Exhaust or jake brake or neither?

[k_jensen6]

How do I know if I have a jake brake, an exhaust brake or is it possible that we don't have either of these? We have a 2001 holiday rambler imperial with an Allison 3000 transmission.

Am extremely nervous going down hills.

Thanks

[wolfe10]

Electrix wrote:
You should always manually select the gear when going down a hill, don't just leave the selector in D. The transmission is likely to upshift, instead of downshifting to keep the engine revs high for maximum exhaust brake retardation.

All correct, though a slight correction to this sentence. With the exhaust brake on, as long as you don't touch the throttle, it will not upshift unless engine RPM increases to where it could damage the engine. At that point, it WILL upshift.

But, as long as you are below that RPM, the transmission will not upshift unless the throttle is pushed.

But, I do like to use the down arrow to "hold" a gear-- that way if that gear with exhaust brake on gives a little too much braking and that gear with exhaust brake off, not quite enough, one can toggle the exhaust brake switch on/off/on and won't have the transmission continually up/down shifting.

[Electrix]

The Allison ECU with a MD3000 will activate the exhaust brake automatically when the following conditions are met;
Torque converter in lockup,
Throttle pedal released,
Dash mounted exhaust brake switch is on,
Cruise control not active,
ABS not active.

The exhaust brake works independently from the foot brake, but some vehicle manufactures wire a switch into the system requiring the brakes to be applied before the exhaust brake operates. Others will fit a foot operated switch that has to be pressed.

When the ECU activates the exhaust brake, it also switches to a secondary shift schedule that downshifts the transmission earlier. This is done to keep the engine revs higher to increase the exhaust brake performance. It is also possible to force downshifts even quicker by programming the Exhaust Brake Preselect Parameter to a low gear, eg 2nd. The options for this parameter are gears 2 through 6. When the exhaust brake is activated the display will show the preselect gear that is programmed in the ECU. The display will only change if a lower gear than the normal top gear is programmed.
Selecting 2 can be a bit brutal as the transmission will try to downshift to 2nd gear as soon as possible. 4th is often a better choice. At low engine speeds in a high gear the transmission may drop two gears when the exhaust brake activates.

As previously advised it is often suggested to go down a hill in the same gear and engine revs that you would go up it. If you would go up a particular hill at 1800rpm in 3rd, then it is probably a good idea to manually select 3rd and use the exhaust brake to hold the engine speed at about 1800rpm going down. This will depend on how effective your exhaust brake is.

You should always manually select the gear when going down a hill, don't just leave the selector in D. The transmission is likely to upshift, instead of downshifting to keep the engine revs high for maximum exhaust brake retardation.

[JimM68]

The post that says a pacbrake doesn't work until you are in 4rth is for sure incorrect. (tho I've never gone in the bedroom and took the cover off and made sure the actuator moves with the coach in 5th or 6th....)

OP, some just leave the switch on. Take your foot off the gas, and the coach slows like it hit a wall. I find that tiresome, and only switch mine on when I'm going to need it, including exit ramps.

As for hills... you are screaming up the hill, 4th or maybe 3rd gear at redline, foot on the floor. Just turn on the engine brake now, it really doesn't matter. When you get to the top, ease the loud peddle but don't completely release it. As you start down, release the loud pedal. Your trans indicator will go (usually) to 2, the trans will downshift a gear or two, and you'll go down the hill. Stab the brakes hard and release as needed.

The system is smart. It won't let the engine over rev. It will mostly keep your speed down.
Don't ride the brakes down the hill. hit them when you need them, then release to let them cool.

[mtrumpet]

Electrix wrote:
Did they give you any advice on using the exhaust brake?
There has been a bit of misinformation given here.

Perhaps you should enlighten us as to which of information given is incorrect(?) Most of us here are always open to learning and updating our technical knowledge.

[mtrumpet]

Executive wrote:
(snip)...Also, usually it will not engage if the cruise control is ON.....

....Dennis

Mine (Jacobs Exhaust Brake) does in fact engage even with the cruise control on. That's usually what wakes me up to the fact that I'd left the switch "on" - as we start a descent with the cruise on, the exhaust brake kicks in as the cruise backs off on the throttle. The first time it happened, my immediate reaction was "Uh oh. Loosing power! Something must be wrong with the engine!":E ..Then, I looked down and saw that Allison control pad showing "2" and saw that I'd left the exhaust brake on. 😮

[Canadian_Rainbi]

Our Itasca Horizon has an Exhaust Brake but the control and indicator lights say Engine Brake. :S

It is probable that your is an Exhaust Brake. It doesn't really matter, they are used in the same way.

[Electrix]

Did they give you any advice on using the exhaust brake?
There has been a bit of misinformation given here.

[k_jensen6]

Just an update. Finally took our coach in, turns out our exhaust brake was seized. Had to have it replaced.

Oh the things you learn. Our big one, don't take the dealers word for anything, hire a private inspector.

[wolfe10]

BarbaraOK wrote:
Most pacbrakes do not engage until you are down around 40 mph and the transmission in 4th gear - at least that is for us. Start going down by slowing down to 40 or less (depending upon how step the down side is - - use the signs as an indication of how slow you need to be) and engage the brake and take your foot of the brake and let her walk down.

Barb

Barb,

You need to verify, as an exhaust brake not engaging until you are slowed to 40 MPH is NOT CORRECT.

The instant you turn on the exhaust brake and close the throttle, you should see the transmission shift pad change from "6" to your pre-select gear (usually 2 of 4) AND, repeat AND the exhaust brake close. No, it doesn't have as much effect at higher speeds, because it takes more braking HP to go from 60 to 50 than, say, 40 to 30.

As you continue to slow, the transmission will continue to downshift toward the pre-select gear and the exhaust brake butterfly stay closed until you are down in 2nd gear, at which time the exhaust brake turns off, as the engine won't idle with the exhaust closed.

[BarbaraOK]

First, you always want to go downhill in the same gear as you climbed the hill. Most pacbrakes do not engage until you are down around 40 mph and the transmission in 4th gear - at least that is for us. Start going down by slowing down to 40 or less (depending upon how step the down side is - - use the signs as an indication of how slow you need to be) and engage the brake and take your foot of the brake and let her walk down. If the speed picks up, use the vehicle brakes to slow back down, then release them and let the pacbrake do its job. And remember you can always shift down another gear (slow down first, then shift) if you feel you are going to fast.

Barb

[Executive45]

calewjohnson wrote:
Do these brakes need to be turned off when entering towns that have restrictions stating such, or is that for semi trucks? I have seen that in towns through Nevada and CA.

Cale

Like California with their 55mph towing law, many communities are changing the wording on their signs. Instead of "No Jake Brake", we're seeing more "No compression brakes" or "No engine brakes"...most,if not all those ordinances were written for UNMUFFLED ENGINE brakes not exhaust brakes or muffled engine brakes. They are different animals as they utilize different methods of slowing the coach. Most modern RVs utilize muffled engine brakes so it's a non issue..all they're really asking is that we be considerate of the neighborhoods.....Dennis

[wny_pat1]

calewjohnson wrote:
Do these brakes need to be turned off when entering towns that have restrictions stating such, or is that for semi trucks? I have seen that in towns through Nevada and CA.

Cale

I personally do not believe that they make enough noise to worry about such restrictions. Those laws are written to stop trucks with "Jake" brakes that sound like this. Problem is that their law is often not enforceable because the truck may not have a "Jake" brake. "Jake brake" is a nickname for the Jacobs Engine Retarding systems. Jacobs manufacturers several type of systems such as exhaust brakes, bleeder brakes, compression release brakes. Adding to the confusion, Cummins, Cat, Mack and others also make engine retarding systems. Your exhaust braking system should not make enough noise to get you into trouble. But it may be best to avoid using it in residential or business district areas.

[MCDDY]

k.jensen

You and I have basically the same coach & drive train with a PAC Exhaust brake. Mine has a foot pedal and a switch on the panel by the tranny controls. Just remember that the engine, tranny and pac brake combo is pretty smart. Maintenance is pretty easy since you have a side radiator and the whole rear opens up for engine access. Keep good lubricants and filters in everything and the coach will give you years of near trouble free service.

Dave

[calewjohnson]

Do these brakes need to be turned off when entering towns that have restrictions stating such, or is that for semi trucks? I have seen that in towns through Nevada and CA.

Cale