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

[Rookie2]

flintknapper- here's the text:

1-2: You're on the flat, before descent. And you've done all the usual stuff: checked the descent by getting out and eyeballing it, locked the centre diff (constant 4WD) or engaged 4WD (part-timer), and you've selected low-range on the transfer case and 'L' or '1' on the transmission. You know where you're going, and you're back in the vehicle, buckled up and ready to rip.

Give yourself plenty of room before the hill begins. Advance forward on the flat at 1500 rpm, on the tacho, and lock your right foot at that throttle setting.

3: Using your left foot, brake the vehicle until the tacho reads 800rpm. Don't move your right (throttle) foot.

4: As you progress onto the hill, keep your right foot fixed in position, keep one eye on the tacho, and adjust the force your left foot aplies to the brakes so that you maintain that 800rpm position on the tacho.

5: If the wheels lock up, do what you've always had to: reduce brake pressure until directional control resumes.


timbercruiser: here's what the article says about it - "I reckon auto 4WD's are better at everything - except descent. During descent, most auto fourbies aren't able to effectively transmit engine braking to the driving wheels. Basically, the torque converter is to blame. It allows slip at low speed between the engine output (crankshaft) and the gearbox input shaft. It's what allow autos to sit, stopped in gear at the lights, without stalling. During descent, however, it slips, and the vehicle tends to run away unless some other means of retarding its progress is orchestrated by the driver."
In descents where traction is high (and therefore the possibility of wheel skid is low), the brakes may simply be used - provided the driver is trained to release brake pressure in the event of a wheel locking up. (If the wheels lock, steering control is lost - bad, especialy if you're aimed at a cliff or thousand year-old red gum).
However, in descents where traction is low, there is far less of a margin between acceptable downhill progress and fully locking the wheels. On a muddy, scrabbly hill, you can quickly become a spectator on a expensive toboggan looking for something to go 'crunch' against. Here's a solution:"


Rookie2

 

[flintknapper]

flintknapper

flintknapper- here's the text:

1-2: You're on the flat, before descent. And you've done all the usual stuff: checked the descent by getting out and eyeballing it, locked the centre diff (constant 4WD) or engaged 4WD (part-timer), and you've selected low-range on the transfer case and 'L' or '1' on the transmission. You know where you're going, and you're back in the vehicle, buckled up and ready to rip.

Give yourself plenty of room before the hill begins. Advance forward on the flat at 1500 rpm, on the tacho, and lock your right foot at that throttle setting.

3: Using your left foot, brake the vehicle until the tacho reads 800rpm. Don't move your right (throttle) foot.

4: As you progress onto the hill, keep your right foot fixed in position, keep one eye on the tacho, and adjust the force your left foot aplies to the brakes so that you maintain that 800rpm position on the tacho.

5: If the wheels lock up, do what you've always had to: reduce brake pressure until directional control resumes.


timbercruiser: here's what the article says about it - "I reckon auto 4WD's are better at everything - except descent. During descent, most auto fourbies aren't able to effectively transmit engine braking to the driving wheels. Basically, the torque converter is to blame. It allows slip at low speed between the engine output (crankshaft) and the gearbox input shaft. It's what allow autos to sit, stopped in gear at the lights, without stalling. During descent, however, it slips, and the vehicle tends to run away unless some other means of retarding its progress is orchestrated by the driver."
In descents where traction is high (and therefore the possibility of wheel skid is low), the brakes may simply be used - provided the driver is trained to release brake pressure in the event of a wheel locking up. (If the wheels lock, steering control is lost - bad, especialy if you're aimed at a cliff or thousand year-old red gum).
However, in descents where traction is low, there is far less of a margin between acceptable downhill progress and fully locking the wheels. On a muddy, scrabbly hill, you can quickly become a spectator on a expensive toboggan looking for something to go 'crunch' against. Here's a solution:"


Rookie2

Rookie, thanks for taking the time to post the text. It would seem that "timbercruiser" is on track, and that the purpose would be to try to lock the converter.
I will try the technique with my '97 and see if the converter will lock up at those rpm.
I know a manual TC lock up kit is available for the A442F tranny, but requires the special valve body to have that control in 1st and reverse. About $1100.00 total.
I don't know if it is available for the A343F yet.
I believe the ABS on my '97 is automatically disabled in low range so that is already taken care of. Wouldn't it be nice to be able to take full advantage of "engine braking" with the TC locked.
What are the thoughts of others?

 

[timbercruiser]

I tried it in my yard today (97 FZJ80). It didn't seem to work. It "ran away" down the incline. It also overpowered my brakes at 1200 RPM. So I would call the test inconclusive.

 

[MoJ]

I'd think that specific RPM setting is based on the brakes/engine/weight of a Disco. Try reducing the RPM's?

Heh - So I'm not the only one that does backyard wheeling.

 

[flintknapper]

I tried it in my yard today (97 FZJ80). It didn't seem to work. It "ran away" down the incline. It also overpowered my brakes at 1200 RPM. So I would call the test inconclusive.

I'll try it this weekend and see what happens. I am not adverse to learning something new but, I am not interested in overheating my tranny either. We'll see.

 

[Rookie2]

I'll try it this weekend and see what happens. I am not adverse to learning something new but, I am not interested in overheating my tranny either. We'll see.

Not sure why it would adversely affect the tranny. Seems like it would see similar load as without brake application. You're still pushing the skinny pedal the same amount right?


Rookie2

 

[semlin]

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 =)

great thread and helpful for me.

are you supposed to apply throttle on a downhill for compression for engine braking? I have always coasted in 4-lo unlocked (except the CDL) with intermittant brief brake application. I find this gives good engine braking on what I would consider plenty steep logging roads. I assumed more throttle would mean more speed not less?

 

[flintknapper]

I'll try it this weekend and see what happens. I am not adverse to learning something new but, I am not interested in overheating my tranny either. We'll see.

Well, I couldn't wait....when wifey got home with the cruiser I jumped in and headed over to my hill. Put in low range and applied brake. A little over 1000 rpm the engine simply overpowered the brakes. I am sure I could have really put on the binders and gotten it to hold at 1500 but it would be a real strain.
I didn't want to try it over and over to see if it would work because a Torque Converter when unlocked is basically just a "Wet Clutch" and can heat up faster than you might think.
So, I don't know...the technique might work fine with a Disco, but I'm done with it!
Interesting question though.

 

[Rookie2]

Flintknapper-

I wonder if it would make any difference in high range with the CDL locked? Or if that would still over power the braking?

I guess I need to go find a hill and try it too.


Rookie2

 

[flintknapper]

Flintknapper-

I wonder if it would make any difference in high range with the CDL locked? Or if that would still over power the braking?

I guess I need to go find a hill and try it too.


Rookie2

It might not in high range because there is less mechanical advantage (gear reduction).
I have not yet done the CDL switch mod. so I couldn't lock up the T-Case in high anyway.

 

[IdahoDoug]

I have had professional offroad driving instruction and have also provided instructions to some of my automotive clients over the years, and am reasonably familiar with most offroad techniques short of extreme wheeling. The RPMs and such are really meaningless and should have been noted as "Examples of RPM to be adjusted to the terrain being descended". Incredible that they were not. Here is what they are trying to accomplish with this technique.

This is known as power braking and is intended to do nothing more than ensure that all 4 of your tires continue to rotate as you descend while braking on a slick surface. That's it. The power from the engine helps discourage a tire from being stopped by the brakes, which could create a nasty lateral skid. A rolling tire provides directional control, a locked tire does not.

There is no need to go to "1500 RPM", there is no need to sit at "800 RPM", etc. Merely use the brakes to choose your descent speed as you normally would, but apply a bit of throttle to prevent a wheel from being stopped by the brake pressure. It doesn't take much.

It's a very simple technique, but honestly I don't recommend it when conditions would most dictate it - a slippery descent that's so sketchy this is the only thing that's going to prevent the vehicle from locking tires even with competent everyday brake modulation. Under these conditions, I recommend your vehicle descend the slope either controlled by a winch, or controlled by a strap from another vehicle up on the flat. In other words, if things are that dicey, it's pretty nutty to think you're going to master it under pressure and there's no way to truly practise it without actually being on such an edgey slope. Kinda like "practising" cliff diving if you know what I mean.

So spare the wear and tear testing this to see if you get "extra braking power from the torque converter" etc. Nope.

DougM

 

[Nay]

Remind me to stay really far away from anybody attempting this technique so that at least when you come hurtling off of an obstacle I don't get whacked, too.

Use your brakes so that you are going as slow as necessary on steep descents, and for god's sake, stay off the throttle.

This is dangerous advice for inexperienced wheelers, and experienced wheelers know better.

Nay

 

[reffug]

Heh - So I'm not the only one that does backyard wheeling.

Glad to hear that, My lane to my house (from which I am moving) counts as wheeling. The only way the house is accessibly by vehicle is with 4 wheel drive and if its rained that 4 wheel needs lockers or its a total no go.

 

[timbercruiser]

I would agree that threshold braking is the way to go-just take it easy.

Heck, I have a manual in my '40, so this is pretty acedemic for me. The 80 is the family truckster. And when I do buy one for wheeling (this winter), I plan on doing a manual tranny install.

 

[flintknapper]

I have had professional offroad driving instruction and have also provided instructions to some of my automotive clients over the years, and am reasonably familiar with most offroad techniques short of extreme wheeling. The RPMs and such are really meaningless and should have been noted as "Examples of RPM to be adjusted to the terrain being descended". Incredible that they were not. Here is what they are trying to accomplish with this technique.

This is known as power braking and is intended to do nothing more than ensure that all 4 of your tires continue to rotate as you descend while braking on a slick surface. That's it. The power from the engine helps discourage a tire from being stopped by the brakes, which could create a nasty lateral skid. A rolling tire provides directional control, a locked tire does not.

There is no need to go to "1500 RPM", there is no need to sit at "800 RPM", etc. Merely use the brakes to choose your descent speed as you normally would, but apply a bit of throttle to prevent a wheel from being stopped by the brake pressure. It doesn't take much.

It's a very simple technique, but honestly I don't recommend it when conditions would most dictate it - a slippery descent that's so sketchy this is the only thing that's going to prevent the vehicle from locking tires even with competent everyday brake modulation. Under these conditions, I recommend your vehicle descend the slope either controlled by a winch, or controlled by a strap from another vehicle up on the flat. In other words, if things are that dicey, it's pretty nutty to think you're going to master it under pressure and there's no way to truly practise it without actually being on such an edgey slope. Kinda like "practising" cliff diving if you know what I mean.

So spare the wear and tear testing this to see if you get "extra braking power from the torque converter" etc. Nope.

DougM

Doug, if the technique above is indeed "power braking" then I agree with your position of not recommending it. In virtually every decent I've made in the last 35 years I have been able to do so safely using engine braking, light brake pressure, and judicious use of the throttle to straighten up. Gravity, and letting off the brakes a little has always been suffient to keep the tires turning (in front) for me. I have elected not to attempt certain areas before because frankly there was no traction to be had using any technique. Yeah, I've made my share of controlled skids down short sections, winched up and down some pretty rough stuff but I don't recall ever seeing anyone try power braking.
Still, I would like to know more about it as I do not profess to know all of the "fine" points of offroad driving. Do you suppose it is designed to get you through only short sections of trail that have little traction? Otherwise, I guess I don't see the value of it.
Thanks....

 

[IdahoDoug]

Flint,

The idea here is to minimally (key) provide forward rotating pressure to the tires to prevent perhaps one sticky brake from locking its tire. On any braking system, the brakes are actually providing uneven braking force at each tire - a fact that is disguised on a normal high or moderate friction surface such as encountered in road and most wheeling conditions. But where the surface friction is extremely low, the braking threshold for 3 brakes may be fine, but the fourth is above that surface's ability to grip and it will lock.

All you're doing is removing engine braking by pushing gently with the drive train rather than letting the drivetrain try to slow the wheels as would be the case with engine braking. You can remove engine braking slightly, altogether, or actually push against the brakes - whatever it takes to keep a sticky brake from locking its wheel. This dates back to the olden days when vehicles had dramatically different braking forces at each wheel due to cruder systems. Todays have very little difference apart from that designed into the system. Naturally, the conditions of offroading can change this due to a recent stream crossing, dust, etc and this technique still may have its application under these circumstances. But I would term it *extremely* rare and would not advise its use as noted in my earlier post. This would not be something I'd ever try to teach as a descending technique as it takes an extraordinary attention to what's happening at the tire/terrain interface, a top notch driver, and deep familiarity with the vehicle to take advantage of this subtle technique.

Far better to use engine braking and simply modulate the brakes. If that wouldn't have worked to get you down safely, then using this technique would only have made a barely measurable difference if done correctly, but done incorrectly it would almost certainly have placed the vehicle and passengers in danger.

DougM

 

[flintknapper]

Flint,

The idea here is to minimally (key) provide forward rotating pressure to the tires to prevent perhaps one sticky brake from locking its tire. On any braking system, the brakes are actually providing uneven braking force at each tire - a fact that is disguised on a normal high or moderate friction surface such as encountered in road and most wheeling conditions. But where the surface friction is extremely low, the braking threshold for 3 brakes may be fine, but the fourth is above that surface's ability to grip and it will lock.

All you're doing is removing engine braking by pushing gently with the drive train rather than letting the drivetrain try to slow the wheels as would be the case with engine braking. You can remove engine braking slightly, altogether, or actually push against the brakes - whatever it takes to keep a sticky brake from locking its wheel. This dates back to the olden days when vehicles had dramatically different braking forces at each wheel due to cruder systems. Todays have very little difference apart from that designed into the system. Naturally, the conditions of offroading can change this due to a recent stream crossing, dust, etc and this technique still may have its application under these circumstances. But I would term it *extremely* rare and would not advise its use as noted in my earlier post. This would not be something I'd ever try to teach as a descending technique as it takes an extraordinary attention to what's happening at the tire/terrain interface, a top notch driver, and deep familiarity with the vehicle to take advantage of this subtle technique.

Far better to use engine braking and simply modulate the brakes. If that wouldn't have worked to get you down safely, then using this technique would only have made a barely measurable difference if done correctly, but done incorrectly it would almost certainly have placed the vehicle and passengers in danger.

DougM

That makes sense. Thanks

 

[timbercruiser]

I tried it again today in a sand pit. It did not "hook up" as I thought it might, I only went faster.
IdahoDoug is correct: use light braking pressure when you descend a hill.

 

[IHWillys]

If at all possible, you want to rely on engine "braking", as this is not restricting wheel rotation in any way and should never cause a loss of traction on its own.

Engine braking can cause loss of traction. I was in an '82 Toyota pickup that ended up upside down not too far from Deckers(Rampart Range) due to loss of traction while engine braking. So the need for modulating the amount of engine braking is certainly real, albeit a rare necessity.

I broke my right wrist as a result of it. I wasn't driving but when the rear kicked out(steep downhill), it did so rather quickly. We picked up speed very rapidly sideways still on the road. He almost saved it as evidenced by the tracks, but a front tire got over the edge and we went on over into the creek well below. Totalled the truck, bent frame, thoroughly smashed body, shaken crew. Funny part was the bed toolbox that was flung out and into a tree, still right side up.

There's plenty of good advice here. Learning with as low a danger level as is reasonable is good advice, but you do have to do it to learn it.

Ken

Oh, and having an upside down vehicle on rocks is not necessarily stable. I had quite a "pucker" experience when I was halfway out the window and the truck started rolling toward me.