How Dangerous Is A Jake Brake In Poor Road Conditions?

Topic 27604 | Page 1

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Wild-Bill's Comment
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I was driving I-80 in PA this morning between exit 97 and exit 224. As you probably know it’s one hill after another. I started early so it was dark and there were light snow squalls off and on all morning. The roads had a dusting of snow on them and it was about 20 degrees so I assume there was some icing underneath. I felt safe at all times and took the curves and bridges slow and at a coast as much as possible.

Last time I drove this area it was ideal road conditions and I used the Jake brake pretty liberally. This morning, I kept thinking about everything I’d read that said not to use the Jake brake in poor conditions. So I used control braking every time I got to my safe speed I’d brake to get back to 5mph under.

With that long intro out of the way, I have some questions. Why not use the Jake Brake in possibly slippery roads. It seems like it would have felt more controlled on the decent. My guess is that the retarder is only slowing down the drive tires, so the heavier trailer could possibly want to try to pass the tractor and cause a jacknife? Which leads to my follow up questions; what actually goes wrong if the Jake is used on bad roads. what constitutes a bad road? Would the conditions I described be enough to say no Jake brake? And finally, isn’t there just as much opportunity for things to go wrong when braking on possibly slippery roads?

I’m sure I’m over analyzing. I just want to make sure I understand the right thing to do.

OWI:

Operating While Intoxicated

Turtle's Comment
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My guess is that the retarder is only slowing down the drive tires, so the heavier trailer could possibly want to try to pass the tractor and cause a jacknife?

That's correct. The Jake is only slowing down the drive axle, making it a weak pivot point. The heavy trailer, having no resistance in the way of braking, wants to keep pushing, making the pivot point very prone to slippage.

Controlled braking with the service brake applies even resistance to all wheels, drastically reducing the chance of slippage.

OWI:

Operating While Intoxicated

Turtle Protege (formerly 's Comment
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double-quotes-start.png

My guess is that the retarder is only slowing down the drive tires, so the heavier trailer could possibly want to try to pass the tractor and cause a jacknife?

double-quotes-end.png

That's correct. The Jake is only slowing down the drive axle, making it a weak pivot point. The heavy trailer, having no resistance in the way of braking, wants to keep pushing, making the pivot point very prone to slippage.

Controlled braking with the service brake applies even resistance to all wheels, drastically reducing the chance of slippage.

Although I don't have experience driving a CMV tractor-trailer, I do have experience pulling trailers with and without trailer brakes, including U-Haul trailers which, as I understand it, have "surge brakes."

I can definitely feel the difference stopping without trailer brakes. I can feel the trailer "pushing" against the rear of the towing vehicle. Even the U-Haul trailer surge brakes initially push against the towing vehicle before the trailer brakes engage. Although I generally don't brake in corners, when towing a vehicle without trailer brakes, I have made an extra point to ensure that the trailer is directly in line with the towing vehicle in any hard braking situation. Otherwise, that "trailer surge" will push the rear of the towing vehicle left or right. Even if it doesn't cause the rear tires to slide, it requires an adjustment to your steering because of the lateral forces against the rear of the towing vehicle.

With regard to a trailer with trailer brakes, with a correct trailer gain you don't really feel the trailer much at all while braking. However, increasing the trailer gain above the optimal balance point creates the feeling that the trailer is "stopping" the towing vehicle.

Am I understanding what you're saying about the drive axle pivot point?

CMV:

Commercial Motor Vehicle

A CMV is a vehicle that is used as part of a business, is involved in interstate commerce, and may fit any of these descriptions:

  • Weighs 10,001 pounds or more
  • Has a gross vehicle weight rating or gross combination weight rating of 10,001 pounds or more
  • Is designed or used to transport 16 or more passengers (including the driver) not for compensation
  • Is designed or used to transport 9 or more passengers (including the driver) for compensation
  • Is transporting hazardous materials in a quantity requiring placards

OWI:

Operating While Intoxicated

G-Town's Comment
member avatar

double-quotes-start.png

My guess is that the retarder is only slowing down the drive tires, so the heavier trailer could possibly want to try to pass the tractor and cause a jacknife?

double-quotes-end.png

That's correct. The Jake is only slowing down the drive axle, making it a weak pivot point. The heavy trailer, having no resistance in the way of braking, wants to keep pushing, making the pivot point very prone to slippage.

Controlled braking with the service brake applies even resistance to all wheels, drastically reducing the chance of slippage.

Wild Bill you are not over analyzing things. Please refer to what Moderator Turtle replied with above.

Rule of thumb; on snow covered roads use the service brakes and downshift to a lower gear (switch to manual mode, if you can, in an auto shift and hold the lower gear). Be under control before you get to crest of a downhill section. The lighter the trailer, the more likely to loose traction. Exercise extreme care and finesse' on any snow covered road.

Safe travels.

OWI:

Operating While Intoxicated

OOS:

When a violation by either a driver or company is confirmed, an out-of-service order removes either the driver or the vehicle from the roadway until the violation is corrected.

Turtle's Comment
member avatar
Am I understanding what you're saying about the drive axle pivot point?

Yup.

The pivot point of a tractor/trailer combination is the kingpin/fifthwheel. The drive axle is directly under the kingpin. Apply too much resistance to only the drive axle, such as under Jake, it can potentially drag, lock up, or break loose in slippery conditions. Add a heavy trailer whose un-braked momentum wants to keep rolling, and you have the recipe for a tractor jacknife.

HOS:

Hours Of Service

HOS refers to the logbook hours of service regulations.

OOS:

When a violation by either a driver or company is confirmed, an out-of-service order removes either the driver or the vehicle from the roadway until the violation is corrected.

Wild-Bill's Comment
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Thanks all for the insight. It’s a good thing I decided to keep it off even though I wasn’t sure why. For some reason my company turned off the manual mode for the trans. I can paddle up or down a gear but it won’t hold it once the engine revs a bit. The service brakes worked fine for the trip, but, it makes the ride seem a bit more intense. Perhaps that’s a good thing to keep the focus.

Noob_Driver's Comment
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Thanks all for the insight. It’s a good thing I decided to keep it off even though I wasn’t sure why. For some reason my company turned off the manual mode for the trans. I can paddle up or down a gear but it won’t hold it once the engine revs a bit. The service brakes worked fine for the trip, but, it makes the ride seem a bit more intense. Perhaps that’s a good thing to keep the focus.

Is it an auto shift? I know in my 17 kenworth t680 i can drop it in manual and actually shift up or down in manual. They changed something in the 18s or maybe its just my company but in my trainers truck you would downshift in drive then have to drop it in manual to hold that gear. If you wanted a lower gear slide it back to drive and hit the button again then slide it back to manual. It was a huge pain. I think Pete has an 18 he might have a better explanation.

Susan D. 's Comment
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I was in PA on I-80 too yesterday. My truck is an auto shift, and my company, in their infinite wisdom, has locked out the manual mode completely.. cant even paddle up or down a gear. Such fun, but yeah, just take it easy and use your service brakes only.

I loaded in Williamsport to get me home today. The dock area was muddy (big mud hole right in front of the dock I needed in) and I got stuck when trying to dock. Thought I was actually going to have to call for a pull out, but with the drives locked in and some well placed rocking I managed to get unstuck.. this time. Another truck was in the dock beside me and there wasn't any room for sliding around lol but I somehow managed to keep the mudding activity and severe trailer cleaning, away from his truck.

Susan D. 's Comment
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*leaning not cleaning. But my truck definitely needs cleaning now.

Noob_Driver's Comment
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I was in PA on I-80 too yesterday. My truck is an auto shift, and my company, in their infinite wisdom, has locked out the manual mode completely.. cant even paddle up or down a gear. Such fun, but yeah, just take it easy and use your service brakes only.

I loaded in Williamsport to get me home today. The dock area was muddy (big mud hole right in front of the dock I needed in) and I got stuck when trying to dock. Thought I was actually going to have to call for a pull out, but with the drives locked in and some well placed rocking I managed to get unstuck.. this time. Another truck was in the dock beside me and there wasn't any room for sliding around lol but I somehow managed to keep the mudding activity and severe trailer cleaning, away from his truck.

When you say locked out... Can you downshift in drive then move the selector to manual to hold that gear or is the whole thing useless?

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