Brake booster?

Tiny
TSTONER
  • MEMBER
  • 1991 CHEVROLET SILVERADO
  • 3.5L
  • V8
  • 2WD
  • AUTOMATIC
  • 200,000 MILES
My wife has the truck listed above, she says the brake pedal goes down like sounds to me there would be air in the line. I've bled the brakes, I never experienced that when driving it but I did experience the brakes worked fine except one time it was very hard pedal, didn't think I was going to stop getting off a highway ramp. It stopped but I had to push really hard to get it to. Since that one time, no issues when I'm driving but she says she still has the same issues with pedal going down sometimes. Is there something that would cause both symptoms, booster or master cylinder? I've worked on cars for over 40 years for myself and never had issue with both at once. Any suggestions would be appreciated.
Thank you,
Terry S.
Saturday, February 20th, 2021 AT 10:19 AM

1 Reply

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,256 POSTS
This sounds like the brake booster is bad. I would remove the vacuum check valve to see if you here vacuum escaping if not the booster is bad. Here is how to change it out in the diagrams below. Check out the diagrams (below). Please let us know what happens.
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Monday, February 22nd, 2021 AT 6:18 PM

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