Truetrac in the front axle

Solar Dude

Solar Dude

New member
Trying to give a buddy of mine good advice. He's got a 2015 JKU Sport with an automatic with 3.73 gears. He had the dealer install a 3.5" pro comp lift and 315/70-17's. He is also towing a somewhat large pop-up trailer, 2500lbs. As you can expect his towing performance is less than ideal, I finally talked him into getting new 4.56 gears. I recommended he install a new differential since he's getting the gears done. It's his DD and he isn't doing anything too radical yet but we are tossing around the idea of doing the Rubicon next year. With that said he's not going to throw down for air lockers, nor would he be thrilled about installing something that would negatively affect the JK's road manners like a full locker, I.E Detroit locker. My first question is how well does the factory limited slip work and is it worth re-installing? Second, has anyone here installed a truetrac in the front axle before? I had one in the rear of one of my service trucks and it worked great, no bad road manners or clunking or knocking. My idea was the best bang for the buck was to leave the factory limited slip in the rear and install a trutrac in the front. Or should he just shit can the factory limited slip and install the truetrac in back and leave the front open? For what it's worth we drive a lot in the snow here in the Sierra's too, so if the truetrac in the front would negatively affect that he probably wouldn't be happy.
 
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He shouldn't listen to you either.

4.56 won't be what he wants. He is running a big tire. He will want at least 4.88's and a locker would be a waste since he doesn't wheel.
 
The Factory limited slip in the rear works pretty well. It takes getting used to.
2011 Sahara with front auto locker and rear Lsd, can do most the trails in Moab with no problem shy of the more extreme ones. So with your friend not wheeling much the rear Lsd is more than good enough.
 
OverlanderJK said:
He shouldn't listen to you either.

4.56 won't be what he wants. He is running a big tire. He will want at least 4.88's and a locker would be a waste since he doesn't wheel.
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I disagree, 4.56 puts him at 2544 rpms at 70. This is still 200 rpms higher than the factory set-up of 3.73 and 31's. 4.88's will have him well above optimal engine speed at hwy speeds, if he was a dedicated rock crawler that would be different. I told him he needed new gears and not engine mods, I recommended 4.56's but gave him the tools to research it on his own and he came up with the same conclusion. The argument could be made that heavier weight of the tires and pulling the trailer would justify the lower ratio but like I said, the 4.56's are still a lower ratio than the stock set up. Also, 80% of the time he's just commuting to work with it. It's all about compromise, there's no perfect set-up for everything. Compared to his 3.73's it will be a huge upgrade.
 
xflstl said:
The Factory limited slip in the rear works pretty well. It takes getting used to.
2011 Sahara with front auto locker and rear Lsd, can do most the trails in Moab with no problem shy of the more extreme ones. So with your friend not wheeling much the rear Lsd is more than good enough.
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It's good t0 know that the factory LSD works pretty good, it's probably best he sticks with the factory diffs until he gets more serious about off-roading.
Thanks!
 
Solar Dude said:
I disagree, 4.56 puts him at 2544 rpms at 70. This is still 200 rpms higher than the factory set-up of 3.73 and 31's. 4.88's will have him well above optimal engine speed at hwy speeds, if he was a dedicated rock crawler that would be different. I told him he needed new gears and not engine mods, I recommended 4.56's but gave him the tools to research it on his own and he came up with the same conclusion. The argument could be made that heavier weight of the tires and pulling the trailer would justify the lower ratio but like I said, the 4.56's are still a lower ratio than the stock set up. Also, 80% of the time he's just commuting to work with it. It's all about compromise, there's no perfect set-up for everything. Compared to his 3.73's it will be a huge upgrade.
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Gotcha, you are a self proclaimed expert. All makes sense now.
 
To answer the OP's first question..... The rear factory LSD works ok, like others said, it takes some getting used to. By that I mean that the driver needs to understand not to let off the gas when a wheel starts spinning, maintain the same gas pedal pressure and then the power will eventually transfer to the wheel with more traction. As far as reliability....not so much in my case. I pulled my rear LSD last weekend and replaced it with a Truetrac. The LSD spider gear teeth were chipped and some of the clutch packs were falling out, my Jeep only has 23k on it, I had re-gear done about 15k ago, and I haven't wheeled it too hard.

The OP's second question...I also installed a Truetrac in my front diff last weekend, I have a 2014 JKUS automatic with 4.56 gears. Whats your question exactly?

Truetracs are not auto lockers, they don't put your Jeep into limp mode, they don't have any quirky binding or traction control issues. I will say that the Truetrac in the rear is far more effective at transferring power than the factory LSD, and both tires spin at the same time with the Truetrac as long as both wheels have contact with the ground. I played in the sand last weekend and confirmed that both wheel spin at the same time providing some really good traction, not a full lock, but great alternative to a full locker.

Regarding the 4.56 gear ratio, they work great for me. If your friend is going to be towing a trailer 4.88 wouldn't hurt. As others have mentioned, you are allowed to disagree but if you come on a forum asking for advice then you should expect different opinions in return. If you already know the answer why did you post in the first place?:hmm:
 
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Honor2afault said:
Or, quite possibly, it's asking for honest advice and then saying that advice is wrong because you've already come to a conclusion from which you are unwilling to veer away from.
Just a thought.
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I wasn't asking for advice on the gearing, that's simple math. I was asking for personal experience with the factory LSD and installing trutracs in front differentials.
 
Jeepfan30 said:
To answer the OP's first question..... The rear factory LSD works ok, like others said, it takes some getting used to. By that I mean that the driver needs to understand not to let off the gas when a wheel starts spinning, maintain the same gas pedal pressure and then the power will eventually transfer to the wheel with more traction. As far as reliability....not so much in my case. I pulled my rear LSD last weekend and replaced it with a Truetrac. The LSD spider gear teeth were chipped and some of the clutch packs were falling out, my Jeep only has 23k on it, I had re-gear done about 15k ago, and I haven't wheeled it too hard.

The OP's second question...I also installed a Truetrac in my front diff last weekend, I have a 2014 JKUS automatic with 4.56 gears. Whats your question exactly?

Truetracs are not auto lockers, they don't put your Jeep into limp mode, they don't have any quirky binding or traction control issues. I will say that the Truetrac in the rear is far more effective at transferring power than the factory LSD, and both tires spin at the same time with the Truetrac as long as both wheels have contact with the ground. I played in the sand last weekend and confirmed that both wheel spin at the same time providing some really good traction, not a full lock, but great alternative to a full locker.


Regarding the 4.56 gear ratio, they work great for me. If your friend is going to be towing a trailer 4.88 wouldn't hurt. As others have mentioned, you are allowed to disagree but if you come on a forum asking for advice then you should expect different opinions in return. If you already know the answer why did you post in the first place?:hmm:
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Thanks, this is exactly the info I was looking for. To restate, I was asking for personal experience with factory LSD and a trutrac in the front diff, I never asked for help with the gears.
 
Solar Dude said:
I wasn't asking for advice on the gearing, that's simple math. I was asking for personal experience with the factory LSD and installing trutracs in front differentials.
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Because the real world means math is absolute right? If you're so concerned about math, how about you go back to math 101, and understand the simple concept of variables. Yes, 4.56s are perfectly fine in NJ...nice flat roads, no elevation, stock jeep, excellent. Now add in steep grades, elevation, added weight from maybe a winch, armor, a fat wife, large testicles, etc...add in some heat, add in larger rotational mass, and, oh, a fvcking 2500lb trailer and suddenly your math doesn't quite add up. The worst part about a "friend" like you is you're going to fvck your friend royally, and then scratch your ass in his face saying "that's odd, according to the math, you should be 200rpm above factory, and factory was fine, I don't know what could be wrong."

Finally, unless your friend is driving in tons of snow and ice, having a diff in the front axle is sort of a waste. Putting one in both axles will give you a similar feeling of stability on the road like an audi or a subaru...which is fine for road driving in alaska, not sure how necessary it is in Nevada, although you do live in northern nevada, so he'll have to make that call.


But hey, you weren't asking for advice on gears, so maybe show your friend this thread and let him make the call eh?
 
315/70/17 tire is about 34"...5 sp auto 5th gear is .83...with 4.56 gearing, your rpm at 70 mph is 2618...with 4.88 gearing, rpm at 70 mph is 2800. You would get better gas mileage with 4.56, but you would have better power with 4.88 (especially uphill, not to mention towing, which means a lower cruising speed as well)...and with 4.88, better crawl ratio offroad.

Put the locker in the rear and leave the front open if your trying to save money (put a locker in the front later when you can afford it)...and when you can afford it, go up to 35" tires...it will lower your cruising rpm as well.

Check out this site for gearing/tire size/crawl ratio info... http://www.novak-adapt.com/knowledge/gearing/
 
NFRs2000NYC said:
Because the real world means math is absolute right? If you're so concerned about math, how about you go back to math 101, and understand the simple concept of variables. Yes, 4.56s are perfectly fine in NJ...nice flat roads, no elevation, stock jeep, excellent. Now add in steep grades, elevation, added weight from maybe a winch, armor, a fat wife, large testicles, etc...add in some heat, add in larger rotational mass, and, oh, a fvcking 2500lb trailer and suddenly your math doesn't quite add up. The worst part about a "friend" like you is you're going to fvck your friend royally, and then scratch your ass in his face saying "that's odd, according to the math, you should be 200rpm above factory, and factory was fine, I don't know what could be wrong."

Finally, unless your friend is driving in tons of snow and ice, having a diff in the front axle is sort of a waste. Putting one in both axles will give you a similar feeling of stability on the road like an audi or a subaru...which is fine for road driving in alaska, not sure how necessary it is in Nevada, although you do live in northern nevada, so he'll have to make that call.


But hey, you weren't asking for advice on gears, so maybe show your friend this thread and let him make the call eh?
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Mic drop.......
 
Brute said:
315/70/17 tire is about 34"...5 sp auto 5th gear is .83...with 4.56 gearing, your rpm at 70 mph is 2618...with 4.88 gearing, rpm at 70 mph is 2800. You would get better gas mileage with 4.56, but you would have better power with 4.88 (especially uphill, not to mention towing, which means a lower cruising speed as well)...and with 4.88, better crawl ratio offroad.

Put the locker in the rear and leave the front open if your trying to save money (put a locker in the front later when you can afford it)...and when you can afford it, go up to 35" tires...it will lower your cruising rpm as well.

Check out this site for gearing/tire size/crawl ratio info... http://www.novak-adapt.com/knowledge/gearing/
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Higher RPM doesn't mean worse MPG. TPS is the only thing that matters when it comes to MPG...throttle position sensor. If you had 3.00 gears, and your engine was at 600rpm on the highway, and you needed to mash the pedal to the floor to get the jeep to pass, you would dump a WOT amount of fuel even though you are barely moving. The load is what matters. With 4.88 gears, the LOAD on the engine is lower, so you need to use LESS throttle to achieve the same amount of force required. With 4.56 gears, you would need to add more throttle (more fuel) to achieve that same amount of force...say passing from 50-70. There are CERTAIN times where 4.56s will give you better mpg, but unless you are driving MOSTLY highway and MOSTLY 75mph+, changes are, you will not have better MPG with the 4.56s, they would be roughly about the same, or not even perceptible. For someone looking to tow, it's not even a contest, the 4.88s are the clear way to go.
 
NFRs2000NYC said:
Higher RPM doesn't mean worse MPG. TPS is the only thing that matters when it comes to MPG...throttle position sensor. If you had 3.00 gears, and your engine was at 600rpm on the highway, and you needed to mash the pedal to the floor to get the jeep to pass, you would dump a WOT amount of fuel even though you are barely moving. The load is what matters. With 4.88 gears, the LOAD on the engine is lower, so you need to use LESS throttle to achieve the same amount of force required. With 4.56 gears, you would need to add more throttle (more fuel) to achieve that same amount of force...say passing from 50-70. There are CERTAIN times where 4.56s will give you better mpg, but unless you are driving MOSTLY highway and MOSTLY 75mph+, changes are, you will not have better MPG with the 4.56s, they would be roughly about the same, or not even perceptible. For someone looking to tow, it's not even a contest, the 4.88s are the clear way to go.
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when I changed tire size from 35's to 37's prior to regearing from 4.10 to 4.88, I was doing mpg calculations for 4 months...my fuel consumption was far better with lower rpms with 4.10 than with 4.88...that's my personal factual experience....
 
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