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Old 02-21-2013, 04:28 PM   #57
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Pre select on Allison

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Originally Posted by Air Baron View Post
Being new to motorhoming, I am certainly no expert. The exhaust brake is evidently not intended to be on all the time...that is why there is a switch. I engage it coming down steep inclines, short exit ramps and coming up on traffic lights that suddenly turn yellow in 50 mph zones. Other than that, I find the exhaust brake's forced downshifting to be more annoying than helpful. I would rather be in control of vehicle speed in traffic and only engage the cruise control when on the open highway. The idea of a foot switch (and indicator light) wired in parallel to the panel switch is definitely on my short list before this year's western swing.
Air Baron, just stop by a Authorized Allison transmission shop and have them change your "pre select" to 5th gear or 6th gear instead of 2nd or 4th, I had mine done a year ago to just stay in 6th and my switch is on all the time, no more harsh downshifting, and at interstate speeds (1600-1800 rpm's) the braking works well for me on the hills.On back roads on hills I just downshift manually if I need to to pick up rpm's. No matter how fast I am going when I let off the pedel the exhaust brake is on and the transmission downshifts right down to 5mph and is programed at 5mph to shutoff. When they done mine, laptop out to the parking lot,10 minutes max, done, no charge.
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Old 02-21-2013, 06:19 PM   #58
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If you do have Allison change the pre-select gear downshift changed from the factory '2' to another gear (I chose '4'), remember, you can always manually select a lower gear to help the exhaust brake along.

It always works better with higher RPM's, thus why the factory programs it to a lower gear when the exhaust brake is engaged.

I agree it makes the coach much more drivable with the exhaust brake engaged, when the tranny downshifts maybe 1 or 2 gears only - no heavy downshifts to a lower gear.
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Old 02-21-2013, 10:33 PM   #59
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Originally Posted by Dr4Film View Post
I don't want to sideline this thread but I feel that this point is important.

Hopefully, when only using one hand on the wheel "in town" your speeds are slow enough that if you were to experience a front tire blow-out you would be able to handle the rig and steering appropriately without veering off the road. However, once out of town and driving at highway speeds I would fully recommend that you have two hands on the wheel.

Also, the Exhaust Brake is only active once the coach gets to a minimum speed but I can't remember what that speed happens to be.

As you are passing or in my case being passed by OTR big rigs, take a look at most of those driver's. You will noticed that they have both hands on the wheel, 10 & 2 positions

Having a front tire blow-out is my worst fear while driving. I have read about too many RVer's along with having friends who have had front tire blow-outs that have caused major damage and death.

Installing Tyron Bands would be one method to help with those situations, but they are expensive. However, that expense is peanuts when compared to what a front tire blow-out can cause.

Just a word of caution and opinion.

Dr4Film ----- Richard
Clarity in communication is everything: I drive using both elbow rests with one hand on the wheel and the the other on the other elbow rest on interstates within an inch of the wheel. Being passed or passing or changing lanes or braking or anything out of the ordinary I use both hands. No accidents, tickets, three dead deer and a coyote....My preference from for the EB is to leave it off until I need it......just being honest with the way I drive and not recommending it for others.
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Old 02-22-2013, 02:16 AM   #60
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On our 400 hp ISL, I believe the low compression brake setting activates the VGT while the high setting activates the Jake on all 6 cylinders? Am I correct?

I normally drive with the low setting on. It seems to disengage completely at <15 mph. Our Allison has not been reprogrammed and with the compression brake on in either position the selected gear drops to "2" although the gears drop as the speed drops. I prefer to turn off the compression brake on city streets in order to reduce noise. Shifting manually to keep the rpm's up and turning the compression brakes on and off as needed helps to keep me alert.
Even tho' our coaches are much quieter than commercial diesel powered vehicle, I would caution that many cities and towns are sign posted that "Use of Engine Brakes is Prohibited". My guess is that applies to us too!
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Old 02-22-2013, 07:24 AM   #61
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Again, let me emphasize that this is an Exhaust Brake discussion that doesn't include Engine Brakes so as not to confuse some people that don't know the difference.

For those that have factory programming in their Allison transmission that interacts with the Exhaust Brake, you will or should not feel any sudden jerk when the Allison downshifts to 2nd gear when activating the Exhaust Brake. That's because when it happens, it does NOT really go into 2nd gear. It is solely the "target" gear that is displayed in the Keypad. If you happen to be in 6th when the Exhaust Brake goes on, then the Allison will downshift to 5th. If in 5th, then it will downshift to 4th. The Allison is smarter than its operator and it will NOT let you do anything to it that would damage the transmission. Even if you do the downshifting manually, it still won't actually downshift until your speed has been lowered enough to allow the Allison to safely go into the lower gear.

The most important aspect of managing your Exhaust Brake is to know your specific up-shift speeds. Where does your Allison up-shift at for 2nd to 3rd to 4th? Once you are in 5th gear, your Exhaust Brake is fairly ineffective.

To get the most out of my Exhaust Brake, I attempt to keep the Allison in 2nd or 3rd for really steep grades and 4th for moderately steep grades. Once my coach reaches 54 mph it will up-shift to 5th and then it will gain speed like there's no tomorrow.

Also, remember that if you have an Engine Brake, this discussion is not for you as the Engine Brake is an entirely different animal.

Just to clarify the weights of my total rig, my coach is 37,000 lbs and the trailer I tow is 11,000 lbs so I am constantly managing my speeds when descending grades of all types.

Dr4Film ----- Richard
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Old 02-22-2013, 07:41 AM   #62
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Quote:
Originally Posted by EZDZIT
On our 400 hp ISL, I believe the low compression brake setting activates the VGT while the high setting activates the Jake on all 6 cylinders? Am I correct?

I normally drive with the low setting on. It seems to disengage completely at <15 mph. Our Allison has not been reprogrammed and with the compression brake on in either position the selected gear drops to "2" although the gears drop as the speed drops. I prefer to turn off the compression brake on city streets in order to reduce noise. Shifting manually to keep the rpm's up and turning the compression brakes on and off as needed helps to keep me alert.
Even tho' our coaches are much quieter than commercial diesel powered vehicle, I would caution that many cities and towns are sign posted that "Use of Engine Brakes is Prohibited". My guess is that applies to us too!
Although few things are impossible, I would be surprised if your ISL is using both the VG turbo and a compression brake. The more likely case is, the low setting activates the compression brake on 3 cylinders and the high setting uses all 6 cylinders.
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Old 02-22-2013, 08:59 AM   #63
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I don't leave mine on all the time on hwy or Interstate driving. If it is on when going 65MPH and I let off the gas it shifts down immediately and slows the coach and is annoying. I only switch it on when needing to slow down immediately. I leave it on when driving in heavy traffic or stop and go traffic in town to save on breaking.
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Old 02-22-2013, 09:27 AM   #64
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Again, let me emphasize that this is an Exhaust Brake discussion that doesn't include Engine Brakes so as not to confuse some people that don't know the difference.

I would say we are using a generic term that people use to refer to auxiliary braking generally and to most drivers, whether it is a transmission retarder, engine brake, simple exhaust brake, variable geometry turbo or even some sort of electric brake, the actual nuts and bolts don't matter very much but the techniques and limitations and cautions do.
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Old 02-22-2013, 09:28 AM   #65
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This thread has a lot of good information going back and forth. I just want to remind everyone of this ( one of our most important ) rules.
" Please think before you post and keep your comments limited to the topic at hand; above all be nice. We encourage everyone to participate in and enjoy the Community while at the same time adhering to these rules:"

It's what makes this a great forum.
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