How do you know if your exhaust brake is working?

univmd wrote:
How do you know if your exhaust brake is working?

It seems my exhaust brake is not stopping the coach as much as it used to. The transmission will still downshift & rpm goes up upon activation of the exhaust brake button, does this mean the exhaust brake is really working too? how to tell if exhaust brake mechanism is really working too?

With warm regards, James

Cummins ISC 360 8.3 engine

Cummins Doesn't run an exhaust brake, they run an intake choke. it is not as effective as Cat's exhaust brake.

Wait-- look at the exhaust side of the turbo. Do you have an exhaust brake there?

What brand?

To prove if working/not working: Use the down arrow on the Allison shift pad to select, say, 4th gear. Leave it there for the duration.

Accelerate to close to governed RPM in that gear. Let off throttle, exhaust brake OFF. Turn on exhaust brake. Turn it off. Turn it on.

You have eliminated the transmission as a factor, since it is in the same gear for the whole test. There should be a significant increase in braking HP with the exhaust brake on vs off, particularly at higher engine RPM.

Let us know what you have and what you find.

And, yes, some newer Cummins engines have VARIABLE VANE TURBOS instead of exhausts brakes.

A 08 Cummins ISC probably has a variable vain turbo/exhaust brake. The best thing you can do for it is to get on the throttle hard through all the gears once a week when traveling to keep the moving parts in the turbo from freezing/carboning up. Brett's test should tell you if it's working.

univmd wrote:
How do you know if your exhaust brake is working?

It seems my exhaust brake is not stopping the coach as much as it used to. The transmission will still downshift & rpm goes up upon activation of the exhaust brake button, does this mean the exhaust brake is really working too? how to tell if exhaust brake mechanism is really working too?

With warm regards, James

Cummins ISC 360 8.3 engine

My exhaust brake switch is attached to the Gear shift just below the knob (6 sod. manual). There is a little red light on the switch, if the EB is on the light is on, if off, the no red on. I can also get the truck up to about 60mph, then turn the EB off, you should feel like your are coasting with little resistance. When you turn the EB on you should feel the truck slowing down as if you were going head on to a fairly strong wind. When my EB is on, the sound of the exhaust from the engine is louder and with a rumbling like sound. At that speed, I can turn the EB on and off there is a an obvious different feeling and sound.

This is a good question, as we have wondered the same thing. Our issue is when we use the EB, we slow down but the rpm's get too high when and we have to use the foot brake. This happens going down hills.

Klueck wrote:
This is a good question, as we have wondered the same thing. Our issue is when we use the EB, we slow down but the rpm's get too high when and we have to use the foot brake. This happens going down hills.

Miss read this the first time. Sometimes the EB requires brake assist. But I would think if u drop a gear & let the rpm's hold it back that might work.

Klueck wrote:
This is a good question, as we have wondered the same thing. Our issue is when we use the EB, we slow down but the rpm's get too high when and we have to use the foot brake. This happens going down hills.

On a steep decline, the exhaust brake is not going to hold back your RV completely. It still requires judicious use of your braking system to maintain the proper decent speed. You need to crest the hill a little slower on steep descents and not let the coach get away from you by accelerating too fast. Make sure that you downshift to a lower gear and using the exhaust brake AND your foot brake keep the descent at a slow enough speed so that you are not overheating your foot brakes. Every hill is different so it just takes practice to find out what works to keep your speed under control, especially if you have a toad that is pushing you down that hill.

Klueck wrote:
This is a good question, as we have wondered the same thing. Our issue is when we use the EB, we slow down but the rpm's get too high when and we have to use the foot brake. This happens going down hills.

Do not guess whether the RPM's are too high.

There are several numbers you need to get from your engine manufacturer (call them with your engine serial number):

Peak torque RPM-- do not operate below this except at very light throttle settings.

Peak HP RPM-- just what it says.

Governed RPM-- the RPM at which the engine's fuel system will reduce fuel to keep RPM from going higher.

And, the one of interest for your question:
Maximum no-load RPM-- how fast may the engine turn while coasting/descending a grade.

While you can "get away" with just using the service brakes when coming to a stop, you will BURN THEM UP were you to use them on a long downgrade.

The service brakes should only be used on a long downgrade to allow you to slow down enough to shift to a lower gear. The exhaust, engine compression brake or properly functioning variable vane turbo is essential to safe mountain driving with a heavy vehicle.

I don't know about your IC Cummins but my C7 Cat has a Pac brake which is just a butterfly that shuts off the exhaust flow on the outlet side of the turbo. I bought my coach in 2008 which was a 2007 model with a 2006 pre-emission engine. I was always suspicious that the pac brake wasn't working. Last fall I removed it and it was set tighter than a drum. After a lot of heating, penetrating oil, and pounding I free it up. I lubricated it with the Pac Brake lubricant and watched it while someone drove the coach. It still didn't engage unless I tapped it with a hammer. On the activating rod there is turn buckle that is adjustable. I lengthen out out and It now works as when I brake my turbo pressure is 0 which it should be when it engages.If you have turbo pressure of more than 1 lb the brake isn't working. Now this only pertains to the pacbrake system. I don't think mine ever worked from day one as it was never adjusted right.

When descending off Mt. Washington pass on highway 20 east bound where we have 6-8 miles of 6% down grade I nearly stop at the top, place my transmission in 3rd gear, put the brake switch in the on position and allow the coach to descend the hill, It will stay around 25 MPH all the way down. same thing on Highway 2 west bound, There I must use the airbrakes 3-4 times to stop the RPM from exceeding 2200RPM.