2004 expedition Advance trac vs: limited slip differential
 

According to Ford, a 2004 4X4 with advance trac cannot use a limited slip differential. I deal with lots of snow (Canadian North) and have felt that when stuck in deep snow a standard axle would not provide more than 1 drive wheel in the rear and 1 in front. According to the owners manual when things get tough they recommend turning the advance trac off for better traction in deep snow or mud. For this reason I have factory ordered a 2004 "without" advance trac and "with" limited slip rear axle.

Does ford have anything on the advance trac that would bridge the gap when using a standard rear axle? In view of the fact that I need the truck to perform in deep snow, did I make the right decision to drop the advance trac system in favour of a limited slip rear axle?

Thanks in advance for your input.

Wecome to FTE! I have moved your question to a tech forum.

I believe the Advance Trac is like automatic traction control systems in 2WD vehicles in that when the tires start to spin engine power is cut back and the brake is applied to the wheel that is spinning. In other words if you get caught in a snowbank or stuck you're going to tear up something with either Advance Trac or automatic traction control system on and keep trying to bull your way out,and when switched off you don't have limited slip. That's why I didn't opt for Advance Trac.

Summery of AdvanceTrac:

AdvanceTrac is an innovative new approach to traction control. Traditional traction control systems use variations in individual wheel rotation to determine a vehicle's direction. Depending upon this input, the system then applies brake pressure at selected wheels to help make directional corrections as deemed necessary. AdvanceTrac goes a step further. Not only does it monitor the variations in wheel rotation, there is also a sensor that notes the position of the steering column to determine the driver's desired direction, plus there are other sensors positioned near the centre of the vehicle the yaw or the rotation that the vehicle is experiencing, as well as any lateral or sideway motion. Based on the premise - being better informed leads to better decisions, the system then gathers input from these extra sensors and applies selected brakes to help keep the vehicle on the desired route.

http://www.trentyne.com/driventodriv...vanceTrac.html

Ford Definition:

The optional AdvanceTracTM interactive vehicle dynamics system constantly monitors the driver's steering input and the vehicle's actual direction to help prevent spinouts and fishtailing on tight curves and slick pavement.

Using the vehicle's anti-lock braking system, AdvanceTracTM automatically slows the rotation of individual wheels, correcting oversteer or understeer, to bring the vehicle back to the direction the driver intended.

Re: 2004 expedition Advance trac vs: limited slip differential
 

Hard to argue with a tried and true method of negotiating snow.

I think you made the correct decision.

(And just in case you're wondering, I haven't always lived in Hawaii. ;) I do know a thing or two about driving in the deep stuff.)

Thanks everyone! Well, according to Ford's web site, my wife noted that she could not build the truck with Advance trac and LLS. Since we need to tow a trailer and wanted LLS it made the decision easier and we are happy with the limited slip option.

I hope to comment on all that we learned later but for now we need to busy ourselves with returning my F 150 7700 off lease and a couple of Chevy Astros for the service company.

Speaking of Astros...I wish Ford had a good mini service truck. I would love to drop the Astros in favour of Ford. Ford was happy to extend our Taurus lease while we wait for the new Expedition on factory order.

THANKS FORD for great service and great vehicles!

THANKS FTE!!!

Maybe you won't have to have your limited slip replaced like myself and many others. I hope for you that a lot of the bugs have been worked out in the 2004. If you can, you need to ask not to have the crappy Continental tires. I have had 4 different repairs on my Exp and the tires are the last thorn in my side.

2003 EB 5.4L 4x4:-X09

Good choice. I thought about the advance trac and decided it is for on road, normal driving safety. A great idea, but not for serious offroad or deep sand, mud, or snow. Having two wheels in the air on opposite sides of the truck, one in front, one in rear is a very common situation in rough country due to limited wheel travel. Same as deep snow over ice on rough roads, but air is a lot more slippery! In this case, applying brakes and sensing steering wheel angle isn't going to do anything but make the situation worse, even dangerous if you are climbing up a steep hill of boulders and lose momentum. A low range, locked up transfer case and limited slip will get you out ot there while you control the throttle as needed.
I've spent hours climbing mountain trails and desert washes without ever hitting the brakes because the engine and low gears were brake enough whether all four were on the ground or not.

Where the rubber meets the road, that’s a fact. I’ve had my share of disappointments when it comes to tires. Someone needs to hold the tire manufacturers accountable for their product quality.

A quick history lesson: Picked up a brand new extended cab pickup and found an unusual amount of vibration on the highway. Went back to the dealer and had the tires removed and balanced on the machine. SHAKE, RATTLE AND ROLL! Amplified the problem! Truck dealer sent me to a tire dealer who tried high speed balancing. It’s a machine that marries to the tire and balances it while on the truck. I guess they figured the drums might be out of balance a bit, so they tried to kill two birds with one stone. SHAKE, RATTLE AND ROLL. They could not get the tires to balance for love nor money. Took each tire off and put them on their balancing machine for closer examination. WOW!!! Rolling at low speed with the guard up, you could see the tread wobble from left to right and the surface move up & down… up & down… “Defective tire”, says the specialist. “Let’s try the rest”. Tire # 2… same thing. Tire # 3…same thing. Tire # 4…same thing. Full size spare…not bad. Four out of five tires with manufacturing defects! In case you are wondering what kind, Goodyear Tracker AT. Called Goodyear rep for warranty and they offered to replace the tires with a set of new AT’s. NO THANKS! Truck had about 3000 km so the tire dealer took the warranty replacements and threw them on the shelf and gave me a handsome credit towards Michelin LTX M/S…oh baby! Like coming off a gravel road onto fresh pavement…just like glass!

Jump ahead to my current truck an F-150 7700. I could have died when I saw Goodyear Tracker AT tires on the rims. I figured some time had elapsed and thought by now Goodyear would have worked out the flaws with the AT’S. NOPE! Since it’s a work truck, I reluctantly left them on and rode them out to the sum of 142.000 km. I was surprised that they wore well with moderate tire rotation, however, they thumped and bumped all the way. As they wore, I would move the noisy ones to the rear and grind my teeth.

On another note: Started looking around for tires for one of our service trucks and was told by a tire dealer that the Continental tires were on the bottom of the food chain. They carried Continental and said they would sell me a set, but since I was looking for good advice, they suggested trying something better for the trucks.

The point to all of this: Why?…Why?….Why does Ford or GM etc. put such crap on their vehicles??? Having done the time for someone else’s crime, I know that the tires can kill all the efforts of a truck manufacturer to ensure a smooth ride.

If I worked for Ford, designed a fantastic riding truck, and the tire guy bolted this kind of tire on my design, I would go over to his department and choke the life out of the SOB.
:-rip

Doesn't control trac apply the brake to a spinning wheel?

Just thinking about how a differential works, it seems like that would work better than limited slip. If one wheel is spinning and the other wheel is stationary, slowing down the spinning wheel FORCES the other wheel to turn. That's what a differential does, it distributes the incoming power to the wheels. Slow one down and more goes to the other one.

Limited slip on the other hand just puts friction in between the wheels to resist letting them turn at different speeds. But it can't possibly get past 50% of the power to the wheel with traction. Even a locked rear would be a 50-50 power split.

Seems like control trac *could* put 100% of the power to the wheel with traction, if it was designed right.

As I understand it, Advancetrac is just Control Trac with the factoring in of the steering wheel position and some estimation of what the vehicle must be doing.

I guess I just don't see the downside of an open differential considering the Control Trac/Advance Trac feature.

The way it's been explained to me, the spinning wheel is slowed but there is no mechanism to increase torque to the non spinning wheel. If there were, then it would act like a true all wheel drive where any wheel that is not turning gets the power. That would be ideal, if a system could work that way. There was a time in NM when I thought I was going to be trapped in a moutain gully in my Jeep Cherokee because two wheels were off the ground one front, one rear on opposite corners. One rear wheel was on solid rock and the front on the ground was on loose gravel. Couldn't open the doors for the boulders were too close. The LSD allowed me to rock it back and forth enough to gain momentum to get the front wheel also on solid rock. It'd been nice to be able to put all the power to that one wheel.

But it's impossible to slow the spinning wheel without applying power to the stationary wheel; that's how a differential works. It takes the input from the driveline and distributes it to the rear wheels. It can send all of it to one wheel, or all to the other wheel, or any point in between, but it's gotta come out out the wheels.

For example, with a 3.73 differential, 3.73 turns of the driveline causes 1 turn of both wheels. If one wheel is stationary, the other wheel will turn 2 turns instead. Freeze that wheel and the other wheel will make two turns.

This allows you to go around corners, because the inside wheel has a shorter path and therefore will need fewer turns, and at the same time the outside wheel has a longer path and therefore needs more turns. The differential allows that to happen.

All a limited slip does is put a friction device in place to resist unequal movements of the wheels. Which is why limited slip rears sometimes have chatter problems in turns and need friction modifiers to, well, modify the friction of the clutch pack.

Anyway, considering all this, it sure seems like Control Trac *could* be better ... you slow down a spinning wheel and the other wheel HAS to turn faster (either that or the driveline has gotta slow down). It doesn't rely on the friction of some clutch pack to make the other wheel turn, it's a mechanical connection.

AdvanceTrac
 

Hopefully I can clear up some confusion.
Control Trac is the Torque on Demand 4x4 system. It's purpose is to transfer torque front to rear through the transfer case to the front axle.

AdvanceTrac is the Stability Control system. It's purpose is to provide understeer or oversteer control, and also provides 4 wheel, full speed traction control. The system uses both braking and engine torque reduction to stabilize the vehicle as well as prevent overspinning tires.

AdvanceTrac is not available with a limited slip axle for two main reasons. 1) Limited slip is really not necessary when you have a brake-based traction control system. Limited slip would be redundant, for the most part. The 4 wheel traction control system can transfer up to 100% of the available drive torque to any single wheel, which is superior to either a limited slip or the Control Trac system by itself. It also gives you side to side traction transfer on the front axle, which you don't get with a limited slip rear axle. So if you have 2 or 3 tires with no grip (off the ground, or on a loose surface), then you can still move the vehicle as long as just one tire has grip. 2) Second reason why limited slip is not available with AdvanceTrac is that the stability control system wants to be able to apply brake torque to individual wheels. With a limited slip, some of that braking torque is transferred to the opposite tire, just as drive torque is transferred across the axle to the opposite tire. This is not a desired effect when trying to stabilize the vehicle. Yes, stability control can be done with a limited slip, but the system can provide better control without a limited slip.

When Ford developed the 4 wheel traction control system for it's SUV's, it had the off-roader in mind. A vehicle with the AdvanceTrac system can definately out-climb a vehicle with just a limited slip. Because the vehicle will still climb when just one tire has traction, the system is limited only by the tire grip and horsepower. The only things that will make the Expedition climb better than having AdvanceTrac would be better off-road tires, more horsepower, and maybe things like more ground clearance (if you're crawling over large rocks) or more suspension travel.

ZFMax -- you're right on how the differential works. This is why the traction control system can transfer all available torque by using the brakes to slow the spinning tire.

tsdrallyer -- I think you'd like Ford's traction control system. No need to rock the vehicle to get a rear wheel to find traction. Even just one front tire with grip will still be enough to climb. Any no worrying about wheelslip... just put the pedal to the floor and let the system find the traction.

Another important point, which is why this thread was started... which is better in snow... AdvanceTrac or limited slip. Without question, the AdvanceTrac system is worlds better. It provides superior traction for the reasons I've already stated. The suggestion to turn the system off if the vehicle gets stuck is only if you want to "dig" the tires to what might be solid ground beneath a thin layer of snow or mud. Since the AdvanceTrac system tries to reduce wheelspin, you should turn the system off ONLY IF you actually WANT the tires to spin. If you do happen to get stuck, you are probably better off by leaving the system on, because it provides the side to side and front to rear torque transfer, which is what you want when you are stuck.
One last point on this... on the Ford SUV vehicles with AdvanceTrac, when you press the on/off button with just a momentary press and release of the button, this only shuts off the stability control and engine torque reduction... it DOES NOT shut off the brake-based traction control. THIS IS A KEY POINT of this entire thread. If you should happen to get stuck, or if you are off-roading, by pressing the button with a momentary press, you will have 4 wheel traction control (brake-only) with no engine torque reduction. This gives you maximum engine power and maximum traction at each tire. Putting the throttle to the floor in this case will allow some wheelspin, since the engine is powerful enough to overcome the amount of braking provided by traction control. So if you're stuck, press the button to achieve some amount of wheelspin combined with torque transfer. The owner's manual also explains how to completely shut off the entire AdvanceTrac system by pressing and holding the on/off button for 5 seconds. This disables both engine torque reduction as well as brake-based traction control.

Hopefully some will find this information useful. If you live in a snowy climate, AdvanceTrac is well worth the cost of the option. The first time you experience it's ability to stabilize the vehicle on an ice covered road, you'll agree.

I like Ford Boy 72's response a great deal--I think it is very well thought out. I disagree a bit with the ultimate conclusion, though--and I think intelligent people can disagree on this one. For your on-road applications, and for 99.9% of what most Expeditions do, Advance Trac is a great idea--as a form of traction and stability control. For off-road, however, it still leaves something to be desired. Briefly, here's why:

A 4wd with a limited slip never puts any 'drag' on any tire. Tires may spin in the open air, but the slip limiting device works to shift power around and give it to the tire with traction. At any given time, a tire is either contributing some forward thrust, or no forward thrust, but is never working against the vehicle.

Advance trac, and other brake-based traction control systems, try to control slip by sensing when a wheel is spinning and slowing it with the brakes. If the vehicle was smart enough to know when a wheel was spinning and when it was not, and fast enough to respond, this would be great. Unfortunately, even given the great speed at which the system operates, it is always behind the ball. (I imagine to make the system work well off-road would make it too aggressive on-road...maybe an 'off-road' setting would be helpful.) Off-road, here's what I've seen happen.

Picture an Expy with advance trac climbing a rutted trail uphill. The trail has dips and bumps arranged so that opposite tires are lifted off the ground (LF and RR, then RF and LR, etc). As it goes up the trail, it will lift one tire, and then as it progresses, that tire will come back into contact with the ground. Ideally, the system would apply the brakes progressively as weight on that tire was removed, and would release the brakes progressively as weight returned to the tire. What happens, though, is the system isn't fast enough. Weight is removed from the left rear tire and it starts spinning (and chunking bits of rubber from the tread of the tire). Then, the brakes are applied to the left rear tire. This shifts torque rapidly to the tire on the other side of the axle (right rear)(the tire with traction). This right rear tire then pushes the vehicle forward (with a violent lunge, again, probably stripping some tire off) and the vehicle surges forward. Now, the left rear tire is over the dip, and is back in contact with the ground...but the system hasn't sensed traction at the LR yet, so it keeps the brake applied there, holding the vehicle back. And by now, the RR (with all of the power going through it) is in the air, spinning helplessly. The system then senses slip at the RR, applies brake there, and releases the LR brake...and the vehicle lunges forward again. Lather, rinse and repeat.

Some systems become so hopelessly confused that they start applying both brakes on one axle...or worse.

To see a professional review of this syndrome, see the 4Wheel and Off-Road 4wheeler of the year competition in which they shredded a set of tires on an 03 Expy by using the Advance Trac system off-road.

But I agree it makes perfect sense on-road, and for very light off-road use.

Farmlaw.

I'm no off road expert, but I do consider myself slightly intelligent and here's what I make of it.

Advance track would be better if the system was able to react quickly enough because in your situation, only 50% (slightly more or less, but 50% can be used) of the power is delivered to the wheel (1 wheel on the ground and 1 wheel off in each axle) where the advance track can get 'ideally' 100% of the power on the ground with 1 wheel on and 1 wheel off. Perhaps the flaws are in the implementation of the system, not so much the theory.

On the other hand, I hope my expedition never has any of the tires off the ground, unless it's because of a jack/lift/etc..