How Dangerous Is A Jake Brake In Poor Road Conditions?

80 cleared up nicely after the sun came up, but before sunrise between the snow squalls, the hills, 45 mph curves and just generally being new it was quite a fun roller coaster.

Sounds like an interesting docking experience. So far most of the docks I’ve been in have been pretty clean thank good because I can still make the easy ones look hard...

Noob, my truck has the manual switch, but the company disabled it. I can paddle up or down a gear, but the auto will override if the rpm changes. I occasionally use the paddle to go down a gear on an incline, but, so far it doesn’t seem to do much on a downhill because once it revs a bit it’ll go right back up a gear.

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.

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.

If you downshift to a lower gear, isn’t that doing the same thing as using the Jake brake? It is slowing only the drive axle

Grumpy asks an excellent question.

If you downshift to a lower gear, isn’t that doing the same thing as using the Jake brake? It is slowing only the drive axle

I often had the same question early on. The answer to that as I see it is a little tricky to explain. I wrapped my mind around it this way:

A Jake is designed to slow the truck. The braking action is continuous, and occurs whether you're going 65 or 20, in any gear. The risk of traction loss is continuous when braking with the Jake.

Downshifting however, isn't necessarily done to slow the truck. It's simply selecting the proper gear for the speed after you've already slowed to a safe speed with your service brakes. Once in the proper gear, there is minimal continuous resistance to the drive axle, with minimal risk of traction loss. Service brakes are then used to maintain that safe speed.

...adding to Turtle’s reply to Grumpy;

Here is a link that does a fairly good job of describing how the Jacobs Engine Brake functions:

Jacobs Engine Brake

Here is a link found in Trucking Truth:

Engine Brake Description found in TT Wiki

Having read both links will help to understand the answer to Grumpy’s question:

Although downshifting effects the drive line (drive wheels), it does not retard the speed of the truck in the same fashion as the engine brake. The engine brake when applied produces significant reverse torque or braking resistance, far more than downshifting to the next lowest gear.

I’ll leave you with one other thought; use of the Jake Brake on wet or snow covered roads is a potential policy violation at Swift. Thus if a driver is involved in any accident while using the Jake Brake on wet or slippery roads, the resulting action is likely to be more severe than a “preventable accident” recorded on the DAC.

I’ve seen several jackknife accidents on the Walmart account. The culprit was using the Jake while empty on wet roads.

Downshift and apply service brakes before descending a wet or snow covered grade. Finesse’ the application...no sudden braking or steering input. Maintain control.

Okay, so the reason you'd avoid downshifting going downhill then is the possibility you could lose the gear and start to accelerate too fast, right?

Is that still a risk in the automatics with the manual mode disabled?

Is that still a risk in the automatics with the manual mode disabled?

No

Not to highjack the thread but on the opposite side of this i thnk i would lose my mind if i couldnt lock in a lower gear in manual mode while climbing hills with a beer load. If my truck gets any chance to jump back in 10th it seems like it does unless i put it in manual. I feel for you guys locked out.

Is that still a risk in the automatics with the manual mode disabled?

No

Thanks. I've got a follow-up question, since aside from having to change lanes in stop and go city traffic, going down grades is my biggest concern.

I'd read deep searching on here that a driver should always put it in manual mode when going down steeper grades. I'd also read the on-board computers are able to regulate the engine braking by the weight of the load, the present grade, and even terrain maps (or at least Turtle had mentioned this i re some of the trucks at Prime).

Does it work like that shifting without the jake brake too, if it's an automatic and the manual mode has been disabled?

Midnight Fox inquired:

I'd read deep searching on here that a driver should always put it in manual mode when going down steeper grades. I'd also read the on-board computers are able to regulate the engine braking by the weight of the load, the present grade, and even terrain maps (or at least Turtle had mentioned this i re some of the trucks at Prime).

Does it work like that shifting without the jake brake too, if it's an automatic and the manual mode has been disabled?

"Always?" If it's dry, not necessary to invoke manual mode, bypassing the auto-shift operation.

In the newer "auto-shift" trucks, cruise control and the engine brake (Jake) are electronically linked. Called "Drive Wyze" (on Swift equipment), this control is programmable and may vary slightly from truck to truck. Most of the major carrier have this type of control system on their newer, auto-shift trucks.

At a high level it works like so; set cruise for 65 mph and the system will maintain that speed invoking the engine brake as the speed approaches 69, such as it occurs descending a steep grade. As a rule, when I am running in the mountainous terrain of North Eastern PA & NJ (Interstates 80, 81, 84, 78, PA-TP NE Extension, etc), as I approach a downhill grade I will reduce the speed setting to about 60-62 mph (depending on grade steepness) so I can maintain control descending the hill. The system will invoke the Jake in whatever intensity required (low, med. or high) to control the truck, holding no more than 4 mph above the set speed. As the terrain flattens out, I'll resume the cruise setting to 65. It is very, very rare that I will need to assist with the service brake/ disabling cruise. As such, when cruise is set to "off" or "cancelled", manual application of the engine brake is required.

All of the above is NOT applicable in wet or snowy conditions.

Some really good technical discussion here I appreciate everyone’s answers. And the clarification

G-Town, I’m curious about the cruise in the mountains. My OTR trainer said not to use cruise in the mountains as it won’t be able to keep up with the inclines. He seemed to indicate it would just kick itself off. Could be a just the way the company has them set up as Roehl apparently stands for Rolls Over Every Hill Last. I like the idea of setting the cruise at a lower speed on the downhill. I always seem to need to slow it down manually before the Jake kicks in automatically.