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post #31 of 45 Old 09-01-2012, 11:59 PM
05Unlimited
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Oooohhhh .............I have an age old question that I'll bet you can answer! Literally about 21 years ago I remember something happening that I still to this day do not understand. When I was in college we lived close to this "good ol' boy" who sometimes did some backyard mechanic stuff. I had a 1979 Buick Regal with a 301 4V and 200 Metric Trans (obviously it had an open diff rear end...yes ..for sure ...2.73's and all). I was in his yard one time trying to drive it up onto some ramps and couldn't get enough traction in the gravel lot to make it up. He said "put it in 1st gear ...it puts more torque to the rear end". Knowing that it was an automatic and started out in 1st gear by default anyway, I was puzzled by his instruction. None the less, I pulled the old 3 speed automatic lever down into "1" and feathered the throttle ....the car climbed right up the ramp! To this day I have never understood this ...but always forgot to pursue "why????". So now I finally remember to ask in an appropriate venue. So ....why on Earth did my old 3 speed automatic have a posi-effect on an open differential when the trans lever was placed into "L1".??????????? I'm telling you ...this was not my imagination ...it was a NIGHT AND DAY effect!!!!


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post #32 of 45 Old 09-02-2012, 04:43 PM
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Can't wait to hear an answer to this one!
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post #33 of 45 Old 09-03-2012, 11:53 AM Thread Starter
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Quote:
Originally Posted by 05Unlimited View Post
Oooohhhh .............I have an age old question that I'll bet you can answer! Literally about 21 years ago I remember something happening that I still to this day do not understand. When I was in college we lived close to this "good ol' boy" who sometimes did some backyard mechanic stuff. I had a 1979 Buick Regal with a 301 4V and 200 Metric Trans (obviously it had an open diff rear end...yes ..for sure ...2.73's and all). I was in his yard one time trying to drive it up onto some ramps and couldn't get enough traction in the gravel lot to make it up. He said "put it in 1st gear ...it puts more torque to the rear end". Knowing that it was an automatic and started out in 1st gear by default anyway, I was puzzled by his instruction. None the less, I pulled the old 3 speed automatic lever down into "1" and feathered the throttle ....the car climbed right up the ramp! To this day I have never understood this ...but always forgot to pursue "why????". So now I finally remember to ask in an appropriate venue. So ....why on Earth did my old 3 speed automatic have a posi-effect on an open differential when the trans lever was placed into "L1".??????????? I'm telling you ...this was not my imagination ...it was a NIGHT AND DAY effect!!!!
Shifting into Low had no effect on the axle or its ability to not spin. You might have been more careful with your application of the gas at the time after shifting into Low, that is the only possible reason.

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post #34 of 45 Old 09-05-2012, 08:07 AM
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Originally Posted by Jerry Bransford View Post
Shifting into Low had no effect on the axle or its ability to not spin. You might have been more careful with your application of the gas at the time after shifting into Low, that is the only possible reason.
Makes perfect sense to me, although I was there at the time and witnessed an unbelievable difference in traction. I wasn't trying to apply the gas any more carefully ...it was a night and day difference and it has always bewildered me. Maybe the good old boy knows something we don't just from repeated experience if nothing else. To me it makes no sense at all. Maybe it was a freak thing but I'll never forget how differently it dug into the gravel after being shifted into L1 (like it had no chance whatsoever in D but when shifted to L1 it just went right up the ramp effortlessly). I had said ..."yeah right, like shifting into L1's going to make any difference" ...then I tried it and was like "WTF?!!?!?!?"

2005 LJ, NSG-370 6-spd (close-ratio), 3.73's, three tops incl. custom Sunrider-Safari top, 38"x22" hardtop sunroof, OME 2.5", JKS 1.25 BL/1.0 MML, seats 2"^, 285/75/16 Duratracs, Ion 171's (16x8), Alpine CDE135-BT/KTP-445/Polk521Db/650Db, full soft/hard doors, Harley L.Stms, "I swear my Jeep is staying stock"
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post #35 of 45 Old 09-12-2012, 01:11 PM
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As i was reading through this thread i was remembering a feature on my dad's tractor I used to use a lot, left and right brake controls for the rear wheels. Then i started wondering, if i had individual control in applying the emergency brake to the left or right rear tire, then I could almost have a locked rear axle (assuming i understood all of what i read). Not that it would be very practical to keep applying/removing the braking to each rear tire when needed on a long run, but if it was just a once in awhile thing on a run it might be nice to have...of course someone would have to make the new 2 in one brake handle.
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post #36 of 45 Old 12-08-2012, 03:28 AM
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Originally Posted by harleysilo View Post
As i was reading through this thread i was remembering a feature on my dad's tractor I used to use a lot, left and right brake controls for the rear wheels. Then i started wondering, if i had individual control in applying the emergency brake to the left or right rear tire, then I could almost have a locked rear axle (assuming i understood all of what i read). Not that it would be very practical to keep applying/removing the braking to each rear tire when needed on a long run, but if it was just a once in awhile thing on a run it might be nice to have...of course someone would have to make the new 2 in one brake handle.
Modern vehicles including some Jeeps do this through the ABS for traction control, stability control etc. Some vehicles can get pretty complicated actually. Some AWD systems use a clutch in the t-case that can transfer power to the frt or rear, then they can apply braking effect to individual wheels to control wheel spin and some even reduce engine power to control wheel spin.

2 in 1 brake handles are out there already and a lot of their uses are in sand rails/buggys for turning brakes. One type uses a simple handle when you pull up it engages one side, push down it will engage the other, others might have 1 handle for each brake, then you also have a regular brake pedal for both. Some crawlers get 2 center hump mounted park brake pull levers and hook them up to the individual rear parking brake cables on rear, they are manily used for turning brakes too and you can pull the locking button off for quick grabbing and releasing.
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post #37 of 45 Old 12-14-2012, 01:38 AM
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Originally Posted by Jerry Bransford View Post
Shifting into Low had no effect on the axle or its ability to not spin. You might have been more careful with your application of the gas at the time after shifting into Low, that is the only possible reason.
I think I figured out this mystery.

The torque converter is a torque-multiplier until it reaches its stall speed. He was spinning tire because while trying to climb the ramps in "D" it was below the stall speed and applying too much torque.

Shifting it down into "1" didn't provide more torque or more traction. The solution that allowed it to climb the ramp was actually less torque applied to the wheels.

I'm thinking there was some sort of solenoid or somesuch that allowed the torque converter to lock up sooner (much like how O/D off in our Jeeps disengages the TC lockout). So in effect, he was getting the converter to a lower stall point and therefore NOT magnifying applied torque to the axle.

At least that's a possible mechanical answer for what happened. Whether said solenoid or low-stall converter exists is beyond me. Just pulling an idea out of my *** that could possibly explain the situation.


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post #38 of 45 Old 08-19-2013, 07:18 AM
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Originally Posted by billzcat1 View Post
I have to address this because this question hasn't been answered correctly, and the replies show some misunderstanding about the QuadraDrive system.

The QuadraDrive system found on WJ Grand Cherokees uses a gerotor-driven hydraulically-actuated progressive clutch pack in the transfer case as well as in both front and rear differentials. When there is a speed differential front/rear or side/side, the gerotor develops hydraulic pressure which then compresses the clutch packs and progressively locks the axle (or transfer case). There is a bleed port with a spring that tunes the amount of pressure generated - without it, the axle would engage the clutch pack during every turn. With that bleed port, it allows enough slip to negotiate corners without binding but still provide nearly-full-lock up when significant enough wheel spin is detected.

There is nothing electronic about it, no traction control, no ABS actuation involved. It doesn't detect slip and then clamp that brake caliper to stop it or "redneck locker" when it slips. It's also a lot more durable than the older Traclok differentials since the clutches are not engaged during 99% of all driving.

The WK Grand Cherokees have a similar system but the differentials have a small revision to the bleed port. Instead of a spring, it is now an electronically-controlled aperture so lock-up can occur more quickly when needed. However, you are at the mercy of electronics - while more tunable there is also a delay while the system decides what to do and also you have the potential for damage to the wiring while on-trail.
Richard,
As a new to me 99 WJ with quadratrac, thanks for the explanation. I have been out of the Jeep world for a few years, been missing my 06 TJ Rubi Unlimited, I am now back. The WJ fits the niche for people hauler/RV toad/light recreational vehicle.

Darin
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post #39 of 45 Old 11-29-2013, 01:31 AM
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The idea that the engine is not creating torque without resistance is incorrect. It is true that it does take a source of resistance to be able to measure
that torque, but the torque coming from the engine is the same whether resistance is present or not. The differential does not split the power 50/50 but rather
sends the power through the path of least resistance. If you have one wheel off the ground and the other on the ground the one off the ground will be receiving
all of the power. With all do respect as I am new here and I can see that this was posted by a moderator, there is a lot of misinformation in the original post.
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post #40 of 45 Old 11-29-2013, 09:25 AM
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I understand where you are coming - it makes "logical" sense that the engine is still making the torque. BUT it does not mathematically balance to have all this engine torque being produced but not being used to accelerate something (be it the vehicle or even just the rotating assembly/driveline/wheel/tire during a burnout). That force (and as an extension) energy has to go somewhere. *SOME* of it gets put into accelerating the driveline, and *SOME* of it is used up in friction/heating of the spinning tire but this is a negligible amount compared to what the engine is capable of producing when there is a load. Have you ever looked at dyno sheets done in different gears? In theory, it shouldn't matter what gear you are in, the engine always "makes the same amount of torque" according to you. But you'll notice a drastic difference in power/torque output as you go across the gears (no, not as a result of gear reduction) but as a result of additional load added on the dyno. I watched the very same effect doing dyno pulls on a Dynapack where the load is regulated hydraulically and you can watch the engine make minimal power/torque at WOT with no resistance and then make its rated/expected power when the resistance is increased.

And you are flat out wrong on the function of an open differential. It ALWAYS splits torque 50/50. The wheel that is not spinning is providing the same accelerative force that the spinning wheel is - not very much. When you have one wheel off of the ground, that wheel spins and the other wheel provides the same accelerative force - zero. How is that not equal distribution?


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post #41 of 45 Old 12-02-2013, 10:01 PM
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I was wrong. My bad. Ha ha!
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post #42 of 45 Old 12-12-2018, 05:55 PM
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Originally Posted by Jerry Bransford View Post
Since questions about the frequently misunderstood subject of 4x4 and how torque is delivered to the wheels is a common one, I thought I'd make this a "Sticky".

All four tires are driven equally by the 4x4 system and all four pull equally if they all have equal traction. If all four wheels have equally good traction, then all four will pull equally well. So even if your Jeep does not have a locker or limited slip differential, each of the four wheels will receive approximately 25% each of the torque from the engine, when traction is equal under each of the four tires.

A standard open differential always (always!) splits the torque 50:50 between both sides. The problem is that when one tire starts spinning due to poor traction, that reduces the amount of torque seen by either side by an exactly equal amount. So if one side starts slipping, the other side's power (torque) is reduced by an equal amount which usually means insufficient power to keep you moving.

The engine can develop no more torque than the tire with the least amount of traction can accept before spinning.

So the short answer is 'yes', all four tires pull in 4wd. But the moment one side starts slipping, neither side gets enough power to keep you moving even if the non-slipping side still has traction.

Why does the power (torque) get reduced to both sides and not just the side that is slipping? Again, because the differential always (!) splits whatever torque it receives 50:50 to both sides. Why does the amount of torque get reduced at all? Because the engine only develops torque when it is working into resistance. Run an engine with a torque meter connected and watch what happens to the amount of torque produced as resistance to the engine is varied. When the engine is working into zero resistance and just running free, it produces nearly zero torque. Apply a braking force to the engine and the amount of torque will increase in direct proportion to the amount of resistance the engine is working into. The more braking force applied to the engine's output shaft, the more torque the engine produces.

So because the engine only produces torque when working into resistance, a spinning tire reduces the amount of power (torque) the engine produces because the engine is working into less resistance caused by the spinning tire. This works the same way with 2wd and 4wd, it's just that with 4wd, you have more of a chance that at least one of the two axles will have enough traction to allow the engine to produce enough torque to keep you moving. Which is why you get stuck in the first place... when one side is spinning, there is insufficient power being delivered to the other side to get or keep you moving.

And all of this is why a limited slip differential (LSD) can help since it helps to "couple" (via a clutch or a gear-based device) the resistance the side with good traction is seeing to the other side with poor traction, increasing the amount of resistance seen by the engine... thereby increasing the amount of torque delivered to both sides. Which is why the simple technique of stepping on the brakes a little when a tire is spinning can often get you unstuck... because it too increases the resistance the engine is working into which increases the amount of torque that is delivered to the wheels. Or if a rear tire is spinning constantly, pulling the parking brake up a couple clicks can often help by acting as a poor-man's limited slip differential. Pulling the parking brake up a few clicks when you already have a limited slip differential will help improve its operation. A key drawback to a LSD whether it be clutch or gear based is that when one tire is spinning up in the air, it doesn't help create enough torque for the other tire still on the ground to keep you moving. Without you helping it by stepping on the brakes or pulling the parking brake handle up if it's a rear tire that is spinning, a LSD doesn't do much for you. On flat terrain they help a lot, but on uneven terrain when both tires can't always be on the ground, a LSD is not very helpful. That's a situation where a locker reigns supreme over a LSD.

What does a locker do? It mechanically locks the left and right wheels together so when one turns, they must both turn at the same speed. This arrangement prevents one side from spinning uselessly while the other side does nothing. Automatic lockers are always locked but they unlock automatically to allow the outside wheel in a turn to 'ratchet' faster as the outside tire must do through the turn. Once the turn is completed, the locker re-locks both sides together. A manual locker is one that doesn't lock the left and right sides together until it is actuated either via a push-button or lever. An ARB Air Locker is air-pressure actuated, others like the Detroit Electrac are electrically actuated. The Ox Locker is actuated via a lever and cable. Manual lockers have an advantage for on-road driving in that when unlocked, they act like an "open" axle... i.e. one without a locker or limited slip differential... which means it drives like an unlocked vehicle until the locker is activated via the push-button or lever.

Part-Time and Full-Time 4x4 systems...

A part-time 4x4 system called Commandtrac is in all Wranglers together with low-end Cherokees and Liberties. A part-time 4x4 system locks the front and rear driveshafts together inside the transfer case so they drive the front and rear axles together in lock step. Because they are locked together, the front and rear tires must rotate at the exact same rpms. However, the front tires must rotate faster than the rear tires during any turn so a part-time system fights that... which makes a part-time system inappropriate on a paved road because the high level of traction on a paved road prevents the tires from slipping which would otherwise allow the front and rear tires to grudgingly rotate at different rpms. Offroad this is not a problem since the poor traction of an offroad trail allows the tires to slip as needed. But when they try to slip/rotate at different rpms on a high-traction surface, the entire drivetrain is stressed which is bad for it. This problem is called "wind-up".

In reality however, the front and rear axles really don't even turn exactly the same RPMs when you're in 4wd so you still get "wind-up" if you drove in 4wd on the street even if you drove in a perfectly straight line. Why? Because 1) you can't drive in a perfectly straight line and 2) the front and rear axle ratios are usually .01 different from each other. Like a 3.73 and 3.74, 4.10/4.11, etc.. Why the .01 ratio difference between the front and rear axles? Because the front and rear axles usually have different ring gear diameters which makes it nearly impossible for the gear manufacturers to economically make the front and rear axle ratios exactly the same. And no, they are not made .01 different on purpose to make the front or rear pull more when in 4wd, that is an old wive's tale.

Finally, a full-time 4x4 system like Selectrac is available on Grand Cherokees, Cherokees and Libertys couples the front and rear axles together, but they are not mechanically locked together like they are with a part-time 4wd system. The front-to-rear axle coupling can be done via either a differential like the Selectrac system uses (just just like what is in the center of an "open" axle) or a fluid (viscous) coupler. The benefit to a full-time 4wd system is that because the front and rear axles are not mechanically locked together, the front and rear tires/axles can rotate at different rpms from each other. This allows a vehicle with a full-time 4wd system to drive in 4wd "full time" on a paved road without problem since there is no 'wind-up' problem to harm the drivetrain. You cannot get a full-time 4x4 system in a Wrangler from the factory.

Hope this helps!
There is an excellent discussion of torque distribution bias at Torsten.com explaining how this works.
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post #43 of 45 Old 03-05-2019, 03:01 PM
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GREAT discussion! Here is a question. With torque only being produced upon resistance, and a tire having zero traction, if the brake is applied to INCREASE torque, then released, should the tire WITH traction on the axle with the tire with NO traction, then be able to utilize the remaining torque which the motor has produced until the torque has subsided?


In short, Will a good ole brake stand help out?
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post #44 of 45 Old 03-06-2019, 06:59 PM Thread Starter
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Originally Posted by 70sbudget View Post
GREAT discussion! Here is a question. With torque only being produced upon resistance, and a tire having zero traction, if the brake is applied to INCREASE torque, then released, should the tire WITH traction on the axle with the tire with NO traction, then be able to utilize the remaining torque which the motor has produced until the torque has subsided?


In short, Will a good ole brake stand help out?
Yes, very often it will. That's how old farmers in their Model T and Model A Fords were able to often keep going on their often muddy roads.

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post #45 of 45 Old Today, 10:35 AM
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that was a lot to read but great info, thanks....
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