Exhaust brake behavior questions

[GJolicoeur]

I have a 2016, 3500 dually Cummins with the Aisin transmission and 4.10 gears with 11,000 miles on it.
My question has to do with how to get the maximum braking power from downshifting with the exhaust brake on full.
I always use the tow/haul mode (and exhaust brake on full) and notice when decelerating on the highway, if I just cancel the cruise control with the steering wheel button, the truck and trailer combo slows down at a moderate rate - down to about 19 mph. This is also the case if I just lift my foot off the accelerator.

If I cancel the cruise by tapping the brake pedal, I got full on downshifts and exhaust brake power - the transmission keeps the revs up so the exhaust brake does its work. I can touch the brake as I enter the deceleration lane to a highway rest stop and the truck will bring itself down to 20 mph without touching the service brakes even while towing a 20,000 lb. trailer.

My question is - why can't I get the truck to slow down like this while towing all the time? Why is it so weak slowing when canceling the cruise with the button and strong when I cancel the cruise by tapping the brake?

 

[petersonj]

It's all about programming. You can do the same by selecting the gear yourself.

- John

 

[JLandry]

The difference in behavior is probably the programming taking into account driver intent. It seems reasonable to assume a driver wants the truck to slow gently when merely turning off the cruise control, yet when pushing the brake pedal (even briefly), the driver wants the truck to slow down more aggressively.

 

[AH64ID]

Just tap the brake each time, since that’s what tells the ECM to start the downshift schedule.

 

[GJolicoeur]

Just tap the brake each time, since that’s what tells the ECM to start the downshift schedule.

That doesn't work if the cruise isn't on. If my foot is on the accelerator and I tap the brake, it doesn't start the downshifting and exhaust brake - only the exhaust brake.
The only time I get full power braking and downshifting to keep the revs in the best range for the exhaust brake is when the cruise is on and I touch the brake.
I'd like to know if that's the only way it works, or if there's a failsafe way to always get maximum deceleration.

 

[NIsaacs]

Leave the cruise on, thats the way I drive, not always set but it is on. With auto exhaust brake, it will come on, stay on and downshift if I keep my foot lightly on the brake. Just enough to light the brake lights. Obviously, if I need more brake, then I push more on the brake pedal.

Mine is a 2500, so maybe different than the Aisin.

 

[GJolicoeur]

Leave the cruise on, thats the way I drive, not always set but it is on. With auto exhaust brake, it will come on, stay on and downshift if I keep my foot lightly on the brake. Just enough to light the brake lights. Obviously, if I need more brake, then I push more on the brake pedal.

Mine is a 2500, so maybe different than the Aisin.

Yes - I always leave the cruise on. But the full exhaust brake and downshift only comes on when I tap the brake while the cruise is engaged. If simply on, and I tap the brake, weak deceleration. If I just cancel the cruise - weak deceleration. Honestly I'm just frustrated I can't figure out how to get it to work at maximum beyond that one situation.
Pushing harder on the brake doesn't bring in the downshift schedule unfortunately.

 

[Ozymandias]

Which makes sense, I wouldn't like it at all to shift 3 gears down screaming engine to max EB everytime I only tap the brake lightly.
There must be an algorithm that takes more into account for the downshift pattern then just tap the brake. For example gradient of the road, driving uphill or downhill, turning into a curve, driving habits of the driver and so on. Vehicle has all this info through its sensors.

Of course the setting of the EB is also very important here, Auto or Max.

 

[AH64ID]

Yes - I always leave the cruise on. But the full exhaust brake and downshift only comes on when I tap the brake while the cruise is engaged. If simply on, and I tap the brake, weak deceleration. If I just cancel the cruise - weak deceleration. Honestly I'm just frustrated I can't figure out how to get it to work at maximum beyond that one situation.
Pushing harder on the brake doesn't bring in the downshift schedule unfortunately.

What if you tap and hold the brake lightly on? Will it downshift different?

 

[NIsaacs]

Yes - I always leave the cruise on. But the full exhaust brake and downshift only comes on when I tap the brake while the cruise is engaged. If simply on, and I tap the brake, weak deceleration. If I just cancel the cruise - weak deceleration. Honestly I'm just frustrated I can't figure out how to get it to work at maximum beyond that one situation.
Pushing harder on the brake doesn't bring in the downshift schedule unfortunately.

Have you tried auto e-brake?

 

[GJolicoeur]

Which makes sense, I wouldn't like it at all to shift 3 gears down screaming engine to max EB everytime I only tap the brake lightly.
There must be an algorithm that takes more into account for the downshift pattern then just tap the brake. For example gradient of the road, driving uphill or downhill, turning into a curve, driving habits of the driver and so on. Vehicle has all this info through its sensors.

Of course the setting of the EB is also very important here, Auto or Max.

I would only use Auto if I wanted the truck to hold speed downhill on cruise. While towing, I always use Max.

 

[GJolicoeur]

Have you tried auto e-brake?

Sure - Auto works fine when I'm using the exhaust brake to control downhill speeds on cruise. We don't need that much around here since it's so flat. It just uses the exhaust brake - no heavy duty downshifting.

 

[GJolicoeur]

What if you tap and hold the brake lightly on? Will it downshift different?

I'd have to try that. Usually, when I'm coming to a stop while towing, I'll tap the brake if on cruise control and all works well. If I use the service brakes while cruise is off and I'm just taking my foot off the accelerator, it just brings in the exhaust brake, no downshifting until very slow speeds, like from 25 down to 12 mph.

 

[GJolicoeur]

Which makes sense, I wouldn't like it at all to shift 3 gears down screaming engine to max EB everytime I only tap the brake lightly.
There must be an algorithm that takes more into account for the downshift pattern then just tap the brake. For example gradient of the road, driving uphill or downhill, turning into a curve, driving habits of the driver and so on. Vehicle has all this info through its sensors.

Of course the setting of the EB is also very important here, Auto or Max.

If there's an algorithm, I've not seen any evidence of that. Whether I have 20,000 lbs. behind me or nothing, if I have Tow/Haul selected and Max exhaust brake, the full braking power only works under the conditions I mentioned.

 

[GJolicoeur]

I have a 2016, 3500 dually Cummins with the Aisin transmission and 4.10 gears with 11,000 miles on it.
My question has to do with how to get the maximum braking power from downshifting with the exhaust brake on full.
I always use the tow/haul mode (and exhaust brake on full) and notice when decelerating on the highway, if I just cancel the cruise control with the steering wheel button, the truck and trailer combo slows down at a moderate rate - down to about 19 mph. This is also the case if I just lift my foot off the accelerator.

If I cancel the cruise by tapping the brake pedal, I got full on downshifts and exhaust brake power - the transmission keeps the revs up so the exhaust brake does its work. I can touch the brake as I enter the deceleration lane to a highway rest stop and the truck will bring itself down to 20 mph without touching the service brakes even while towing a 20,000 lb. trailer.

My question is - why can't I get the truck to slow down like this while towing all the time? Why is it so weak slowing when canceling the cruise with the button and strong when I cancel the cruise by tapping the brake?

I really appreciate all the replies and suggestions. I'd like to ask you guys how this works on your trucks? Should I post a video?

 

[AH64ID]

I'd have to try that. Usually, when I'm coming to a stop while towing, I'll tap the brake if on cruise control and all works well. If I use the service brakes while cruise is off and I'm just taking my foot off the accelerator, it just brings in the exhaust brake, no downshifting until very slow speeds, like from 25 down to 12 mph.

From what I recall that’s how my 18 worked. I generally would lightly hold the brake pedal to get a little trailer braking during EB decel.

 

[petersonj]

Reading these last several posts makes my head spin! It reminds me of why I like my 6 spd manual transmission / exhaust brake setup so well. I get to choose whatever I want to do with the transmission or exhaust brake AND I get to choose whenever I want to do it. Life is good.

- John

 

[GJolicoeur]

Reading these last several posts makes my head spin! It reminds me of why I like my 6 spd manual transmission / exhaust brake setup so well. I get to choose whatever I want to do with the transmission or exhaust brake AND I get to choose whenever I want to do it. Life is good.

- John

I hear you man! I didn't want an automatic for decades for just that reason and was very happy until the Aisin came out and I was wooed - especially since the manuals have not been uprated they require the engine to be derated when paired with the newer 6.7s.

 

[Topzide]

@GJolicoeur, Have you had any software updates done on your truck? This is very important as software improvements may have fixed this issue. If you have had updates done, you could disconnect the batteries and do a reboot on the systems that will allow trans to relearn your driving style. My 2014 acts pretty close to the same whether coming off cruise or tapping brake pedal. Although most times that I'm running cruise, I just tap brake to come off cruise, so that might have a different programing. Also I have the 68RFE and you would think the Aisin would be more aggressive in it's handling. Good luck with issue.

 

[GJolicoeur]

@GJolicoeur, Have you had any software updates done on your truck? This is very important as software improvements may have fixed this issue. If you have had updates done, you could disconnect the batteries and do a reboot on the systems that will allow trans to relearn your driving style. My 2014 acts pretty close to the same whether coming off cruise or tapping brake pedal. Although most times that I'm running cruise, I just tap brake to come off cruise, so that might have a different programing. Also I have the 68RFE and you would think the Aisin would be more aggressive in it's handling. Good luck with issue.

Yes - I have all the latest updated software. I can use my scanner to make the transmission relearn my driving style, but that just affects shift points and governor pressure - not the way it responds to deceleration command input from the brake application.
I guess I'm going to have to make a video to demonstrate what I'm talking about. Timing the deceleration speeds from 60 mph until 10 mph would also be illuminating.
Yes - I had a 2013 dually (4.10 gears) with the 68RFE before this 2016 with the Aisin and yes, the combination of the newer turbo and the Aisin transmission has almost double the deceleration power that the older setup had. Both trucks had the max tow package.