Cruise and Jake Brake operation

[Mike Jones]

Does anyone know what wiring needs to be changed on a 2001 Marquis to make my cruise work on with the jake brake switch on? I have done the cruise settings in the ecm on my C12 Cat but it still does not work. I have heard there is a wiring change that needs to be done also.

Thanks in advance.

Mike

[David T. Richelderfer]

On our coach, a 2004 Marquis Sapphire, the cruise control works with the Jake Brake on in either position - meaning the "full Jake" or "half Jake" positions on the Jake Brake 3-position toggle switch.  Our coach used to go into 4th gear from 6th gear when the Jake Brake engaged but I got that changed at the Kenworth shop in Pasco, WA.  The technician hooked his computer up to the engine/transmission plugin located under the removable dash panel to make that change.  Now the transmission stays in 6th gear when the Jake Brake engages so that the engine RPMs don't go well over 2,000 RPMs as it did when it shifted from 6th to 4th gears in the past.

I have not heard of a wiring change.  Our change was a programming change made by the technician.

[Mike Jones]

David,

 I had the transmission change so that it stays In sixth when the jake comes on. I just down shift on my own. When I have my cruise on and turn on my jake the cruise shuts off and if my jake switch is on the cruise will not even engage.

Thanks

[Mike Shumack]

I don't know if the 2005 and 2001 Marquis are wired the same - but if you look at the diagram attached, the Cruise turns off when the brake lights come on. The Jake brake turns on the brake lights when it is engaged/active. If you rewire the Jake so that the brake lights don't come on, that would allow the cruise to stay operational with the Jakes active and still turn off when you set on the brake pedal. I'll see if I can find a diagram for the Jake wiring - I sort of remember seeing a post about a while back about preventing the brake lights from coming on with Jake activation.

[Fred Cook]

Am I missing something here??? I thought when the Jake brake was applied it shifted to a lower gear which is what slowed the coach down. How does the coach slow down if it remains in 6th gear?

[David T. Richelderfer]

From a GOOGLE search:


"The Jacobs Engine Brake® (also known as the "Jake Brake®") is a diesel engine retarder that uses the engine to aid in slowing and controlling the vehicle. When activated, the engine brake alters the operation of the engine's exhaust valves so that the engine works as a power-absorbing air compressor."

"It is recommended to operate the Jake Brake in the shifting range, about 1,100-1,400 RPMs. The brake will work in a higher range; however, the motor might decline at a faster rate if it's in a higher range too frequently."

The latter quote would indicate it is best to NOT shift from 6th gear to 4th gear too soon/quickly... because the engine RPMs would go into a range well above the recommended operational range for the Jake Brake.

[Lee Welbanks]

 The main reason Monaco programed the trans to shift into a lower gear when engine brake came on is that most drivers of motor homes do not know how a engine brake works so they took out the step of shifting down with your finger. If your running down the road at 65 or 70 and you slam the trans into 4th gear your $30k dollar Cat doesn't like it too much. My book state that the trans will not shift down if the rpm's are too high, well I can state this is not true the trans will shift down.

Another reason to take out the down shift is if you are just floating down a slight grade and want to slow just a bit without hitting the brakes you use the engine brake, I drive with mine on most of the time.

[Mike Jones]

Lee,

Mine has done the same thing. it shifted to down to 4th way to soon. Engine rpm went to 2500 real quick. I would rather control it myself.

[Mike Jones]

Thanks Mike, I will take a look at it.

Thanks again

[Mike Jones]

Mike Shumack.

My cruise will not even activate if the Jake switch is even turned on . Jake does not even have to be activated. Even if I use the cruise for high idle, the minute I turn on the jake switch it shuts the cruise off

[William Jordan]

Over rev for the c12 is 2300 I believe but I was told that's under power, not with no throttle as in a jake.  I haven't had mine changed but am very careful to not engage so I won't exceed 2100rpm.
 I honestly thought its just  programing that removed the cruise lockout with the Jake Brake on. I know My brake lights on jake were removed so as to not "ride " my car hauler's electric brakes. and my cruise still doesn't work with Jake on. I know many who can do both so it must be possable.

[Lee Welbanks]

On my 06 PT the down shift was one of the first things I had changed. The cruise control works with the engine brake switch in the on position, going down hill if the coach gets about 10 mph above the cruise set point the engine brake will come on and slow the coach down. The 06 wiring system is probably completely different from you coach, but they both will work this way.

[David T. Richelderfer]

Our combination of cruise control and Jake Brake work much as Lee described.  I can have the Jake ON and cruise OFF, Jake OFF and cruise ON, both OFF, or both ON.

Our coach has a Silverleaf screen that has three colored icons (green, yellow, red) for signifying what level of Jake Braking is engaged.  If we are traveling down a hill, steep enough that the coach wants to run, then the Jake Brake will engage with a Silverleaf green icon at 3 mph over the cruise set speed.  Add a few mph to perhaps 5 mph over the cruise setting and the Silverleaf yellow icon comes on and the Jake Brake's braking goes up a level.  Add a few more mph and the Silverleaf red icon comes on and the Jake Brake goes to full braking.

So it seems our engine has the three-stage Jake Brake but the console has a three-position toggle switch (LOW, OFF, HIGH), not a four-position switch which would include a MEDIUM setting.  Thus, with the cruise control OFF, I am able to toggle only between LOW and HIGH braking on the Jake.