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Old 05-18-2017, 04:04 PM   #1
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Question Cruise control/ exhaust brake

New to me a month ago this is different than the Cat in my prior rig.

it's an 8.3 ISB Cummings, was up in rt 64 N on 81 and going over some hills.

With cruise on it went really nice, better than I can do it myself.

But when I lost momentum up a grade due to traffic it was just dog slow in 4th doing 45 then 50 ish but giving it more throttle made no difference.

that that was strange?

Other than that all went great locked in at 65 for 600+ miles from Savannah Ga

Up a grade it would drop to 63 sometimes 62 but recovered to speed.

then I tried using the exhaust brake, that was smooth nothing like the old Cat in my HR that would slam into lower gears.

My question using it in conjunction with cruise down grade it would get up to 68-70.

Is the brake supposed to limit that?

What happen in real grades like out west, will it not slow down?

Should I turn off cruise down hill?


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Old 05-18-2017, 05:04 PM   #2
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On my Cummins/Allison the cruise control cannot be on when the exhaust brake is engaged. You can leave the exhaust brake switch on all the time and it will work as long as the cruise isn't on. To engage the exhaust brake when the cruise is on I just have to tap the brake pedal.

If you are going coming up on a steep grade you can drop a gear and get the RPM's up a little which will help you get across the hill. No matter you will loose speed and once you loose the momentum it's almost impossible to get it back causing a loss speed.

My coach is heavy with a 350 HP 8.3 ISC Cummins. My biggest obstacle is traffic, if there are big rigs in the right lane and they start slowing down I either have to make a decision to pass them on the grade or just stay tucked behind them. If there is traffic it can be difficult to do that, not to mention the faces/gestures I get from other motorists who got stuck behind me.
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Old 05-18-2017, 07:27 PM   #3
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Your Pac Brake can be set to any of 3 modes.
Coast Mode- Engages exhaust brake when foot brake is engages and releases with the foot brake.

Latch Mode- (most common) Engages when brake pedal is engaged and remains engaged until throttle is applied, engine speed below is 800 rpm or PacBrake switch is turned off.

Manual Mode- Cruise control is not on and operates with the switch at the drivers discretion.

When the PAC brake is engaged the transmission wants to shift to 2nd gear. The computer will not allow the engine to overspeed so the transmission only downshifts when the rpm in the lower gear will not result in an overspeed. The target gear for braking can be adjusted by the computer as can the mode of operation above.

Recommend you start down a steep grade at the speed you want to maintain. (Start down no faster than you climbed the grade) If your speed is high, the tranny can't downshift without overspeeding and only being able to go from 5th to 4th gear on a 8-10% grade isn't going to slow you much at all.

Pac Brake Drivers Guide: http://pacbrake.com/wp-content/uploads/L5046.pdf
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