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Unread 03-12-2007, 02:33 PM   #16
Hydro97ZJ
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thanks for clearing up the difference between automatic and manual lockers for me.

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Unread 07-08-2007, 08:45 AM   #17
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great writeup. I also would like to see more detail on the braking technique if anyone has more thoughts on it.
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Unread 08-21-2007, 08:56 AM   #18
Jerry Bransford
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The more resistance the engine sees, the more torque it can produce. In a low-resistance situation like when you're in ice, the engine can only put so much torque out to the driving wheels before they slip, which creates the upper limit of torque it can produce.

Stepping on the brakes in that situation increases the amount of resistance the engine works into, thus it can produce more torque which can be used by the tire that has more traction. Remember, the tire with the least amount of traction is the limiting factor so stepping on the brakes makes the engine think it has more traction (it feels the added resistance from your braking action) which can often provide enough additional torque to the side with better traction to get you moving again.

So step on the brakes fairly firmly as you give it gas at the same time, it's a balance thing that can only be learned by a little practice. When one tire is spinning, step on the brakes (or pull the parking brake lever up a few clicks if it's a rear tire) to eliminate the ineffective tire spin and give it some gas. If conditions are not too bad and you've done it right, odds are you'll start moving.

This age-old technique has been around since the Model-T days, too bad it's a lost art for most drivers today.
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Unread 08-21-2007, 12:45 PM   #19
pigphish
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any tips for manual tranny's.

I tried doing this with my jeep when i was in some dirt with some spinning wheels but it was too easy to stall trying to negotiate all three peddles.
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Unread 08-21-2007, 01:26 PM   #20
BradG
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Quote:
Originally Posted by pigphish
any tips for manual tranny's.

I tried doing this with my jeep when i was in some dirt with some spinning wheels but it was too easy to stall trying to negotiate all three peddles.
While the tires are spinning and you've got a decently high number of RPMs (I don't try it below 2000 or so) that's when you get on the brakes. You don't really need to be slipping the clutch since your tires are already slipping lol. It's really fun (and you know you're in it pretty good) when you can have it idling in first gear and you're not moving and the clutch is all the way out and it's not stalling.
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Unread 01-18-2008, 06:00 AM   #21
brian674
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Awesome write up, I will try it just for fun the next time I can. . . I'll have to do the manual method. I noticed it most when I used to brake torque my Ranger to burn the tires. I could see 2 even black marks when brake torquing, but only one black mark when I would just dump the clutch and burn out. I never understood why until now. Thanks for the technical info!!!
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Unread 01-20-2008, 09:37 PM   #22
Fjguercio
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HUMMM Nice Write UP. Some confusion I see on TORQUE & TRACTION, and not many guys have been stuck in the ditch with 2 wheal drive car.

The idea is to MAX Traction. Std Jeep will spin two tires and on min traction like ICE very easy to spin tires. The WRITER also refers to ICE as a LOW TORQUE TO ENGINE SITUATION. So is we increase TRACTION by spinning more tires by using rear axle limited slip avail as jeep option, installing rear or front locker we can ALL increase traction, THUS AS WRITER SAYS MORE TRACTION IS MORE TORQUE FORCE ON ENGINE. If We Have More Traction We Have More Force ON Engine, He is calling that engine force Torque.

Second if you find youself in the driveway stuck on ice patch or in the ditch with car or jeep with the A SINGLE REAR WHEEL SPINNING. STOP!!! You can apply THE EMERGENCY BRAKE about 1/3 force with wheels stopped. Try to accerate gently again and E BRAKE may stop the spining wheel with enough force the wheel with traction will turn with enough force to move your car. If not, go to 1/2 force on EMERGENCY BRAKE and see if that gets you out. THIS IS STRICTLY AN EMERGENCY GET UNSTUCK SOLUTION. YOUR REAR BRAKES CAN GET HOT AND IT IS A STRAIN ON JEEP / VEHICLE TO TURN & SPIN YOUR REAR WHEELS. This has no effect on your front wheels. This is for use with open axles for the most part, not limited slip axles. EMERGENCY USE!!!!
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Unread 02-10-2008, 11:20 PM   #23
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This is a great topic for newbies and old timers alike! Although I have only had my jeep for about 5 yrs, this was one of the first "tricks" I learned while on the trails. Having open diffs kind of made it a requirement to keep up with more modified rigs. With a manual tranny, as mention previously, knowing how to run three pedals with two feet is something that takes a lot of practice to do properly. The end result though is priceless... Having a buddy in a brand new rubi being astonished at what you can drive over, and it takes all he's got to get through with lockers!!!

Maybe I missed it, but was there a thread for "Driving Finesse"?? I am sure there are more of these items out there...

Rick
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Unread 09-07-2008, 07:12 PM   #24
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I was raised in Colorado. I was taught to transfer additional torque to the "wheel on the pavement" while the "wheel in the snow" was spinning away when I learned to drive. It will absolutely make your open diff behave very much like a locker. Jeep incorporates this function into the newer models today and it works automatically. There are sensors that just try to keep the wheels turning at the same speed, when one slips under 18 mph on a Wrangler with open diffs the brake is automatically applied to the spinning wheel thus rebalancing the torque applied to each axel. It works great. Not quite a full locker but it definitely adds to the traction of the newer jeeps.

Here is a pointer to the article below and all credit to the engineer who wrote the article.

http://blog.chryslerllc.com/blog.do;...id=270&p=entry


February 11, 2008 7:00 AM
Jeep Brake Traction Control Explained

Loren Trotter is an engineer in Active Chassis Control Systems, as well as a die-hard Jeep® enthusiast and avid off-roader. Some of the shots below come courtesy of his trips to Moab, demonstrating the capable off-road system he's speaking about below.

Jeep® has long been the leader in four wheel drive systems and in 2005 introduced Electronic Limited Slip Differentials (ELSDs) and brake based traction control tuned specifically for off road driving on the Grand Cherokee. Since then, traction control has been added to the Commander, Liberty and Wrangler.

From reading several articles written about these vehicles, I feel that there may be some misconceptions about Jeep brake based traction control and even some misconceptions about ELSDs.
There are several parts to traction control and they are enabled or disabled depending on the driving mode the driver has chosen. When the vehicle is in 4wd high range and the Electronic Stability Control System (ESC) is on, traction control uses the brakes and engine torque control to limit how fast the driven wheels can spin relative to the actual speed of the vehicle.
This helps provide maximum traction along with stability. In addition to controlling how fast the driven wheels are spinning, there is a feature of brake traction control that controls wheel speed side to side across a driven axle and is called BLD, or "brake lock differential."

BLD does not care how fast the wheels are turning, just that they are turning at the same speed. It provides improved traction capability similar to a locking differential.

There are times when controlling how fast the wheels spin may not be desirable for driving conditions such as mud or deep snow. In this case, pushing the ESC button once (in 4wd high range) will disable the brake and engine portions of traction control that control how fast the wheels are allowed to spin but leaves BLD on. In 4wd low range, only BLD functions so there is no need to turn off traction control.

Just to get this out of the way; from the Jeep perspective, BLD is not a substitute for locking differentials. It is a means to greatly expand the off road capability of vehicles that were not purchased with or do not offer locking differentials.

A Jeep vehicle with BLD will negotiate almost any obstacle or driving situation that a similar vehicle with locking differential will. BLD does require a change in driving style and more torque to negotiate the obstacle.
We have worked very hard to make the BLD on Jeep vehicles work well off-road and reduce, and in most cases eliminate, the complaints about brake based traction control.

This time I will write about BLD but I can write a future blog about ELSDs if there is enough interest from all of your readers out there.
To understand what BLD does, it is necessary to understand how and open differential works. Open differentials have many attributes that make them the best choice for most vehicles. They are simple, proven and reliable requiring only an occasional fluid change to last for many years.
For rear wheel drive vehicles, they also provide a stability advantage over locking differentials (such as a Detroit Locker) that are always engaged.
The main drawback to an open differential is that torque is always split 50/50. Each wheel receives 50% of the input torque (ignoring losses). This means that if one wheel is in the air and it takes almost no torque, say 10 ft-lb., to turn the wheel, the other wheel will only receive 10 ft-lb. of torque. If 10 ft-lb. is not enough to move the vehicle in the desired direction, it will not move.
Using the vehicle’s wheel speed sensors, BLD knows when one wheel on a driven axle is turning and the other is not. BLD will apply brake pressure to the wheel that is turning.

The applied brake pressure increases the torque required to turn the wheel in the air and this allows more torque to go to the wheel on the ground. The one drawback is that the input torque must be twice as much as required to negotiate the obstacle because of the brake application. The required extra torque is not usually a problem especially in 4wd low range.

In order to get the most out of BLD, the driver must adapt their driving style to characteristics of BLD. For example, when in a situation where one or more wheels loose traction and the vehicle will not continue in the desired direction, the driver should carefully and smoothly apply the throttle to allow more torque to go the wheels with traction as the brake(s) are applied.
BLD looks at individual driven axles and tries to keep the wheels turning at the same speed. BLD does not try to limit how fast the wheels turn, just that they turn at the same speed.

Some may fear that using the brakes for traction control (BLD) can cause them to overheat. The electronic brake control system uses a model to estimate the brake temperatures not only from use during traction control but also braking. If the model temperature reaches a level that could possibly affect brake performance, the brake traction control is shut off automatically.
Since BLD is only trying to keep both wheels on a driven axle turning at the same speed and not control overall wheel speed, the actual energy input to the brakes is relatively low. In all of the testing done at Moab, I have never seen brake temperatures reach a point where the thermal model turned off traction control.

In my opinion, brake based traction control has received undeserved criticism in the press and from off-road enthusiasts. Brake based traction control on Jeep (and Dodge) vehicles performs well off-road and is a useful feature for customers. Magazines should not lump all brake based traction control together.

Jeep engineers, along with partners Continental Automotive, Bosch and TRW, have worked very hard to make Jeep brake based traction control a system that performs extremely well.

Many diehard Jeep enthusiasts agree that brake traction control can work well off-road once they have seen it and tried it. Many trips to Moab and a number of other off-road areas have proven how well it works. How many other stock vehicles can do the Zuki Shuffle without locking differentials or would even try to climb where eagles dare to tread?
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Unread 11-04-2008, 11:08 PM   #25
extremecj7
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thanks to everyone for clearing this up for me
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Unread 11-10-2008, 02:38 PM   #26
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dang, nice write up!

Im a new jeeper and this really helps out
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Unread 12-17-2008, 11:08 PM   #27
bucks11
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Just came across this and it definitely clears up "locker-talk" for me...

I wish I had half of your Jeep knowledge Jerry....thanks.
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Unread 01-28-2009, 10:44 PM   #28
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yes, we neek the locker in sand, snow, mud.
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Unread 01-29-2009, 06:53 PM   #29
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awesome write up.

I just learned so much my head hurts.
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Unread 03-05-2009, 02:35 PM   #30
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See sticky in this section with video on how a diff works:

Video showing how Diff's work
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