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Discussion Starter #1
I have a couple of questions about QT and QD diffs. My 08 has the QT2's and one of my questions is there a limited slip or posi kit available for the QT2's? The other question is other than buying the diffs ( QD 2's ) and installing them and being their of the electric variety is it possible to install them or will I run into trouble because the computer wouldn't recognize them or is it just a programing thing? Thanks.

Mark
 

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Discussion Starter #3
My bet would be not able to input the pcm and it also won't give the output to engage it either.


Swanny

Thanks Swanny. Would you happen to know if there's an after market limited slip available for the QT2's that doesn't require the computer to engage Swanny?

Mark
 

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Discussion Starter #5
I'm been trying to find out what kind of diffs are in the Commander I guess I'll call the dealer they might know. I was poking around on You Tube but didn't find anything QT2 related as to what they might be.

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I'm been trying to find out what kind of diffs are in the Commander I guess I'll call the dealer they might know. I was poking around on You Tube but didn't find anything QT2 related as to what they might be.

Mark
The rear diff is easy. It's a 8.25" Chrysler rear diff with 29 spline axles. There are a lot of aftermarket limited slip differentials for that rear axle. Check Jegs, Summit Racing, JC Whitney or any other "performance" shop for prices and choices. You might expand the possibilities if you either don't look specifically for a Jeep Commander, or if you look for a late 1990's through maybe 2010 or so Dodge truck (Durango? Dakota?) that came with the 8.25" rear gears.

Expect to pay $600-$800 for a good LSD or torque sensing diff for the rear axle. There are some less expensive choices also, which help, but aren't true "limited slip" or "torque sensing" devices. One goes by the trade name "the Grip." I'm not sure who owns the name and markets that one these days, but it's a spring gizmo that fits between the idler gears on a standard open diff. It provides some benefit, and has it's own set of drawbacks. The biggest "benefit" is that it's usually about half the price of a true limited slip diff.

The front diff is a big mystery on these vehicles. I know it's a Mercedes Benz unit of some kind, and the documentation says it has a 200mm ring gear. The thing is, I've worked on a lot of MB cars, and I've only seen 185mm and 210mm ring gears/diffs on those cars. That means one of three things:

  1. It's a MB 185mm diff with an oversized ring gear
  2. It's a MB 210mm diff with an undersized ring gear
  3. It's a completely unique diff built by MB with a 200mm ring gear and has nothing in common with other MB diffs.
The last option there seems most "unGerman," and I doubt that's the case. I'm in touch right now with a very good Mercedes Benz expert and I'm trying to fully identify which MB diff this is. If it's a "stock"(ish) MB unit, then there are MB factory LSD's and aftermarket LSD's for the standard 185mm and 210mm MB diffs.
 

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Discussion Starter #7
Thanks Racer X that's the info I've been looking for. I called the local Jeep dealer and he told me that the diffs were corporate and he gave me the size and as far as he knew there was nothing available for the diffs as far as LSD goes. I think if I went to all the trouble to do something with the rear diff I would buy a good LSD unit thanks again.

Mark
 

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The rear diff is easy. It's a 8.25" Chrysler rear diff with 29 spline axles. There are a lot of aftermarket limited slip differentials for that rear axle. Check Jegs, Summit Racing, JC Whitney or any other "performance" shop for prices and choices. You might expand the possibilities if you either don't look specifically for a Jeep Commander, or if you look for a late 1990's through maybe 2010 or so Dodge truck (Durango? Dakota?) that came with the 8.25" rear gears.

Expect to pay $600-$800 for a good LSD or torque sensing diff for the rear axle. There are some less expensive choices also, which help, but aren't true "limited slip" or "torque sensing" devices. One goes by the trade name "the Grip." I'm not sure who owns the name and markets that one these days, but it's a spring gizmo that fits between the idler gears on a standard open diff. It provides some benefit, and has it's own set of drawbacks. The biggest "benefit" is that it's usually about half the price of a true limited slip diff.

The front diff is a big mystery on these vehicles. I know it's a Mercedes Benz unit of some kind, and the documentation says it has a 200mm ring gear. The thing is, I've worked on a lot of MB cars, and I've only seen 185mm and 210mm ring gears/diffs on those cars. That means one of three things:

  1. It's a MB 185mm diff with an oversized ring gear
  2. It's a MB 210mm diff with an undersized ring gear
  3. It's a completely unique diff built by MB with a 200mm ring gear and has nothing in common with other MB diffs.
The last option there seems most "unGerman," and I doubt that's the case. I'm in touch right now with a very good Mercedes Benz expert and I'm trying to fully identify which MB diff this is. If it's a "stock"(ish) MB unit, then there are MB factory LSD's and aftermarket LSD's for the standard 185mm and 210mm MB diffs.
Great info Racer_X;

Lets us know what you find out please.
 

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Discussion Starter #9
Looks like I'll probably just go down to Summit and pick up a Detroit locker when I get ready to do this they're only about a 45 min ride from the house.

Mark[
 

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Summit is a good source, and they have several diffs that will work in our rear axle (some might need a bit of clearancing to fit, or alternate bolts to hold them to the ring gear). They also offer free shipping on differentials for those of us who aren't within an hour of one of their locations.

Of what they offer, the Detroit True-Trac would be my choice. It's the same design as the Torsen diffs. Very smooth in operation, and very reliable, with no degradation in operation from "normal wear" and no need for a rigorous maintenance schedule (the standard lube change schedule for the factory diffs is sufficient). The Torsen diffs were used for the front and rear diffs on military Humvees.

The Detroit Locker has one thing going for it in off road use: If one wheel has zero traction, the other wheel will get power. Good if one wheel is off the ground, for example, or on ice. Still, I'm not sure I'd put up with it's quirky handling for daily driver use. On pavement, or even on gravel roads with relatively good grip/traction, they are very quirky in the way they affect handling (I'm trying to be nice here). I also doubt a Detroit Locker would play nice with the Electronic Stability Program in these vehicles on a gravel road when driving in the high, unlocked range on the transfer case. Don't ask me to be your test driver for that experiment.

BTW, a True-Trac or Torsen diff in the rear axle can be partially "locked" with the parking brake and a bit more right foot (throttle) if you know you're going to put one wheel on a zero grip surface or in the air. It's best to set it a bit before you hit the low grip obstacle, and drive through it. That's not an option for more than a few hundred feet, and only at low speeds (you'll roast the parking brakes if you do it very long or very fast) but it works great for most challenging spots you'd find in a trail ride.

BTW, I sent pix to my Mercedes guy, and he wants me to bring our Commander down so he can take a look. He agrees that it's definitely a Mercedes Benz diff of some kind, but isn't sure what's in there. I might get down there today or tomorrow, but more likely it will be the week of the 24th before I can get there. We have some travel plans for next week.
 

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Discussion Starter #11 (Edited)
Thanks for the info RacerX. So then you think the Detroit True-Trac would place nice with the Commanders 4X4 system then ? It will be interesting to hear what your Mercedes mechanic friend has to say about the front diff.

Mark
 

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Thanks for the info RacerX. So then you think the Detroit True-Trac would place nice with the Commanders 4X4 system then ?
I'm more concerned about the electronics, especially the Electronic Stability Program.

When you get in a "stability event," that system reduces power and will fire off one rear brake to "steer" the vehicle back to a stable condition. It all seems to happen simultaneously. If you're accelerating enough to lock the detroit Locker and you get into a yaw situation, I'm not sure the power reduction is enough to unlock the thing, and firing a brake on one rear wheel is going to apply braking force to both rear wheels equally with it locked. First, that's probably not going to help or have the intended effect on the vehicle's attitude, speed and direction. I also think computer is probably going to notice and be somewhat confused and unhappy about what happened.

Also, a Detroit locker takes a bit of time to "clunk" and disengage when input torque is reduced. Even if the power reduction is enough to unlock it, if the brake on one wheel is applied before it unlocks, it's a problem. Binding the locker with one side braking could even keep it locked when it's trying to unlock.

The True-Trac is much more gradual, much smoother, and much quicker to respond. You'd get some crossover on the brakes in a stability event, but it wouldn't be anywhere near 100%, and the power reduction would ease tension on the thing and reduce the "locking effect" instantly. Nothing moves to given the locking effect on the True-Trac, the tension just binds things up, and easing the tension unbinds the helical gears pretty much instantly.

The True-Trac (or similar torque sensing diffs like the Quaiffe and Torsen units) are much easier to drive, and much less quirky and clunky than a Detroit locker.
 

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Discussion Starter #13
Thanks RacerX I'm going to have to think about doing this. But I guess the only way to find out if the Tru Trac would work alright is just try it. I think I remember seeing a Mopar LSD at Summit but I think it was a 27 spline.

Mark
 

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I would love to know what MB axle we are running as well.

On a different note I believe Adam use to run a Power Trax no-slip and likely a few others as well that seemed to work well.... Whatever happened to Adam (jeep07xk or similar)?
 

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Click on parts list button to see parts and prices bud. What part were you after?
@Flex; I wasn't after any parts, just curious to see what the price on a rebuilt differential was - should I ever happen to need one somewhere down the road.

Differentials for the Commander have been notoriously hard to find from what I have heard over the years.

I saw a differential master rebuild kit for $490.00 after I drilled down into the parts list a couple of times, but, I did not see a complete rebuilt differential - which is what I was looking for and actually expecting to see.
 
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