Trying to help a buddy resolve a spring brake problem.
2005 Sterling (div of Freightliner?) tandem drive truck with no trailer hookups. Looks like it has ABS and a modulator that works via the spring brake system. When you push the dash park brake release it vents air but the brakes do not release. He thinks its throwing a 74 code but can't get any info from the dealer as to what it means. There's a small supply air line on the brake valve/modulator that when disconnected lets the brakes release. The line has constant air pressure that I think should not be there when the park brakes are released. I'll search the net to see about the code but anyone here have any tips/pointers that I could relay to help him out? Thanks in advance.
2005 Western Sterling spring brakes won't release
Discussion in 'Trucks [ Eighteen Wheelers ]' started by 55_cans, Aug 5, 2014.
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check park brake/trailer supply tank pressure.
Unhook red glad hand and press red knob. if no air goes out from red glad hand - check park brake tank valve. it may stuck.
Other problem - park brake release relay valve - may go bad too!55_cans Thanks this. -
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if it is rigid truck w-o trailer - tank #3 (park brake and trailer supply) is used anyway, but smaller.
It may be combined with other tanks with valve inside inner wall, like on freightliner, so inspect air lines to find what is the park brake tank and check for pressure inside with moisture drain valve55_cans Thanks this. -
The brake ABS modulators and relay valves are one unit. A relay valve between two modulators - one modulator for passenger wheels, one modulator for drivers wheels. There's a modulator/relay valve for the service brake system - one unit for the front axle and one unit for the tandem rear axles. Then there's a modulator/relay valve for the spring/park brakes. Kind of looks like the spring/park brake system will take over and act as a secondary braking system if the service/primary braking system fails. Don't think the modulators act as traction control devices because the modulators operate both tandem wheels at the same time. -
abs relay modulator is the different thing, check park brake relay. lines from park brake relay run to spring port, not for service brake ports
http://www.suspensionspecialists.com/techinfo/Bendix_Brake_Handbook_2009.pdf
Park tank lines are of red color, park control - yellowbaha Thanks this. -
Wait a minute...what is a Western Sterling? LOL.
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Do the brake lights stay on ? The foot valve pedal may be sticking. Pull the cap off the brake camber cageing spring brake hole look at the plate an have some one push the park brake valve in . The plate should move to the back cover. If it moves the problem is on the service side bad valve , foot valve .
55_cans Thanks this. -
to check tank pressure I use moisture draining valves. Just pull it!
what is the specification of vehicle? is it class 6-7 rigid truck? I saw Sterling trucks with Mercedes Powertrain (OM906LA engine and 6 st tranny). really it was like conventional design version of MB Atego.
Air system is very simlpe. One supply tank (also used for air syspention) and four air tanks: Primary, Secondary, Park and Accesory tank (sleeper suspention, transmission spliter, seat air suspention).
So things are very simple.55_cans Thanks this. -
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