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valleybusman
Top Member

USA
799 Posts

Posted - 11/18/2016 :  10:08:01 PM  Show Profile  Send valleybusman an AOL message  Reply with Quote
I have been working on air brakes for 37 years . One thing I know is that if the needles move more than 10 pounds apart they are out of adjustment . I mean if one gauge says 100 and the other gauge reads 115 after application they need looked at . What I have either for gotten or never really knew was . How much air should be use after an application ? I had one driver who tried their brakes and it took almost 10 lbs of air for primary and secondary brakes . Is this normal ? I always thought 5 lbs or more and they need adjusting ? I have automatic slacks if that is a question ? Thanks

BJ Henderson
Advanced Member

USA
280 Posts

Posted - 11/19/2016 :  12:16:12 AM  Show Profile  Send BJ Henderson an AOL message  Reply with Quote
Nothing in the world wrong with 10 PSI on brake application. Your foot valve or, treadle valve is graduated not just on and off. If the driver applies the brakes on the road it takes more force to stop the bus than just checking them in the shop with the typical air brake test on inspection. On commercial vehicles hauling passengers, two minute build up time between governor on and off well takes care of the need for air.

Now, as for auto slacks, if one or more is out of adjustment, it can seem as if you are using more air, and you are. Do the stroke test with an assistant, at above 90 psi. I usually get under the bus and check one slack as the extend, roll over and check the other side when released. This saves air for the front where you will not have to start the bus up again. Always do the rear first. These are the brakes that typically have a larger cubic inch area on the service brake diaphragm.Depending on the size of the diaphragm, the indicated stroke is different.

Hope this helps!

CMTT,CMAT,CMBT
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BJ Henderson
Advanced Member

USA
280 Posts

Posted - 11/19/2016 :  01:12:16 AM  Show Profile  Send BJ Henderson an AOL message  Reply with Quote
http://www.bendix.com/en/servicessupport/brakeschool/on_linetraining/onsitetraining_1.jsp maybe this can help more than I can.

CMTT,CMAT,CMBT
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RonF
Top Member

867 Posts

Posted - 11/29/2016 :  04:54:40 AM  Show Profile  Reply with Quote
You can buy OTC 5052 cam brake slack adjuster tool and check the stroke without and assistant or using any air to do so.

Google the number and you will see the tool. WHen inspecting the bus, release the parking brake, hook the tool around the slack adjuster and pull. Takes less them 5 minutes to do all 4 wheels.

US Army retired CMBT
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aaronwilmoth80911
Top Member

538 Posts

Posted - 11/29/2016 :  08:34:02 AM  Show Profile  Visit aaronwilmoth80911's Homepage  Reply with Quote
Depending on where you're at, this may or may not be acceptable to use. In Colorado, all of our measurements must be taken using the applied method. This tool may be good to have though for doing certain checks.
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