[Kieran]

Am I missing something, or did Jeep do away with Vari-Lok with the WK? I thought Vari-Lok was just about the best stock diff design one could imagine. Now it seems they've gone to electronically controlled brake-assist limited slip diffs. WTF? Vari-Lok ruled over designs like that. Are Vari-Lok diffs used anywhere in the Jeep lineup anymore?

Confused newbie,
-Kieran
(sorry for the cross post... not sure where to put this)

[ArloGuthroJeep]

The brake assisted ones are more effective from what I have seen. Saw a WK with a wheel in the air not even hesitate in moving forward...Vari-lock requires wheel spin to activate the LSD...

[mendelmax]

Kieran, not true about this brake assist- QDII uses ELSD diff, which performs much better than vari-lok. On the other hand this system is far more complicated, but it's long discussion with many pros and cons.

I've also read somewhere that you can still get it with 2WD WK. Not sure about it though.

Arlo, you were faster, but are you talking about new QT II or QDII? Because if about the second one, then there is no brake assist LSD- it's all in the diff.

[Wheelin98TJ]

Welcome to the forum.

I deleted your other thread and moved this one here.

There is a WK section. It is located within the "Grand Cherokee and Commander Forums Group". There is also a shortcut on the main page.

[///BHRpowered]

for daily driving and things like snow the brake assist would be better, but for deep mud I think the vari-loc and quadra-drive would be better.

ideally you would have a vari-loc quadra-drive...like say a 2000, and then combine the drive by wire systems to brake say 1 wheel and activate the ones with traction, this is provided ones in the air. if all 4 tires are on the fround you don't want to brake one and push with another.

[rob92xj]

The Quadra drive systtem used on the WJ is gone, the new system used on the WK and XK are electronically controlled variable locking differentials it works like the vari-lock in the WJ only there is no pump inside the diffs it has elactronic solenoids and they went to the new system as it works with the ESP system better as it can now allow one wheel to spin or lock up in a bad situation. I loved the old system as it worked with out ever knowing it was there the new system has too many electronics for my taste.

[mendelmax]

But, despite I don't like this ESP based stuff, I have to admit, that by design it simply HAS to perform better in the mud or snow- spinning tire always dig a hole. Here the spin is basically eliminated.

[Kieran]

Sorry, I don't agree with any of you who think that an electronically controlled brake-assist traction control system is better than Quadra-Drive1 was. QD1 was a QT2 center diff/transfer case, with vari-lok front and rear diffs.

ArloGuthroJeep - vari-lok was not a limited slip diff. It was/is an automatically locking diff that was locked by a clutch that was activated by a gerotor-driven hydralic pump. The speed with which the clutch locked the diff could be tuned.

Mendelmax - Both systems (vari-lok and brake assisted LSD's) require *some* wheel spin to activate.

The vari-lok based QD1 system worked great. Unless the QD2 system is LIGHTYEARS better than the QD1 (hard to believe) then it's not worth the extra complexity and decreased reliability of the electronically controlled system.

The original Quadra Drive was a beautiful implementation of the K.I.S.S. design principle. I morn it's departure from the Jeep lineup. You'd think they'd at least have let it trickle down to the lower end platforms...

[mendelmax]

QDII is really lightyears better than QDI was. Satisfied?
QDII indeed requires wheel slip. You know how much? I haven't seen it making even half turn. And it can be done with low rotational speed, since the system know if the wheel is in air (thanks to ESP system). Therefore until it will detect that this tire is back on the ground, it will keep diff locked.
And, don't call it "brake assisted", since brakes has nothing to do with that

Oh, one more- vari-lok is an LSD, not a locker


Edit: to make everything clear here- I still would like QDI more Just for it's simplicity- not a big fan of electronics...

[Kieran]

Originally Posted by mendelmax

QDII is really lightyears better than QDI was. Satisfied?
QDII indeed requires wheel slip. You know how much? I haven't seen it making even half turn. And it can be done with low rotational speed, since the system know if the wheel is in air (thanks to ESP system). Therefore until it will detect that this tire is back on the ground, it will keep diff locked.
And, don't call it "brake assisted", since brakes has nothing to do with that

http://en.wikipedia.org/wiki/Freedom_Drive#Jeep_BTCS
"ALL 4WD systems in the WK come coupled with Jeep's brake traction control system (BTCS)."

Originally Posted by mendelmax

Oh, one more- vari-lok is an LSD, not a locker

It could be classified as an LSD, since it can vary the amount of torque transfered, but it doesn't work like a traditional LSD. To me, the design is more like a progressively locking diff, rather than a diff that "limits slip".

With an LSD, the less the difference in shaft rotational velocity, the more the torque transfered. As wheel slip increases, an LSD becomes less and less effective (which is why the trick of barely applying the brakes with a posi-traction diff works, and also why brake controlled LSD systems work). The opposite is true with the vari-lok diff (aka Dana's Hydra-Lok diff) - the more the difference in shaft velocity, the greater the tendency of the diff to "lock".

Now, I may be wrong on this next point, but my understanding was that once the clutch packs fully engaged, the vari-lok diff behaved like a fully locked diff. Maybe some slip is actually allowed still, but I don't think so. Either way, it's still the opposite of a traditional LSD.

Originally Posted by mendelmax

Edit: to make everything clear here- I still would like QDI more Just for it's simplicity- not a big fan of electronics...

Cool.

[mendelmax]

Well, vari-lok never fully locks, one wheel always spin a little faster, therefore I think progressive LSD is better word. Don't get it wrong- I love this idea and I think it is one of the most universal design you can find, but I just wouldn't call it locker, since for me locker is a thing that locks both wheels 100% for the duration you want, and whenever you want, not only after slip is sensed.
The QDII system is also classified as LSD.

But who cares- long live simplicity!

[brandoncrone]

Your right, progressive lock is a better word for it. The diffs are never fully locked, a small amount of slippage always occurs. The only diffs out there that can 100% lock are ones like the ARB air locker, or a detroit locker. Even traditional limited slip differentials never lock 100% during wheel slip. The elctronic controlled diffs are of course much more sophisticated, it had to be done to incorporate progressive lock differentials with ESP. Now the final drive control module decides the brake pressure in sync with the necessary locking of the differentials. Its by far surperior to even the QDI (don't get me wrong its an awesome system), the elctronics make it that much better.

A test was done by DCX in 05 with almost every kind of SUV on the market, an incline was made at 15% with alternating diamond plate and rollers like they have on assembly lines. The GC with QDII was the only SUV able to climb this incline, all the others slid back down.

[JeepCollector]

The ELSD differential IS a vari-lok differential with electronic control and having 'wheeled both of them I can tell you QD II is light years ahead of QD I. The same gerotor pump concept is used to force the clutches together, but instead of bleeding off pressure all the time like the simple mechanical system, the ELSD electronic control can close the valve. Once pressure is built it can hold it for a pretty long time and I can't tell the difference between it and a locker (yes I think it's that good).

The brake based limited slip is far better than open differentials, but still nowhere near ELSD's.

[brandoncrone]

The brake assist, helps the ELSD and works together with it. The other nice thing about this system is that the Jeep needs only one wheel to have contact in order to move the vehicle. That is very impressive in my book! The vehicles that only have the brake assisted axles are nice, you don't have to spend a ton of money like for a limited model and still have some sort of "locking" differential

[rob92xj]

The WJ Quadra drive system in my option is better it had no electronics to rely on and it just plan worked and worked really good, the system now in use in the WK and XK is supposed to be better but I have replaced more final drive control modules and control solenoids then I ever replaced on the WJ Quadra Drive system's hydraulic components. It is still a good system and when everything gets worked out with it may be as good as the WJ system. The brakes limiting diffs are not used on the Quadra Drive 2 system as when more traction is needed the final drive module will lock up the axle(been told it can lock to 98%) If that is not enough then the ESP sytem will apply brakes as needed to get the vehicle moving again. I have had a few customers that have gone off road in the shop and the owners have been happy with them except one who had gotten hung up on a tree stump and ripped the wiring harness off the rear axle for the differential solenoid.
Quadra Trac 2 is the system that uses brake limiting differentials to control wheel spin.