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Discussion Starter #1
Hi,
greetings from Italy.

I own a 1997 ZG 4.0 Limited with the NV249 TCase; ZG is the european version of the ZJ. It is currently stock and it is my daily drive (mostly road, some light off-road, some snow).

I would like to add some modifications. I'd start by adding two Truetrac differential, front and rear. I've read lots of post (on this and other forum) and some technical papers about the torsen differential and sbout the truetrac and I know (more or less) what to expect; but most of the times OR experiences was reported and I am interested also in "road experiencies". Most experiences was reported by GC owners that swapped to a 242 (2HI) or TJ/YJ owner (no full-time at all !).

So, is there anyone out there with a truetrac in the front and with a NV249 in place ?

Thank you for your help !!!
 

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Well, i have one on order for the jeep in my signature! I havent got to drive it yet, im still over in iraq. Im a mechanic in the Army, Tanks and Wheeled Vehicles, But I do drive Humvees everyday with them, front and rear. Being full time four wheel drive, just like our 249, i can tell you, they work AWESOME. You never notice it day to day, or on hard surfaces, but they provide excellent traction. All Humvees have used torsen's in the diff. When i started looking for a locker for the front of my Grand, I checked them out, and cant go wrong. Any front wheel drive application, or all wheel drive, should use them over a standard "locker". Just my .02 cents. Nick
 

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Discussion Starter #3
Hi Nick,
I just saw the pics of your car, and it's great !! Mine will stay more "stock".

What is there in your rear differential ?

Actually my car is understeering in respect to a normal sedan, but it can be corrected by appling a bit of gas while cornering; so it's not a problem for me. From what I've learnt about torsen differentials they add some understeering because they send more torque to the internal wheels. So, I may found myself unable to "close" while cornering. That's my greatest concern.

Humvees are great vehicles. The torsen they use has a TBR of 1,72; while truetracs seems to have an higher TBR, so I think they will be a little more noticiable. I have been unable to find the exact TBR, sometimes they are said to be 2,5 in the front and 3,5 in the rear but i read those numbers not in any official documentation, so I'am unsure. But they are said to have good "street manners" while used in 2WD trucks, and in fact, your're confirming the same also in AWD trucks.

A couple of interesting videos:
http://video.google.it/videoplay?docid=-4302901886234298355&hl=it
http://www.youtube.com/watch?v=qqruegVRMhY

Sorry if I didn't use the correct technical terms in my post, but I hope that they are at least understandable.

I hope the best for the rest of your staying in Iraq and a quick and safe return home.

Thank for your help.
 

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That will be a great choice. I doubt you will ever notice the front besides maybe in very tight turns or maybe in 4-lo and on pavement. I have an Aussie locker in the back of my Jeep with a 249 and almost never notice it so a Truetrac will be even better.
 

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Discussion Starter #5
Hi Sporer,
very tight turn is my second concern. I have a couple of them to get into my home. They are usually done with no throttle, so since the "locking" properties of the truetrac is proportional to the applied torque, I don't think that they will be a problem.

Just before Christmas I contacted a shop to ask a quote for the installation, but they were closed. I have to wait until mid January.

Thank you for your help.
 

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Hey, thanks for the support, and well wishing. I should be back in the states in about 2 months. And yes, my jeep is a little towards the exteme side, haha. Thanks for the compliments. =)

The understeering your describing is kinda common on AWD, depending on the torque split of the transfer case, in this case the 249 is the viscous coupling, being pretty neutral, until there is slippage. Which is why under throttle, it goes back to neutral steering as the rear recieves power. If it were another transfer case, some are 70/30 front to rear or vice-versa, some have more or less understeer. The torsen shouldnt make that problem any worse, due the the gear driven nature of it. If it were a true "locker" or ratchet type gear (quick lok or aussie locker), u would notice the inside wheel being driven more, applying more understeer.

As for very tight turns, I dont think you'll ever notice it is in there. U-turns are not bad at all, u dont get any "chirpping" or lock-up action at all and turn radius should be un-effected. At most if anything, when you apply hard throttle coming out of a VERY tight turn, you may notice torque steer in the steering. As common with like FWD imports but thats an extreme case.

As for my rear, I left it open for now, I am only running the True-Trac in the front. When i did my gears (4.88) i didnt have the new shafts yet, and with 35 inch tires, the stress of a locker would have broken the stock weak axle shafts.

Let me know if you have any other questions. Nick
 

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Discussion Starter #7
Hi Nick,
I think I have all the information I was looking for. Thank you. Now I have to wait until next month for the shop to re-open. I will keep you informed.

Happy new year to you and to all the great people on this forum :)
 

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Discussion Starter #8
I just found this: http://www.tellico4x4.com/product_info.php/products_id/22431

There are an article and a FAQ, one of the questions is specific to AWD vehicles (short: yes, it could be put in the front). Another one is about "locks up": the answer say that torsen diffs never "lock up", they just transfer tourque between axes. I think it's worth reading it.
 

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I've been looking at the True-trac for the front of my ZJ and trying to decide between the True-trac and a Detriot "soft-locker" for the rear. I have the 242 transfer case and I do run full time 4wd in bad weather. My rig is my daily driver but I also want to be able to run the intermediate level trails, hence at least one locker. Too bad they couldn't sort out the electrac. True-trac with full lock up with the flip of a switch option. That would have been perfect for both ends.
 

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It is doable and Jeep did it in the Quadra Drive II system. The difference is that the LSD that Jeep uses is electronicly controlled so that it can read what the transfer case is doing.

In your case, your front LSD will not get a warning from your transfer case, so it will not be able to anticipate the torque transfer. So, is it likely that you WILL feel the front LSD at times. It will occasionally affect your steering (hard to turn), and might cause momentarly torque steer.

Now, with that said, in my opinion a front LSD will give you a HUGE noticable improvement in traction and capability. Just like every mod, you just to remember that it is there, and learn to anticipate the way it will react to different conditions.
 

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Discussion Starter #11
@Warhorse
I've read many opinions of people who have a couple of truetracs (mostly in TY/YJ). Almost all say that they do not need a full locker unless for doing rock crawling, and even there the brake-throttle-modulation can help sometimes. Putting a locker in the rear and a truetrac in the front seems to be an even more popular set-up, but it is said to be a little tricky in snowy conditions. Never tried myself, it's just the sum of what I read on the argument. For a car like the GC that is used also as i daily drive, I would go for a selectable if you think think that an LSD is not enought.

@Dmntxn77
The QD-I was totally hydraulic and the three differential was independent one from another. But the torque was sent for the most part to the rear by the transfer case. Truetracs may be a little worse from this point of view, the vary-locks are probably set-up for not to engage where the difference of speed rotation between axes is low and act as an open diff, while torsen type diffs react even to these situations.

You score a relevant point, I'm going to try this mod more out of curiosity and willing to learn than out of real necessity. Do you think that if I let someone else drive my GC, she could have some problems ?

Just as a curiosity, in Italy all the WJs sold from the year 2000 had QD-I as standard trasmission and you could buy the actual WK only with QD-II (even Laredos). 4x2 GC has never been sold.

Thank you for your valuable contributions :)
 

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From the article: "You can't run a traditional limited slip or an 'automatic' locking diff on the front axle of a constant 4x4," he says, "but the TrueTrac is a gear-type torque proportioning differential. Instead of having a clutch pack it uses a helical gear set to split torque so there's no sudden transition between it being 'in' or 'out'.
Why can't you use a limited slip in the front? Before reading about the Truetrac, I was thinking of putting a ECTED up front and a Detroit in the rear. Just curious.
 

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@Warhorse
I've read many opinions of people who have a couple of truetracs (mostly in TY/YJ). Almost all say that they do not need a full locker unless for doing rock crawling, and even there the brake-throttle-modulation can help sometimes. Putting a locker in the rear and a truetrac in the front seems to be an even more popular set-up, but it is said to be a little tricky in snowy conditions. Never tried myself, it's just the sum of what I read on the argument. For a car like the GC that is used also as i daily drive, I would go for a selectable if you think think that an LSD is not enought.
I doubt I'll ever go anywhere where I actually need a locker so I'll probably go the Truetrac route front and rear. Most of the trails around here that would require a locker also guaranty body damage and I really don't want to bend up my "baby". Just for what it's worth though, I had a mini pickup truck years ago with a Corvette V8 under the hood and a welded rear out back. I actually drove it through the winter with snow and ice and didn't have too much trouble with it. Yeah, it could get squirrely but I doubt a locker in the back could be any worse. If I was careful, it wasn't really a problem (and it didn't get stuck either).
 

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Discussion Starter #15
Why can't you use a limited slip in the front? Before reading about the Truetrac, I was thinking of putting a ECTED up front and a Detroit in the rear. Just curious.
It may be because in a clutch type LSD the wheel are forced to turn at the same speed by the clutch, or at least the clutch try to slow down the fastest wheel. And this could affect the vehicle while turning. In a torsen diff the wheel can turn at the speed they like, it is just the torque that it is sent in a different manner to the driveshaft. This could affect the vehicle less. But I've found that there so many opinion on this subject (and I have mine, by the way), so it is difficoult to say what he was thinking when he wrote those words.

The ECTED is an interesting piece of engeneering. Some time ago i checked selectables, but I discarded the idea beacuse of the complicated set-up they need (you need to run electric cables and/or air-lines, install switches and so on). And, at the time, I did not even realize that I would have need to strengthen the trasmission !! The truetrac is more easy to install, and I like that.

Bye the way, the Quadra-Drive (I and II) actually has a front clutch-type LSD.
 

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Discussion Starter #16
I doubt I'll ever go anywhere where I actually need a locker so I'll probably go the Truetrac route front and rear.
So we will end up with quite the same set-up. :)

Just curious, did you make the 249->242 swap, or was the latter standard on your car ? Mine came with the 249.

Most of the trails around here that would require a locker also guaranty body damage and I really don't want to bend up my "baby".
Trails here mostly require short wheelbase cars. I bought the GC more because I liked the car than with the intention to do some serious wheeling. Land Rover Defender 90 is the most common choice here for that kind of off-road.

I had a mini pickup truck years ago with a Corvette V8 under the hood and a welded rear out back.
It must have been really fun :D
You must be a powerdrift master :cool:

Happy New Year !!
 

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Discussion Starter #17
I'll probably go the Truetrac route front and rear.
Do you plan to upgrade any other part of the trasmission (driveshaft, axles, joints,...) or will you keep it stock ?

I'm not planning any other upgrade to the trasmission since it is not the V8 and i run stock tyres (225/70-R16).
 

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So we will end up with quite the same set-up. :)

Just curious, did you make the 249->242 swap, or was the latter standard on your car ? Mine came with the 249.



Trails here mostly require short wheelbase cars. I bought the GC more because I liked the car than with the intention to do some serious wheeling. Land Rover Defender 90 is the most common choice here for that kind of off-road.



It must have been really fun :D
You must be a powerdrift master :cool:

Happy New Year !!
Do you plan to upgrade any other part of the trasmission (driveshaft, axles, joints,...) or will you keep it stock ?

I'm not planning any other upgrade to the trasmission since it is not the V8 and i run stock tyres (225/70-R16).
Somebody did the 249 > 242 swap before I got it. Personallly, I like the 242 case better anyway and would probably have swapped it if it hadn't already been done. The only other mod I plan at this stage is swapping out the Dana 35c for a Explorer 8.8 rear I got a couple months ago and then regearing both ends to 4.56 which should put the speedo and everything pretty much back to where everything was stock. Other than eventually the truetracs, maybe stronger axles and u joints for the front Dana 30. The trails around here are pretty mild and I won't go on the ones where body damage is possible (this is my DD after all).

Yeah, I never thought about the "Powerdrift Master" thing. Back then, I don't think anyone thought about drifting. It was just crazy fast (327ci 350hp Vette motor in a 2000lb mini truck) and hard to keep pointed in a straight line. I scared the hell outta myself a few times with it. It kept wanting to swap ends when the rear tires broke loose. :eek:

I had an old Chevy V8 Vega with an even bigger motor that wasn't as squirelly.
 

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Discussion Starter #19
Personallly, I like the 242 case better anyway and would probably have swapped it if it hadn't already been done.
I've read lots of posts on the NAGCA forum before joining it, and I know that there's a little minority that actually likes the NV249OD. They have just hired a new member :D
I like my tcase, I just miss a 4 Part Time position.

Yeah, I never thought about the "Powerdrift Master" thing. Back then, I don't think anyone thought about drifting.
When I was a kid (15/18 years old) I had a "plated dirt bike" (I mean a dirt bike that can go legally on the road, we call them "enduro", I don't know how to traslate), and I spend countless of saturday afternoons with my frind on same dirt road or trails just "powerdrifting". That's why I developed an interest for off-road vehicles, and bought a Jeep.

I had an old Chevy V8 Vega with an even bigger motor that wasn't as squirelly.
That's because it missed a truetrac in the rear end :D
 

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That's because it missed a truetrac in the rear end :D
I don't think the Torsen type differential had been invented yet. It's been at least 25 years ago that I had those two monsters!
 
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