Lost braking power
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Senior User
Joined: Feb 2010
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Lost braking power
Truck sat for 2-3 weeks and than I drove the idi to work. It seemed like the brakes worked as usual. Went to get a bite to eat for lunch and truck was difficult to stop. No lights came on and no fluid on the ground or fluid lost from master cylinder reservoir. Brakes are still hard and will stop the truck but there is not nearly enough braking power to drive regularly. Thoughts anyone?
Lead Driver
Joined: Oct 2003
Posts: 8,476
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From: Madison, WI
HARD brake pedal, but it still stops the truck if you "Chuck Norris" it? That's boost. Either the booster, or more likely the vacuum pump or a vacuum line. Your '92 has a serpentine belt, right? If so, the vacuum pump is on the left (DRIVER'S) side of the engine; has a smooth pulley that runs on the "back" side of the belt. You can take the hose off it, start the truck and put your finger on the port to feel for suction; should be fairly strong.
Does your truck have A/C? If so, try working the controls (A/C - vent - heat, etc) and see if it actually changes. That works off the vacuum pump as well, so if that control is on the fritz, that would also indicate a vacuum problem.
Does your truck have A/C? If so, try working the controls (A/C - vent - heat, etc) and see if it actually changes. That works off the vacuum pump as well, so if that control is on the fritz, that would also indicate a vacuum problem.
Fleet Mechanic
Joined: Jan 2011
Posts: 1,709
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From: 8600 ft in Colo
The vent controls work on vacuum whether it has AC or not. Turn the blower on and see if you can switch between defrost & floor. If there's no vacuum, it will stay on defrost regardless of the control.
Postmaster
Joined: Dec 2011
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(actually, I swapped it out with a Hydroboost unit, so a direct swap should be a lot easier).
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Senior User
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Pulled check valve out of booster and plugged my vacuum pump into end of check valve. Reading was 24 inches/Hg. And when I released the vacuum on the pump the reading never went below 14 inches/Hg and quickly returned to 24. I feel safe in saying its not the pump.
How do I test the booster? Plug my vacuum pump in where the grommet is for the check valve and pull 24 inches/Hg and see if it holds?
Also could it be a caliper is hung up? Truck sat for a few weeks before this happened.
How do I test the booster? Plug my vacuum pump in where the grommet is for the check valve and pull 24 inches/Hg and see if it holds?
Also could it be a caliper is hung up? Truck sat for a few weeks before this happened.
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Lead Driver
Joined: Oct 2003
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From: Madison, WI
Also could it be a caliper is hung up? Truck sat for a few weeks before this happened.
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Senior User
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Went out to test the booster and 2+ hours later it was still holding vacuum. I could hear it as I took out the check valve.
Hand held vacuum pump couldn't create enough vacuum but the fact it was holding vacuum for 2+ hours makes me think the problem is elsewhere.
Hand held vacuum pump couldn't create enough vacuum but the fact it was holding vacuum for 2+ hours makes me think the problem is elsewhere.
Freshman User
Joined: Mar 2014
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From: Birmingham Alabama
I had a similar experience.
I had to really stand on the pedal to get it to stop.
It turned out my problem was that the rear brake cylinders were seized.
My front brakes were doing all the stopping.
there was no indication from the brake warning light, at all
I had to really stand on the pedal to get it to stop.
It turned out my problem was that the rear brake cylinders were seized.
My front brakes were doing all the stopping.
there was no indication from the brake warning light, at all
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Jacked the rear end up of the truck and placed it in neutral while wife hit the brakes. Rear brakes seem ok on both sides. Did the same with the front and no problems identified. At this point I am back to the booster.
Tried to plug my hand held vacuum pump in the check valve port of the booster and apply 24 inches/Hg of vacuum but could not do it. I am thinking its cause it takes a tremendous amount of pumping with my little hand held pump to displace the diaphragm. Any other ways to test the booster? Thanks
Tried to plug my hand held vacuum pump in the check valve port of the booster and apply 24 inches/Hg of vacuum but could not do it. I am thinking its cause it takes a tremendous amount of pumping with my little hand held pump to displace the diaphragm. Any other ways to test the booster? Thanks
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I hooked the pump directly to booster (check valve not inline).
Also I took the truck for a ride as I am thinking given the age of the booster and the cold spell we are having in NJ now that maybe the diaphragm is stiff from the cold and its age. I drove around the block and brakes are intermittently good and than pedal is hard. Thinking I swap out the booster since its likely 10+ years old anyway.
Also I took the truck for a ride as I am thinking given the age of the booster and the cold spell we are having in NJ now that maybe the diaphragm is stiff from the cold and its age. I drove around the block and brakes are intermittently good and than pedal is hard. Thinking I swap out the booster since its likely 10+ years old anyway.