Total Noob learning experience
 

On the Saturday morning of my weekend journey I had an unsettling thing happen with my Freightliner. When I approached the first traffic light of the day on a 55mph road, the engine brake almost stalled the truck, instead of just letting go once the truck was sufficiently decelerated.

Needless to say I was bewildered and thought it was a fluke, until it did it again at the next light. Still in denial, I guess, I just switched the engine brake off and back onto high.

At the third light, just about when the brake was about to stall the engine, the engine fought back and gave itself a little throttle! It took both feet planted firmly on the service brake to hold the rig while the engine and the brake fought it out and I reached for the brake switch.

Fortunately, the brake gave up and let go of the engine before I could reach the switch!

I switched off the engine brake and drove without it for the remainder of my Saturday journey.

After a protracted period of internet research, I resorted to digging out the Freightliner manual, where I found this (in bold print):

WARNING
...If the engine
brake is engaged when the transmission is
in neutral, the braking power of the engine brake
can stall the engine, which could result in loss of
vehicle control, possibly causing personal injury
and property damage.

I must have switched it on along with the headlights and cruise control or something...what a dummy!

That's pretty weird. I have a Cat motor with a true Jacobs 2 stage. I don't know if your Detroit uses a true Jacobs or some competitor. I'm pretty sure I've left the Jake brake switch on when shifting in/out of neutral. Never heard of something like that happening. Can't wait to hear how it worked when you took it for a drive and didn't turn on the engine brake until you were rolling in gear. That will be the true test.

When departing, I did not activate the engine brake until the truck was warmed up and we were idling down the street. At the first light (and all subsequent stops), the brake worked as it should.

My truck is equipped with a generic electronically actuated Hi-Low engine brake. Apparently it calibrates itself when it is first turned on. I guess that is why you want the engine warm and in gear for the first activation. After that, it doesn't seem to matter when you switch it on and off.

thats weird - with our MBE4000 (aka dd13) the exhaust brake won't operate when the truck is in neutral.

Mine doesn't operate in neutral either, but it can be switched on while in neutral. That is what causes the problem.

I'm confused, because once i turn ours on i don't usually turn it off until i am rolling/accelerating (i.e.: re-entering the interstate, or thru the traffic light/intersection, etc)....ive sat idling at an intersection many times with the exhaust brake on, with out a problem.

You are all right, I am just not conveying the matter improperly. It is a one time thing at startup. The brake switch must remain in the off position until the truck is warmed up and out of neutral for the first time. Once rolling for the first time after startup, the brake switch may be moved to hi or lo, and even back to off with no ill effect. It just must be initiated that first time after startup.

Once underway, the switch can be in any position and the brake will respond accordingly. It can even be switched off again.

Clear as mud...Right?

I think i understand now (that ours is different).

Is yours a proper (valved) jake brake or an exhaust brake (creating back pressure in the exhaust by blocking the flow) ?

On our MBE4000 engine we have an exhaust brake (integrated inside the turbocharger) - that blocks or reduces exhaust flow - it will not stall the engine when its on (idling or when started that i am aware of)....im pretty certain as forgetful and distracted (my wife calls it ADD/ADHD) that I've left the brake on when starting too.

The manual states that it is an engine brake. I think somewhere in my reading I read that it is a true "Jacobs or Jacobs style" brake, not an exhaust brake.

I'm not an expert but i could see how having a JAKE brake on could prevent an engine from starting (since it alters the valve timing), but I'm still confused about how it could stall an engine....hopefully someone will educate me (too).

The SOP for a true Jacobs brake is 2 pedal switches. One on the clutch and one on the brake. if you just pull the shifter into neutral and let the jakes slow you to a stop. It SHOULD stall the engine. It should have disengaged when the clutch (whether you or the auto shift) was pressed. If you have a three pedal truck you should have your switches checked. A 2 pedal truck should be serviced by a dealer.

makes sense - having the tranny in neutral and having a jake brake on does nothing to help slow the vehicle.

If you read what you wrote (in red) and think about it a little further (if you had to step on the brake with both feet to keep it stopped the transmission was not in neutral, it was in gear and the clutch was engaged, lugging the engine down)you will see that it was not the engine brake trying to stall the engine it was the transmission, more correctly the clutch, not releasing at close to a stop, causing the engine to lug almost to the point of stalling. The transmission ECM may have been having a bad day-my 12speed Freedomline has an occasional,rare, questionable action that usually corrects itself, or once in a blue moon requires a power off reset. You flipping the engine brake switch was purely coincidental.

Your truck chassis is pretty much identical to mine only a year older

Any computer controlled engine, when running properly, will NOT stall the engine with the engine/jake/exhaust brake switch turned on. There are settings in the ECM that control when and how the engine brake comes on/off etc. The only time I have seen the engine brake stall an engine is if you are decelerating hard (on the service brakes) while downshifting at the same time and miss a shift or if the engine is mechanically controlled.

As an aside Detroit Diesel uses an actual Jacobs Engine Brake system.

I think I'm with Porky on this one. I bet it's something funky with the transmission.

Great. Mystery unsolved.

I also agree with Porky, sounds like your clutch is not disengaging. The engine brake helps slow you down, but then at low speed, it should not be engaged. However your clutch is still engaged and that is what you were fighting. It could be a sensor adjustment or something mechanical, hard to say what is going wrong.

My engine brake has to be manually turned on each time the engine is started, the default is no engine brake unless I turn it on. So at least for me it is not possible to start the engine brake with the brake on. I also have to select which of the three levels of engine brake. It does engage and do its thing automatically once turned on.

Did a quick round trip to Key West last week. No transmission or engine brake issues to report.