Community Forums

swagn · 09-24-2018, 06:50 AM

There have been several discussion on this but am I correct?I am in Mt Rushmore area and will have some descents etc.

1. If descending, you can set cruise control on specified speed and have compression brake switch on and maintain that speed on descents.

2. manually select gear on descending and compression break will maintain speed and rpm. Don't use cruise control.

So I have two choices? Which is better?

Alison 6-speed tran with compression brake

palehorse89 · 09-24-2018, 06:58 AM

Quote:

Originally Posted by swagn

There have been several discussion on this but am I correct?I am in Mt Rushmore area and will have some descents etc.

1. If descending, you can set cruise control on specified speed and have compression brake switch on and maintain that speed on descents.

2. manually select gear on descending and compression break will maintain speed and rpm. Don't use cruise control.

So I have two choices? Which is better?

Alison 6-speed tran with compression brake

If you are asking about the 300 hp 5.9 in your signature, it would have a exhaust brake, not a compression brake.......

swagn · 09-24-2018, 07:20 AM

According to my manual, they reference compression...how do I tell difference? Regardless are my two assumptions correct? Thanks

palehorse89 · 09-24-2018, 07:26 AM

On the dash, do you have a on/off rocker switch? If so, exhaust brake. Compression braking will have a rocker switch with 2 or 3 position's for the different stage's of braking. Cummins did not put compression braking on engine's till the ISL 400 HP, and some of them had the exhaust brake.
If it is set up in the ECM & TCM to work while the cruise is on like mine, I use it on the highway's and rolling hills to maintain set point speed.
When on lower speed limit back road's, I don't use the cruise control, my rocker switch is on all the time for engine braking.

Quincy · 09-24-2018, 07:31 AM

I cannot tell you about the operation of an exhaust or compression brake but I can tell you that even without either. the Allison will automatically down shift when declining to the next lowest gear after braking. The Allison will handle the hill all by it self.

Finance · 09-24-2018, 07:33 AM

On mine, if in cruise it will engage the EB (if enabled) but hold the same gear. If speed continues to increase it will downshift, however by that point it’s probably either too fast to drop a gear -into 4th say- or too much gradient for 5th to be effective. In summary it’s really only capable of handling a mild grade in cruise.

With CC off, and the brake enabled, the ECM commands a shift to second if you back off the throttle. So you’ll get maximum braking from the start.

Now your programming may well be different, as the Allison is very customizable. Next stop in a Cummins shop I’m having mine reprogrammed to not automatically command 2nd gear. I’ll chose my own gear when braking.

TonyMac · 09-24-2018, 07:36 AM

On my rig, the cruise is disconnected once the exhaust brake is engaged. I wish it weren't so, but it is on my rig. Yours might be different. Regardless, some hills will require you to apply the foot brake, the engine brake can only do so much. If you are at or near redline rpm, mine is about 2400, and the eb is not slowing you and you are still gaining speed, the foot brake is your only option. Step firmly on the foot brake, get your speed and rpm down enough to allow you to select the next lower gear, and get off the foot brake completely. Never ride your foot brake. Stab firmly and get off. Do not pump air brakes.

The term is compression release brake. This is a set of valves installed in the head with your intake and exhaust valves, that open during the compression stroke and release the compression, and then close at the start of the unpowered power stroke, creating a vacuum on the power stroke and retarding the engine -- rather rare in motorhomes like yours. You likely have an exhaust brake. Google PacBrake, look at the pictures, and read up on the care and maintenance of such, they are NOT maintenance free by a long shot. This is a valve after the exhaust manifold and before the turbo that mostly closes off the exhaust flow causing pressure in the cylinder during the exhaust stroke, retarding the engine. Go look, the exhaust brake is very obvious.

swagn · 09-24-2018, 07:41 AM

Quote:

Originally Posted by palehorse89

On the dash, do you have a on/off rocker switch? If so, exhaust brake. Compression braking will have a rocker switch with 2 or 3 position's for the different stage's of braking. Cummins did not put compression braking on engine's till the ISL 400 HP, and some of them had the exhaust brake.
If it is set up in the ECM & TCM to work while the cruise is on like mine, I use it on the highway's and rolling hills to maintain set point speed.
When on lower speed limit back road's, I don't use the cruise control, my rocker switch is on all the time for engine braking.

Yes, I have rocker switch, on/off. Thank you all for feedback.

Spk64 · 09-24-2018, 07:45 AM

Not sure which brake you have Compression\Engine or Exhaust but on my engine brake it is setup such that when cruise is engaged the Engine brake does not engage. The transmission does downshift to try to control speed. But on a steeper grade I have to disengage cruise control to allow the engine brake to slow down.

caninecop · 09-24-2018, 07:58 AM

Quote:

Originally Posted by palehorse89

On the dash, do you have a on/off rocker switch? If so, exhaust brake. Compression braking will have a rocker switch with 2 or 3 position's for the different stage's of braking. Cummins did not put compression braking on engine's till the ISL 400 HP, and some of them had the exhaust brake.
If it is set up in the ECM & TCM to work while the cruise is on like mine, I use it on the highway's and rolling hills to maintain set point speed.
When on lower speed limit back road's, I don't use the cruise control, my rocker switch is on all the time for engine braking.

I learned something from your post

I have seen many post about the compression brake and exhaust brake but didn't know the difference, now I do thanks for your post.

palehorse89 · 09-24-2018, 08:10 AM

Quote:

Originally Posted by Spk64

Not sure which brake you have Compression\Engine or Exhaust but on my engine brake it is setup such that when cruise is engaged the Engine brake does not engage. The transmission does downshift to try to control speed. But on a steeper grade I have to disengage cruise control to allow the engine brake to slow down.

Steve, through the Cummins Insite program, for the "Cruise option" under the cruise control, there are 2 option's. Engage or not engage, your must have the selection not to engage.......but they can change that if you desire.

palehorse89 · 09-24-2018, 08:12 AM

Quote:

Originally Posted by caninecop

I learned something from your post

I have seen many post about the compression brake and exhaust brake but didn't know the difference, now I do thanks for your post.

This forum is a Wealth of knowledge and very useful......I learn something everyday

Thank you for your kind post!!

Spk64 · 09-24-2018, 08:16 AM

Quote:

Originally Posted by palehorse89

Steve, through the Cummins Insite program, for the "Cruise option" under the cruise control, there are 2 option's. Engage or not engage, your must have the selection not to engage.......but they can change that if you desire.

Thanks I was thinking it could be changed. I use it as the poor mans 2 stage for now. It confused me for a long time as my engine brake was actually not working at all. Traced it down to a missing jumper in the harness and now I know what the engine brake really feels like when it engages.

agilabs · 09-24-2018, 08:32 AM

I had the 6.7L with the exhaust brake on my RAM truck. I would set the exhaust brake and use a lower gear down the hills through the mountains. You will still need to brake going into corners, but the exhaust brake will help to keep your speed down on the descent and help to save your brakes.