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Busskipper · 02-01-2021, 07:47 AM

Quote:

Originally Posted by wolfe10

YES, normal as long at 2,300 is not above your engine manufacturer's MAXIMUM RPM NO LOAD SPEED.

The "2" is the "shift toward" gear (downshift a gear at a time as long as it will not over-speed the engine). The "5" (only for those with two window shift pads) indicates the current gear.

"Shift toward" is not hard to understand-- no different than it showing "6" when you are sitting at a stop light. It is the gear toward which the transmission will upshift as road speed and load permit.

Brett,

Thinking you are saying what I'm Asking! Even if the Transmission is set to go all the way to 2nd it should Never skip a gear to get there - if in 6 it will show 2 but progress down to 2 one gear at a time , 6-5-4-3-2 Correct?

When they installed the new transmission, they reprogramed the trans mission to only drop to 5 (I think, maybe 4) so unless I manually downshift it will not give me any Real Braking in the mountains. As I spend a substantial amount of time in the Rockies or other Mountains here on the East Coast, and until the reset I seldom used my brakes - Because the Transmission gave me plenty of Braking, Now - not hardly any braking is gained with either High or Low braking.

So to repeat my issue - the TCM - this super smart TCM allowed the transmission to shift from 6 to the Lower gear pack at High Speed - This should not Happen! Result was the Transmission was Shot/Blown - for a second time is less than 70,000 miles. As you say - I was also Lucky to have not totally Blown the Engine .............Not Good.

Trying to Understand How Allison could have this MISTAKE built into the Transmission - Thought it was Just TOO SMART!

So the recommendation from the Allison tech I spoke with was to get the Trans reset to drop to 4th gear that that would give me the braking I needed, Not thinking that is what I need or what I'll be Comfortable with.

So the more I hear the more my poor little brain just is Confused and very tentative with this Transmission - $10,000 every couple years is just not an expense I can ever justify.

Thanks, for listening,

Bill

wolfe10 · 02-01-2021, 07:55 AM

Bill,

Basically correct. The ONLY time the transmission will downshift more than one gear at a time is if it is safe to do so. Generally that would be when you are at lower RPM in 6th gear and let off the throttle and turn on the exhaust brake. If speed is low enough that it can go directly to 4th without over-speeding the engine it will.

As far as pre-select gear, there is NO IDEAL CHOICE. When coming to a stop, 2nd is a great choice.

When driving in the mountains, 5th is the best choice, IF (yes big IF) the driver is comfortable making manual selections. Example-- I 40 westbound into Albuquerque. 5th gear exhaust brake on is fine for the entire descent. If you have a 4th or lower gear pre-select, you will be over-braking, then on the throttle, repeat 20 times.

So, what gear you have the Allison tech program as your pre-select gear depends on you and your desired driving style.

BTW, mine are set to 5th and then I, not it choose lower gears.

In any case, neither the user or a low pre-select gear should allow the engine to over-speed. Said another way, it is BOMB-PROOF.

I still can't wrap my head around the transmission being the "weak link" if it malfunctioned and WAY over-sped the engine. By the time there was enough torque generated by the over-speeding engine to damage the transmission, I suspect the engine would be in pieces. And sure, if the engine locked up at speed, it could THEN result in transmission damage.

Busskipper · 02-01-2021, 08:24 AM

Quote:

Originally Posted by wolfe10

Bill,

Basically correct. The ONLY time the transmission will downshift more than one gear at a time is if it is safe to do so. Generally that would be when you are at lower RPM in 6th gear and let off the throttle and turn on the exhaust brake. If speed is low enough that it can go directly to 4th without over-speeding the engine it will.

As far as pre-select gear, there is NO IDEAL CHOICE. When coming to a stop, 2nd is a great choice.

When driving in the mountains, 5th is the best choice, IF (yes big IF) the driver is comfortable making manual selections. Example-- I 40 westbound into Albuquerque. 5th gear exhaust brake on is fine for the entire descent. If you have a 4th or lower gear pre-select, you will be over-braking, then on the throttle, repeat 20 times.

So, what gear you have the Allison tech program as your pre-select gear depends on you and your desired driving style.

BTW, mine are set to 5th and then I, not it choose lower gears.

In any case, neither the user or a low pre-select gear should allow the engine to over-speed. Said another way, it is BOMB-PROOF.

I still can't wrap my head around the transmission being the "weak link" if it malfunctioned and WAY over-sped the engine. By the time there was enough torque generated by the over-speeding engine to damage the transmission, I suspect the engine would be in pieces. And sure, if the engine locked up at speed, it could THEN result in transmission damage.

Not to beat this to Death - My understanding what you are saying is that the TCM should NEVER - NEVER - allow this to happen, the big - But - here is that it did happen and it did not Blow the engine - But it has blow the Bottom End of the Transmission Twice - the exact same way.

As I've just rebuilt the Transmission, again, and now Reset the TCM - even with the two year warranty - I am just not Comfortable - as I still have not found or ID'ed the exact issue/item that caused the issue.

Guess what I'm saying is until I KNOW exactly what really caused it I will drive with the "fear" that it will just happen again. Me being a Simi Engineer type, I've always solved the issue before I let it Go!

What I'd really like is for Allison to explain how it Happened - and then make me feel it will Never Happen Again!

Thanks for your help,

TR4 · 02-01-2021, 08:37 AM

I’ve found the adaptive learning on the transmission takes many miles to relearn after a power disconnect. My transmission was programmed to downshift into 4th, which to me was very harsh. I’ve only used 3rd once and never 2nd, the engine brake holds the downhill speed with no problem at under 2300 rpm.

For more control I had the transmission reprogrammed to downshift into 5th. I use my shift pad, high and low switch and watch my Rpm’s to select the best combinations to get down the hill. I rarely use my service brakes.

Learn how to use your shift pad without having to look down at it. Learn how many Rpm’s your engine is increasing with each downshift. Toggle between high and low to keep your engine at a safe rpm.

Bill