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Old 01-14-2013, 10:28 AM
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differential type / 2wd 3.7

Hey guys!

got a question i SHOULD know the answer to.. but i don't.

It's actually a bunch of questions in one.. hopefully someone more mechanically inclined can answer.

ive got a 3.7 2wd.. im in south texas, don't need 4wd, my little guy gets me through mud, dirt, and climbs just fine. however... id like to know how i can find out if i have the factory lsd that was offered ( 3.07 gears i think ) ..

I don't know if both tires spin.. ive never been outside to look, i can't jack it up and test it, and honestly.. doing a burnout is pretty hard to do on dry ground with a v6 that weights close to 5k pounds. is there a way i can check via vin ? or the bolt's on the actual diff ?

On a side note.. traction control. I was up in michigan a few weeks ago.. lots of ice, lots of sliding, and lots of snow. I turned off the traction control ( holding for 10 seconds ) but.. what does that do exactly, when i would lose traction i could hear something going on up front ( no 4wd ) , so what's the difference in pushing the button once, making the light come on, holding it down making two lights come on, and not holding it at all ?

Thanks everyone!
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Old 01-14-2013, 01:04 PM
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Re: differential type / 2wd 3.7

Hey,

I don't believe you have an LSD. ELSDs were only available on Quadra Drive 2 models and I thought that the SRT8 had an LSD or ELSD on the rear diff but I might be wrong on that. As far as traction control goes, pressing it once will turn off the torque limiting, if I'm remembering correctly, and holding it down will completely turn off both torque limiting and braking. The reason you were hearing noise in the front was probably it braking the front wheels. In the snow, I think it's better to just press the button once. This is a great read about our ESP system: Jeep Grand Cherokee WK - Electronic Stability Program (ESP)
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Old 01-14-2013, 03:39 PM
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Re: differential type / 2wd 3.7

jjt250 , sweet link. thanks.

although, if the jeep doesn't have any type of lsd, how is it able to provide torque to each wheel as it needs. Isn't that what an lsd really is / does ?

Forgive my ignorance on what LSD'd and ELSD's are.. I was under the assumption that torque was provided to both wheels equally, by something tangible, I.E a physical. If that isn't there, how can the computer give a wheel that has no physical way to get torque.. give it torque ?

Again, pardon my ignorance. and thanks for the reply.
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Old 01-14-2013, 03:55 PM
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Re: differential type / 2wd 3.7

Quote:
Originally Posted by Yillb View Post
jjt250 , sweet link. thanks.

although, if the jeep doesn't have any type of lsd, how is it able to provide torque to each wheel as it needs. Isn't that what an lsd really is / does ?

Forgive my ignorance on what LSD'd and ELSD's are.. I was under the assumption that torque was provided to both wheels equally, by something tangible, I.E a physical. If that isn't there, how can the computer give a wheel that has no physical way to get torque.. give it torque ?

Again, pardon my ignorance. and thanks for the reply.
Because the inside and outside wheels turn at different speeds when going around a turn, vehicles that are driven on the road require what is referred to as an open differential (allowing each side to spin at different speeds). A by product of this system is that if one wheel is slipping, no power gets routed to the non-slipping wheel. An electronic limited slip differential uses circuity in combination with a hydraulic clutch pack to slow the spinning wheel and offer resistance so that the wheel with traction receives torque. It is my understanding that only the QDII system utilizes ELSDs (for the first few years on both the front and rear axle, currently only on the rear axle). Instead, what your vehicle (and many others) use is a re-tuning of the ABS technology to act like a locking differential - when wheel spin is detected at one of the wheels in the ABS hardware (specifically the wheel speed sensor), the computer applies the brake to that wheel, providing the resistance needed to route torque to the non-slipping wheel. This is likely what you were hearing. Even with ESP off, the "limited-slip" function remains active.

This is quite effective in the vast majority of situations, though for the real tricky off-roading ELSDs are preferred amongst many for their relatively quicker engagement, durability, and presumably less brake wear. Basically, an ELSD will slow the spinning wheel via mechanics within the differential itself, whereas other systems control the spinning wheel using the brakes. That's all there is to it.
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Old 01-14-2013, 03:57 PM
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Re: differential type / 2wd 3.7

Dr. LEE Splended! good read as well.

My question ( ultimately ) is if i were to be in water, or ice, and i floored the gas , would both tires spin, or just a single tire spin. ?
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Old 01-14-2013, 04:18 PM
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Re: differential type / 2wd 3.7

Tough to say. The most precise answer would be one, both, or none!

The system relies on differences between the wheel speeds across the axles to determine whether to apply the brakes.

If you floor it on ice, like both rear wheels will spin. The computer detects that the rear wheels are moving faster than the front and will hit the brakes on both and/or cut the engine to reduce power. This is the "traction control" part. Once all the wheels are spinning at the same rate, the system will consider it job done.

On mixed surfaces, it is not unusual for one tire to have less traction than the others, and to break loose. As this happens, the system will step in and apply the brakes on that tire that is spinning faster than the rest.

When you disable traction control, in a 2wd it will allow the rear pairs of wheels to spin, but will still brake one wheel if it is spinning faster than its axle buddy.

It's all fairly complicated when you try and think of all the possible scenarios. It's a little bit simpler when you remember the whole purpose of the system is to keep all tires spinning at the same rate. Whatever the conditions are, this is what the system is considering its endpoint. That's why when stuck in mud or snow it is sometimes advisable to turn off traction control to allow you to get some wheel spin and start rocking the vehicle back and forth.
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Old 01-14-2013, 04:51 PM
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Re: differential type / 2wd 3.7

Quote:
Originally Posted by Yillb View Post
jjt250 , sweet link. thanks.

although, if the jeep doesn't have any type of lsd, how is it able to provide torque to each wheel as it needs. Isn't that what an lsd really is / does ?

Forgive my ignorance on what LSD'd and ELSD's are.. I was under the assumption that torque was provided to both wheels equally, by something tangible, I.E a physical. If that isn't there, how can the computer give a wheel that has no physical way to get torque.. give it torque ?

Again, pardon my ignorance. and thanks for the reply.
Yes, exactly what dr.lee said. Since you don't have an ELSD, your system uses the ABS system to limit wheel spin and transfer torque. Still very effective.
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Old 01-15-2013, 11:31 AM
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Re: differential type / 2wd 3.7

great info guys.. I think im still not asking my question right, and sorry for that. Maybe im just not understanding. Let me try again.

2WD on a trail, the left rear tire is in the air, if the ABILITY for torque to go to either wheel, would that one tire on the ground have enough torque to actually do anything, such as... move the vehicle ?

hope that is a better idea of what i mean
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Old 01-15-2013, 01:22 PM
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Re: differential type / 2wd 3.7

Quote:
Originally Posted by Yillb View Post
great info guys.. I think im still not asking my question right, and sorry for that. Maybe im just not understanding. Let me try again.

2WD on a trail, the left rear tire is in the air, if the ABILITY for torque to go to either wheel, would that one tire on the ground have enough torque to actually do anything, such as... move the vehicle ?

hope that is a better idea of what i mean
That I am not sure about. You don't see a lot of 2WD GCs on the trails, especially trails that will get bad enough that wheels are leaving the ground.

In theory, the system should work. In practice, I could see the brakes not being able to hold the tire with enough force to prevent it slipping if you are trying to get over a rock or something with the one drive tire on the ground.
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Old 04-17-2014, 06:39 AM
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Re: differential type / 2wd 3.7

for climbing w/ 2wd, holding the brakes, IMO, would be a disadvantage. you wouldn't be able to utilize the engine power like you should. I also have a rwd like you but im building it for a different purpose. I did find a mechanical LSD for our trucks and should be getting it in the coming months.

Our truck's came from the factory with the Corporate 213mm rear end. This is a conventional open type diff. you are correct on the axle ratio of 3.07. I found different gear sets for it too.

Manufacturer: Corporate Axle
Size: 213mm (8.25 inch)
Type: Conventional Open
Ratio: 3.07
Spline Count: 29

There is very little in the way of aftermarket on this rear end. I did find a mechanical lsd and different ratios. I have em posted in my build thread so if you are interested, give it a look. Hope this helps some!
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Old 04-17-2014, 06:46 AM
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Re: differential type / 2wd 3.7

Quote:
Originally Posted by Yillb View Post
great info guys.. I think im still not asking my question right, and sorry for that. Maybe im just not understanding. Let me try again.

2WD on a trail, the left rear tire is in the air, if the ABILITY for torque to go to either wheel, would that one tire on the ground have enough torque to actually do anything, such as... move the vehicle ?

hope that is a better idea of what i mean
The ELSD uses the brakes to transfer power laterally. In this case, the one wheel in the air will still get power over the on the ground. While the system on our RWD's controls wheel spin in two ways. One, it cuts engine power (torque limiting) and applies the brakes to control wheel spin.

if you get rid of the torque limiting aspect of the TC system, then it would be more effective. Turning Off TC, turns off Torque limiting, but not the function to apply the brakes to control wheel spin. We also have stability control that also applies the brakes to get the jeep back under control.
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