "mushy" feel to the brake pedal.