Vacuum booster
Printed From: Unofficial Allis
Category: Other Topics
Forum Name: Shops, Barns, Varmints, and Trucks
Forum Description: anything you want to talk about except politics
URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=210565
Printed Date: 29 Mar 2026 at 9:33pm
Software Version: Web Wiz Forums 11.10 - http://www.webwizforums.com
Topic: Vacuum booster
Posted By: bobkyllo
Subject: Vacuum booster
Date Posted: 29 Mar 2026 at 5:22pm
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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 |
Replies:
Posted By: DMiller
Date Posted: 29 Mar 2026 at 5:25pm
| You have a Bad booster chamber. Is not applying the stored vacuum. Inner works are screwed. |
Posted By: bobkyllo
Date Posted: 29 Mar 2026 at 5:49pm
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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. |
Posted By: DMiller
Date Posted: 29 Mar 2026 at 6:23pm
| Can fail either way. |
Posted By: Ed (Ont)
Date Posted: 29 Mar 2026 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!
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