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Old 07-06-2016, 07:12 AM   #15
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Originally Posted by CountryFit View Post
this is a good info. i have a pacbrake. when it's turned on, the gear will drop from 6 to 4. if i press the fuel pedal, the gear will not change upward, stays in 4. does cummins or chassis shops do the programming so that the gear remains in 6 though the pacbrake is turned on? only then will coast mode make sense i assume.
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My Allison shifter pad displays 2nd gear as the "selected gear" whenever the PacBrake is activated, (aka: on/closed/working).
On some coaches that "selected gear" is 4th gear.

However the Allison will not actually "attain", (downshift into), a lower gear unless/until the coach slows to a speed safe for it to do so.

If "COAST MODE" is set in the ECU ...when the PacBrake is activated, (aka: ON/working/slowing the coach), tapping the throttle turns the PacBrake OFF and the shift pad displays the "attained gear", (aka: the gear the transmission is in... which may be 6th, 5th, 4th, 3rd, or 2nd gear)...depending the speed of the coach when the throttle was tapped.

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Old 07-06-2016, 08:40 AM   #16
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I am in the process of upgrading to the PacBrake PRXB and have a question for those who have an exhaust brake that is set to latch mode. I am also considering reprogramming to latch mode. As I understand it, in this mode, the exhaust brake, when switched on, will only activate when the service brakes have been applied. It then releases as soon as the accelerator is depressed and stays off until the service brakes are applied again.

For those whose exhaust brake works in this manner, I have a question.

When going down a steep grade, if you have activated your exhaust brake by using the service brakes, can you then toggle you EB switch (usually on the left console) on and off to control your speed? Or if the switch is turned off and back on, do you need to use your service brakes again to activate the EB?

Thanks for any input.
Download THIS PDF file from PacBrake. Read specifically page three.

My coach and trailer combination is close to 48,000 lbs. After making one trip to Alaska and back to CA in 2010 I chose to upgrade to the PRXB to get as much horse-braking out of my Exhaust Brake as possible. I am very happy with the upgrade. However, like Dutch Star Don states, there is very little affect at higher speeds. You get the most benefit at lower speeds like 50 mph and below.

In regards to the latch mode, does your coach presently allow you to have the cruise control on or in use PLUS have the Exhaust Brake Switch ON at the same time? If not then having latch mode installed with solve that issue.

My coach has been programmed with the latch mode as as I know. PLUS I leave the Exhaust Brake Switch ON all the time. I have never turned it off so I never have to think about whether it is on or not. Plus I don't have to use the service brakes to activate the Exhaust Brake.

I can use the CC anytime I want and usually do when driving unless I am in very mountainous terrain. In those situations the CC is usually on but not in use.

When using CC, once I approach a steep descending grade I simply hit the CC cancel button and a second later the Exhaust Brake has activated. Depending on the steepness of the grade I keep the coach within 40-53 mph. It will stay in 4th gear when maintaining those speeds. If the coach hits 54 mph the Allison shifts up to 5th and takes off like a bat out of hell. So it's important to keep it in 4th or 3rd gears. Each time the speed creeps up I trounce on the brakes to cut the speed back down about 10 mph less or so. Because of the weight and the steepness of the grade I always have to use the service brakes to keep the speed in check. If the grade is 3-4% then I don't have to use the brakes as much if at all.

Under normal terrain driving I will have my foot on the fuel treadle but once I remove it completely the Exhaust Brake activates. If I choose to coast I simply remove any pressure on the fuel treadle but leave my foot there with no pressure. The Exhaust Brake will not activate unless I remove my foot from the treadle completely.

Homer Hawks, when he was in business, made a device called the BrakeSwitch which basically did something similar as having the latch mode programmed. Here is an ARTICLE about one person’s installation of the BrakeSwitch. You can also do a search on iRV2.com to read more from people who have installed and used the BrakeSwitch.

I remember reading about someone on iRV2.com that had designed his own BrakeSwitch circuit based on Homers design. I have attached his diagram below. You could probably find his post about it if you do some searching.

Dr4Film ----- Richard
Attached Files
File Type: pdf Custom BrakeSwitch Diagram.pdf (149.7 KB, 16 views)
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Old 07-06-2016, 09:11 AM   #17
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Dr4Film, Glad you chimed in, because one of your post was one of the reasons I wanted to upgrade to the PRXB, (although the degradation of the performance of my existing Pacbrake also helped).

My coach is currently configured as yours is, and I drive it exactly as you described you drive yours. The reason I want to change to latch mode is that I really do not like the downshifting every time I take my foot off the treadle. I would like to coast sometimes. I realize that with a light touch on the treadle the EB will not activate, but in my coach, it is a little uncomfortable to hold that position for long periods.

In most of the mountain driving I do, mostly in Colorado, I am usually below 50 mph, and frequently less than 30 mph. So, the promise of the low RPM holding power of the PRBX is very attractive to me. (I am hoping I will be happy with it)

So, for now, the upgrade to the PRBX and the changing to latch mode, (if I can get it done someplace), are very much anticipated. I’ll report back after the change to share my experience.

Also, my coach does have the ability to have the Pacbrake switch and the cruise control on. I am always surprised by those who say theirs does not operate this way. I am on cruise 99% of the time, and as soon as I hit the service brakes, the cruise goes off and the EB comes on. Exactly as I think it should be.
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Old 07-06-2016, 09:45 AM   #18
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My coach has been programmed with the latch mode as as I know. PLUS I leave the Exhaust Brake Switch ON all the time. I have never turned it off so I never have to think about whether it is on or not. Plus I don't have to use the service brakes to activate the Exhaust Brake.

Under normal terrain driving I will have my foot on the fuel treadle but once I remove it completely the Exhaust Brake activates. If I choose to coast I simply remove any pressure on the fuel treadle but leave my foot there with no pressure. The Exhaust Brake will not activate unless I remove my foot from the treadle completely.
Actually, this does not sound like what I understand "Latch Mode" to be? It sounds like "Manual Mode" per the Pacbrake document you mentioned above. (My coach is in "Manual Mode" per that document). My understanding is that latch mode will not activate the EB until you touch/apply the service brakes, and will stay on until you touch/apply the accelerator?

Are you sure you have the latch mode, or am I missing something?
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Old 07-06-2016, 10:15 AM   #19
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Actually, this does not sound like what I understand "Latch Mode" to be? My understanding is that latch mode will not activate the EB until you touch/apply the service brakes, and will stay on until you touch/apply the accelerator?

Are you sure you have the latch mode, or am I missing something?
I'm confused as well.
You had originally asked;
When going down a steep grade, if you have activated your exhaust brake by using the service brakes, can you then toggle you EB switch (usually on the left console) on and off to control your speed? Or if the switch is turned off and back on, do you need to use your service brakes again to activate the EB?

Was this question answered?

When going down a steep grade I toggle between high and low. It's a rocker switch with a low-off-high setting. If the switch goes to off while toggling, will you have to reapply the brakes?

I don't know what my transmission is set to, but it operates like Dr4Film's coach.

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Old 07-06-2016, 10:33 AM   #20
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I'm confused as well.
You had originally asked;
When going down a steep grade, if you have activated your exhaust brake by using the service brakes, can you then toggle you EB switch (usually on the left console) on and off to control your speed? Or if the switch is turned off and back on, do you need to use your service brakes again to activate the EB?

Was this question answered?

When going down a steep grade I toggle between high and low. It's a rocker switch with a low-off-high setting. If the switch goes to off while toggling, will you have to reapply the brakes?

I don't know what my transmission is set to, but it operates like Dr4Film's coach.

Bill
TR4, It certainly can be confusing. I am no expert by any means, but I have read hundred of posts on this subject.

Yes, my original question was answered by Don in post #5.

On your next issue, because you mentioned “low-off-high setting” on your coach, I think you have an “engine brake”, this is different than my exhaust brake. However, both systems can be configured in several ways. In yours, mine, and I think, Dr4Film's case. The EB/Engine Brake, comes on as soon as we take our foot off the accelerator. The Pacbrake document refers to this as "Manual Mode". I have never had an engine brake, so I cannot comment any further on it.

But, another option only activates the EB/Engine Brake when the service brake pedal is used/tapped, it then stays on until the accelerator pedal is used/tapped. This is the "Latch Mode", and is what I want to try.

My original question was only about "Latch Mode" with a "Exhaust Brake".

Clear as mud, right? So many options, so little time.
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Old 07-06-2016, 11:28 AM   #21
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TR4, It certainly can be confusing. I am no expert by any means, but I have read hundred of posts on this subject.

Yes, my original question was answered by Don in post #5.

On your next issue, because you mentioned “low-off-high setting” on your coach, I think you have an “engine brake”, this is different than my exhaust brake. However, both systems can be configured in several ways. In yours, mine, and I think, Dr4Film's case. The EB/Engine Brake, comes on as soon as we take our foot off the accelerator. The Pacbrake document refers to this as "Manual Mode". I have never had an engine brake, so I cannot comment any further on it.

But, another option only activates the EB/Engine Brake when the service brake pedal is used/tapped, it then stays on until the accelerator pedal is used/tapped. This is the "Latch Mode", and is what I want to try.

My original question was only about "Latch Mode" with a "Exhaust Brake".

Clear as mud, right? So many options, so little time.
OK, thanks. Yes I have an engine brake. I reread post #5 and think I'll stay with what I have. On steep grades I have my foot off the throttle and toggle between high and low to keep my speed. I do this about every 10 sec. on some grades. Having to step on the brake to reset the engine brake each time adds more work.

Thanks for sorting this out.

Also this page has interesting information regarding this subject: http://www.peterbilt.com/resources/b...ming_Guide.pdf

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Old 07-06-2016, 11:54 AM   #22
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When going down a steep grade I toggle between high and low. It's a rocker switch with a low-off-high setting.
You have an Engine Brake which operates completely different than an Exhaust Brake.

An Engine Brake can have High- Medium-Low and Off or High-Low and Off. But an Exhaust Brake is either On or Off.

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Old 07-06-2016, 12:05 PM   #23
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Actually, this does not sound like what I understand "Latch Mode" to be? It sounds like "Manual Mode" per the Pacbrake document you mentioned above. (My coach is in "Manual Mode" per that document). My understanding is that latch mode will not activate the EB until you touch/apply the service brakes, and will stay on until you touch/apply the accelerator?

Are you sure you have the latch mode, or am I missing something?
Nope, my mistake. I do not have the Latch Mode. It would behoove me to read my own posts.

Sorry about the confusion.

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Old 07-06-2016, 06:30 PM   #24
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Dr4Film, I personally have never made a mistake, but you are forgiven.

The last post I read about your PRXB, you had just returned from Alaska, and were about to change to the PRXB. I would love to hear about your experiences in changing, and what were the real world results of its effectiveness.

Maybe you already posted something about this and can point me to the post so I can read it.

Thanks Much!
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Old 07-06-2016, 07:07 PM   #25
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The last post I read about your PRXB, you had just returned from Alaska, and were about to change to the PRXB. I would love to hear about your experiences in changing, and what were the real world results of its effectiveness.

Thanks Much!
I purchased it through a company in northern CA and had it sent to me in Santa Clarita CA. I then had the Cummins shop in Ventura CA install it for me.

Early in 2011 we traveled across the country to Florida, upstate NY, back to Florida and then back to Alaska for the summer of 2012 so I gave the PRXB a good workout with about 18,000 miles during that time.

I was happy with the extra braking that you get at the lower speeds as it meant less trouncing on the brakes to keep my speed in check while descending grades. However, as stated before you won't see much difference when you get over 50 mph and there is no difference once 5th gear hits and you are racing down a grade at 55 or higher. The PRXB performs very well between 15-45. It doesn't do much at all at the higher speeds in fact the normal PacBrake and the PRXB are pretty much the same at the higher speeds.

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Old 07-07-2016, 06:21 AM   #26
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For an explanation of how the 3 different modes (Latch, Coast and Manual), work see:
Exhaust Brake On/Off Switch
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Old 07-07-2016, 08:44 AM   #27
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OK another question. A lot of these articles talk about the three modes. They say they are setup when the cruise is on and not active. Does it default to manual mode when the cruise is not set? In other words, is there a difference in modes with the cruise off verses cruise on and not active?

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Old 07-07-2016, 09:37 AM   #28
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OK another question. A lot of these articles talk about the three modes. They say they are setup when the cruise is on and not active. Does it default to manual mode when the cruise is not set? In other words, is there a difference in modes with the cruise off verses cruise on and not active?
Bill
Not on my Cat powerd coach.

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