Testing brake booster
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From: South Carolina
Testing brake booster
My truck surges bad running down the highway, I thought it was the carb but now, I suspect my booster is bad. I can hear a whooshing sound in the cab when pushing on the pedal. Also the feel on the pedal has changed, it's real touchy now. I got out my hand vac pump, connected it to the booster. I cannot get any vacuum reading. Is it possible using a hand pump to pull enough vacuum on the booster to get a reading? I checked the vac reading coming from the motor to the booster, it's a steady 19". I also checked vacuum at the intake just below the carb, it's also is a steady 19". Working on a 86 F100 300 I6. Any thoughts, don't want to buy a new booster for nothing.
Thanks
Mark C.
Thanks
Mark C.
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Yes, you can use a hand pump, but it takes a lot of pumping to start a vacuum by hand in you booster. I just put a new one on, and with the new booster I could pump the hand pump about 25 times real fast and it would start to get a few inches on the pump and hold. My old one wouldn't do that.
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Just because it doesn't hold like a new one may not mean it's bad, but it can't be good. After the truck sits overnight and you get in in the morning, before you turn it on, push the pedal. If it has one shot of power it probably isn't leaking. If it is stiff, it leaked the vacuum overnight. Mine quit on me all of the sudden, but it could also die a slow death.
My booster was only about $50 plus the core, but I think the regular price was around $80. It was pretty easy to change. If you think it's a problem I'd just do it, it isn't too expensive.
My booster was only about $50 plus the core, but I think the regular price was around $80. It was pretty easy to change. If you think it's a problem I'd just do it, it isn't too expensive.
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I can't get any vacuum reading, the needle stays pegged on zero, using the hand pump, thats what leading me to think it might be bad. I'll have to try the pedal test in the morning. On the way home last night, it also seemed like maybe my one of brakes is grabing. Advance Auto has one for $73 plus core. Hopefully I can get some time off from work, this weekend to check everything out. Thanks
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If you put one on and the old one is stuck to the firewall, get a 1"x1"x6" piece of wood and put it between the brake pedal and inside of the booster (after linkage is disconnected) and step on the pedal. It will push the booster off without damage. Also, make sure the rod to the master is adjusted to the same length as the old one. It has a small nut on the end, hold the shaft with pliers and turn with another pair. I just did this over the weekend. Good luck, it's an easy job.
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From: South Carolina
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From: South Carolina
I tried the brake pedal this morning. It was stiff. Thanks for the testing tip, I guess mine is leaking down during the night also. Never thought of hitting the pedal before starting my truck. I'll be changing it out this weekend. I'll keep the piece of wood in mind also.
Thanks nickmobile67
Mark C
Thanks nickmobile67
Mark C
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From: b.c. canada
the brake booster will leak the vaccume over a short time,
here is how you test it... leave the truck off, pump the brake pedal till its firm, hold the brake pedal and turn the engine on, if your foot sinks then the booster is good..........
-gbm-
here is how you test it... leave the truck off, pump the brake pedal till its firm, hold the brake pedal and turn the engine on, if your foot sinks then the booster is good..........
-gbm-
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gingerbreadmaniac, I tried your test, and yes my foot went to the floor. So I guess it's good then. My only concern is when the motors running, and I push on the pedal, there is a very loud whooshing noise from under the dash by the pedal. After I shut the motor off, and continue to pump the pedal, the whooshing sound fades. After 6 pumps the sound is completely gone. I tried your test twice, with the same results. What do you think??? If it wasn't for the sound, I wouldn't have any doubts about the booster being good. I don't have much brake booster experience, so I need your input.
Thanks
MarkC.
Thanks
MarkC.
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From: b.c. canada
Originally Posted by MSC
gingerbreadmaniac, I tried your test, and yes my foot went to the floor. So I guess it's good then. My only concern is when the motors running, and I push on the pedal, there is a very loud whooshing noise from under the dash by the pedal. After I shut the motor off, and continue to pump the pedal, the whooshing sound fades. After 6 pumps the sound is completely gone. I tried your test twice, with the same results. What do you think??? If it wasn't for the sound, I wouldn't have any doubts about the booster being good. I don't have much brake booster experience, so I need your input.
Thanks
MarkC.
Thanks
MarkC.
my truck does the same whoosh thing and every truck iv ever owned or driven has done the same thing.....
Your brake booster is just fine my friend,
if your concerend about some surging in your pedal when you ride the brakes its probly a drum or rotor problem, what kinda shape are your pads etc. in?????
My pedal surges when my brakes get a little warm, i have 414,000k on the original drums and rotors......
I say pull the wheels and see what it looks like in there....
if the brake pads are still good chances are everything is in good enough shape for an old pickup.......
-gbm-
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This is only my second truck I've owned. My brakes don't surge, it's my carb. Sorry for the confusion. I had all four wheels off two months ago, and everything looks good. When I'm running down the highway, the truck surges. I was looking at checking out the carb. But before I did, my brakes seemed to have a different feel, or so I thought. I've had a couple guys say that it seemed like the booster went bad, and that would also cause the surging problem. Thanks for the info, I'm going to check the carb out this weekend. A carb kit is much cheaper than a booster. Thanks again for your patience.
Mark C.
Mark C.
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Joined: Dec 2001
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From: b.c. canada
Originally Posted by MSC
This is only my second truck I've owned. My brakes don't surge, it's my carb. Sorry for the confusion. I had all four wheels off two months ago, and everything looks good. When I'm running down the highway, the truck surges. I was looking at checking out the carb. But before I did, my brakes seemed to have a different feel, or so I thought. I've had a couple guys say that it seemed like the booster went bad, and that would also cause the surging problem. Thanks for the info, I'm going to check the carb out this weekend. A carb kit is much cheaper than a booster. Thanks again for your patience.
Mark C.
Mark C.
man if it is surging as you simply drive down the highway it definatly isnt the brakes or brake booster, the test i gave you is what a certified mechanic did to one of my trucks at his shop when i had concerns about my booster, your booster is just fine....
p.s. i am only on my second truck aswell....
-gbm-
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there is a vacuum check valve where the vacuum line attaches to the booster that may be leaking down overnight, but that would not be a likely cause of hiway surge or brake touchiness. check the master cylinder for the touchiness and maybe your egr for the surge.
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