Weak Jakes

Mechanics Hub Forums Bus & Coach Other Weak Jakes

This topic contains 4 replies, has 5 voices, and was last updated by  Hector 6 months, 2 weeks ago.

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  • #25733 Reply


    We often get complaints from drivers of “weak Jakes”. The coaches I work on have two speeds, high and low. First we verify that the jakes are in fact coming on. If they are active in both speeds, most then do a rebuild of the jakes. My question is, if the springs aren’t broken and the solenoid is working properly, is there any point of doing a rebuild? Keep in mind these are series 60s with over a 1,000,000 MILES.


    #28291 Reply


    If I have went thru the trouble to pull the top off to get to the jakes, im replaceing what I can if its out of spec.

    #28292 Reply


    Replacing the control valves and springs in the jake housings will improve performance, as springs will shorten over time and control valves will wear or start to stick in their bores. However, before replacing any parts I always power up the heads with the engine running at idle and valve covers off to check for any hydraulic leakage coming from the solenoid seals, control valves, or slave and master piston bores. If oil is leaking out, the pressure inside the brake housing will be diminished, and the exhaust valve will not be opened far enough or at the right time for effective braking. You can usually power up the solenoids with a test harness tapped into a 12v (or 24v for coaches) power supply and connect directly to the solenoid, or manually depress the solenoid plunger with a screw driver. If you find significant leakage from a slave piston bore, you will want to check the housing for scoring or cracks at the time of re-build. Some other things to consider for jake brake performance if there are no apparent problems with the brakes themselves, is the condition of the turbo charger turbine wheel, engine oil level and quality (should be the first check actually) and checking for boost leaks. I hope this helps.


    #28295 Reply

    Jim Owen

    This is another example of dead ended oil galleries. Oil in the jakes are not refreshed often enough to prevent the oil from deteriorating inside the jake head. When the jake is not being used, engine oil pressure keeps it full. Little oil escapes, and the contaminates start to settle out; the heat starts to thicken the oil; varnish starts to form and all of the things tend to add up to jakes that don’t do what they’re supposed to, when they’re supposed to do it.

    Even though there nothing mechanically wrong, the head needs to be removed and cleaned. And given that it has been removed, as was said earlier, replace parts that might be a problem in the near future.

    Similar things occur inside the HUEI injection system, another place where the oil does not circulate well enough, and results in injector failure, hard starting and loss of power.

    #48822 Reply


    Hello,I just bought a 2013 Hinternational prostar with maxxforce engine then when I going running I apply the jake break the engine motor start failing and get off, please somebody can help me.

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