Engine braking vs foot braking in snow/Ice.

Turn the jakes off in snow and ice. Refer to your Mercury Marquis owner's manual for the location of the jake switches.

 

I agree..or at least don't have the jake set at the highest settings..
i've seen a few trucks get crooked on ice after lifting off the gas and then having the jakes "Hammer"down..truck goes sideways on ice.

 

I was always taught to leace the Jakes off in icy or slippery conditions when driving big rig. Kept to those teachings, and can honestly say I never had a problem.

With your car, yes. Lower gear will help you in both climbing and descending safely. Especially in a rear-wheel drive vehicle like your Merc.

Also, make sure you've got good tires on both ends of the vehicle. I've found that light truck tires on the rear of something as big as your Mercury are a god-send (I used to drive old chevy caprice classic station wagons). You need good traction on the rear for climbing, and good traction on both front and rear for braking and downshifting.

Braking on a downgrade does make it easier for your car to break traction and start sliding, while downshifting (at the appropriate road speed, or at least as close as you can safely get) carefully will help you maintain control.

Obviously, you want to maintain safe speeds, and slow down in treacherous conditions. My rule is generally 5 miles slower than my "comfort" speed. Does mean that I gotta plan ahead a bit more, and schedule more time for my driving, but I'm the guy everybody comes to when they need to get out on cruddy roads.

 

Brakes cause more trailer jack knifes. Meaning that the trailer looses traction and passes the tractor.
Jakes cause more tractor jack knifes. Meaning that the tractor drives loose traction and the trailer pushes the tractor sideways.

Of the 2 types. The trailer jackknife can be easer to get out of. You have to accelerate with the tractor and pull the trailer straight.
Also it will straighten some as soon as the brakes release.

With the tractor jack you have to straighten out and slow down that trailer some. Many times the slide started due to getting off the throttle too fast and either the engine or the jake (if on) causes the tires to slow too much. Applying a little pressure on the throttle can help with this.

With either type you are in trouble if you get past around 30%. At that point recovery is almost not possible.
In the old days drivers would tell you to use the trolley valve when in a tractor jack. To slow the trailer. But on snow and ice this will not do much for you. Since the valve reacts fairly slow. So the trailer will lock it's brakes before it can help. And then you have a slide on both ends even faster.

 

Yep..all true.

 

going down a steep hill in snow or ice you want a low gear, low speed, and no jakes. i will use about 6th gear if conditions warrant a slower speed than that im probably parked or chained haha
if i have chains on i sometimes use the jake on a low setting.

 

I think the biggest difference between braking a big truck and a 4-wheeler in bad conditions comes down to two factors. Gross vehicle weight, and wieght distribution. Max big truck wieght without permit is 80,000lbs. Broken down, that's 12,000 on the steer tires, 34,000 on the drive tires, and 34,000 on the trailer tires. Obviously, this isn't always gonna be the case, but you get the idea. With that much weight pushing down, provided you have decent tread, using your foot brake is gonna be much safer. If you are not going too fast for conditions! If you are speeding, you are already in trouble.

In your 4-wheeler, weight is gonna be considerably less (actual wieght depends on your car). My '97 GMC Jimmy is stickered at 5300lbs. My old ECHO was stickered at something like 1300lbs. Like I said, a considerable difference. But the Gross vehicle weight doesn't change all that much in normal day to day driving, unlike big trucks. In a big truck, I might pull 43,000lbs. of freight one day, and 15,000lbs. of freight the next. That's a big difference from one day to the next, yes? So while I depended on maintaining a safe speed and using the foot brake in a big truck. In my lil' truck, I'll rely on maintaining a safe speed, and downshifting my transmission rather than use the foot brake until neccessary. Either way, speed is the biggest concern. Keep her slow and steady, and always leave plenty of stopping distance in front of you. After all, it's always better to stop to soon, and ease on up, than to stop too late...

 

Note: I am NOT A TRUCK DRIVER. Yet. So this is mostly about cars, but some of it relates to trucks as well.

Any automatic transmission in a car has a bit of slippage built in, via the torque converter. This is why the engine doesn't kill when you come to a stop with the car in gear. It also means that the full power generated by the engine is not fully transferred to the transmission until a certain rpm is reached.
Shifting into neutral completely negates the possibility of wheelspin from power to the wheels, but it's a negligible benefit compared to idling in gear with an automatic. Plus it helps to be in gear should you need to reapply power.

SHIFTING into a lower gear can be worse than careful pressure on the brake, depending how crisply your transmission shifts, and how many gears you drop. Hard to recommend downshifting over the use of ABS.

Best thing is to be in the proper gear and speed BEFORE beginning to descend a hill.

When climbing a hill, a higher gear is better for traction. The low gears multiply the torque produced by the engine to a greater degree:
1st gear might be something like 3:1, while 2nd might be 2.5:1.
If torque is 200 lb-ft, you'll have 600 lb-ft at the wheels in 1st, compared to 500 lb-ft in second. More torque at the wheel = more likely to break traction under power.

Finally, automatics do not shift like manuals. The computer or vacuum control determines the gear in any position but "1".
"Drive" at low speeds is the same gear as "1", which is probably why you noticed no improvement using "Drive". Unfortunately, there's no way to use second gear at low speeds in an automatic, unless it's designed that way - shifting into "2" will just start in first gear anyway, until it determines it needs to upshift. However, if you do manage to build speed while getting up the hill, it would be better to be in "2" or "Drive" so that the car can upshift to a "taller" gear, rather than holding it in first, if traction permits.

Hope this helped.

 

My dad was in a Peterbilt 362 hauling doubles (getting a load of landscaping bark) back in his day, on I80 near Truckee, CA. Black Ice...Let his foot off the throttle to begin down shifting, next thing he knew, he was looking at the side of his 2nd trailer and dang near parallel with his first trailer. He was not hurt, ended up upside-down on the better side of the road (not the cliff side) and lived to tell me not to use my jakes if there was ever a possibility of ice.