How do you test a power brake booster? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

crawdad · 10-01-2007, 02:31 PM

Brake pedal on my truck is hard to push. Brakes feel spongy so I'm certain I need to bleed the system, but how can I test the power brake booster to see if it if functioning properly?

gkolmatycki · 10-01-2007, 02:52 PM

The easiest way......Take the truck for a drive and slam on the brake pedal. It should stop very quickly and almost throw you out of your seat.

If you originally had manual brakes and converted to power brakes, one drive and you'll know the difference.

Plus, you should always bleed your brakes after you disconnect any lines. I did mine when I converted to a power brake booster.

crawdad · 10-01-2007, 02:58 PM

Well, I'm still building on it so I can't take it out on the road. Trying it in the yard though, the truck will stop, but its not a throw you out of your seat stop. It's more a hard pedal and a spongy stop. Doesn't feel like its working at all, but then again, it might just be that the system needs bleeding/adjusting real bad, so that's next. I was just wondering if there was some test, i.e., vacuum test or something to tell if it was working properly. Easier to replace it now while the fenders are off than later. Thanks.

hvychve · 10-01-2007, 02:58 PM

Hey Crawdad, I have my own way of checking to verify booster is good or bad, I usually pump all the air out of booster by operating brake pedeal about three to four times firmly with engine off. than while holding the pedal down I start engine, if the booster is good, vacuum will pull the pedal down just a tad, usually about a 1/4"....... hope this helps and if I am wrong, please feel free to correct me, also there is usually a hissing noise when brakes are applied with engine running, or engine shakes and runs rough when pushed hard and engine is running, sorta like a vacuum leak, good luck

wibilly · 10-01-2007, 10:54 PM

hard peddel ,little brakes =bad booster, often times you will have a bad vacume leak as well

**PICKMUP** · 10-02-2007, 12:17 AM

I use a vacuum pump with an in-line vac gauge and shut off valve. Draw 20lbs and close the valve. The booster should hold that reading and not leak down (diaphram leaks). You can even operate the booster by hand with the pump drawing vacuum and see that is is working freely.
Another test is to run the engine to draw vacuum, shut off the engine and wait about 30 seconds, then pull the plastic valve off the booster...you should hear the vacuum bleeding off if there are no leaks.

**MySons68C20** · 04-01-2019, 02:03 PM

Old thread but very helpful! I just tried both methods and the brand new 2 year old booster won't hold any vacuum.
Thanks to all!

Blake

10-01-2007, 02:31 PM	#1
crawdad Senior Member Join Date: Sep 2004 Location: Georgia Posts: 614	How do you test a power brake booster? Brake pedal on my truck is hard to push. Brakes feel spongy so I'm certain I need to bleed the system, but how can I test the power brake booster to see if it if functioning properly? __________________ 2012 Silverado LT 1500, 5.3, 6 speed auto '86 SWB C-10 Silverado

10-01-2007, 02:52 PM	#2
gkolmatycki Love that '69 Join Date: Oct 2005 Location: Sherwood Park, Alberta, Canada Posts: 109	Re: How do you test a power brake booster? The easiest way......Take the truck for a drive and slam on the brake pedal. It should stop very quickly and almost throw you out of your seat. If you originally had manual brakes and converted to power brakes, one drive and you'll know the difference. Plus, you should always bleed your brakes after you disconnect any lines. I did mine when I converted to a power brake booster. __________________ I AM CANADIAN & PROUD OF IT!!! 1969 Chevy C10, SBC V8, TH-350 Transmission, Metallic Blue, B&M Megashifter, GT Grant Steering Wheel, 2.25" True Dual Magnaflow Exhaust System w/ SS Magnaflow Embossed Tips, 700W Rockford Fosgate Stereo System, Lowered 1" Front & Stock Rear, 4.56 Rear with Positraction, 15" Chrome Rims w/ Chevy Center Caps & Michelin Tires, 4.5" K&N Air Filter, Edelbrock 'Elite' Engine Accessories, Chrome Powdercoated Engine Parts 2001 Cavalier Z24, 2.4L DOHC, Silver, Spoiler, AEM Intake, 2.25" Magnaflow Exhaust System, Clear Euro Tails, Tinted Windows, 400W Clarion Stereo System

10-01-2007, 02:58 PM	#3
crawdad Senior Member Join Date: Sep 2004 Location: Georgia Posts: 614	Re: How do you test a power brake booster? Well, I'm still building on it so I can't take it out on the road. Trying it in the yard though, the truck will stop, but its not a throw you out of your seat stop. It's more a hard pedal and a spongy stop. Doesn't feel like its working at all, but then again, it might just be that the system needs bleeding/adjusting real bad, so that's next. I was just wondering if there was some test, i.e., vacuum test or something to tell if it was working properly. Easier to replace it now while the fenders are off than later. Thanks. __________________ 2012 Silverado LT 1500, 5.3, 6 speed auto '86 SWB C-10 Silverado

10-01-2007, 02:58 PM	#4
hvychve To The Levy Join Date: Jan 2007 Location: california Posts: 391	Re: How do you test a power brake booster? Hey Crawdad, I have my own way of checking to verify booster is good or bad, I usually pump all the air out of booster by operating brake pedeal about three to four times firmly with engine off. than while holding the pedal down I start engine, if the booster is good, vacuum will pull the pedal down just a tad, usually about a 1/4"....... hope this helps and if I am wrong, please feel free to correct me, also there is usually a hissing noise when brakes are applied with engine running, or engine shakes and runs rough when pushed hard and engine is running, sorta like a vacuum leak, good luck

10-01-2007, 10:54 PM	#5
wibilly Senior Member Join Date: Nov 2005 Location: northwestern wi Posts: 2,111	Re: How do you test a power brake booster? hard peddel ,little brakes =bad booster, often times you will have a bad vacume leak as well __________________ common sense isn't so common anymore

10-02-2007, 12:17 AM	#6
PICKMUP "Trucks with Class" Join Date: Jul 2000 Location: OLYMPIA, WA, USA Posts: 8,139	Re: How do you test a power brake booster? I use a vacuum pump with an in-line vac gauge and shut off valve. Draw 20lbs and close the valve. The booster should hold that reading and not leak down (diaphram leaks). You can even operate the booster by hand with the pump drawing vacuum and see that is is working freely. Another test is to run the engine to draw vacuum, shut off the engine and wait about 30 seconds, then pull the plastic valve off the booster...you should hear the vacuum bleeding off if there are no leaks. Attached Images

04-01-2019, 02:03 PM	#7
MySons68C20 Senior Member Join Date: Sep 2014 Location: Wenatchee, Wa Posts: 924	Re: How do you test a power brake booster? Old thread but very helpful! I just tried both methods and the brand new 2 year old booster won't hold any vacuum. Thanks to all! Blake



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