ronjenx

The brake lock differential works on the brakes only. It has nothing to do with the inside of the differential.

BLD is part of the traction control system. TCS can be disabled, but the BLD will remain active.

One of the things the TCS will do is throttle back when you lose traction on both wheels on an axle, which in most cases, the driver would do anyway. The option to shut it off is for those occasions when you want all the wheels to spin a little.

GregD

In the Jeep Wrangler 2009 owner's manual, which covers all Wrangler models, there is no mention of BLD or brake lock differential at all. As far as Jeep is concerned, we don't have anything called BLD on our Wranglers. Also, all of the electronically controlled systems apply to all Wranglers, with some adjustments for automatic versus manual transmission, and with or without the tow package.

There seems to be a lot of confusion of what the different systems on the Jeep do, so here's what the manual says about the various systems. There's a lot more in the manual; I'm just quoting the summaries.

ELECTRONIC BRAKE CONTROL SYSTEM
Your vehicle is equipped with an advanced electronic
brake control system that includes Anti-Lock Brake System
(ABS), Traction Control System (TCS), Brake Assist
System (BAS), Hill Start Assist (HSA), Electronic Roll
Mitigation (ERM), Electronic Stability Program (ESP) and
Trailer Sway Control (TSC). All of these systems work
together to enhance vehicle stability and control in various
driving conditions, and are commonly referred to as
ESP.

Anti-Lock Brake System (ABS)
This system aids the driver in maintaining vehicle control
under adverse braking conditions. The system controls
hydraulic brake pressure to prevent wheel lock-up and
help avoid skidding on slippery surfaces during braking.
Refer to “Anti-Lock Brake System” in Section 5 of this
manual for more information about ABS.

Traction Control System (TCS)
This system monitors the amount of wheel spin of each of
the driven wheels. If wheel spin is detected, brake
pressure is applied to the slipping wheel(s) to provide
enhanced acceleration and stability. A feature of the TCS
system functions similar to a limited slip differential and
controls the wheel spin across a driven axle. If one wheel
on a driven axle is spinning faster than the other, the
system will apply the brake of the spinning wheel. This
will allow more engine torque to be applied to the wheel
that is not spinning. This feature remains active even if
TCS and ESP are in either the “Partial Off” or “Full Off”
modes. Refer to “ESP (Electronic Stability Program)” in
this section.

Brake Assist System (BAS)
The BAS is designed to optimize the vehicle’s braking
capability during emergency braking maneuvers. The
system detects an emergency braking situation by sensing
the rate and amount of brake application and then
applies optimum pressure to the brakes. This can help
reduce braking distances. The BAS complements the
anti-lock brake system (ABS). Applying the brakes very
quickly results in the best BAS assistance. To receive the
benefit of the system, you must apply continuous braking
pressure during the stopping sequence. Do not
reduce brake pedal pressure unless braking is no longer
desired. Once the brake pedal is released, the BAS is
deactivated.

Hill Start Assist (HSA)
The HSA system is designed to assist the driver when
starting a vehicle from a stop on a hill. HSA will maintain
the level of brake pressure the driver applied for a short
period of time after the driver takes their foot off of the
brake pedal. If the driver does not apply the throttle
during this short period of time, the system will release
brake pressure and the vehicle will roll down the hill. The
system will release brake pressure in proportion to
amount of throttle applied as the vehicle starts to move in
the intended direction of travel.

Electronic Roll Mitigation (ERM)
This system anticipates the potential for wheel lift by
monitoring the driver’s steering wheel input and the
speed of the vehicle. When ERM determines that the rate
of change of the steering wheel angle and vehicle’s speed
are sufficient to potentially cause wheel lift, it applies the
appropriate brake and may reduce engine power to
lessen the chance that wheel lift will occur. ERM will only
intervene during very severe or evasive driving maneuvers.

Electronic Stability Program (ESP)
This system enhances directional control and stability of
the vehicle under various driving conditions. The ESP
corrects for over/under steering of the vehicle by applying
the brake of the appropriate wheel to assist in
counteracting the over/under steer condition. Engine
power may also be reduced to help the vehicle maintain
the desired path.

The TCS system uses only the brakes. The ESP system uses the brakes, and can cut power.

GregD

From a mechanical standpoint, there are three different types of differentials used on Wranglers: open, Trac-Lok, and Tru-lok.

An open differential has no locking or limited slip capability, but the TCS system of the Wrangler will still use the brakes to simulate a limited slip capability. On the road, TCS works as well as a limited slip differential like Trac-Lok in my experience.

Trac-Lok is optional or standard depending on the year and model of the Wrangler, and is a traditional limited slip type differential using clutch packs to limit the slip between the wheels. It has only been installed by the factory on X, sport, and Sahara models. The main advantage of a Trac-Lok versus the TCS is that you can spin both wheels in slippery conditions. This can help a lot in some offroad and deep snow conditions. In a very low traction situation, TCS allows the wheels to turn very little. Trac-Lok differentials are always working, but they still work pretty well on the streeet since they allow some slippage between the wheels. Trac-Loks are normally not installed on front axles, since they cause some weird steering effects.

Tru-Lok is standard on all Rubicon models for both the front and rear axles. It is a true locked, or spool, type differential, that rigidly connects both sides of the axle together. For very difficult terrain, this is better than a Trac-Lok which can still allow some slippage between the two sides of the axle. But for the street, locked axles don't work well since they don't allow any slippage between the wheels which causes problems with steering and stress on all of the drivetrain components. When the Tru-Lok isn't engaged, Rubicons have open axles, and only the electronic systems assist the vehicles traction.

ronjenx

GregD,

You used a quote from me when you posted there is some confusion about the electronic features of the JK, and further said there is nothing on the JK called brake lock differential.

Just so you know, I and a lot of other folks are not the least bit confused. The phrase "brake lock differential" is used in this forum because, as shown in your cut-and-paste from the manual, Chrysler has no name for the feature in our manuals.
This is what you posted regarding the feature:
"A feature of the TCS
system functions similar to a limited slip differential and
controls the wheel spin across a driven axle. If one wheel
on a driven axle is spinning faster than the other, the
system will apply the brake of the spinning wheel. This
will allow more engine torque to be applied to the wheel
that is not spinning."

As you can see, they avoid naming the feature. So, it has become accepted by those who wish to refer to the feature to generically call it brake lock differential. I think that is a good name for it because it also gives an idea how it works.

BLD is how the Jeep Engineering Department refers to the feature.

h**p://blog.chryslerllc.com/blog.do?p=entry&id=270

GregD

The way that Jeep is using the TCS in the manual seems to be identical to the BLD. In your link, BLD and "traction control" seem to be used interchangeably. As far as I can tell, TCS = BLD. Your prior post seemed to be confusing TCS with ESP. ESP can be disabled, but TCS remains active.

From the manual -
Maybe I'm missing something. Is there something that TCS does besides BLD?

ronjenx

Yes. TCS will also slow the wheels if the wheels on an axle start to spin together. In most cases, this is the action the driver should take by backing off the throttle. If the driver fails to do so, the TCS will do it by slowing the wheels.
The BLD portion of TCS will only kick in if one wheel is spinning faster than the other wheel on the axle.

Slippery

TJ Rubi's had limited slip rears until locked, but that went away in the new JK 44 design. Don't know why. I felt it was the perfect setup.

I tried an ECTED in an 8.8 once, because I felt a limited slip and locker switch was the ideal setup, but not with an ECTED!

jeepherder

:what ?:That makes it all so clear now

GregD

Oh, I see, now the partial off mode of the ESP makes more sense. So if I need some wheel spin, I can get it by doing the partial off on the ESP, and it still works as if it had a limited slip diff. Nice.

dstock

Damn...look what I started! LOL

This is great information, I really appreciate it. I probably not going to go with the Rubicon as it is overkill for my needs, and the difference in price will buy alot of mods.
So I have been looking at the Unlimited Sport versions and it seems limited slip is hard to find unless you order it, but it seems with the TCS it may not be as needed as in the past. Certainly something I can add later if I change my mind.

Thanks for all the input.