Engine Brake: When To Use?

When should I use an engine break? I leave it on almost 100 percent of the time like my trainer did. You end up picking up too much speed without it. With good weather and heavy city traffic, I have it on high or medium. Out of the city cruising, on medium, and in snow, on low. I don't agree with turning it off in snow since on low it acts like a very light pressure on the brake pedal, so there's no risk of skids or jack-knife. I wonder if other truckers leave it on most of the time like me.

A good driver will not jackknife if forced to go down a snowy hill with 'high' engine braking because he feels the truck and trailer

Keep in mind there are two types of jackknives - a tractor jackknife and a trailer jackknife.

A trailer jackknife tends to happen when you're empty on slick roads. You hit the brakes, the trailer brakes lock up, and the back end of the trailer starts sliding to the left or right. The tractor often keeps pointing straight ahead and has full traction.

A tractor jackknife tends to happen on slick roads when you're loaded heavy, your tractor and trailer are not quite lined up in a straight line, and you hit the brakes. It can also happen if you hit the gas too hard on slick roads causing the drive tires to break loose. Maybe you're going around a curve. Maybe your trailer tandems are out of alignment a little bit. Anything that makes your tractor point in a slightly different direction than your trailer...and I mean slightly....can cause this. The drive tires on your tractor will lose traction and the rear of your tractor spins around to one side or the other as the weight of the trailer pushes your tractor around. The trailer stays straight ahead and often times does not lose traction. The tractor spins around and slams into the side of the trailer.

Now trailer jackknives tend to happen rather slowly and are normally pretty easy to get out of if you can let off the brakes a little and lightly touch the gas. Once you let off the brakes the trailer tires can begin finding a grip and touching the gas will pull the trailer back in behind you. I've had this happen on slick roads with an empty trailer in strong crosswinds without hitting the brakes. I've also had this happen when hitting the brakes with an empty trailer on slick roads. As soon as you notice that trailer is moving to one side or the other you let off the brake, touch the gas a little, and you're usually fine. Of course if you aren't in a position to be able to let off the brake and touch the gas a little you're in big trouble. Once that trailer loses traction and starts coming around it's not going to stop coming around until you allow it to. Fortunately because the trailer is so long it comes around rather slowly.

A tractor jackknife normally happens so fast that by the time you realize what's happening your tractor is facing the wrong direction on the highway and you get smashed into the side of your own trailer. Because the wheelbase is so short on the tractor it whips around way more quickly than a trailer jackknife. The only time I had this happen in a scary way was when I was climbing a hill on slick roads with a light load and the drive tires broke loose. I heard my engine wind up and suddenly my tractor was on a 45 degree angle toward the snowy field to my right. From the time I was going along quietly until I was facing that field was less than one second. Fortunately the moment I heard the engine rev I knew exactly what it was and instantly let off the gas and started steering left. The entire tractor and trailer went about halfway into the hammer lane, which was empty fortunately, but I saved it and continued on.

Now I'll say this.....having the drive tires break loose like that when you're on the gas like mine did isn't nearly as bad as having them break loose when you're on the brakes. I was able to save a tractor jackknife caused by too much power to the drives on slick roads. But you normally won't be able to save a tractor jackknife caused by over-braking on slick roads because:

1) The trailer is "pushing" the tractor harder if the drive tires break loose when you're on the brakes than it does when you're on the gas so the tractor tends to spin around more quickly if you're under braking.

2) There is a delay in the air brake system that you don't have with hydraulic brakes. Hydraulic brakes react almost instantly. Air brakes react more slowly. So even if you react almost instantly to a tractor jackknife caused by heavy braking that 1/2 of a second or so can mean the difference between saving it or wrecking it. Here's a quote from air brake section of the High Road Training Program regarding this delay:

With air brakes, there is an added delay – the time required for the brakes to work after the brake pedal is pushed. With hydraulic brakes (used on cars and light /medium trucks), the brakes work instantly. However, with air brakes, it takes a little time (one-half second or more) for the air to flow through the lines to the brakes.

That same delay that exists when you step on the brake also exists when you're letting off it. From the time you release your brakes until the pads leave the drums is about 1/2 second. That's an eternity when you're in the middle of a tractor jackknife. Now there is no delay with Jake brakes themselves, but there will be in your reaction time when turning them off.

So there's almost no way you're going to save a tractor jackknife, especially if it's caused by over-braking (Jakes or foot brake) on slick roads. You're going to smash your face off the side of your own trailer and run over anything in the path ahead....unless of course there's a cliff ahead of you in which case the last thing you'll see is your trailer landing on top of you as you fall backwards and upside down to the bottom of the ravine.

I don't agree with turning it off in snow since on low it acts like a very light pressure on the brake pedal, so there's no risk of skids or jack-knife.

Unfortunately that's not exactly true.

Using the foot brake applies braking pressure to all axles on the vehicle, starting with the trailer axles first. The foot brake begins to slow the trailer just a bit before you begin slowing the tractor to help prevent a jackknife. It also puts just a tiny bit more pressure on the trailer axles than the tractor axles for the same reason.

When you apply the Jake Brakes at any level you're only applying braking force to the tractor drive axle(s). It could be one axle, it could be both, depending upon whether or not you have the axles locked together. But regardless, the Jake only applies braking pressure to the drive axles which makes the vehicle more prone to jackknifing.

Now I have to say for safety's sake that you are taught never to use your Jakes at all on slick roads and that's what I'm going to recommend you do. However, let's say hypothetically that someone was holding a gun to your head during a snowstorm and said, "Use your Jakes or I'll shoot." In that case, make sure you use the foot brake along with the Jakes and make sure you never have the Jake Brake on without the foot brake being used. Apply some pressure with the foot brake and then consider kicking your Jakes on at a low setting. When you're going to let off the brakes turn off the Jake Brake first and then let your foot off the foot brake. That way you won't get shot in the head, nor will you jackknife (hopefully).

That is an extremely bad habit to have. I'm not sure what company you're with but at my company we get safety messages all the time about engine brakes. You absolutely should not be using them at all on roads that are anything but dry. Going the way you're going, I'll be honest, you're an accident waiting to happen.

Your trainer was probably a lease operator and he does that because he doesn't want to wear out his brakes drums/linings. In other words, he wants to preserve his equipment to save on repair costs over the long term. My trainer was the exact same way so I know what you're going through.

But now that you're solo you must drive the safest way possible. In bad roads conditions, never use the jake brakes and use the brake pedal lightly, never slam on it or do anything abruply.

That is an extremely bad habit to have. I'm not sure what company you're with but at my company we get safety messages all the time about engine brakes. You absolutely should not be using them at all on roads that are anything but dry. Going the way you're going, I'll be honest, you're an accident waiting to happen.

Your trainer was probably a lease operator and he does that because he doesn't want to wear out his brakes drums/linings. In other words, he wants to preserve his equipment to save on repair costs over the long term. My trainer was the exact same way so I know what you're going through.

But now that you're solo you must drive the safest way possible. In bad roads conditions, never use the jake brakes and use the brake pedal lightly, never slam on it or do anything abruply.

No he had a company truck and worked for gordon for 2 years, and now may trucking for 5. The purpose to keeping it on all the time is that you can put cruize control on and the engine brake comes on 4mph after your set speed. If you set it to 60, it will come on at 64, so it maintains your speed. The two systems are meant to be used together. I've never even come close to jackknifing but I'm more cautious in cold conditions where ice may come up fast.

The thing with jackknifing is, once you lose control you're pretty much done. It happens in the blink of an eye.

I understand the deal with trying to maintain your speed, but that's what the brake pedal is for. Relying that heavily on the engine brake will make you a lost, blind puppy during times when you absolutely cannot use it because the road is covered in ice. You won't know what to do or how to drive properly because you've relied so much on those engine brakes. It only takes one time, one little slip, one error and you're done. Those chances sky rocket with those engine brakes engaged - especially if you're using them on curves.

The start of this video shows a jackknife on an icy bridge in Texas (?). Not looks like cruise control may be on as the truck shoots into the median once it is back on a dry road surface. Alas, the jackknife pointed the tracker at the median and that's where it ended up.

The thing with jackknifing is, once you lose control you're pretty much done. It happens in the blink of an eye.

I understand the deal with trying to maintain your speed, but that's what the brake pedal is for. Relying that heavily on the engine brake will make you a lost, blind puppy during times when you absolutely cannot use it because the road is covered in ice. You won't know what to do or how to drive properly because you've relied so much on those engine brakes. It only takes one time, one little slip, one error and you're done. Those chances sky rocket with those engine brakes engaged - especially if you're using them on curves.

Those are bad drivers you're thinking of. A good driver who feels his trailer and has good instincts knows when he's coming close to tipping, skidding, or jack-knifing. He knows when to use his EB. I see veteran drivers taking turns way too fast in poor conditions. They'll do turns at 65mph that I would do at 55mph because I can feel the trailer start to tip. I've been on semi-icy roads where owner operators were going past me at 65-70mph. And you'll find these same drivers pulled over to the side of the road if the sign says "icy conditions, use caution." If a sign doesn't tell them, or if it's not blatantly icy, they think they are safe. I can tell it's turning into ice by the reflection of the on-coming vehicle lights on it. I can feel my drives slipping slightly. Yet these guys are still going past me like its a summer night even though its below 30 degrees.

So the point I'm making is it's about skill, intelligence and common sense, combined with confidence,rather than rules. Bad drivers are highly reliant on rules rather than feeling and knowing their tractor and trailer. Those drivers are dangerous. A good driver will not jackknife if forced to go down a snowy hill with 'high' engine braking because he feels the truck and trailer. It's a bad idea of course, and serves no purpose, but can that person do it? We're not supposed to drive on black ice either, but can you do it confidently and safely?

I'll keep you in my prayers this winter. And by the way, contact your Safety Department because they're the experts on how to drive properly and as safe as possible. They'll fill you in.

Good luck out here this winter man.

A good driver will not jackknife if forced to go down a snowy hill with 'high' engine braking because he feels the truck and trailer

Keep in mind there are two types of jackknives - a tractor jackknife and a trailer jackknife.

A trailer jackknife tends to happen when you're empty on slick roads. You hit the brakes, the trailer brakes lock up, and the back end of the trailer starts sliding to the left or right. The tractor often keeps pointing straight ahead and has full traction.

A tractor jackknife tends to happen on slick roads when you're loaded heavy, your tractor and trailer are not quite lined up in a straight line, and you hit the brakes. It can also happen if you hit the gas too hard on slick roads causing the drive tires to break loose. Maybe you're going around a curve. Maybe your trailer tandems are out of alignment a little bit. Anything that makes your tractor point in a slightly different direction than your trailer...and I mean slightly....can cause this. The drive tires on your tractor will lose traction and the rear of your tractor spins around to one side or the other as the weight of the trailer pushes your tractor around. The trailer stays straight ahead and often times does not lose traction. The tractor spins around and slams into the side of the trailer.

Now trailer jackknives tend to happen rather slowly and are normally pretty easy to get out of if you can let off the brakes a little and lightly touch the gas. Once you let off the brakes the trailer tires can begin finding a grip and touching the gas will pull the trailer back in behind you. I've had this happen on slick roads with an empty trailer in strong crosswinds without hitting the brakes. I've also had this happen when hitting the brakes with an empty trailer on slick roads. As soon as you notice that trailer is moving to one side or the other you let off the brake, touch the gas a little, and you're usually fine. Of course if you aren't in a position to be able to let off the brake and touch the gas a little you're in big trouble. Once that trailer loses traction and starts coming around it's not going to stop coming around until you allow it to. Fortunately because the trailer is so long it comes around rather slowly.

A tractor jackknife normally happens so fast that by the time you realize what's happening your tractor is facing the wrong direction on the highway and you get smashed into the side of your own trailer. Because the wheelbase is so short on the tractor it whips around way more quickly than a trailer jackknife. The only time I had this happen in a scary way was when I was climbing a hill on slick roads with a light load and the drive tires broke loose. I heard my engine wind up and suddenly my tractor was on a 45 degree angle toward the snowy field to my right. From the time I was going along quietly until I was facing that field was less than one second. Fortunately the moment I heard the engine rev I knew exactly what it was and instantly let off the gas and started steering left. The entire tractor and trailer went about halfway into the hammer lane, which was empty fortunately, but I saved it and continued on.

Now I'll say this.....having the drive tires break loose like that when you're on the gas like mine did isn't nearly as bad as having them break loose when you're on the brakes. I was able to save a tractor jackknife caused by too much power to the drives on slick roads. But you normally won't be able to save a tractor jackknife caused by over-braking on slick roads because:

1) The trailer is "pushing" the tractor harder if the drive tires break loose when you're on the brakes than it does when you're on the gas so the tractor tends to spin around more quickly if you're under braking.

2) There is a delay in the air brake system that you don't have with hydraulic brakes. Hydraulic brakes react almost instantly. Air brakes react more slowly. So even if you react almost instantly to a tractor jackknife caused by heavy braking that 1/2 of a second or so can mean the difference between saving it or wrecking it. Here's a quote from air brake section of the High Road Training Program regarding this delay:

With air brakes, there is an added delay – the time required for the brakes to work after the brake pedal is pushed. With hydraulic brakes (used on cars and light /medium trucks), the brakes work instantly. However, with air brakes, it takes a little time (one-half second or more) for the air to flow through the lines to the brakes.

That same delay that exists when you step on the brake also exists when you're letting off it. From the time you release your brakes until the pads leave the drums is about 1/2 second. That's an eternity when you're in the middle of a tractor jackknife. Now there is no delay with Jake brakes themselves, but there will be in your reaction time when turning them off.

So there's almost no way you're going to save a tractor jackknife, especially if it's caused by over-braking (Jakes or foot brake) on slick roads. You're going to smash your face off the side of your own trailer and run over anything in the path ahead....unless of course there's a cliff ahead of you in which case the last thing you'll see is your trailer landing on top of you as you fall backwards and upside down to the bottom of the ravine.

College trained me to drive without it, even on some downhills since not all trucks will have an engine brake.

Make no mistake the moment I started driving after graduating I slapped it on just for the cool sound.

With that out of my system.

I use it to help me brake here and there and when going downhill only. But dont leave it on all the time.