How do you use the jake brake on a truck with an automatic transmission?

Straight from Detroit Diesel's Youtube channel:


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turn on the jake button and lift of the gas pedal works every time yea i know nobody likes a smart ###

 

Every truck, every driver, every load is different in how high you rev the engine with the engine brakes. I'll back Otter on this, my old Mack the engine brakes worked the best in 8th thru 10th gear between 1700 and 2000 RPM's, unless I was pushing 80K, I never let them get above 1800. I'd always adjust gear selection. My current KW, if I apply MAX engine brakes, which I do frequently by accident, the trans will drop 1 gear and rev to 2300, the three times it's been in the mountains have been very light loads so far, but I still don't want it to rev very high. It's all about driver preference.

Also, it's sometimes about driver exp., as you mentioned in the beginning, you've been driving 7 yrs, I've been doing it 23 yrs, running the mountains regularly, Otter has quite a bit of exp. too. I drive the way that I'm comfortable with, my last truck got 400K out of the drum brakes. I've only got 26,000 miles exp. on this KW with disc brakes, it takes some getting used to.

 

If your truck isn’t holding you back at 1600 rpm, you’re in the wrong gear and going to fast. My X15 has never seen 2300 rpm, hopefully it never will. That’s so far out of the normal operating RPM range.

Edit to add: “The X15 Performance Series engine for 2017 delivers the most powerful engine and engine brake combination in the industry. The engine brake delivers increased braking power where it is needed most, in the 1300-1700 rpm range.”

 

I know this is an old thread, but I found it trying to figure out the nuances of my new 2025 Kenworth W990, with an X-15 Cummins and Eaton TX-18 Automatic Transmission. I'm a newer driver with 3+ years and 400,000+ miles running agriculture commodities around Utah, Idaho and Nevada. I've been in a manual until about 3 weeks ago. So far I like the auto but it has some minor adjustment to my techniques......

First in this truck, when in full auto and with Jake set in medium or high, when you let off the accelerator it immediately drops 1-2 (sometimes 3) gears and Jakes slow it down fast, but its a trip watching it do that and dropping gears so fast while taking rpms to almost 2000. I never used to get my rpms even close to that, and definitely couldn't have been able to catch that big of a downshift. It was annoying when I'm just coming down a 2 to 6% downgrade and want to hold the speed but not try to stop. I solved this by using the "manual" mode (pushing button on the end of the shift lever in). So now whenever I want to use Jake during a downgrade without needing to actually bring rig to a halt I use the Manual mode which prevents the automated downshifts. I can still upshift, downshift or adjust amount of Jake as needed. Why I was searching for answers, was after taking my first trip on a regular run from Gabbs, NV to Utah along US-50. It's a great place to test your mountain driving skills.... My route from Gabbs to central Utah on 50 includes 16-17 mountain passes ranging from 3-9% grades up and down, including 2-3 that are 8-9% grades and tight switchbacks requiring 15-30 mph corners on narrow (especially when passing opposing tractor trailers) on the 2 lane highway. I'm hauling agriculture commodities with GCVWs of 103,000 to 108,000. Never had issues before of selecting right gear with full Jakes to crawl down theses passes. But with this new rig I found myself having to use service brakes way too much to keep appropriate speed and avoid rpms in the 2000+ range.... Trying to run away .... Knew something was up .... But automatics are new to our fleet and I couldn't get answers from mechanics, or other more experienced drivers. Well long story short after talking to Kenworth Rep, who referred me to Eaton Rep, who finally got me in touch with the Cummins Rep...... It's a computer parameters setting. The default settings from factory are set so the Jakes don't kick in below 35 mph. So because I was starting at the summit (after long 9% climb) at only 25-30 mph and not letting it get higher than than coming down back side, no matter what I tried with manual, auto or feathering (tap let off) accelerator, the Jakes wouldn't activate. It's just a computer parameters setting that now we know the mechanics just plug their computer into truck and change. Cummins Rep also pointed out this set up is normal to run up to 1700-2000 rpms to give full braking power. Also normal for it to go to 1800 rpms before upshifts so it can do its "skip shift" when it seems appropriate for acceleration or climbing. Now that's fixed, I'm finding myself happy with this new truck. It shifts fine in climbs, downshifts as needed with no problem, and I still can tell it if I want to downshift or upshift before it does, in automatic (if you know from your manuals the right ranges in rpms where you can shift it's never denied me a shift request). Anyway just thought I'd add an update on what I learned with this new rig. Just turned 9000 miles.