Pressure relief valve sound from under the dash

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turbo_bu

Member
Mar 27, 2007
199
7
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Central IL
Not sure where to put this, but hoping I am not the only one this has happened too.

Slow speed driving (think parking lot), when I apply the brakes (slow light brakes, not climbing on them) and turn the steering wheel (slow steering), I hear what sounds like the hydraulic pressure relief valve coming from under the dash. The only reason I am suspecting this, is when you do a balance rate test, it says to climb on the brakes and listen for a hiss. This is the same sound that I am hearing when doing this combined braking and steering.

My truck (2004) just starting doing this the last month and I am able to do it pretty regularly if I try. So far, I haven't noticed any loss of performance from either the brakes or the steering, I'm just trying to figure out what's going on ... or if something is broken ... or about ready to break. Anyone else ever noticed this? Does anyone happen to have a hydraulic schematic of the brakes / steering circuit? I would like to try and determine where to start looking.

Thanks,
 
Kappa9012

Kappa9012

MAN.... I Broke it again.
Aug 5, 2008
694
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16
Peoria Il
did you get this figured out? My truck does this when turning left, but it does it regardless of the brakes. I assume it's the powerboost since the power steering fluid is good.
 
T

turbo_bu

Member
Mar 27, 2007
199
7
18
Central IL
nope - not yet. My dad did pick up a used LB7 the other day, and I plan on taking his for a test drive in the next week or so to see if I hear his or not. I am now fully sensatized to mine, so it shouldn't take long to see if I am just crazy or not. My guess is that his is probably OK, and that there is something going on in the hydro-boost circuit. Unfortunately, the 2004 shop manual doesn't give you much for troubleshooting on the hydroboost circuit :(.
 
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turbo_bu

Member
Mar 27, 2007
199
7
18
Central IL
Quick update - I finally zeroed in on where the sound was coming from. It was the ABS unit. The truck finally threw an ABS code ... this finally clicked in my thick skull, that the onlyu times it was doing it was when the truck was coming to a complete stop. Pulled the ABS fuse and now it no longer does it. Now I have to figure out what the code is and/or what the issue is with my ABS.
 
T

turbo_bu

Member
Mar 27, 2007
199
7
18
Central IL
plowboy_lbz said:
Oh nice. Mine does this too. Make a whining grinding noise sometimes.
Click to expand...

Try pulling the ABS fuse under the hood (60 amp'er I think). When you start the truck, it will chime for about 20-30 seconds ... then finally shut up and leave both the ABS light and Parking Brake lights on. You will not have any ABS obvoiusly, but the truck will work and drive just fine. If that makes your problem go away, then you will at least know where to start looking further.
 
duratothemax

duratothemax

<--- slippery roads
Aug 28, 2006
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Wyoming
The other potential source of this noise is the hydroboost unit itself. If its ABS, that is a more distinctive grinding/vibrating noise.

Hydroboost noise is a hissing/pshhhhh that sounds like its coming from under the dash. The hydroboosters can sometimes hiss if they are starting to go bad, or if the power steering fluid is contaminated.
 
T

turbo_bu

Member
Mar 27, 2007
199
7
18
Central IL
Little more of an update. Did some more internet reading (I know ... dangerous), but a couple posts over on the tahoe forums matches my ABS sensor theory. I also have the right front wheel speed sensor code (yeah - something makes sense). So I started to take it apart, but I could not get the mother out without breaking it (DOH!). Anyway, so now I am trying to order a new sensor (got the bearing housing all cleaned up), but it seems like there are about 3 or 4 different sensor part #'s listed out there. Napa, Carquest, and Rockauto all seem to quote similar sensors, but which one is it??????? Even GM pats direct kinda lists a different part #. Some of the descriptions even mention w or w/o 2" body lift? I'm guessing that HD truck = 2" body lift?

Anyone know for sure which part # to order?

Current guesses:
GM = 19300584
Dorman = 970-060
Wells = 9823

Or if any of these brands I should stay away from?
 
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