BENDIX BW1555 User's Manual
Contents
1. Shut off engine CAUTION To avoid possible injury due to automatic application of the parking brakes during testing it is recommended that the parking brakes be mechanically caged 3 Check the vehicle or combination for excessive air system leakage If the combined leakage exceeds the limits below repair the sources of leakage before proceeding Brakes Released Brakes Fully Applied Single Vehicle Tractor w Trailer Tractor w 2 Trailers 4 psi in 2 mins 6 psi in 2 mins 6 psi in 2 mins 8 psi in 2 mins 8 psiin2 mins 10 psiin 2 mins AIR BRAKE PRESSURE BALANCE TEST Objective To determine the air pressure differences between the various axles of a single or combination vehicle Equipment Dual test gauge use a gauge with a 0 150 psi range Testing 1 Perform vehicle preparation and place the vehicle dash control valves in the normal over the road position 2 If the vehicle being tested is a single unit such as a straight truck or bus install one half of the dual test gauge directly in the 1 or primary circuit delivery of the brake valve For tractors or combination vehicles install one half of the dual test gauge in the trailer service control line between tractor and trailer NOTE This half of the test gauge will remain here for the duration of the test Install the other half of the test gauge in a service brake chamber at axle 1 Procedure will be repeated at each axle of the vehicle c2. AIR PRESSURE BALANCE amp THRESHOLD PRESSURE TESTS SON SON SONS a a A N VAE CACAL A CW VW YY CS Nw NS NZ SY ca St Se ee ae ae 1 TT Th Tractor Dolly Dolly Trailer Trailer Trailer kH keH ho Hei si H aca L Brake No 2 4 VEHICLE DATA Vehicle Manufacturer Number Model Year Comments Tractor 1 Trailer Conv Dolly 2 Trailer Conv Dolly 3 Trailer GENERAL INSTRUCTIONS 1 Number the axle and each brake on the axle of the vehicle being tested using the illustration 2 All testing should be performed using both increasing INC and decreasing DEC air pres sure and using our instructions 3 When performing the Air Brake Pressure Balance Tests the pressure from only one chamber of a tandem can be used when the same relay valve delivers pressure directly to all four chambers on the tandem 4 Record test results in the charts provided ON 2142A Ag peyonpuoy s L S SO INSS Jd Ppjoys IyL pue souejeg INSS JId IY 3eq Air Brake Pressure Balance Test Service Chamber Pressure at Axle Increasing Pressures for Axle Nos Decreasing Pressures for Axle Nos Trailer Control Line VEHICLE PREPARATION FOR TESTING 1 Adjust all brakes equally using the vehicle manufacturer s procedure 2 Secure the vehicle on a level surface by means other than the brakes and charge the air system to governor cut out approximately 120 psi
3. iate brake in the chart 5 Increase service air pressure to 40 psi While gradually decreasing the air pressure at the gauge attempt to rotate the wheel Note the gauge air pressure at which the wheel can be freely rotated and record that pressure in the decreasing DEC column for the appropriate brake in the chart 6 Add the pressure recorded in the increasing INC and decreasing DEC columns together then divide by two Record that value in the average AVG column for the appropriate brake This average is the threshold pressure for that brake For example If the number in the increasing column was 9 and the number in the decreasing column was 3 then 9 3 12 12 2 6 and 6 is recorded in the average column BW1555 Bendix Commercial Vehicle Systems LLC EXAMPLE Foundation Brake Threshold Pressure Test Gd a Pettit eS eee ES 7 When testing is complete uncage the parking brakes RECOMMENDATIONS Bendix recommends that all brake threshold pressures for all axles average calculated value from the test results be within a 2 psi range This is to enable the brake force distribution to be within acceptable limits especially at low brake application pressures Industry studies have indicated that 80 of all brake applications made in actual service are below 20 psi For pressure balance on increasing pressures we recommend that the pressure recorded at each axle be with
4. in 2 psi of one another for trailer control line pressures of 10 to 40 psi The decreasing pressures recorded should also be within 2 psi of one another in this pressure range For axles fitted with special valves which enable the threshold pressure recommendation to be achieved or which proportion or limit the delivery to the chambers this recommendation is not valid Under these conditions the specific application must be analyzed in more detail to understand the brake distribution There are many factors that affect vehicle brake balance Balancing the brake threshold pressures and the pressure at the chambers of all axles are important factors in achieving brake balance However this does not necessarily ensure even lining wear or brake force distribution Consideration must also be given such factors as tire size brake size brake type friction material and others NOTE The difference recorded in these tests can be attributed to specific vehicle design considerations Before any brake system modification are made the test data should be reviewed by both the vehicle OEM and our Engineering Departments 11 2002 Printed in U S A
5. ombination NOTE Test gauge connection must be between the air chamber and any control valve ideally directly in or at the chamber 3 Gradually apply the brakes via the brake valve and record the axle pressure in the increasing INC column of the axle 1 when brake valve primary delivery or trailer service control line pressure is at 5 10 15 20 25 30 40 50 and 60 psi Repeat procedure for each axle of the vehicle combination and record pressure readings on the chart See partial example IMPORTANT Readings during this phase of the procedure should be taken with increasing air pressure only Do not over apply and then release as an inaccurate reading will occur Release brakes fully and re apply if pressure is over applied 4 Repeat the procedure using decreasing air pressure Fully apply 75 psi application min the service brakes then gradually release and record the axle pressure in the decreasing DEC column of the appropriate axle when brake valve primary delivery or trailer service control line pressure is at 60 50 40 30 25 20 15 10 and 5 respectively Repeat the procedure for each axle and record the pressure readings on the chart EXAMPLE Air Brake Pressure Balance Test Service Chamber Preus m Acie fiiia Pericles Fit Aah PAH Damin Paih Sie Vict eta Fat IMPORTANT Readings during this phase of the procedure should be taken with decreasing air pressure only Do not under shoot the pre
6. ssure and partially reapply pressure as an inaccurate reading will result Fully apply the brakes and exhaust down to the specified pressure 5 When testing is complete uncage the parking brakes unless you are proceeding to FOUNDATION BRAKE THRESHOLD PRESSURE TESTING FOUNDATION BRAKE THRESHOLD PRESSURE TESTING Objective To determine the air pressure required to make and release contact between the lining and drum at each foundation brake on the vehicle Equipment Test gauge use a gauge with a 0 60 psi range Important A low range 0 60 psi pressure gauge is required for accurate data for the threshold pressure test Using a higher range 0 100 or 0 150 psi gauge can result in bad data Testing 1 Perform the vehicle preparation and place the vehicle dash controls in the normal over the road position 2 If the vehicle being tested is a single unit such as a straight truck or bus install the test gauge directly in the 1 or primary circuit delivery of the brake valve For tractors or combination vehicles install the test gauge in the trailer service control line between tractor and trailer 3 Raise the axle until tires wheel ends are no longer in contact with the floor 4 While manually rotating a wheel gradually make a service brake application as registered on the gauge until braking torque drag occurs Note the gauge air pressure and record it in the increasing INC column for the appropr
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