2014 Western Star 4900 - DD15 - Jake Brake Not Working on One Bank

Question

My jakes aren't biting like they used to. I have a 3-stage switch; stage 1 does nothing, stage 2 feels like stage 1 used to, and stage 3 is weak. I can hear the engine sound change, so something is happening, but it's not holding the load back on the hills.

Pulled the valve cover and everything looks seated correctly. No broken springs that I can see. Oil pressure is good (60psi at cruising). Is this an electrical issue or an oil galley problem in the rockers?

WeldShopWanda · Answer

✅ Confirmed fix: Found the mounting bolts for the engine brake housing had backed off slightly on the rear bank. This allowed high-pressure oil to leak out from under the housing instead of going into the pistons to open the exhaust valves. Torqued them back to spec with new seals and the Jakes are back to full strength.

DIY_Denise · Answer

If you have DiagnosticLink, run the Engine Brake solenoid test. You should hear a distinct click from each solenoid. If one is silent, you have a bad solenoid or a break in the internal harness under the valve cover.

2014 Western Star 4900 - DD15 - Jake Brake Not Working on One Bank

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