How come I can peel out while turning?

[TXAV2003]

So I know our AV's are supposed to have the torque management thing (I forget the official name for it) that prevents us from spinning our wheels when we floor the pedal off the line. So how come I peel out every day when I turn my steering wheel slightly to turn (I mostly notice it when making even a slight left turn). Sometimes I literally sit in 1 place and spin my wheels when trying to turn and have to back off of the gas to get traction.

Now I'm not complaining or anything. In fact, it is helping me to burn through the lousy Goodyear OEM tires faster so I can buy some new Michelins. Just more curious than anything.

 

[orboater]

Heavy right foot

I have to watch for this everytime I go around a corner from a stop.

 

[steelheadchaser]

If you have the locking rear-end the inside wheel is trying to rotate at the same speed as the outside wheel, but has less distance to travel.

 

[sparky]

Try it with a whipple
If there is any water on the road I have to be VERY careful that the back end does not come around to meet me.

 

[n8wrl]

Hmm. I have a Z66 with 'traction control' and I can't make it spin unless I turn it off. I can actually feel it throttle down when I begin to lose traction. Feels kind of weird but I can get it to spin by just poking the 'traction control' button which disables it.

-Brian n8wrl

 

[spork_av]

I think this is more likely to happen on Z71, and especially Z71 with 4.10 ratios. I have been complaining about this for awhile. Then, I decided it was fun. Especially around ricers... scares the crap out of them.

 

[502Hoss=Me]

When I go through town, I have to pull out in front of traffic all the time because it's so crowded. My AV will spin a tire easily (even hitting the gas just a little bit) at any turn, when stopped. Once you get straight though, you can punch it and take off. Kinda embarrasing though when my daughter is with me. Looks like I am being imature and trying to show off by burning my tires. Don't get me wrong though... I Love my POWER! Just wish it didn't spin so easily.

 

[TXAV2003]

Well, I guess I'm not the only one who's noticed this. I thought that the Torque Management System completely prevents our AV's from spinning our tires in order to save the tranny, but maybe it only works when the front wheels are pointed straight and the gas pedal is floored. I haven't tried it lately, but I'm pretty sure the TMS prevents my AV from burning rubber off-the-line when the front wheels are pointed straight. But all I have to do is turn the steering wheel a little to the left or right and I'm standing still burning rubber.

 

[green02]

Two different things are being discussed here. One is the limited slip differential (the culprit), and the other is the traction control system (not present on any 4WD model). These are the only traction aids present on Avalanches.

The traction control uses a throttle retard to prevent/limit wheelspin and will work regardless of steering input. It's nothing more than an anti-idiot system for people who don't know how to modulate a throttle.

The limited slip differntials used in these trucks are Torsen (torque sensing) or Torsen-style differentials. Very basically, when one wheel spins faster than the other, the differential transfers a certain percentage (based on the torque bias or torque multiplication ratio) of power to the other wheel. This ratio can vary, but is generally between 2:1 and 5:1. BTW, that ratio is a maximum. A 4:1 Torsen is capable of transfering up to 4 times the torque to the other wheel.

There are two disadvantages to this style of diff. First, they require some resistance (read: grip) to work (any ratio times zero torque is still zero, right?). So if you've got one wheel in the air or on glare ice, they don't work very well. Second, they require a difference in wheel speed. So, you have to be spinning one wheel before the diff. does anything.

The predominant advantage is that the diff. operates more like an open rear when not under load, which means better fuel economy, no corner entry push, and that it's harder to break both tires loose in a corner (resulting in a possible spin, which the lawyers don't like).

Your truck is working normally.

Brock

 

[jusjoshn]

I have an idea Try slowing down lead foot. The life you save may be your own!

 

[ShapeShifter]

Two different things are being discussed here. One is the limited slip differential (the culprit), and the other is the traction control system (not present on any 4WD model). These are the only traction aids present on Avalanches.

There is also Tourque Management built into the powertrain control computer. This is a software feature that prevents the sudden application of torque to the driveline. Even if you mash the pedal to the floor from a start, the engine will not leap to life, but will "roll on" gradually. This generally prevents the truck from doing smokey burnouts. There is also some reduction in power when shifting gears.

This is not a closed loop "traction control" which either limits the power, or applies the brakes when wheels are detected to be slipping. Torque Managment is an open loop system with no feedback from driveline sensors.

The traction control uses a throttle retard to prevent/limit wheelspin and will work regardless of steering input. It's nothing more than an anti-idiot system for people who don't know how to modulate a throttle.

True.

The limited slip differntials used in these trucks are Torsen (torque sensing) or Torsen-style differentials. Very basically, when one wheel spins faster than the other, the differential transfers a certain percentage (based on the torque bias or torque multiplication ratio) of power to the other wheel. This ratio can vary, but is generally between 2:1 and 5:1. BTW, that ratio is a maximum. A 4:1 Torsen is capable of transfering up to 4 times the torque to the other wheel.

There are two disadvantages to this style of diff. First, they require some resistance (read: grip) to work (any ratio times zero torque is still zero, right?). So if you've got one wheel in the air or on glare ice, they don't work very well. Second, they require a difference in wheel speed. So, you have to be spinning one wheel before the diff. does anything.

This is at odds with my understanding of things.

The Z-66 and Z-71 (and I think NFE?) have Eaton mechanicall locking differentials, they are not limited slip. There is a spinning governer inside that is driven by the difference in speed of the two axles. When that difference is more than 200 RPM, a mechanical lock is engaged, and you have essentially a solid rear axle with no differential action at all.

By personal experience, this works even when one wheel is on glare ice. You hit the gas, even lightly, and that wheel begins to spin while the truck does not move. A second later, the rear end locks with a clunk, and full power is applied to both wheels. The truck then accelerates smoothly away.

Sometimes, it takes a while for the diff to unlock. Shortly after pulling away from a curb where one wheel was on glare ice (and locking the diff) I had taken a turn, and the inside wheel was chirping and hopping through the turn because the diff had not yet unlocked: it was essentially a solid rear axle, and the two tires did not like being forced to turn the same speed around the turn.

Not an automotive engineer, just talking from my personal experiences with the truck. And, also from watching a video on the Eaton site where they talk about the diff in our trucks, it works very well with one wheel completely off the ground: the other wheel gets full power, and the raised wheel does not spin out of control.

-- SS

 

[speeder]

green02, your explanation is greatly appreciated. I have been to the eaton site and read many posts about the rear end in our avs and have always been left with 1 major question. When I was in the sand with my Z71 I had 1 rear tire in the air and the other just sat on the ground doing nothing. Why?? I know the eaton is supposed to lock but in my own (non-engineer) personal experience, I had to be towed out by a ford and I have not yet heard the end of it from my "buddies"

 

[s5uewf]

Not trying to be a PITA but I am confused by this:

"So if you've got one wheel in the air or on glare ice, they don't work very well. Second, they require a difference in wheel speed. So, you have to be spinning one wheel before the diff. does anything."

If I have one wheel in the air or on glare ice I have one wheel spinning - so
shouldn't the LSD kick in? With any type of LSD or locker, once one wheel
is spinning, any transfer of torque should send some power to the
other side of the differential (other wheel) - right?

I also thought the Eaton was a positive locking assembly driven by
a fly spring/weight which engaged a locker in the diff when
differences in the speeds of the two sides of the exceeded a certain point. I was
fairly sure the Eaton is not an LSD unit...?

Just trying to understand the whole setup.

Emery

 

[ShapeShifter]

Here is information on the Eaton G80 locker, straight from the source: The Eaton Locker?When the Three Most Important Words Are Traction, Traction, Traction

There are a couple of interesting movies on that page. The one where the Suburban is crossing the ditch is particularly interesting: notice that at times it is balancing on two wheels, and it still has power with two wheels in the air.

Finally, take note of this comment:

Where can I buy a mechanical locker?

The Eaton Locker is option code G80 Locking Differential on GM light trucks and SUV's. Go to Chevrolet, GMC, Cadillac or Oldsmobile websites for more information.

The G80 is the diff on the Z-71, Z-66, and I think the NFE.

I particulary like the flash animation that is used on the intro page of the Eaton traction site: Where Others Fear To Tread. Check it out.

-- SS

 

[steelheadchaser]

The G80 is the diff on the Z-71, Z-66, and I think the NFE.

You are correct, SS. The NFE has all the off-road goodies of the Z71 package, including the G80 locker.

 

[n8wrl]

Hmm. If you were stuck in sand with one wheel spinning and the other motionless it seems you have an open diff. I know my Z66 has the locker because I've heard (more like felt) it lock up and I've seen the effect. Once I was half on a cement drive with one tire in mud. When I gave it some gas the tire in the mud spun for a second or so before there was a slight 'klunk' and the other tire engaged pulling me out.

I'm not as familiar with the Z71 package - are we sure it has a locker? Or, is that an option? I seem to recall a locking differential listed as an option but I'm not sure about the packages.

-Brian n8wrl

 

[docopharm]

I'm not as familiar with the Z71 package - are we sure it has a locker? Or, is that an option? I seem to recall a locking differential listed as an option but I'm not sure about the packages.

-Brian n8wrl

From Chevy site:

AVALANCHE Z71 4x4
Build It
4x4 starting at $38,285*

Key standard features include everything standard on Avalanche 1500 plus:


Autotrac 4x4 system
46mm specially tuned shocks
Z71 suspension
One-year OnStar(1) Safe & Sound Plan
Locking rear differential
17-inch wheels and tires
High-capacity air cleaner
Skid plates
Deep-tinted rear window glass
Rubberized vinyl floor mats

1 Call 1-800-ONSTAR-7 or visit onstar.com for system limitations and details.

 

[ShapeShifter]

I'm not as familiar with the Z71 package - are we sure it has a locker? Or, is that an option? I seem to recall a locking differential listed as an option but I'm not sure about the packages.

I know my Z-71 has it, from similar experiances.

If anybody want;s to confirm that they have one, look at the list of three letter option codes on the label on the glove compartment door. If it lists "G80" you have the locker.

When I was in the sand with my Z71 I had 1 rear tire in the air and the other just sat on the ground doing nothing. Why?? I know the eaton is supposed to lock but in my own (non-engineer) personal experience, I had to be towed out by a ford and I have not yet heard the end of it from my "buddies"

If you have the locker, (you should on the Z-71, look for the code) and you have experiances where one rear wheel spins on slippery surfaces, it's broken. Get it fixed.

-- SS

 

[bekind]

I must agree withthe majority here. I am fairly confident the locker I have works perfect when one tire is in the air. I know this from experience and have seen it work outside the truck while playing around. Once the airborne tire started to spin, you can hear and feel the locker kick in. I am/was impressed with how it works. i have been in many situations where my roomies 4x4 explorer has sat in gravel or mud and spun only a single front and single rear wheel. I am at a loss as to why they call it 4x4, seems more like 2 wheel drive to me!

~bekind

 

[TXAV2003]

I was invited to test drive various GM vehicles a few years back on some road courses they set up at Texas stadium. One course was an "off-road" course they set up that had various ditches and hills, etc. They designed it to show how the Chevy Tahoes and Suburbans with locking differentials were superior to the Dodge Durango 4x4's with limited slip diff, Toyota Sequoia 4x4's (with traction control and limited slip diff), etc. when only one wheel in the rear had traction. The other vehicles did indeed get stuck in various parts of the course and either had to be pushed along or you had to rock the vehicles back and forth (drive-reverse-drive-reverse) until they got free. And of course, the Tahoes and Suburbans did not, as long as one rear wheel was on the ground. You could actually feel the rear diff locking up and pushing the vehicle along until the front wheels were back on the ground and gaining traction. It was a pretty cool demonstration.

BTW, my Z-71 also has the G80 option (as it should) and I have felt the diff lock up when it is wet as well. But I guess the question I have for Shapeshifter et. al. is whether the TMS that Shapeshifter discussed above (and which I was ineptly trying to refer to on my 1st post) somehow disengages when you turn the steering wheel, hence allowing you to peel out like a drag racer even when you don't floor it. Just curious since I've read many other posts where guys like JonBoy, I believe, have gone to custom programming to totally eliminate the TMS.

 

[green02]

There is also Tourque Management built into the powertrain control computer. This is a software feature that prevents the sudden application of torque to the driveline. Even if you mash the pedal to the floor from a start, the engine will not leap to life, but will "roll on" gradually. This generally prevents the truck from doing smokey burnouts. There is also some reduction in power when shifting gears.

Guess I stand corrected- I was not aware of this. The owner's manual forgot to mention this...

This thread really took off. In glancing through the replies, I see some references to the OEM diff's being provided by Eaton. If this is correct, then my explanation may not apply (I'd have to look at one). The explanation is accurate for a Torsen diff.

There is a spinning governer inside that is driven by the difference in speed of the two axles. When that difference is more than 200 RPM, a mechanical lock is engaged, and you have essentially a solid rear axle with no differential action at all.

A mechanically locked, solid diff is very hard on the drive train. I can't say you're wrong, Shapeshifter, but I'd surprised if an OEM used a solution like this today. It also does not jive with my experience.

If I have one wheel in the air or on glare ice I have one wheel spinning - so
shouldn't the LSD kick in? With any type of LSD or locker, once one wheel
is spinning, any transfer of torque should send some power to the
other side of the differential (other wheel) - right?

There's several different kinds of differentials. And a locker is not the same as a limited slip. I could spend a day describing various diff's, so I'll just answer your question regarding the Torsen.

The internal gears in a Torsen diff. have to bind (I know that sounds bad, but I can't think of a better way to put it) in order for the diff. to transfer power. This requires both a difference in speed and a resistance on both sides. If one wheel is in the air, there's no grip or resistance. To counter this effect, torsen does offer a race version with a clutchpack to provide some resistance even when a wheel is off the ground.

In 2002, limited slip diff(s) were included with the Z66/Z71 packages. I don't think this changed for 2003. This would mean Speeder's truck has locking diff's.

Brock

edit: found and followed the Eaton link...

My work computer won't let me view their nifty video, but I did read through the discription.

Sounds like these diff's are essentially a mechanically activated clutch pack. This makes sense. The clutches will slip, allowing wheels to turn at different speeds through a corner and avoiding drivetrain wear. Looks like engagement is also limited to very low speeds (<20mph) to prevent damage.

Without a better description of this "flyweight governor", there's no way to know whether this diff. is dependent on a resistance at both wheels for operation, or not.

 

[Tree_Hugger]

Limited Slip diffs are better than open diffs offroad.
Torsen diffs are also better than open diffs offroad. It is debatable whether limited slip diffs are better than Torsen diffs offroad.
Locking diffs (lockers) are substantially and unequivocally better than limited slips or Torsen diffs offroad, but may have adverse effects on non-level icy surfaces. Torsen diffs are a better choice for a purely on-road vehicle, because they avoid the off-camber ice problems of lockers.

I definitely prefer manual rather than automatic lockers (and view them as essential on front axles), but of automatic lockers I find the Eaton speed-sensing type. a better compromise with on-road use.

The Av uses the Eaton G80, and the Eaton website's explanation of it's operation is outstandingly clear and specific. It's a locker, not a Torsen diff, there's no ambiguity on that, it does not require resistance at both wheels for operation, and it's an appropriate choice for an automatic locker for an on-road vehicle that is expected to also perform well off-road.
FWIW, The function of the Torque Management is not to prevent burnouts (though it tends to have that effect), but to prevent shock loading of the drive-train given a very heavy vehicle and a somewhat marginal transmission (adequate, but by no means over-engineered).
HTH.

 

[green02]

Limited Slip diffs are better than open diffs offroad.
Torsen diffs are also better than open diffs offroad. It is debatable whether limited slip diffs are better than Torsen diffs offroad.

Torsens are limited slip differentials. The term "limited slip" applies to any number of brand and style differentials that limit a difference in wheel speeds. "Lockers" are a special category of limited slips that are designed to not only limit, but completely eliminate, any difference in wheel speeds.

The Av uses the Eaton G80, and the Eaton website's explanation of it's operation is outstandingly clear and specific. It's a locker, not a Torsen diff, there's no ambiguity on that, it does not require resistance at both wheels for operation, and it's an appropriate choice for an automatic locker for an on-road vehicle that is expected to also perform well off-road.

No, the link ShapeShifter provided (thank you, BTW) provided a general description of how it works, but no real details: Where is the "flyweight governer" attached (what internal movement allows it to spool up)? How fast can the governer spool up for repeated locking/unlocking situations? How does the diff. disengage? When does the diff. disengage? What prevents the diff. from locking above 20mph?

Where exactly does it say resistance from both wheels is not required? You're quite possibly right, but the simple fact that it is not mentioned does not make it true. The website is nothing more than a marketing tool. It uses proprietary terms like "flyweight governer" that we can interpret, but still have no real understanding of their operation. The only really useful bit of information comes from this statement:

"During lockup, a self-energized clutch system causes a cam plate to ramp against a side gear. This ramping action compresses those disc packs mentioned earlier."

We can guess those disc packs are clutch discs, and surmise the diff is simply an inertially activated clutch. Regardless, this description specifically precludes the diff from being a locker.

Brock

edit: re-worded for clarity and brevity

 

[ygmn]

Agent MAXWELL posted this in the 2500 performance section but may help some..may confuse others....

national drivetrain

 

[Tree_Hugger]

We can guess those disc packs are clutch discs, and surmise the diff is simply an inertially activated clutch. Regardless, this description specifically precludes the diff from being a locker.

Brock

edit: re-worded for clarity and brevity

I'm now dropping out of this thread, as it appears to have turned into an argument about semantics, not engineering.....

I'll just add one more piece of info, in case anyone finds it useful..

I don't believe 'flyweight governor' is a proprietary term. They've been around since the mid 1800's. The original, and simplest, widely used form was as a shaft-speed steam/pressure venting device on steam engines. These needed to be run on vertical shafts and were very effective and not very efficient. Later developments used multiple weights, spring closing instead of gravity, and could be used on horizontal shafts. Efficiency was dramatically improved by controlling fuel feed (in controlled combustion engines - internal or external) rather than steam pressure. This was later 'simplified' into 'throttle control' as engine speed control became more sophisticated.
I hope this helps everyone's understanding (that's a good thing, right? )

Peace and understanding to all...