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Old 04-15-2014, 06:14 PM   #1
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Exhaust Brake!

We are currantly on our first trip where we are going to
Experience some mountain passes. On our way to Ca.
My question is do I leave trans in 6th gear auto. With the
Exhaust brake going down hill.
Or gear down manually to like 3rd or 4 th with the exhaust brake on
Came thru Guadalupe pass, 2mi,7% down grade. Had to stab brakes
3-4 times to maintain 35-40 mph. In man. 4th.Have just over 10500 Mi.
on coach (see sig.):
THANKYOU!
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Old 04-15-2014, 06:56 PM   #2
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Start by leaving the transmission in '6' with the engine brake ON. See how it drives for you, as it will downshift itself until it can get to '2', which will really slow you down.

The Allison is pretty intelligent. It knows how to slow you down by auto downshifting, but downshifting to '2', which it is pre-programmed to do, may be too agressive.

It can be re-programmed to downshift to a lesser gear, but try what you have first to see how it works for you.
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Old 04-15-2014, 07:06 PM   #3
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On steep passes you will probably still have to use brakes.
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Old 04-15-2014, 08:14 PM   #4
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Going down a long 6-7 percent grade…….I like to shift down to 4th gear at the top of the hill….if that doesn't hold us below 2500 rpms during the descent, then i'll switch on the exhaust brake and then use the service brakes as needed to hold the speed steady………if the exhaust brake causes the speed to drop below that 2500 rpm, then I switch off the exhaust brake.
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Old 04-15-2014, 09:05 PM   #5
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Rule of thumb I use is the gear range that keeps engine in the power curve going up the hill is the gear you come down in, with the exhaust brake on. Yes, you may still need to use the brakes
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Old 04-15-2014, 09:18 PM   #6
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Do a google search for "snub braking" or "Heavy vehicle downhill control" and similar.

The engine braking management isn't really very intelligent as all it does is slam the transmission back to second gear, close the exhaust brake valve and monitor the engine speed to make sure it doesn't go too high and drop the gears as an when it can. Snub braking is part of the operator input to manage speed at whatever is optimum for your circumstances and without it you will usually either crawl down or go down too fast
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Old 04-16-2014, 09:41 AM   #7
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My exhaust brake (factory setup) goes to 4th, not to 2nd. And I would NEVER start down a 6-7% grade in 6th gear and expect the exhaust brake to get me down safely.

A week or so ago we went down the 15 mile 6% grade on US 82 from Cloudcroft NM to Alamogordo. Posted speed limit was 45 and sometimes less. I manually hit 3rd at the top. That held my speed to 40-45 very well, and I had to stab the brakes a couple of times. If I allow it to try to manage itself, 4th will be too fast on that steep descent. Several days later we drove the same route back up, and as we started the climb I when we got down to 45 I manually shifted to 3rd, and kept it there all the way up the mountain. If I allow it to manage itself, it WILL lug down, the rpm will be too low too much, and the engine would DEFINATELY overheat. When I keep the engine rpm around 2k or slightly above on a steep climb like that, the engine temp does creep up but it stayed a bit below 200 for the entire 15 mile climb.
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Old 04-16-2014, 12:09 PM   #8
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I leave my exhaust brake on all the time. I installed the BrakeSwitch option so the exhaust brake doesn't engage every time I take my foot off the throttle, but only when I press the brake pedal and release it.

With the exhaust brake on, my Allison 3000 tranny automatically shifts down to 2nd at the right time. Works for me!
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Old 04-16-2014, 12:36 PM   #9
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Quote:
Originally Posted by Tony Lee View Post
Do a google search for "snub braking" or "Heavy vehicle downhill control" and similar.

The engine braking management isn't really very intelligent as all it does is slam the transmission back to second gear, close the exhaust brake valve and monitor the engine speed to make sure it doesn't go too high and drop the gears as an when it can. Snub braking is part of the operator input to manage speed at whatever is optimum for your circumstances and without it you will usually either crawl down or go down too fast
Tony Lee
X2 on "snub braking"!
Riding the service brakes when descending a grade can leave you with NO brakes in short order.

However, if you have an Allison 6 speed transmission that slams into, or out of, any gear something needs fixing!

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Old 04-16-2014, 12:48 PM   #10
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Spare time.......

Quote:
Originally Posted by poppopc View Post
We are currantly on our first trip where we are going to
Experience some mountain passes. On our way to Ca.
My question is do I leave trans in 6th gear auto. With the
Exhaust brake going down hill.
Or gear down manually to like 3rd or 4 th with the exhaust brake on
Came thru Guadalupe pass, 2mi,7% down grade. Had to stab brakes
3-4 times to maintain 35-40 mph. In man. 4th.Have just over 10500 Mi.
on coach (see sig.):
THANKYOU!
Here is some other threads on the "exhaust brake"
https://www.google.com/search?q=exha...earch=irv2.com
for you to read in your spare time, After reading some of them, your answers might be answered.........
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Old 04-16-2014, 01:13 PM   #11
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I tried to manually downshift when needed and I found that the Allison knows best. I let it do the shifting and I use the EB on down grades and hit the brakes as needed. The tranny seems to do a fine job matching the gear with the RPM ascending or descending grades and so far have not had any issues with overheating. I also use the economy mode on the flat (and near flat) hwys.
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Old 04-16-2014, 04:27 PM   #12
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Quote:
Originally Posted by MSHappyCampers View Post
I leave my exhaust brake on all the time. I installed the BrakeSwitch option so the exhaust brake doesn't engage every time I take my foot off the throttle, but only when I press the brake pedal and release it.

With the exhaust brake on, my Allison 3000 tranny automatically shifts down to 2nd at the right time. Works for me!
I was at the dealership this past weekend and the salesman said he leaves the exhaust brake on all the time, never turns it off. That seems odd to me, since when coasting on a flat road, we lost momentum with it on and coasted freely with it off. So like you explained, it seemed to engage when my foot was off the throttle.

I went to BrakeSwitch.com and they state they are no longer taking orders. Yet, it seems like this might be something that should be standard on any chassis.

If I don't or can't get one, do you recommend leaving the exhaust brake on all the time while I drive anyway?

Thanks!
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Old 04-16-2014, 04:52 PM   #13
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Exhaust Brake!

Quote:
Originally Posted by MSHappyCampers View Post
I leave my exhaust brake on all the time. I installed the BrakeSwitch....

X2...great device! I also manually change gears and do snub braking on steep grades.

Craig
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Old 04-16-2014, 06:15 PM   #14
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Quote:
Originally Posted by bobguigley View Post
Going down a long 6-7 percent grade…….I like to shift down to 4th gear at the top of the hill….if that doesn't hold us below 2500 rpms during the descent, then i'll switch on the exhaust brake and then use the service brakes as needed to hold the speed steady………if the exhaust brake causes the speed to drop below that 2500 rpm, then I switch off the exhaust brake.
I understand your strategy of downshifting at the crest of a hill preparing to go down. I don't understand why you don't engage the exhaust brake at the same time. That's what it's designed for.

The Allison tranny / exhaust brake IS very intelligent, assuming it's programmed for the way you want it to operate.

For those of you who like the operational logic of the Brake Switch, simply have Allison reprogram your exhaust brake operation to 'Latch' mode. Does the same thing.

For those of you who don't want the transmission to downshift towards '2' when the exhaust brake is engaged, have it reprogrammed to pick a higher gear when the exhaust brake is engaged. I chose '4', and it works great. No 'slamming to 2nd gear'. If I need more aggressive braking going down a long descent, I manually downshift to '3' or further if needed. But I have the exhaust brake engaged from the onset of going down the hill.

I have mine programmed to 'Latch' mode and preset downshift to '4' when the exhaust brake engages. With this setup, I keep my exhaust brake 'ON' all the time, and it works great! I can coast when I want to w/o exhaust braking, and I can slow down with assist all the time when I want. Not too aggressive. Just right. If I need more assist I downshift to a lower gear manually.

Same logic applies to engine brakes (Jake's). Just works differently, and many times has a lo/hi setting on the engine brake. Still engages the transmission to downshift as both brakes work better at higher engine rpm's.
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