About That Jake Brake And Poor Road Conditions

As truck drivers, every one of us probably has bad habits, and we might not even know what they are. If you tend to keep the Jakes on most of the time, even in wet or icy conditions, you need to remember something.

Your ABS system doesn't control the braking force of your Jakes.

Jake brakes slow your truck down by pretty much the exact opposite effect of pressing the accelerator. When you accelerate, the engine turns the drive shaft one way. When you use the Jake, the engine puts force on the drive shaft going the other way. That reversed force is directly transmitted to the transmission, and then to your drives, and then to the ground through your tires.

The ABS system is an Antilock Braking System. It releases your brake pads when it detects the tires are slipping, so they can get a new grip on the road. If the truck starts to slip under Jake brakes, the ABS system can't let the tires start to roll again, because the Jakes are completely separate from the brake pads.

You're correct about the Jake and ABS being two different systems but you're way off about how the Jake Brake works. It doesn't provide opposite force against the driveline, it works more like a vacuum cleaner on the engine by keeping the exhaust valves open and sucking the compression right out of it. The engine loses the ability of the top of the compression stroke to help spring the piston back down to the intake stroke point and has to work harder, expending more energy and vents the compressed air into the atmosphere which is what makes that beautiful music. The 3 ranges on your rocker switches indicate what level you're using it at but for the motor, it correlates with how many cylinders it's going to hold the exhaust valves open on. 1 = 2 cylinders 2 = 4 cylinders 3 = all 6 for maximum engine braking An engine is nothing but a giant air pump, the Jake is an intentional and controlled hole in the line.

Robert Dragon, you got into the How Stuff Works of engine retarder braking. It is good to know about the the levels of that switch. But Farmerbob is right in describing the final result: "slowing power" happens only on the drive axles.

For knowing what to do in icy/ slippery conditions, is most important to know that Jakes only affect the middle axles, while the steers and tandems are still freewheeling. And that's a recipe for a jackknife.

Slowing power yes but it's not putting engine power in reverse on the drive shaft, that was the point I was addressing. The Jake literally sucks the power out of the engine, forcing the vehicle to slow down and yes of used improperly can cause loss of traction and a potential jackknife. While it's important to teach new drivers the ins and outs of safe driving, I think it's also important to pass along info on how things work when they're presented improperly.

Robert Dragon points out:

Slowing power yes but it's not putting engine power in reverse on the drive shaft

because Farmerbob used the word "reverse":

[The Jake's] reversed force is directly transmitted to the transmission

which can be confusing. Engine retarders won't move the truck backwards, but they do send the "force" through the drive shaft in the reverse of the normal direction, ... making the breaking.

As the Trucking Truth resident science + math teacher, I'd say you're both right. A's for everybody!

Resistance might be the best word to describe the effect the engine brake has on the "live" drive axle.

Actually - the mechanical force of "retarding" the engine - puts DRAG on the drivetrain. (ok, technically, exerts forces in the reverse of the normal direction - but simply - asserts "drag").

If the force of this "drag" exceeds the ability of the tires to maintain traction on a wet/slippery road - then the tires will no longer be rolling at the speed they are moving over the road - and traction is lost (skid).

Steers and trailer tandems can also skid - but not from the action of the engine (jake) brake. Freewheeling is probably a bad term for the "normal" activities of these wheels - they are still interacting with the road due to the friction between the rubber tire and the road surface (friction is what creates traction). Steers and tandems can skid from use of brakes on slippery surfaces - or the surface can just become so slippery that they lose friction (and contact) with the actual road surface due to water (hydroplaning) or ice (hydroplaning again - since ice is WATER).

Either way - once you lose traction - get off ALL POWER (brakes, jakes, engine) and PRAY that you regain traction. Otherwise - gravity and momentum are the only things that determine your direction/speed of travel.

I watched a few seasons of "Highway Through Hell" recently - about a heavy wrecker company (tractor trailer tow trucks) working along a real treacherous part of a pass in the Canadian mountains. To watch what these trucks do when they hit packed snow or ice - even chained up - makes you want to just turn the bunk heater on HIGH and stay in the truckstop when it starts snowing/icing.

Always remember - you have NOTHING TO PROVE OUT THERE IN BAD WEATHER. When you start seeing trucks sliding around or in ditches - it's time to safely and slowly get the heck off the road. Shoot - when you start HEARING ABOUT IT IN THE CB (because poor weather is actually one of those time you should actually turn the thing on), get off the road while there's still parking.

Rick

Rick contradicts himself:

Always remember - you have NOTHING TO PROVE OUT THERE IN BAD WEATHER. When you start seeing trucks sliding around or in ditches - it's time to safely and slowly get the heck off the road

You do have something to prove in "bad weather": that you're a smart and safe driver by calling your DM and saying you're not moving till the road is cleared.

I'm just sayin', Rick!

Rick contradicts himself:

Always remember - you have NOTHING TO PROVE OUT THERE IN BAD WEATHER. When you start seeing trucks sliding around or in ditches - it's time to safely and slowly get the heck off the road

You do have something to prove in "bad weather": that you're a smart and safe driver by calling your DM and saying you're not moving till the road is cleared.

I'm just sayin', Rick!

you have NOTHING TO PROVE OUT THERE IN BAD WEATHER BY CONTINUING TO DRIVE...

Is dat better?

Thought you were SCIENCE AND MATH - now yer ENGLISH TOO?

Rick

I was just trying to say there is two "prove" outcomes in yer "bad weather" situation. The issue is probably more philosophical than in language.

(Do you see the grammar error in my first sentence?😊)