Vacuum booster

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   I'm at my wits end with this customers 1999 chevy silverado pickup.  Comes in with a broken brake line. Of course gm had to put the abs module under the can so you have a bundle of lines running along the frame rail and that's where it's leaking.  Put in new lines and bled it.  Took it for a drive and the pedal was hard with little braking effort.  

Bring it back in.  All the calipers move nicely and I cleaned up the pads so they float.  

Took it out again same story.  Doing some investigation I find that I have next to no fluid coming from the abs to one of the front wheels. Seen this before abs fails. Got a junk yard abs and now I have good fluid flow to all wheels using my pressure bleeder.  

Drive it again and same thing.  I've run out of things to check except for the master and the vacuum booster.  

Pull the vacuum line and the booster woosh's. So I know it holds air.  Start pickup with line off and you have good vacuum. 

My question is can I have a booster that's junk but yet still holds vacuum?  What are your guys thoughts

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bobkyllo Members Profile Send Private Message Find Members Posts Add to Buddy List Orange Level Joined: 14 Sep 2009 Location: minnesota Points: 1568	Post Options Post Reply Quote bobkyllo Report Post Thanks(0) Quote Reply Topic: Vacuum booster Posted: 2 hours 37 minutes ago at 5:22pm
	I'm at my wits end with this customers 1999 chevy silverado pickup. Comes in with a broken brake line. Of course gm had to put the abs module under the can so you have a bundle of lines running along the frame rail and that's where it's leaking. Put in new lines and bled it. Took it for a drive and the pedal was hard with little braking effort. Bring it back in. All the calipers move nicely and I cleaned up the pads so they float. Took it out again same story. Doing some investigation I find that I have next to no fluid coming from the abs to one of the front wheels. Seen this before abs fails. Got a junk yard abs and now I have good fluid flow to all wheels using my pressure bleeder. Drive it again and same thing. I've run out of things to check except for the master and the vacuum booster. Pull the vacuum line and the booster woosh's. So I know it holds air. Start pickup with line off and you have good vacuum. My question is can I have a booster that's junk but yet still holds vacuum? What are your guys thoughts

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DMiller Members Profile Send Private Message Find Members Posts Add to Buddy List Orange Level Access Joined: 14 Sep 2009 Location: Hermann, Mo Points: 35647	Post Options Post Reply Quote DMiller Report Post Thanks(0) Quote Reply Posted: 2 hours 34 minutes ago at 5:25pm
	You have a Bad booster chamber. Is not applying the stored vacuum. Inner works are screwed.

bobkyllo Members Profile Send Private Message Find Members Posts Add to Buddy List Orange Level Joined: 14 Sep 2009 Location: minnesota Points: 1568	Post Options Post Reply Quote bobkyllo Report Post Thanks(0) Quote Reply Posted: 2 hours 10 minutes ago at 5:49pm
	I was leaning to the booster but I was unsure if you could have a bad booster but yet have no leak or poor driveability. All the bad boosters I've ever come across would not hold vacuum. Thank you for the reassurance.

DMiller Members Profile Send Private Message Find Members Posts Add to Buddy List Orange Level Access Joined: 14 Sep 2009 Location: Hermann, Mo Points: 35647	Post Options Post Reply Quote DMiller Report Post Thanks(0) Quote Reply Posted: 1 hour 36 minutes ago at 6:23pm
	Can fail either way.

Ed (Ont) Members Profile Send Private Message Find Members Posts Add to Buddy List Orange Level Joined: 08 Nov 2009 Location: New Lowell, Ont Points: 1590	Post Options Post Reply Quote Ed (Ont) Report Post Thanks(0) Quote Reply Posted: 47 minutes ago at 7:12pm
	I find on a lot of this newer stuff you have to hook up computer and activate brakes with it. I had a 99 GMC2500. Did all the brake lines at once due to rust issues - plow truck. Could not get a pedal at all even after lots of manual bleeding. Finally hooked up computer, activated ABS a couple times. Quick manual bleed and 100% brake operation!!!! Drove it for a few years after that with no issues and great brakes. Finally sold the truck and it is still working today. New owner turned it into a tire service truck and loves it! Edited by Ed (Ont) - 43 minutes ago at 7:16pm