Power assist brake Problem
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Power assist brake Problem
Hey guys, I bought a 96 f350 powerstroke a couple months ago and yesterday I was driving, and it has been a relatively warmer winter for the most part, but the past few days it's been in the -5 to -15 range. But I was driving down the road and i started hearing a squeeling or hissing noise, not like a squeeky brake or looseing air out of a tire. I assessed it was comeing from my belt, but at the same time that happened my power assist for my brakes was gone, my pedal was rock solid, the brakes still work but not good at all, and i have to push down pretty hard. I shut the truck off and the noise went away, started it and had no problems, so I went and drove trying to see if it would happen again, and it did, and this time the noise went away but I still have no power assist, it makes the noise when my truck is shutting down when i turn it off, but not when driving. It makes a clicking noise when its running now sounds like its comeing from the belt, but my main concern is my power assist for my brakes. Could it be the vaccume pump? Please share similar stories and help me solve this problem.
Fleet Mechanic
Joined: Aug 2007
Posts: 1,508
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From: The boonies by Dallas OR
Your vacuum pump is shot.
It is between the power steering pump and the A/C on the drivers side of the engine. It sort of looks like an idler pulley with a diaphram behind the pulley. Get it fixed before the bearing seizes up and the belt shreds.
If your brake light isn't on, then the vacuum switch is shot too.
It is between the power steering pump and the A/C on the drivers side of the engine. It sort of looks like an idler pulley with a diaphram behind the pulley. Get it fixed before the bearing seizes up and the belt shreds.
If your brake light isn't on, then the vacuum switch is shot too.
Posting Guru
Joined: Jun 2005
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sounds similar to what happened when my vac pump went out. i think air would only come out my defroster vent or something like that as well. i cant remember what exactly it was but something didn't work right with the vents when the pump went out as well.
Senior User
Joined: Apr 2006
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From: Santa Barbara and Ottawa
squeaking and loss of power assist on the brakes happened to me. I didn't even think to check the cabin climate controls but that should be a good give away too.
It was very easy to replace, but I think I needed pulley tools, the replacement pump didn't come with a pulley. I think it is the same as a power steering tool to put on.
There was just another post about a vacuum pump, and someone mentioned making sure it was lubed appropriately. I don't recall reading anywhere (else) about that. I didn't lube mine (about 7k miles ago).
It was very easy to replace, but I think I needed pulley tools, the replacement pump didn't come with a pulley. I think it is the same as a power steering tool to put on.
There was just another post about a vacuum pump, and someone mentioned making sure it was lubed appropriately. I don't recall reading anywhere (else) about that. I didn't lube mine (about 7k miles ago).
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Thanks for the replys guys, I replaced the vaccume pump and that was it, it was getting close to welding the bearings together. But she works perfect, wasn't hard at all just needed to rent a pulley puller. I will defenately use these forums for any further problems, very nice community.
Cross-Country
Joined: Apr 2003
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From: Montana
I'm having a problem with my 95 PSD... now that I know the vacuum is created by a pump it will maybe be easier to isolate. It happened not long after I redid all of my injector rings, so I figured throughout that process maybe I damaged a vacuum line or something.
It started like this: At low RPMs I would lose power assist, and the brake light would be on, as the RPMs came up I would regain power assist. It slowly degraded and would take more and more RPM to gain power assist and the brake light would turn off.
It was always very consistent with the brake light - as in, if the light was on, no power assist, when it was off I had power assist.
It is at a point now at which the light is on all of the time, and I have no brake assist. I don't remember hearing any hissing or squeaking though, but it was a few months ago and I'm just now getting around to doing this.
So, vacuum pump? Or maybe just check the lines from the vacuum pump?
One more thing: This truck has 197K on it, I have had it seince 132K, and i've never messed with the vacuum pump.
It started like this: At low RPMs I would lose power assist, and the brake light would be on, as the RPMs came up I would regain power assist. It slowly degraded and would take more and more RPM to gain power assist and the brake light would turn off.
It was always very consistent with the brake light - as in, if the light was on, no power assist, when it was off I had power assist.
It is at a point now at which the light is on all of the time, and I have no brake assist. I don't remember hearing any hissing or squeaking though, but it was a few months ago and I'm just now getting around to doing this.
So, vacuum pump? Or maybe just check the lines from the vacuum pump?
One more thing: This truck has 197K on it, I have had it seince 132K, and i've never messed with the vacuum pump.
How do you test the vacuum pump? 
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