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My truck has started to have a longer Jake brake delay.I haven’t timed it but I would say 5-7 seconds and once engaged and I downshift another 5-7 seconds.What could be causing this change? 2004 CM870.

Any recent repairs?
Could be a number of things, first thing to check is engine oil level and viscosity.

(05-21-2021 )DieselKid Wrote: [ -> ]Any recent repairs?
Could be a number of things, first thing to check is engine oil level and viscosity.

The turbo control box was just replaced.Replaced intake temp,pressure,and exhaust pressure sensor. Oil can affect it?

Yes, the engine brakes are oil pressure driven. As the actuators age the seals and cam bearings will start to leak more oil and take longer and longer to actuate the brake as it takes longer to build enough pressure to overcome the springs.

A bad harness can also cause it's the spade connectors stretch over time as well. Mine were so lose I could knock them off just by bumping them during an overhead set and they had around a 3 second delay.

Unilevers brought up that the very small oil galleries in the rocker shafts often clog with soot. While you have the top apart you may want to spray some brake clean and some shop air down in these galleries to ensure you getting proper oil flow to everything up there.

(05-22-2021 )Nilao Wrote: [ -> ]Yes, the engine brakes are oil pressure driven. As the actuators age the seals and cam bearings will start to leak more oil and take longer and longer to actuate the brake as it takes longer to build enough pressure to overcome the springs.

A bad harness can also cause it's the spade connectors stretch over time as well. Mine were so lose I could knock them off just by bumping them during an overhead set and they had around a 3 second delay.

They were working flawlessly and from one day to the next the delay started.

(05-22-2021 )Chamberpains Wrote: [ -> ]Unilevers brought up that the very small oil galleries in the rocker shafts often clog with soot. While you have the top apart you may want to spray some brake clean and some shop air down in these galleries to ensure you getting proper oil flow to everything up there.

This picture was taken six weeks ago when I purchased the truck.

(05-24-2021 )Redland1 Wrote: [ -> ]

(05-22-2021 )Chamberpains Wrote: [ -> ]Unilevers brought up that the very small oil galleries in the rocker shafts often clog with soot. While you have the top apart you may want to spray some brake clean and some shop air down in these galleries to ensure you getting proper oil flow to everything up there.

This picture was taken six weeks ago when I purchased the truck.

Wow, none of the sensors on that engine look like they've ever been touched!. -- Sad indeed.

Messed around with all the wires under the hood especially the ones coming out of the ECM and now the Jake brake works.