What do I need to know about automatic transmission trucks?

That’s true when they brake they won’t be cheap to fix. If someone is O/O maybe stay with manual. I seen video they claimed they don’t even sell parts for them. The warranty is for 750,000 miles so after that it all on the owner of the truck

 

I look at the automatic braking and stuff more as backup to help driver if needed. Drivers don’t need Descent Control, but cool option I think. We can go down hill up to 8% grade and the computer and engine and transmission can basically hold the speed you set truck for

 

The problem is all of this crap. Just adds more electronics and it's one more thing that can and will fail. And will cause the truck to wind up in the shop with more downtime.

 

I drove one once as a company driver for about 3 years and never did feel comfortable in that thing.

 

I just put most this in an old post regarding Jake Brakes in the automatic.... But think it would be helpful here too ....

I'm a newer driver (25 years driving fire trucks) with just over 3 1/2 years and over 400k miles in tractor trailer. I have been exclusively hauling overweight agriculture commodities (103,000 - 112,000 GCVW) around Utah, Idaho and Nevada. We haul our loads in 53', 108 cubic yards, 4 axle (2 stationary axles with duals, 1 drop of duals I. Front and drop steerable tags on rear. Our tractors have additional pusher in front of the drives. Up until 3 weeks ago I've exclusively been using manual transmissions, as had every driver in our small company. Well my previous truck hit its 500k mark and I just started with an automatic. 2025 KW W990 with Cummins X-15 and Eaton TX-18 Automatic Transmission.

Here's my experience in last 10,000 miles.

1) Unlike some of the other set-ups I've read about here, my Jakes do NOT activate when Cruise control is set. Obviously if you apply brake you'll kick Cruise off and they work. But you definitely can't just "set your speed" and come down off a grade and expect the cruise to maintain your speed.

2) In my truck the shifting is smooth and much more agile than I expected. Id heard the autos struggle on climbs...... I'm loaded heavy (even as high as 110,000 GCVW) climbing long mountain passes, even starting from full stop, that are 3-9% grade climbs for 7-15 miles or more. The auto downshifts smoothly to keep torque and horses in best spot based on all the computer calcs.

3) If you are comfortable being able to choose the right gears and shift manually in proper RPM to Speed ranges on your manual transmission, you'll have no problem getting an upshift or downshift anytime you request it on the automatic. I have had times when I know the climb is going to get steeper soon and the truck hasn't gone the last 100 yards or so to recognize it, so I tell it to downshift before it decides to..... Never a problem. Same for upshifts.

4) I can switch to "manual" with push of the button and make all the shifting decisions (as long as you are shifting properly in right ranges, if you lug engine or doing something else dumb the computer will override and make a shift to protect the rig).... But I've found I only need to and/do for a very specific reason....... This was the biggest learning curve for me....

5) The Jake Brake .... In full auto mode on the transmission AND when Jakes set in the "Medium" or "High" level --- as soon as I release the accelerator the Transmission will instantly drop 1-2 gears and almost slam you thru the windshield (especially when empty) and then as you slow keep dropping 1-2 or more gears at a time to put the Jakes to full use and RPMs running in the 1700-2000 range. I can see and even appreciate that for an urgent or emergency stop. But if I'm just come down a grade or even to just slow because I got a little heavy on the throttle I was not liking it. So key here, at least for my KW and maybe other automatics, is when I know I'm going down a grade I now always select "Manual" and adjust gears and Jakes as needed.

6) Along those lines, where I first found this site was because I was bringing a load of Magox from a mine in Gabbs, NV back to central Utah along US-50. If you haven't driven it yet, it's one of the best places to test mountain driving skills. 14-17 mountain passes, ranging 2-9% grades up and down, elevation changes from 3000 ft to almost 8000 ft, all 2 lane narrow highway with wildlife and weather depending on time of day and season. Well I was dropping off the Utah side of one of the biggest passes just East of Austin, NV. 5-9% down grade with narrow switch backs. I'm 108,000 GCVW, in a 285" wheelbase tractor and a 53' trailer. Start at top about 20 mph, not expecting to ever go above 30 mph all the way down, then up and over next pass that's almost the same and back to back. Here's where I found the problem..... My Jakes were no kicking in!!! Not in manual or auto, not after applying brakes, nor trying to get accelerator too 'reset' by tapping and letting off. Because I've never driven an automatic nor had my boss or mechanics or other drivers in our company we couldn't figure out what was up. But I definitely didn't like how much service Braking I had to do to keep the rpms and truck from "running away". Anyway after a week of research, contacting Kenworth, Eaton and Cummins/Jake reps we found out it's a "parameters" setting in the Cummins computer! The factory "default" is set to "minimum speed required for Jake" is 35 mph!!! It's just a computer setting. Once we found that out, the mechanics hooked up the computer and we changed the minimum speed to 15 mph.

Hopefully this helps someone. Now this is set up, I am surprised to say that I actually love this rig! It's much more comfortable to operate and much less fatigue especially on long climbs and in heavy traffic. It also has handles all the climbs, holds on hills when starting with no problems (had it at complete park brake and after sleeping started again fully loaded at 107,000 lbs on a 5,% grade. It started and climbed the increasing grade from 5-9% over about 10 miles reaching 20-25 mph with no problems all automatic.). And the skip shifts it does up and down would be impossible to do no matter how good I got.

I was worried about climbing and holding back on down grades with the loads I haul and the mountains I drive thru. But I'm very happy and impressed. (Especially now the "min speed for Jake" is set right!

BTW the truck this replaced was a 300" wheelbase 2020 KW W900 also with the X-15 Cummins and Eaton 18 speed manual transmission. It had 487000 miles when we replaced it. All our trucks are well maintained and serviced with very talented and responsive mechanics who get right on any problems found. Our company policy for all "non-local" trucks is to replace them at 500,000 miles.

 

If you want the jake to activate with the cruise control there should be a parameter that can be changed.

 

I'm sure there likely is with all the "parameters" but with the weights I am hauling and the topography I rarely use the cruise except on long stretches of relatively level terrain. Like one of the of the previous posters shared, it's the operator that is in charge and should be focused. For my loads and grades I use the accelerator for most of my control.

 

The brand new Cascadias allow the Jake during cruise. Overall, I’d much rather have a manual but the autos are nice in thick/slow traffic.