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Old 11-12-2007, 09:26 PM   #1
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I think I'm doing an apples to apples test here: Going down a hill at 35-40MPH'ish, down-shifted into 3rd. When I turn on the exhaust brake I think the only thing that should change is that the exhaust brake flapper should engage, correct?

I feel very little difference between flapper open or closed in any gear. I tried it from 4th thru 2nd with the same ho-hum results. How much exhaust brake effect should I "feel"? Seems like it's all in the transmission.
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Old 11-12-2007, 09:26 PM   #2
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I think I'm doing an apples to apples test here: Going down a hill at 35-40MPH'ish, down-shifted into 3rd. When I turn on the exhaust brake I think the only thing that should change is that the exhaust brake flapper should engage, correct?

I feel very little difference between flapper open or closed in any gear. I tried it from 4th thru 2nd with the same ho-hum results. How much exhaust brake effect should I "feel"? Seems like it's all in the transmission.
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Old 11-13-2007, 01:48 AM   #3
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Jeff,

You should be able to hear the PacBrake as it is closing off the exhaust to a degree. It sounds like you are putting a hand over the exhaust of a blower. Kind of a compressed air nozzle sound.
From my experience, there is some additional braking but you really don't feel it in the seat of the pants.

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Old 11-13-2007, 01:57 AM   #4
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The exhaust brake is most effective (and noticeable) when your RPM is near maximum. Downshifting to 3rd gear at 35-40 mph, you might already be putting your engine at or near maximum RPM, so the effect of turning on the brake in that gear at that speed would not be as apparent as shifting into 2nd gear at that range. Even so, changing the RPM a couple of hundred RPM might not be the 'jolt' you're expecting.

My experience has been that the exhaust brake is most felt at higher speeds, running lower RPMs (60mph in 6th gear, dropping to 4th gear). Like you, I have not noticed much of an effect in your 35-40 mph range. I just don't think there is enough exhaust gas being compressed in that range to communicate a 'feel' outside of the seat of the pants feel you get from the transmission downshifting.

I have used the speaker in my back up camera to tell me if the exhaust brake is working. If I turn the brake on, at low speed, I make sure I hear it close (wheezing noise starts). Other than that and a little tug through the transmission, I haven't noticed much feel at all.
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Old 11-13-2007, 02:42 AM   #5
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Jeff,

Glad you brought this up cause I've been wondering too. I like Jim's idea about turning on the camera audio and listening for the change.

I did try one little experiment this summer. I was coming down a loooong and very constant grade. I manually downshifted to 4th which got the rpm up around 2200. I then turned on the exhaust brake. My speed reached a point of equilibrium and stayed very constant (around 50, I think). When I turned off the EB, the speed would start creeping up - turn it back on and it returned to the equilibrium speed. The transmission stayed in 4th the whole time. I concluded it was indeed working, but I didn't "feel" anything.
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Old 11-13-2007, 06:20 AM   #6
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On my 2003 ultimate freedom with the 400 cummins -- you can really feel it -- if you take your foot off the accelerator to take an off ramp or even at 35 mph. in town and ready to stop -- there is a very hard braking action --- I usually turn it off on flat land -- works great on the big hills/mountains

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Old 11-13-2007, 06:27 AM   #7
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I'm curious. One could gather from reading this thread that many owners are selective when using the exhaust brake? It would be hard for me to think of a time when I haven't had the brake switched on and I'm on my second DP.
Anything that will slow down the wear and tear on the service brakes I'm all for it. Brake jobs on a DP is not cheap. Plus, when I driving our first DP, a 38' Luxor, the very first Cummins tech I talked to essentially said use it or lose it. The more you use the e-brake the less likely you are to have an issue with it. Thoughts?
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Old 11-13-2007, 06:37 AM   #8
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Mikeso....

I use mine all the time....but I don't leave it on because at certain highway speeds, it fights with the cruise control. My wife complains about the constant 'click, click' of the switch, but I rarely use my service brakes.

By the way, do you have an exhaust brake on your ISL or do you have an engine brake? The engine brake is definitely more noticeable at all speeds than the exhaust brake. I thought the ISL's came with the engine brake (something I'm very envious of.....)
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Old 11-13-2007, 07:00 AM   #9
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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Mikeso....

I use mine all the time....but I don't leave it on because at certain highway speeds, it fights with the cruise control. My wife complains about the constant 'click, click' of the switch, but I rarely use my service brakes.

By the way, do you have an exhaust brake on your ISL or do you have an engine brake? The engine brake is definitely more noticeable at all speeds than the exhaust brake. I thought the ISL's came with the engine brake (something I'm very envious of.....) </div></BLOCKQUOTE>

Jim,
I haven't had the opportunity yet to crawl under the engine cover on this one yet to look but according to the book it says it's an exhaust vs engine brake. Possibly it's the gearing or what not but I haven't noticed any problems with e-brake fighting with the cruise except of course on the long down hills.
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Old 11-13-2007, 07:03 AM   #10
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I'm sorry, Mike. That question was actually directed at Bill (Fenceman).

My bad. Your engine should have the exhaust brake, not the engine brake. Sorry for the confusion.
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Old 11-13-2007, 07:54 AM   #11
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Some info that you might like is the new upgraded exhaust brake from Pacbrake. It's called PRXB for Pressure Regulated Exhaust Brake. Introduced this year, it is now available as a simple upgrade where the original Pacbrake exists. It is also available as a retrofit where the Jacobs exhaust brake is installed.

In a nutshell the new brake holds exhaust back pressure against the engine longer so you feel 50% more braking all the way down through the RPM range while slowing down. Our customers tell us it works better, longer.

Take a look at www.pacbrake.com for photos and info.

We carry the full line here for installation or shipping.

Thanks,
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Old 11-13-2007, 03:37 PM   #12
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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Mikeso:
I'm curious. One could gather from reading this thread that many owners are selective when using the exhaust brake? It would be hard for me to think of a time when I haven't had the brake switched on and I'm on my second DP.
Anything that will slow down the wear and tear on the service brakes I'm all for it. Brake jobs on a DP is not cheap. Plus, when I driving our first DP, a 38' Luxor, the very first Cummins tech I talked to essentially said use it or lose it. The more you use the e-brake the less likely you are to have an issue with it. Thoughts? </div></BLOCKQUOTE>I don't think anyone is being selective about the Exhaust brake. The question was how effective is it vs. the independent down shifting of the transmission by itself.
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Old 11-14-2007, 04:43 AM   #13
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We have a 300 Cummins in our Journey and its an ENGINE brake. Very noticable at all speeds, however very noisy on the outside.
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Old 11-14-2007, 04:51 AM   #14
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Jeff, The exhaust brake works in conjunction with the Allison transmission. As others have stated, the ehxaust brake is most effective at higher RPM's (1500-2000). So the way the system is designed, with the exhaust brake on, the transmission will automatically downshift to a lower pre-programmed gear (default is usually 2nd gear). In combination, the braking power is significant.

You should easily be able to feel the benefit of the exhaust brake, especially when it starts to downshift into lower gears. The exhaust brake benefit over just downshifting should be significant and noticeable.

I had mine reprogrammed to downshift no lower than 4th gear, as I felt the combination was too agressive.
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Old 11-14-2007, 10:59 AM   #15
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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by flashajt:
We have a 300 Cummins in our Journey and its an ENGINE brake. Very noticable at all speeds, however very noisy on the outside. </div></BLOCKQUOTE>

Your 300hp Cummins is an ISB. You have an exhaust brake. No Journey ever came with an engine brake. You have to move up to the ISL to get an engine brake and the ISL was never a Journey option.
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Old 11-14-2007, 12:15 PM   #16
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Old 11-15-2007, 05:24 AM   #17
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In my 32T with the Cummins ISB the exhaust brake is incorporated into the turbo. It also works in conjunction with the 6 speed Allison and works REALLY well. In fact, while going down a slight down grade on an off ramp, the exhaust brake hit at about the same time as the Allison was down shifting. The result was that I cleaned off the kitchen counter The DW was not amused Could have been that 2 gallon jug of water that had been sitting up there.........

As far as leaving it turned on, I turned mine on a year and a half ago when the rig was new, and haven't turned it off yet.

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Old 11-15-2007, 05:28 AM   #18
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IIRC, the only time Cummins/Jacobs recommended that the exhaust brake not be used on my ISB was under low traction conditions where exhaust brake engagement at high RPM could generate sufficient retarding horsepower to cause rear wheel lockup. Otherwise, the exhaust brake saves lots of wear and tear on the service brakes, towing or not.

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Old 11-15-2007, 06:01 AM   #19
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I too keep my exhaust brake switched on all the time. I did, however, have CAT change the ECM programming to the 'Latch' mode, where I can now coast w/o the exhaust brake coming on by turning the cruise 'on', but not engaged. This way I can manage the use of the exhaust brake thru the cruise on/off switch. I can coast w/o the exhaust brake engaging (as stated above), or I can engage the exhaust brake by switching the cruise 'off' or by depressing the brake in either mode.
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Old 11-15-2007, 06:40 AM   #20
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Spartan has recommended NOT leaving your auxiliary brake on all the time, as the service brakes need to heat up to prevent glazing of the front brake shoes.

When applying the service brakes, the rear brakes activate first, followed by the front brakes. The front brakes get the least use and are most susceptible to glazing.

There have been cases where the front brake shoes have glazed, resulting in reduced braking capacity.

This is not covered under warranty, as it is operator caused.

I no longer leave my auxiliary brake on all the time.

At a Spartan seminar, it was asked if anyone had ever replaced their brakes. No one had, so the auxiliary brake was not needed 100% of the time.
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