How to Get the Exhaust Brake to Work at Low Speed

[tmcIlwain]

I'm traveling in Colorado up and down mountains with lots of low speed downhill switchbacks. I'm having fits trying to get the exhaust brake (Full or Automatic) to do any good at speeds below 25 MPH. First I've tried speed control down to 25, but then it drops out when I have to hit the brakes to slow down more. Then it won't take speed control again until I get the truck up to some higher speed like 30-35...??? And I don't want to go that fast!
Trying to use the Automatic Brake... hit the brakes to reduce speed and it doesn't seem to want to do any good below 20-25, and then it seems to have a mind of its own as to when it will activate and when it will not.
Frustrated and still in mountain's and hill to defend yet. By using speed control or manual gear shifting, I am usually down in 2nd gear by 25 mph and still need EB help.

 

[RDHamill]

I would think that at a speed as slow as 20mph you need to be in a low gear ( increased RPM) for the exhaust brake to be effective.
Others with a 68RFE might be about to answer, but that's how it is with my G56.

 

[handtools]

I believe the EB cuts out below 1100 rpm. I use tow/haul and lock out 6th gear most of the time around town and my EB works pretty good until the rpm's drop below 1100.

 

[Bug Out]

What has worked best for me in similar situations is keep the transmission in TH and 4th gear, provided your not going over 45 or so. Even try 3rd if your not going to fast between switch backs. It locks when in 3rd & TH .

 

[Hoefler]

Keeping it in Tow/Haul is the key.

 

[tmcIlwain]

I forgot to say that I always drive with tow/haul on, and always have the EB on (either Full or Automatic).
And yes, even the manual tells us to keep RPMs up for more effective EB action. That's why one way or another I am down in 2nd gear when descending these steep drops. BTW, I have a 15,000 pound trailer behind me!
But my point was that the EB does not stay on when I need it. And, if I'm going down a steep grade with speed control set at say 25 mph, then come to a 15-20 mph curve, I have to hit the brake to slow down, then what do I do? I can't get the Speed control to re-engage until I am up to 30 to 35? mph, and that's too fast!!!!
Now I thought the Automatic EB was supposed to help here, but I can't seem to get it to take over.
One final comment, I've never seen the EB work in 1st gear.

 

[RustyJC]

I suspect the exhaust brake function of the VGT only works when the torque converter is locked. My truck's exhaust brake function drops out at about 20 MPH or so (the difference could be my 4.10 axle ratio) as I'm slowing down in tow/haul mode.

Rusty

 

[RikDavis]

I have felt the interaction between cruise and the EB is not as good as it could be. That is based on limited miles and I have never used cruise off the interstate. Just seemed to behave strangely when I was in West Virginia

 

[Cummins12V98]

For best control set cruise and manually select a lower gear to keep rpm's up. For really slow use manual to 2nd. I am pretty sure mine works in 1st.

Sounds like your trailer brakes are not doing what they should.

 

[AH64ID]

AFIK, the torque converter only locks in 2-6 so 1st isn't at option.

Are you manually selecting 2? IIRC the only way to get it to lock in 2nd is with the selector in 2.. but that could be an incorrect recollection.

 

[gsbrockman]

For best control set cruise and manually select a lower gear to keep rpm's up. For really slow use manual to 2nd. I am pretty sure mine works in 1st.

Sounds like your trailer brakes are not doing what they should.

Ding*Ding*Ding.....we may have a winner.

 

[tmcIlwain]

Well, I may not have manually always selected 2nd, but the Speed Control dropped it to 2nd. I'll try selecting 2nd and with the usual T/H and EB (probably Auto) and see if that is the difference...
Thanks for the idea!

 

[jhenderson]

I believe speed control only works at speeds above 35 mph. It has to do with Govt specs for safety issues. At 35 mph or less it's expected you are in town or on local roads and the driver should be in control of all aspects of vehicle operation.

 

[eng208]

So you are saying you set the cruise on these mountains with a 15K lb trailer behind you? I just don't do that and wouldn't consider doing that. I think you are trying to get the truck to do something unique it probably doesn't need to do if this is the case. I know with my fifth wheel that weighs around 8500 lbs, I can slow it down to a very slow speed just by placing the EB in Auto, (which works to keep speed from INCREASING down a hill or activates with light brake application), and TH mode. If I really want to slow down without using the truck brakes, I lightly activate the brakes and then start downshifting. This activates the trailer brakes, the exhaust brake, and the downshifting keeps the RPMs up to effectively utilize the EB.

 

[AH64ID]

Cruise control in the mountains, where applicable, is a great tool. Unless the road demands a constant speed change for corners I am always in cruise control, up or down. It provides better, EB control, EGT control and a steadier speed. Going down it alternates the throttle and EB as needed, so you don't end up too fast or too slow.

It's always easy to tell who uses cruise and who doesn't, towing or not, based on when/where they speed up slow down. Almost always they notice they are going too slow and speed up in a passing zone, and then slow down again after.

 

[tmcIlwain]

So you are saying you set the cruise on these mountains with a 15K lb trailer behind you? I just don't do that and wouldn't consider doing that. I think you are trying to get the truck to do something unique it probably doesn't need to do if this is the case. I know with my fifth wheel that weighs around 8500 lbs, I can slow it down to a very slow speed just by placing the EB in Auto, (which works to keep speed from INCREASING down a hill or activates with light brake application), and TH mode. If I really want to slow down without using the truck brakes, I lightly activate the brakes and then start downshifting. This activates the trailer brakes, the exhaust brake, and the downshifting keeps the RPMs up to effectively utilize the EB.

Cruise control downhill if VERY effective, down to 25 mph. It's below that that I have a problem. I've tried EB in Auto with brake application and downshifting and it down's seem to do anything at low speeds. (and I'm locked in 2nd by then). How do I get the EB Auto to work below 25 mph???

 

[Powder Extreme]

Unfortunately, you don't. It just won't work below 20mph. I tow extensively and have tried every possible configuration on both of my trucks. The EB just won't stay on below 20mph. The '14 with the 68rfe is a real pain in the *** to use the EB. Sometimes it drops out at 50, most of the time if I use it down to 45 or so, then hit the throttle to maintain speed then let off again the EB will not come again. The best luck I have with it is when pulling off the interstate from 80mph I apply the brakes for a second or two and the EB will stay on and transmission will downshift till it cuts off at 20mph. This is with tow/haul on the entire time. The EB doesn't work worth a hill of beans without TH on.

Another thing I just flat don't understand what Ram was thinking about on these trucks, the 68rfe when on cruise will downshift when gaining speed down hills instead of turning the EB on. Makes no sense to me whatsoever. Why downshift when it isn't needed? It will drop TWO gears before it will turn the EB on, when all it really needed to do was turn the EB on in 6th and the truck would have maintained. (I know this because I drive the same mountain pass every day and usually have a trailer so I've tried every configuration of settings possible). Then we mover over to the Aisin, it turns the EB on when descending, great! But it refuses to downshift so with a really heavy load when the EB isn't enough in 6th, I've let it run up to 85mph descending just to see if it would ever downshift, nope. (Again I know this road like the back of my hand, please no lectures about going that fast loaded)

My GMC when descending on cruise will first turn the EB on, then start dropping gears as needed. The speed NEVER exceeds about 4mph over the cruise set point and does it all automatically. It works so well when I come to a corner, I can just tap the speed down 5-10mph and it will apply the EB harder or drop another gear as necessary. Then tap the speed set point back up after the corner. It's a pleasure to drive in the mountains and the twistys, the Rams I'm always trying to manually shift, constantly hitting the brakes, resetting the cruise, etc. If GM can design it to work so well, why can't Ram? With the Capabilities of the Cummins, these trucks should be leading the way in mountain driving, but Ram won't program them so they can.

And why the H E L L do I have to press the gear select button 15 damn times just to finally get it to drop 4 gears??!!

*rant off.

 

[grabinov]

I keep thinking to myself: This is PURELY a programming issue. Who do we look to for a programmer which can talk to both the ECM AND TCM?

 

[Cummins12V98]

With the EB and TH on and you let off the pedal the EB is working. The amount of retarding can vary on conditions. When I am decending the Grapevine for example I have cruise set at 62 but if I leave it in 6th it may not hold speed. So to make it work well I will select 5th or 4th depending on the grade.

 

[Newt]

I forgot to say that I always drive with tow/haul on, and always have the EB on (either Full or Automatic).
And yes, even the manual tells us to keep RPMs up for more effective EB action. That's why one way or another I am down in 2nd gear when descending these steep drops. BTW, I have a 15,000 pound trailer behind me!
But my point was that the EB does not stay on when I need it. And, if I'm going down a steep grade with speed control set at say 25 mph, then come to a 15-20 mph curve, I have to hit the brake to slow down, then what do I do? I can't get the Speed control to re-engage until I am up to 30 to 35? mph, and that's too fast!!!!
Now I thought the Automatic EB was supposed to help here, but I can't seem to get it to take over.
One final comment, I've never seen the EB work in 1st gear.

When you are on a grade that steep, forget speed control. Sometimes you have to drive the truck. Use the rocker switch to keep speed down. Only use the brakes if the exhaust brake won't keep the speed down. Use lower gears. Some say to go down in the same gear you would go up.

Newt