Who would be interested in a...

[aroundincircles]

Locking rear differential?

I think one would be especially interesting to those with FDI.

I'm thinking of asking around to see if anybody is willing to make one, and if its even possible.

[FailWheelDrive]

Reach out to Phantom Grip. They already make a unit that fits the front.

[aroundincircles]

Really.... Hmmm...

[FailWheelDrive]

A Pat with front & rear phantom grips would be pretty sick and waaaaay more capable than with just the BLDs.

I forget how much $ the PG is for the front is but if you multiply that X2, then add up how much work it is to install (or pay someone to do) it's a decent amount of $ and a pretty big job.

Was considering putting a PG in the front of my Pat and gearing it down while the tranny was out but decided to hold off and just buy a more harcore 4x4 (that I still haven't purchased).

My Pat may become a bigger project down the road but for now I should probably just keep it a practical/economical runabout.

[FailWheelDrive]

oh shiz, I should mention that I asked PG about the M5 only and not the CVT... sorry

They may still offer one but I don't know.

Either way it's probably worth asking PG if they offer (or will make) a unit for the rear diff. Not sure but the Pat may share it's rear diff with other vehicles, which could help.

[aroundincircles]

I asked, and I'll see what they say.

[aroundincircles]

ARB is going to look into seeing if this is even doable. Then if it is will be reaching out for interest... I want one, wondering if anybody else would.

[DJohnson]

This may be a dumb question, but what would be the benefit(s) of having a locking rear differential versus the current configuration?

[MrMischief]

Originally Posted by DJohnson

This may be a dumb question, but what would be the benefit(s) of having a locking rear differential versus the current configuration?

Easier to break an axle with a locker.



Unless you drive like this guy.... First is his Jeep with an open front differential, he doesn't say and I can't tell from the video but I believe he has a limited slip differential in the rear. When he's bouncing it, that's also a quick way to break stuff. Second video is with locking front and rear differentials. Tight turns on slick rock (which is very grippy) with a front locked is a good way to break stuff as well. He's using a Dana 3 front axle, which isn't a very strong axle to being with. I wouldn't be surprised if that axle has broken on him by now being that he's using a detroit locker rather than a selectable locker such as an ARB.


This next video shows the difference better although it's not completely fair. The first one up is a JK Unlimited with front and rear lockers. The second one is a TJ with an open front and I believe an open rear along with an inexperienced driver. Why I say this isn't exactly a fair comparison, the TJ is much smaller than the JK and has to take a different line through the obstacle. The lockers probably helped the JK, but it may also have been tire placement.

[FailWheelDrive]

Originally Posted by DJohnson

This may be a dumb question, but what would be the benefit(s) of having a locking rear differential versus the current configuration?

The current set up is open differential(s) with brake lockers. In other words one wheel starts spinning, the computer notices this and applies the brake on the spinning wheel thus applying power to the other wheel.

This is better than nothing, but if you think about it, if you're trying to move forward up a hill/over a rock/through mud having the brakes applied to any of the wheels isn't ideal as it prevents forward movement.

Having locked differentials just means that both wheels spin together. There are different ways to accomplish this.

Companies like Phantom Grip offer a unit that works off centrifugal force, so when one wheel starts to spin a little spring/clutch type of thing in the diff applies force against the other side and causes both wheels to spin.

There are also viscous limited slip differentials that uses the friction of the diff fluid itself to drive both wheels which are pretty cool.

As far as ARB goes I know they sell air lockers where you basically hit a switch that engages a little pneumatic actuator that somehow forces both wheels to engage. Like a locker on demand.

There are also ways to just weld the gears so that both wheels get powered all of the time but it's not a good option for a daily driver as it will hop around corners.

[MrMischief]

I don't mean to nit pick you, but I think it is important to be clear so you can understand why I don't like the phantom grip.

Originally Posted by FailWheelDrive

The current set up is open differential(s) with brake lockers. In other words one wheel starts spinning, the computer notices this and applies the brake on the spinning wheel thus applying power to the other wheel.

This is not an accurate way of thinking about it as it does not apply power to the other wheel. How a differential works is equal torque always goes both wheels. If one tire is on ice and requires let's just say 10 lb/ft to turn, the other tire on solid ground is also only going to get 10 lb/ft of torque. The idea behind the brake-lock differential (Not brake lockers, it's important that this is a differential not a locker) is when one wheel is spinning faster than the other wheel, the system will apply brake pressure to just that wheel. This slows the wheel while at the same time increasing the amount of torque required to spin the wheel, therefore increasing the amount of torque the other wheel also receives. Where it all breaks down is when the brake system stops the spinning wheel entirely. At this point the system says "the wheels are moving at an equal speed, release the brake!" and it begins to spin again. Of course wheel speed sensors are also not perfect so a wheel does not actually have to stop completely before the system is confused, and the brake system can not perfectly feather the individual brake either, and you add in the heat you're generating on the brakes... Overall, like you said, it's better than nothing but far from a perfect solution. Tapping the brake while trying to move... madness. But I'd also say in certain situations (mud for example) you want that tire spinning and cleaning the tread, not slowing down to match the other wheel speed perfectly.

Originally Posted by FailWheelDrive

Having locked differentials just means that both wheels spin together.

Having Lockers means, you've done something to eliminate the differential which forces the wheels on either side of the axle to turn at exactly the same speed.

Originally Posted by FailWheelDrive

There are different ways to accomplish this.

Companies like Phantom Grip offer a unit that works off centrifugal force, so when one wheel starts to spin a little spring/clutch type of thing in the diff applies force against the other side and causes both wheels to spin.

The Phantom Grip is not a locker, it is a limited slip differential. Basically it is two machined squares made out of steel I imagine. Between these two squares are four springs. You push this into your differential. When the wheels turn at a different speed the squares twist in opposite directions pushing outward on the spider gears and the case. This increases friction between the spider gears and the case, increasing the amount of torque required to turn both wheels, so both wheels will see more torque. IMO; You're basically playing a balancing game between the strength of your case and spider gears and how much of a limited slip function you want in your differential. I'm betting you're either going to chew up your spider gears and case, or you're not going to have much of a limited slip effect. On a vehicle with brake-lock differentials, I question if it would even be noticeable.

Originally Posted by FailWheelDrive

There are also viscous limited slip differentials that uses the friction of the diff fluid itself to drive both wheels which are pretty cool.

Essentially you have a stack of clutch disks. Half of the disks are attached the left wheel, half of the disks are attached to the right wheel. In between all of the disks is a silicone-based oil which the disks spin through. When one wheel spins faster than the other wheel it heats up the oil, which expands, forcing the clutch disks together and "locking" the left and right wheel together. Until the oil cools down. This works well because it's a nice smooth transition from open to locked, and when it "locks" it can lock very tight. You'll find this technology in older Grand Cherokees, I think the Subaru STI still uses it. I know it was in the AMC Eagle. One of the problems with this set up in an offroad rig is you can over heat the oil, essentially boiling it. When this happens you have a sudden and complete loss of the limited slip / "locking" action that is only resolved by flushing the fluid and you'll probably need to replace the clutches as well. Well, most of these systems are not serviceable so you end up replacing the entire unit (see the NP 249 transfer case used in the mid to late 90s grand cherokees, great system, but guaranteed to fail and most replace it with a traditional style 231). Another downside to them is that they "eat" a small amount of your power, being that you're basically slowing your drivetrain through a puddle of goo.
[/quote]

Originally Posted by FailWheelDrive

As far as ARB goes I know they sell air lockers where you basically hit a switch that engages a little pneumatic actuator that somehow forces both wheels to engage. Like a locker on demand.

ARB is a selectable locker and has been the locker of choice of wheelers with lots of money for a very long time. By selectable locker I mean that you, as the driver, can decide when the axle is locked. Basically an ARB locker works by you turning on a little air pump which blows against a piston in the differential. This piston locks the side gear to the housing eliminating the differential action. When the air pressure is released, a set of springs moves the piston back to it's original position releasing the side gear. When powered on the pump is set up to provide a certain PSI of air pressure. When it reaches that pressure the pump turns off. Assuming there are no air leaks, the pump will remain off. If there is an air leak, the pressure of the system will bleed off and the air pump will kick on again, hopefully before the locker releases.

Originally Posted by FailWheelDrive

There are also ways to just weld the gears so that both wheels get powered all of the time but it's not a good option for a daily driver as it will hop around corners.

Known as Lincoln Lockers (Lincoln makes welders) welding the differential is the oldest, easiest way to lock your axle. It's also permanent, so it will cause you the most problems. Is it good for a daily driver? I know plenty of guys who daily drive Jeeps that have the rear ended welded. But most "normal" people will hate it.

I think you missed an important type of limited slip / locker set up and that is the gerotor pump. Basically an electric pump is turned on and it pumps hydraulic fluid into the differential to lock the axle. These are particularly awesome IMO because the axle can go from fully open to a more and more aggressive limited slip until finally fully physically locking in a way similar to the ARB. You don't have to worry about boiling fluid, you don't have to worry about air line leaks, and it can be 100% automated by the vehicles computer, but there is also no reason it can't be controlled by the driver. Jeep's Quadra Drive II used this system until I believe 2011. It is my favorite axle system for vehicles that are not intended to be hard core off road machines.

There are also selectable e-lockers which have gained popularity. They are basically an ARB but it uses an electronically actuated mechanism rather than an air compressor. Nice because you don't have to worry about the air lines cracking or coming off, bad because you have low hanging electric bits that you're dragging through the mud and water.


If it were me, and ARB is serious about making a locker for the Patriot I would jump all over that (assuming the axle can take the abuse). I believe the JKs use an electric locker, but my TJ is air actuated, similar to the ARB. It works very well.

[aroundincircles]

Originally Posted by DJohnson

This may be a dumb question, but what would be the benefit(s) of having a locking rear differential versus the current configuration?

Traction. That's it. The patriot IF you have FDII uses the breaks to transfer power from a side that's lost traction to the other side. A mechanical locker, LOCKS the axles together and both wheels get the same power at the same time. Its something you would only turn on in very low traction/rock crawling situations.

the BLD takes a bit to kick in and is not nearly as effective as a real locking diff.

[aroundincircles]

so, if you are interested in a locking diff, Please email ARB at tech@arbusa.com. All they need to know is how interested people are in such a product. enough interest = potential profits = justification to make the product.

[Kenny-g]

I really like the sound of a gerotor pump styled locker that MrMischief was talking about but am sure that would cost just as much if not more than the ARB's would. I'm definitely interested in at least a rear locking diff but wouldn't have the money for that kind of project until next year. What do you think, 'Circles should I mention I'm interested anyway? It'd probably take them a while to do it anyways.


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[Kenny-g]

I emailed them;

Hello ARB,

I have been informed from a friend on a forum that y'all would be willing to produce lockers for the Jeep Patriots if enough people showed interest.

Well here I am! I would be interested in this product (though I wouldn't be able to fit it in the budget until next year due to a lift, sliders, and tires I plan to purchase for my Patriot this year). I think this would be a fantastic product to have available on the market and personally I believe that internationally it would sell very well (specifically in Australia) so if somehow word could be put out there via FB or y'alls international websites, more potential buyers would voice their desires for this. Just an idea.

I don't know if the item would be 2 separate front and back locking differentials or just the rear but I would be very interested in both for my 4x4 FDII packaged Patriot even if I'd have to save up or buy them separately.

Thank you for your time and I hope to hear good things and new products for the Patriots in the years to come!


Sincerely,

Kenny Wilcox


PS some ARB bumpers are due for the MKs (Jeep Patriot and Compass) by now wouldn't you think? They've been around since 2007. That's another thing I would probably buy if y'all made them, just saying.

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