2015 Prostar - Engine Brake - WTF?

When it fails to engage, stick your toe under the throttle pedal and pull back a little and see if it starts working. I had a 2013 that had a similar issue. Turns out the throttle position sensor was bad. It would stick just enough to keep the jake from working. When they plugged the computer into it, it showed it fluctuating between 1 and 2% throttle. 30 minutes later, a new throttle assembly installed and it cured it and it hasn't done it since.

If you have a Maxxforce engine, as far as the new engine brake, on a Maxxforce, used as recommended by Navistar, they work good. Recommended RPM's for maximum braking power on a Maxxforce is 1900-2100...don't exceed 2350. I roll down Cabbage hill in Oregon with 44,000 lbs between 45 and 55 mph, and only touch the brakes a few times. The old Maxxforce exhaust brake sucked, but since they started using compression (jake) brakes, it was a major improvement.

And BTW, from the factory, Maxxforce has a built in 'float shift' delay on the jake. It hesitates engagement of the jake very briefly so drivers like me can float shift.

If you have the Cummins, then ignore all the parts about the Maxxforce, but it still might be your throttle pedal. It could also be your clutch pedal sensor...Prostars have been known to have their clutch linkages a little out of adjustment causing issues with the sensor

 

I believe youll need to reapply the foot brake,to engauge jake.It does not stay on like the 680.

 

No..he is probably operating it correctly..
I float a lot from different trucks in our fleet and have driven dozens n dozens of different Pro-stars and just this past week I drove one that was as he describes,with a intermittent jake brake..the dam thing just seemed to operate whenever it felt like it (very frustrating and even somewhat dangerous..)
Interesting reply from supersnackbar: possibly he could be onto something?
There was clearly something wrong w the one I drove this week.

 

Alot of the new trucks are coming programed not to engage the jakes until you hit the foot break and they wont kick in 35mph and below. This is on the cummins model and when I asked the dealer about it he said and I quote "it was done in the name of fuel milage" all of our 2014 and above are set up to have to hit foot break first and all the 2015 and 16s have a speed u have to before it to work.

 

Kind of silly to compromise brake wear for 1mpg fuel savings.I hated coming down steep grades,having to reapply foot brake,to engauge the jake.I like the 680,much better,with automatic operation,whenever you release the accellerator.

 

May have a broken clutch switch. They break sometimes if your not careful and your foot slips of the clutch with pressure, or might have accidentally kicked the wall behind the clutch (where most clutch switches are) ... If your cruise control is not engaging too then it's almost a 100% chance you have a bad clutch switch. AND OR you may have a broke or out of adjustment clutch spring

Good luck

 

Simple answer..There IS something wrong with it.(period)
as I said earlier I have driven dozens dozens of the pro stars in our fleet and this last one I drove I experienced exactly what you described and I also tried EVERY remedy I could think of?
Pedal position (lifting up on clutch pedal)is one i didn't think of..
although I did try slapping the throttle(stomp)because the dam thing was SO intermittent?..