98 Tahoe brake booster????

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  #1  
Old 03-04-04, 12:33 PM
ChrisZ
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98 Tahoe brake booster????

Looking for diagnoses help. This may happen 3-5 times a day, when applying the brakes sometimes the brake pedal doesn't push smoothly, gets rough and hard to push, then it passes the rough point and I hear some sort of noise like a groan/moan from the under the hood maybe from the booster. I cannot get it to do this when sitting still and pumping the brakes, it alway happens when driving. Any advice would be greatly appreciated
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Old 03-04-04, 12:51 PM
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moan/groan sounds like...

...an ABS thing to me. any lights coming on? power boosters usually only make a hissing sound inside. i think i'd take it to someone who can do a function test on the ABS with a scan tool...not all scanners are capable of this...so be sure ask specificall if they can do THAT test...it's important because it exercises all of the solenoids and stuff in the ABS system.
 
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Old 03-04-04, 01:51 PM
ChrisZ
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No ABS warning lights coming on when it happens, if it is not the booster do you think this is best left to a certified mechanic to repair? Is it a high dollar fix?
 
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Old 03-04-04, 02:01 PM
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definately...

...always have an ASE certified tech do your work...esp on brake systems.

as for cost...until it's properly diagnosed, it's not predictable.

still...by the sound that you describe, i can't help but think it's an ABS problem...the EHCU makes all sorts of weird moaning/groaning noise when it's functioning.

the thing you need to do is take it to someone and drive WITH them and demonstrate what it does...i know it doesn't do it all the time, but this is the best way to help your tech zero in on the problem...good luck and let us know what is found.
 
  #5  
Old 03-04-04, 02:52 PM
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Does this happen when pulling up to a stop,usually slowly?If so I think you have a front wheel speed sensor dropping out.If someone can duplicate the problem while the scan tool is connected the correct sensor can be replaced.A word of caution sensors for those are available seperate from the hub bearing but usually the entire hub bearing sensor assembly will be required to fix the problem.
 
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Old 03-04-04, 03:25 PM
ChrisZ
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Yes, now that it has been happening for a day and a half, I can say it is usually when coming to a slow stop. I can say it happens when I pull into my parking spot at work and other slower stops. I don't think it happenes when approching a traffic light and it changes and I have to stop faster. I did notice when slow stopping I can pump the pedal slightly and avoid the sound and lessen the rough pedal.
 
  #7  
Old 03-04-04, 03:35 PM
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I think a wheel speed sensor is bad and someone will have to drive it with a scan tool attached to diagnose which one is bad.This condition will not set an abs code.So if they tell you there are no codes they will be correct,they will need to drive it and monitor the sensors during the fault.The system on your truck will not read below 3mph.Typically a sensor will drop out at about 5-6mph causing this problem.Meaning one sensor will drop to a lower mph before the others.If your tires are not all the same size or treadwear it could also cause this problem.Treadwear differance would need to be significant.
 
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Old 03-04-04, 04:20 PM
ChrisZ
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Have any idea of cost estimates to perform this repair?
 
  #9  
Old 03-05-04, 04:16 PM
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I think the bearing is about $250 and labor about 1.5 hours at your garages rate.This is a guesstimate since I'm hourly I don't watch the money too much.
 
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