brake light problem
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Junior User
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brake light problem
ok guys got another head scratcher. my brake light seams to come on alot. i know when you hit the pedal like 3-4 times it will drop psi and it will come on. but if i pull into parking spot hit the brake and back up and hit the brake the light comes on. what could be wrong or is it nothing to get in a bind about. the brakes seam to still work fine when this happens. i just dont rember seeing this before....
Posting Guru
Joined: Jan 2009
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From: Mattawa Washington.
what type of rig are you driving? gas or diesel? is your fluid resevoir low? how far down does your pedal travel? or better yet how far from the floor is it? If it is close to the floor near full pedal stroke you may need to manually adjust the rear brakes tighter, to much travel.
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Junior User
Joined: Jan 2009
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what type of rig are you driving? gas or diesel? is your fluid resevoir low? how far down does your pedal travel? or better yet how far from the floor is it? If it is close to the floor near full pedal stroke you may need to manually adjust the rear brakes tighter, to much travel.
Post Fiend
Joined: Oct 2003
Posts: 5,903
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From: MICHIGAN
The brake light will come on if the vacuum drops off to a certain level. IIRC less than 7 in-Hg. You should normally have 17-21 in-Hg with the engine running. KOER
You may either have a vacuum leak or the vacuum pump is getting weak or the belt is slipping on the vacuum pump.
You can put a vacuum gauge on it and see if it's dropping too low after a couple brake pedal applications. KOER
Also check it with the engine off. Start it up and run the engine for 10-20 seconds, turn it off, the vacuum gauge should not drop more than 1 in-Hg in 1 minute. If it does, you have a vacuum leak.
You may either have a vacuum leak or the vacuum pump is getting weak or the belt is slipping on the vacuum pump.
You can put a vacuum gauge on it and see if it's dropping too low after a couple brake pedal applications. KOER
Also check it with the engine off. Start it up and run the engine for 10-20 seconds, turn it off, the vacuum gauge should not drop more than 1 in-Hg in 1 minute. If it does, you have a vacuum leak.
Thread Starter
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Junior User
Joined: Jan 2009
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The brake light will come on if the vacuum drops off to a certain level. IIRC less than 7 in-Hg. You should normally have 17-21 in-Hg with the engine running. KOER
You may either have a vacuum leak or the vacuum pump is getting weak or the belt is slipping on the vacuum pump.
You can put a vacuum gauge on it and see if it's dropping too low after a couple brake pedal applications. KOER
Also check it with the engine off. Start it up and run the engine for 10-20 seconds, turn it off, the vacuum gauge should not drop more than 1 in-Hg in 1 minute. If it does, you have a vacuum leak.
You may either have a vacuum leak or the vacuum pump is getting weak or the belt is slipping on the vacuum pump.
You can put a vacuum gauge on it and see if it's dropping too low after a couple brake pedal applications. KOER
Also check it with the engine off. Start it up and run the engine for 10-20 seconds, turn it off, the vacuum gauge should not drop more than 1 in-Hg in 1 minute. If it does, you have a vacuum leak.
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Post Fiend
Joined: Oct 2003
Posts: 5,903
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From: MICHIGAN
I only have one belt...pretty sure you do to. The pump is on the driver side....can't miss it.
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Post Fiend
Joined: Feb 2009
Posts: 8,773
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From: Texas Coast
There are cases where the vacuum pump bearings start sliding in the race way on 96 models and crapping the vacuum pump out. So if there is intermittent issues this could be related to your problem. Mine trashed out on me at around 75k. I was hauling at 65 m/hr could not hardly stop her missed taking down some median signs by inches. Had to clean my shorts. Anyhow check your belt for wear and take the tention off of it and test the vacuum pump bearing by simply rotating it by hand. Feeling for rough spots and catches.
Last edited by DRRXR; Mar 7, 2009 at 06:38 AM. Reason: typo
Thread Starter
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Junior User
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There are cases where the vacuum pump bearings start sliding in the race way on 96 models and crapping the vacuum pump out. So if there is intermittent issues this could be related to your problem. Mine trashed out on me at around 75k. I was hauling at 65 m/hr could not hardly stop her missed taking down some median signs by inches. Had to clean my shorts. Anyhow check your belt for wear and take the tention off of it and test the vacuum pump bearing by simply rotating it by hand. Feeling for rough spots and catches.
Senior User
Joined: Jul 2006
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i'm gonna chime in too since i have a similar problem. my light comes on now all the time too. 97 diesel. fluid full. usually when i am backing up. sometimes when it happens my pedal is rock hard though and barely travels 1/2" down, and the truck won't stop at all. very unnerving. but if i let off the light will go out and my brakes are fine. only happens at low speedds like pulling out from a parking spot. 99% of the time my brakes are fine, but that 1% scares me! my level was a little low last week. mabye 3/4" from the full mark so i added fluid to top it off, and my first thought was an air bubble in there somewhere but i thought that would give me a soft pedal not a super firm one.
Post Fiend
Joined: Apr 2004
Posts: 12,835
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From: Silver Lake Dunes, MI
i'm gonna chime in too since i have a similar problem. my light comes on now all the time too. 97 diesel. fluid full. usually when i am backing up. sometimes when it happens my pedal is rock hard though and barely travels 1/2" down, and the truck won't stop at all. very unnerving. but if i let off the light will go out and my brakes are fine. only happens at low speedds like pulling out from a parking spot. 99% of the time my brakes are fine, but that 1% scares me! my level was a little low last week. mabye 3/4" from the full mark so i added fluid to top it off, and my first thought was an air bubble in there somewhere but i thought that would give me a soft pedal not a super firm one.
