Brake Lock Differential (BLD) techniques for open diff (non-locker & non-LSD) JLs

[AcesandEights]

I emailed them maybe three weeks ago and asked, when I saw Tommy was selling his Jeep. I never received a response, but within a couple days they did it with their First Edition Bronco.

@TFL you ever do the roller test with a stock, or modified, JL?

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[Cyber_Jeeper]

@TFL you ever do the roller test with a stock, or modified, JL?

I haven’t seen a roller test on a Wrangler yet. But the 4Runner and bronco did well so I expect the Jeep would too.
You can watch roller tests or off-road in videos of many CUV’s to get an idea of how it works and it’s limitations. On flat ground they work ok. But once you start pointing it uphill it has a hard time putting enough torque to the wheels.
The Wrangler should be similar. It’s not magic. Assuming it works similarly to every other implementation, I agree with the previous posters that steady throttle is needed. Some vehicles needed 5-10 seconds of throttle before it could pull itself out.

 

[Speed331]

Pretty good advice from an off road instructor on using BLD vs Lockers...skip to 1:50 for the good stuff



Great video of a bone stock sport being super capable:

 

[Capt. Don]

You probably shouldn't have both lockers engaged in that scenario. Locking the fronts severely impacts your ability to control where it goes.

BLD can't do anything useful with a locked axle. Of the two tires there's not one that's getting less traction.

Makes sense.

 

[Capt. Don]

You probably shouldn't have both lockers engaged in that scenario. Locking the fronts severely impacts your ability to control where it goes.

BLD can't do anything useful with a locked axle. Of the two tires there's not one that's getting less traction.

Yes, you are right. 2009 in a new JKR. An unexpected snowstorm in June lying over a hard patch of ice on Webster Pass taught me why running with both lockers engaged in off-camber low traction trails with nothing but perdition for a couple thousand feet below you is a terrible idea. I was fortunate to learn that lesson without mishap. Good lesson about watching the weather around you and deciding when to turn around or hunker down were also reinforced that day (same as we do at sea, we call it weather awareness). Took a well built TJ with winch to pull me off the trail edge that day. Lessons well learned.

 

[Capt. Don]

Nothing you said is technically wrong, but it is important to note for most readers that the Jeep Wrangler JL LSD is not a torque biasing limited slip differential. It is a clutch pack based differential which has some minimum torque between the wheels it maintains, before it allows differentiation. This torque is based on the preload in the clutch pack and friction.

BLD probably will work a lot better with a torsen than it does with a clutch pack style LSD.

I keep thinking that Eaton’s newly available for JL axles Detroit Tru-Trac gear driven LSD installed front and rear on my JLUHT M210 Wide HD front and M220 Wide rear would be an interesting upgrade for my BLD system to work with.

 

[Wabujitsu]

I know it’s just a photo, but when I had my Sport I had to traverse this. Ahead of me was a dirt wall I had to climb. Folks watching could see my BLD at work, and I cleared the obstacle.

 

[Wabujitsu]

BLD also allowed me to do this; very off-camber, tread packed with clay, passenger rear tire off the ground. By the way, 33s with a 3.5” lift. Note that I stuffed the one front tire.

Thatis @Roky ’s Rubicon in the background of the final pic.

 

[five9dak]

I keep thinking that Eaton’s newly available for JL axles Detroit Tru-Trac gear driven LSD installed front and rear on my JLUHT M210 Wide HD front and M220 Wide rear would be an interesting upgrade for my BLD system to work with.

Having owned and used OEM style clutch pack LSD in a 9.25 on a drag/street truck, then replacing it with a truetrac - there is no comparison, the true track is a huge upgrade.

The more torque you can apply to the pinion, the harder it locks up.

Unlike the clutch pack styles which only give you a set amount of lock up (enough to help without making parking lot maneuvering a problem.)

 

[five9dak]

Might just be differences in terminology, but any limited slip differential I have heard of are rated the same in regards to the torque bias. I think I know what you are saying but any LSD is technically torque biasing, and I think you mean the difference between a clutch style unit and a gear driven/torsen style like a True Trac. I'm not saying you are really wrong or anything, and the explanation of using the brakes to get a torsen style "working" versus a preloaded clutch setup is accurate. How aggressive, or how much power it can transfer to the the other wheel, is based on the bias ratio. A lot of factory LSD's are pretty mild and have lower bias ratios like 2:1 or 2.5:1. Basically they can only keep both tires on a axle spinning if there is a relatively small traction difference between them. For example the difference between one tire being on dry pavement and one on wet pavement where both will "spin". However if one side in in deep slick mud and the other on pavement there is a good chance only the side in the mud will spin and you are stuck. Good aftermarket LSD's typically have higher bias ratios meaning that there can be a much greater difference in traction between the tires and they can keep them spinning. However there is always a limit on a LSD where the traction difference is so great it can't bias enough torque to the other side to get the vehicle moving. Generally if one tire is in the air and requires almost 0 torque to spin you won't get enough torque to the other side to get going.....after all, zero times any number is still zero..... That's when full locking differentials come into play.

I don't believe a clutch pack style LSD increases lockup torque with increasing pinion input torque. In fact, to verify their operation, they are tested with zero input torque, by using a torque wrench to measure the torque to differentiate one wheel while the other is stationary - this torque is simply measuring the static friction in the clutch pack.

You can change the minimum torque to differentiate by changing the clutch pack preload, material, or the oil and its friction modifier or lack thereof. For example if you use conventional oil without modifier and add none, the parking lot manners will degrade, because the minimum torque to differentiate went up.

I would love to be proven wrong, but I have owned and serviced / installed four clutch pack mopar LSDs in various vehicles as well as an eaton true track. The last person who I had this discussion with failed to produce any documentation that the JL diff was anything more than a simple preloaded clutch pack, a style that has been around for decades.

When you apply increasing input torque to a torsen, especially in a high powered RWD vehicle on pavement, you can feel the lockup increase in proportion to the increasing applied torque. With a clutch pack style the opposite is true, you can feel the lock up staying the same, and wanting to push out less with increasing torque in a turn, as the inside wheel overcomes the preloaded static friction in the clutch pack, and begins to one wheel peel.

I quickly attempted to find some literature about plate/clutch type LSDs being referred to with a bias ratio, and I was not able to. This makes sense to me, since their lockup torque is not related to input torque.

The major pitfall of a torsen in an offroad application is that if one wheel is lifted, you get the bias ratio times zero, which is zero torque transmitted. However BLD can mitigate this pitfall. It is surprising to me this wasnt the implementation in the JL, I suspect for cost reasons. The TJ rubicon was equipped with a rear locker / torsen combination unit, that's the only one I know of.

 

[6.2Blazer]

I don't believe a clutch pack style LSD increases lockup torque with increasing pinion input torque. In fact, to verify their operation, they are tested with zero input torque, by using a torque wrench to measure the torque to differentiate one wheel while the other is stationary - this torque is simply measuring the static friction in the clutch pack.

You can change the minimum torque to differentiate by changing the clutch pack preload, material, or the oil and its friction modifier or lack thereof. For example if you use conventional oil without modifier and add none, the parking lot manners will degrade, because the minimum torque to differentiate went up.

I would love to be proven wrong, but I have owned and serviced / installed four clutch pack mopar LSDs in various vehicles as well as an eaton true track. The last person who I had this discussion with failed to produce any documentation that the JL diff was anything more than a simple preloaded clutch pack, a style that has been around for decades.

When you apply increasing input torque to a torsen, especially in a high powered RWD vehicle on pavement, you can feel the lockup increase in proportion to the increasing applied torque. With a clutch pack style the opposite is true, you can feel the lock up staying the same, and wanting to push out less with increasing torque in a turn, as the inside wheel overcomes the preloaded static friction in the clutch pack, and begins to one wheel peel.

I quickly attempted to find some literature about plate/clutch type LSDs being referred to with a bias ratio, and I was not able to. This makes sense to me, since their lockup torque is not related to input torque.

The major pitfall of a torsen in an offroad application is that if one wheel is lifted, you get the bias ratio times zero, which is zero torque transmitted. However BLD can mitigate this pitfall. It is surprising to me this wasnt the implementation in the JL, I suspect for cost reasons. The TJ rubicon was equipped with a rear locker / torsen combination unit, that's the only one I know of.

So to be clear, I think there is some differences in verbiage so not really trying to say you are wrong or argue but rather just adding some more comments and my opinion.

In regards to "bias ratio" being applicable to all LSD's or just torsen/gear style, I quickly found multiple articles on the web that use bias ratio to depict how much "power" or how "tight" any style of LSD is. In Google I simply typed in "bias ratio of clutch type LSD" and there are pages of threads and articles that come up and it's clear they are referring to any type. Again, might just be a difference in verbiage as you seem to be talking about input torque being part of the equation. I have always considered bias ratio the ability of a LSD to transfer power between the right and left tire. The bias ratio can change or increase based on the input torque, but the input torque doesn't really relate to the bias ratio in a constant manner. Granted, the torque between the left and right tire is always a percentage of the input torque....if you are at idle with basically no input torque than obviously there is not torque between the left and right side tires. Again to be clear, depending on the exact style of LSD increasing input torque can change (normally increase) the bias ratio between the left and right side due to mechanical motion.
There are also different types of clutch style LSD and not all are preloaded. There are some types of clutch style LSD's that only start apply pressure between the clutch packs, and thus causing a bias ratio, based on input torque and thus the bias ratio can increase as input torque is increased. The input torque itself does not cause the bias ratio, but it causes some mechanical action ins some designs that changes it. Preloaded simply means there is something like a spring putting constant pressure between the two clutch packs all the time and doesn't require some amount of input torque to engage. The difference is that one style can actually increase the bias ratio as you apply more power and keep both tires spinning and lock up more, where as in some cases like a simple preload design the bias ratio does not increase and as you put more power to the wheels you can basically overcome the LSD ability to spin both tires. I believe this is basically saying the same thing in a different way as the poser I quoted.

 

[five9dak]

I was mis understanding / mis remembering bias ratio - thanks for straightening me out.

Do you know if the JL LSD unit is a static preload or one which increases clutch force with input toque?

 

[jimcoffey62]

curious to hear from anyone who has installed a helical LSD (tru trac) in their JL

 

[AA_Jeeper]

Well now I have a night of reading ahead of me... Glad I found this.

 

[azwjowner]

curious to hear from anyone who has installed a helical LSD (tru trac) in their JL

There’s lots of us. What do you want to know? I put one in the rear. It works great but I already knew it would because I had one in my last Jeep.

@ArmyRN has one in the front and rear. For the front you must disable FAD.

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