Safest way to negotiate a potentially slippery dangerous trail with the 80: CDL etc?

[basalt51]

E - This is my first post here and thought I'ld chime in. My advice to you is find a good off-road driving instruction book or pamphlet. Most of teh situations you have described will be covered. Downhill, uphill, sidehill, braking, strapping, winching, etc. I think a big misconception about lockers is that they give you better traction. That's not necessarily true. If I was on an Icy (or just low traction) slope (up, down, or side) I would not want to have the diffes locked, and if possible I wouldn't want to lock the front to rear either and here's why.

While lockers can give you traction even with one tire in the air, they are also capable of breaking loose BOTH tires and loosing ALL traction. That is exactly the situation you want to avoid on a slope. If you are open front and rear on a side slope, you may not be able to move forward, but you won't slip downhill because the tires that aren't spinning actually still have traction and will keep the vehicle from slipping. With the CD open, it may be able to transfer enough power to one of the none spinning axles to move, but not break free. Unless you are going downhill or dropping into something, open diffs have a tendancy to keep you out of trouble. While locked differentials can get you into and through very difficult terrain, they can also result in zero traction at the worst possible moment. Suddenly applying the breaks or gas should be avoided at all times if you have little driving experience.

I have a '97 Cherokee with automatic lockers front and rear so I have to live with the consequences of locked axles. You learn to drive differently and be gentle on the throttle. Hopefully we'll be getting an 80 soon as a DD

 

[Beowulf]

>> but you won't slip downhill because the tires that aren't spinning actually still <<
>> have traction and will keep the vehicle from slipping. <<

Reminds me of a memorable trip down Casper mountain after a day of skiing. It had started snowing and the wind kicked up as only a Wyoming wind can blow. There was an accident somewhere toward the bottom and the traffic was barely moving coming down the mountain. We were sitting in a curve with a fairly steep section to the side of the road when the traffic came to a complete stop. The road was snowpacked and icy. We were in a 4x4, stopped with the brakes applied when it started sliding sideways, across the road and over to the shoulder. Thump, thump, THUMP, THUMP.

The wind blows hard in Wyoming.

-B-

 

[Rookie2]

Any of you try the technique of running the RPM's up to 1500 of so with slight braking to control downhill decents on slippery surfaces?


Rookie2

 

[GXO]

unlocked all around, momentum in this case could cause big oops (kerplunk) so slow going. If you lose traction, ease off throttle, find an anchor point, hook up a winch line, use the winch to encourage forward progress with unlocked diffs.

Locked diffs in slick (4 touching, but no progress) scenarios = side slip, period. When you have no margin of error this is the only way to go.

Slow, unlocked, measured pace with careful spotting and immediate anchor on loss of traction is the sure way to live. If you want to "bump it" while fully open you run the risk or sliding or going off course. If you want to lock it up, you will slide and have to work out of a more tricky situation.

Glad you got by. Been up on the sides of some nasty places in my day. Best bet if the trail is slick and not horribly off-camber is to run the high wall with 2 sets of tires and straddle the mountain side vs. trying to navigate on a slippery slope.

 

[e9999]

unlocked all around, momentum in this case could cause big oops (kerplunk) so slow going. If you lose traction, ease off throttle, find an anchor point, hook up a winch line, use the winch to encourage forward progress with unlocked diffs.

Locked diffs in slick (4 touching, but no progress) scenarios = side slip, period. When you have no margin of error this is the only way to go.

Slow, unlocked, measured pace with careful spotting and immediate anchor on loss of traction is the sure way to live. If you want to "bump it" while fully open you run the risk or sliding or going off course. If you want to lock it up, you will slide and have to work out of a more tricky situation.

Glad you got by. Been up on the sides of some nasty places in my day. Best bet if the trail is slick and not horribly off-camber is to run the high wall with 2 sets of tires and straddle the mountain side vs. trying to navigate on a slippery slope.

what was this last thing about running the high wall? I hope it does not mean what I think it means...

E

 

[GXO]

Hard to describe. You have a cut in the mountain that is your road " |_ "

The lower part of the road suddenly becomes a little bit more slick and rough and there is a danger of taking the plunge.

I have, on occassion (especially on icy or snowy roads) put my DS on the left wall (if not completely sheer) and my PS on the centerline of the questionable surface.

Never for very long, just for the task at hand.

 

[Rookie2]

Any of you try the technique of running the RPM's up to 1500 of so with slight braking to control downhill decents on slippery surfaces?


Rookie2

Was my question stupid/non-applicable to this situation, or are you all just unfamiliar with what I'm talking about?


Rookie2

 

[Big_Moose]

I'll bite

I can't fathom why you would want to "accelerate" the heavy vehicle down a hill, then apply the brakes? You increase the change of the tires loosing adhesion / friction on the slippery surface from acceleration and / or braking. I'm guessing you are trying to "lock-up" the torque converter to utilize engine compression to slow down / control the decent?

On slippery decents, you want to use the low range gears to help maintain control, but you are working against the fluid clutch / torque converter, so controlled application of the big pedal is required. Don't want to step on the brakes too hard to stop the tires / causing them to slip.

The newer crusiers (100 / 120) utilize traction control and / or electronic downhill decent systems to control speed / momentum with automatic transmissions.

 

[Rookie2]

I'll bite

I can't fathom why you would want to "accelerate" the heavy vehicle down a hill, then apply the brakes?

No, what I was talking about is.. when on level surface before making the decent on a slippery slope, running the engine up to 1500 RPM with the brake applied then letting off the brake some and easing into the decent. From what I recall it's suppose to be an enhance form of engine braking, but you don't have to generate speed to get it. Not to be done without some practive first. I read it in a 4WD book. So has anyone tried this?


Rookie2

 

[GXO]

If you are locked down in 1st you can spin up the engine to get max compression (engine braking) to compensate for the weight of the vehicle as you suggested Rookie2.

Please practice on small hills in non-dangerous places before applying to a real world need =)

 

[IdahoDoug]

Pure urban legend...


DougM

 

[flintknapper]

No, what I was talking about is.. when on level surface before making the decent on a slippery slope, running the engine up to 1500 RPM with the brake applied then letting off the brake some and easing into the decent. From what I recall it's suppose to be an enhance form of engine braking, but you don't have to generate speed to get it. Not to be done without some practive first. I read it in a 4WD book. So has anyone tried this?


Rookie2

I can only guess that the technique is supposed to provide a smoother transition into the slope by having the vehicle already engine braking at the crest. As opposed to starting at the crest with the brakes on and then slowly releasing them while going down hill. In any case, the advantage would likely be short lived. Heck, I'll try it...I have a steep clay hill on my property and it will rain here soon. But for now I'm with Doug, "pure UL".

 

[Rookie2]

Well, I found the article last night. It's out of an issue of Australian 4WD Monthly entitled "Steep Downhill Driving - Keeping your auto fourby under control on steep descents". Pretty interesting reading. I'll see if I can scan it in so you can read for yourself, and try it.


Rookie2

 

[timbercruiser]

hmmm..... "can I please hook up to your truck so when mine falls off the cliff, I'll be able to eject before yours is pulled over too...?"

E

You'll find out who your real friends are!

 

[Rookie2]

Okay. Here are steps 1 thru 3.

 

[Rookie2]

Steps 4 and 5. The steps don't talk about it, but the body of the article specifically talks about slippery conditions. So what do you think now. Still UL?

 

[ShottsUZJ100]

The vehicle in the illistration is a Discovery. Does this method only work for Disco's?

 

[flintknapper]

Steps 4 and 5. The steps don't talk about it, but the body of the article specifically thanks about slippery conditions. So what do you think know. Still UL?

Don't know for two reasons:

1. I can only make out bits and pieces of the text. I printed it out and magnified it but still couldn't read most of it.

2. Have not tried it yet. (not oppossed to it, just want to see it work for myself).

Could you clearly post the text here so we can read it? Thanks, Flinknapper.

 

[Rookie2]

The vehicle in the illistration is a Discovery. Does this method only work for Disco's?

HeHe.. well the article is from a magazine that seems primarily LC and LR based. The technique described here was actually by a driving instructor for LR, but I think it applies to any full time 4WD vehicles.

Since I didn't paste in this part of the article... it does stress that you should practice the technique on an asphault hill, to get the feel, before trying the real deal. Damn.., I'm a poet.. and my momma knows it.


Rookie2

 

[timbercruiser]

So, is the purpose of this method to get the torque converter to hook up with the engine and provide compression braking? (kind of like a manual)