Exhaust brake

[Dr4Film]

Anyone doing 65 mph at the top of a steep grade had better know where the "Runaway" exit is located if they make it that far.



Dr4Film ----- Richard

[palehorse89]

Originally Posted by Dr4Film

Anyone doing 65 mph at the top of a steep grade had better know where the "Runaway" exit is located if they make it that far.



Dr4Film ----- Richard

All the "Truck Driver's" know where they are at on the hill.......as they are looking at the "Map of the hill" when they are pulled off to the side of the road at the top of the hill, in the "brake check area"..........as all the Motorcoach's roll past.......and down over the hill....... and see them on the right side as they pass them..........

[TVforMyRV]

I personally snub brake my speed down until I am in a low enough gear that the service brakes don't have to be applied at all (or at least very little) to maintain speed. If someone wants to go down faster, they can pass.

You can go down all the hills you want "Too slow", but you only go "too fast" ONCE!

[Steve Ownby]

Originally Posted by palehorse89

I disagree Steve, they are not like us........I did not and they do not have their engine rpm's anywhere close to where the diesels in Motorcoach's w/Allison transmission" programed to downshift and shove the rpm's up over 2300-2500 rpm's. Most all truck drivers are lucky if their engine is at 2000 rpm's when descending a steep hill, and using their service brakes also, if one pays attention and listens, semi's engine's are not turning the rpm's as these automatic rv's are when using the engine brakes.......
I have logged over 1,000,000 miles in my driving career and know how a engine brake works and what stage to use(3 stage) in different grade conditions.......As most know, my Allison does not downshift on its own when I let off the throttle pedal..........it stays in 6th, and I am in control from there..........

Some of this difference is engine size. A 15-16 liter engine will not have to turn as fast as an ISC or ISL but the Cummins ISX15 is still governed at 2100 & Cummins lets that engine rev to 2300 with trailing throttle. Sure they can descend a grade at 1300-1500 rpm if the speed and gear is low enough. I was around heavy trucks most of my working career and sat in on many safety meetings dealing with Jakes and also correct shifting/clutching technique. The professional drivers are more accomplished than most RVers will ever be, but the basics are the same. I find with my ISM/Allison 4000 pushing about 45k pounds, that on a 7% grade, I can descend in 4th gear & 50 mph. RPMs will be around 2000-2100. If high setting starts dropping my speed I switch to low until the speed gets above 50 again & switch back to high. This is on interstates. If other highways my speed & gear would be lower. I feel most comfortable when the Jake is in high & my speed very slowly drops or in low with steady rpm and speed.


Steve Ownby
Full time since '07

[Koop]

Jeep Puller - it sounds like you have the ISL with the two stage Jake brake. On the three position rocker switch, the middle position is "off" pushing the bottom of the switch is "low" and the top of the switch is "high".

Low activates the Jacobs valve on three cylinders while high activates it on all six.

If you find the low position to be ineffective, you don't have enough engine rpm. I can control a 7% descent by toggling back and forth between the low and high setting. On low, my speed will gradually creep up on a steep downhill. I merely switch to high and reduce the speed.

I drove down I-17 into the Verde Valley in Arizona a couple of days ago. Long, steep downgrade. I never touched the brake pedal.

[JeepPuller]

This has been a great discussion and knowledge infusion for me. I will be much better on my brakes with the experience you all have.

Thanks

[Tony Lee]

Originally Posted by Dr4Film

Anyone doing 65 mph at the top of a steep grade had better know where the "Runaway" exit is located if they make it that far.
Dr4Film ----- Richard

Pretty easy to spot - very nice looking class As with tag axles and a shiny toad behind and several hundred horsepower in the back going past me uphill as if I was standing still (which I sometimes nearly am)