2022 T880 Endurant 12 sp 2.79 ratio

[farmer_luke]

Hello, brand new to this forum so I apologize if this is in the wrong place or has been covered repeatedly.

I'm a grain farmer looking at buying a newer used semi and the one that's caught my eye is a 2022 Kenworth T880 with a 12 speed automated manual, day cab with 2.79 rears (150,000 miles, 4,500 hours). I saw somewhere on this site that that combination (12 sp & 2.79) was disliked by some. Hoping to get more info anyone can provide about this being a good or bad truck for my application.

I currently have a 2002 International 9400i with a 12 speed automated manual; not sure on rear ratio. I only add about 10,000 miles per year to my semi.

[farmer_luke]

Forgot to mention it has the Cummins X15 efficiency engine.

[marek4792]

Problem is with the 2.79s and the usual 2.64s they are usual paired with an overdrive transmission with a .73 final output ratio. Which basically translates into engine speeds well below 1500 and into the beating the engine to death dropped liners excessive wristpin wear bearing wear etc the slower you go with it. That's why we say get 3.55s and up assuming higher weight is involved.

[farmer_luke]

(01-23-2024 )marek4792 Wrote:  Problem is with the 2.79s and the usual 2.64s they are usual paired with an overdrive transmission with a .73 final output ratio. Which basically translates into engine speeds well below 1500 and into the beating the engine to death dropped liners excessive wristpin wear bearing wear etc the slower you go with it. That's why we say get 3.55s and up assuming higher weight is involved.

Thanks. I wonder how long the engine will put up with being lugged at low rpms? Typical trips with grain are 80-90,000 lbs one way, either 20 miles or 80 miles, then back empty. I think the auto shifting can be set to different modes and you can run in manual to keep it in the gear you want.

I've checked with my local shop about demandating and they said it's an option but how do I know if they'll do a good job? What do I need to be able to send the code to be looked at by someone who knows good programming from bad?

[Rawze]

(01-24-2024 )farmer_luke Wrote:  ...
Thanks. I wonder how long the engine will put up with being lugged at low rpms? Typical trips with grain are 80-90,000 lbs one way, either 20 miles or 80 miles, then back empty. I think the auto shifting can be set to different modes and you can run in manual to keep it in the gear you want.
..

With those weights and short haul like that. you will have noting but problems and hate that truck in the end due to torturing it to death!.

And unless there is a specific reason for the auto-s$itter (handi-capped, etc.), I would highly advise against it, as they are very expensive to repair and maintain over the years vs. manual.. and are less fuel efficient across the borad vs. a decent driver.

- From your descriptions.. shorter hauls and over 80,000 lbs often.. you will be looking at something with a set of 3.90's on the tall end, but something with a set of 4.68's would be more appropriate though to get it up and going quickly so that it has a bit of ballz to it.

================

As far as buying used trucks goes lately.. they are all upside down in gearing due to the morons buying them not knowing any better and the stealers$its pushing these tall rear ends that make the engine lug itself to death just after the warranty period, all in the name of 'saving fuel'
at the cost of cutting the the engine lifespan in half or less.

It is very difficult to find a properly spec'd truck these days. It is also getting hard to find trucks with stick too, because the mega-fleets cannot find drivers that have any intelligence .. and just about everything used with those horrible rear end specs also have close to half a million miles on them. This overly-tall rears makes the engine wear 2x, so they already have 1+million worth of wear (due to the torture below 1500RPM) on them. Engine is typically ready for a head gasket and other failures at any moment by then... costing the next guy who buys it big-time, putting them in a dark financial hole!.

Shop around .. and shop some more.. and then still consider replacing the rear ends as part of the cost needed for the operations you are describing.

You buy a truck with those garbage 2.79 rears, and EVEN IF SOMEONE PUTS 800+ Horsepower in it,.. it loaded above 80,000 lbs ... and it will still feel like it won't hardly get out of its own way!,.. no matter what YOU DO! ... because IT IS SPEC'D COMPLETELY WRONG FOR THE APPLICATION!. plain and simple!.

And to add insult to this.. you mentioned short haul .. which usually means several loads a day + a lot of stop and go in an urban setting, unlike a long-haul highway truck that moves at highway speeds for hours on end.

The more stop-n-go type of back and fourth operations there are,... the bigger the gear ratio needs to be to get the truck up and going, so that your not 3/4 a mile down the roads, and still trying to get it up to speed (hence my recommendation of 4.68's). This is exactly why dump-trucks are geared 4.68's and 5.11's.. for this very same reason.

here is a set of selection charts to help figure out the best gearing for an application...
ref: http://rawze.com/forums/showthread.php?t...7#pid63777

[Rawze]

(01-24-2024 )farmer_luke Wrote:  ...
I've checked with my local shop about demandating and they said it's an option but how do I know if they'll do a good job? What do I need to be able to send the code to be looked at by someone who knows good programming from bad?

As far as de-mandating it goes.. I am sure there are a dozen places you could take it to.. but you will not find anything but bad delete programming, though all of them would try to convince you that they are the best in town. This, even if you took it to 100+ places well known and all.. and then you will be crying on here in about 2 years that you f#ucked up and have a bad delete. - It is more than 95+% (without even exaggerating it) of all shops that do that type of work are completely horrible at it and the programming is even worse, severely shortening the life of the engine, at the end of the day.

-- It is an ISX ... They love to be worked on and all info, parts lookup, repair procedures, etc. to anything you need is available for free for them. that IS their only and biggest advantage for owning one.

-- so go buy yourself a cheap win10 laptop and a $300 "inline-6 data-link adapter kit" and then you can become self reliant on troubleshooting it to keep it away from $$$ repair shops every time a check engine light flashes.

-- AND so that you can simply copy the program out of the ecm yourself or with the help of someone .. and then e-mail it to someone trustworthy that can review any programming, make any adjustments (de-mandate, etc.) needed... WITHOUT GETTING RIPPED OFF AND REGRETTING the most likely bad delete you were considering there, ... AND WITHOUT SPENDING any $$$ BIG DOLLARS.

-- This also puts control of any custom files, etc. directly in your own hands so that in the future if the ecm ever goes bad, or the program ever gets lost, etc. ... you will have a backup copy of it yourself + the means to put it back! ... and are not at the mercy of whoever did it the first time.

How does that saying go?... you can lead the horse to water?.

[koliunia]

I believe 2.79 is because it's a direct drive transmission. Last time I checked, there is no rebuild kit or parts available for 12 speed endurance transmission. That thing is a $20k replacement, plus labor and core.

[Rawze]

(03-08-2024 )koliunia Wrote:  I believe 2.79 is because it's a direct drive transmission. Last time I checked, there is no rebuild kit or parts available for 12 speed endurance transmission. That thing is a $20k replacement, plus labor and core.

Then it sounds to me like you purchased into a truck that was not spec'd properly for what your using it for.