I'm a pretty new driver and have a question that I can't seem to get a good answer to. In slick road conditions you don't want to use the jake as it could cause a jack-knife. But, when going down a steep grade you're geared down. Is that not basically producing the same effect as the jake and possibly causing a jack-knife? Thanks.

-Steve

When you use the jakes you are basically increasing the braking effect of the engine over that of being in any given gear.

Think of it like the difference between lightly pushing the brake pedal and smashing it to the floor board.

Yes, which is why you need to control your speed also to match the road conditions, and it is also why in the West, they will require chains when going down steep grades in poor road conditions.

The problem is that in the eventuality of losing grip to your drive wheels, chances are you might not have the cool head to switch off the jake or lightly pressing the accelerator to cancel the jake...Rather, youll mash the brake since thats the perceived 'default fix-all'.

I usually leave my jake on in all kinds of weather, even bobtailing in rain, but it takes experience to become a smoothe operator enough to be able to do the right thing if you slip. Not that leaving the jake on is a trait of a vet...

Usage of the Jake brake is a CDL school topic (or should be). It was when I went to CDL school.

The Jake brake only applies braking effect to the drive axle, from engine compression. The trailor receives no braking effect to its axles, thus the trailor will try to push the tractor, on dry pavement, this should be no problem, as long and both drives and tandems are getting good traction.

Problems can occur on wet (rain/snow etc) or icy pavement. If the Jake is used on this type of surface, the drives may lose traction, putting the tractor into a skid. The trailer will be pushing the tractor, and if there is any angle between the tractor and trailer or if the drives loose traction unevenly the trailer will try and swing out to the side.
The more weight that is on the drives the better the drives will maintain traction, but the heavy trailer would mean a greater push by the trailer.

Basically yes, assuming you a "geared down" without the jakes, the engine compression is still applying a certain amount of braking effect to the drives.

You'd think it would be. Their mantra on many subjects was that the only way to learn something is "to get out there and figure it out". While I agree that there is some truth to that I don't think it's the best approach.

-Steve

most trucks jakes have different settings ... on slick roads i'll turn my jake down on low so i've still got some engine brake and up the setting as needed. I typically run with my jakes on 24/7