This video will be diagnosing an intermittent hard brake pedal on this Chevy Silverado. The hard or stiff brake pedal also applies to most GMC trucks. What we found is the brake booster was not receiving enough vacuum and on this Chevy truck the hard brake pedal was being caused because of the vacuum pump failing.
This GMC truck has an external vacuum pump that is belt driven to supply vacuum to the brake booster. A lot of the older trucks use engine vacuum to supply vacuum to the brake booster but on this truck that is not the case.
When the engine RPMs are brought up on the Chevy truck the brake pedal actually feels much better and that’s because the vacuum pump is spinning faster so it works more efficiently but at idle the brake pedal was very hard. We found that the vacuum pump had failed and will need to be replaced to fix the hard brake pedal in this truck.
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