80 in ice & snow + question re CDL

[Grench]

I did a lot of experimenting with this on the audis at Steamboat (vacuum operated, but same style dog clutch). I could predict within 10 feet - an unlock and a lock event with a quick throttle blip. I ran a ice rallycross using this method for the rear diff - center always locked. 10 feet before a turn, lift off brakes, hit CDL off, blip throttle, disengaged CDL, back on brakes. Then, at apex, hit CDL on, blip throttle, hit gas hard. Worked great!

Within 10 feet at 20mph you would have 0.3 seconds to do your activities.
Within 10 feet at 40mph you would have 0.15 seconds to do your activities.
The CDL from most experience here takes 'a couple of seconds' to engage or disengage.

Math is fun.

What works/is fun on a track will throw you and the 5 cars behind you into the ditch as they panic from your erratic driving. It is irresponsible to drive this way on public roads.

 

[Walking Eagle]

I did a lot of experimenting with this on the audis at Steamboat (vacuum operated, but same style dog clutch). I could predict within 10 feet - an unlock and a lock event with a quick throttle blip. I ran a ice rallycross using this method for the rear diff - center always locked. 10 feet before a turn, lift off brakes, hit CDL off, blip throttle, disengaged CDL, back on brakes. Then, at apex, hit CDL on, blip throttle, hit gas hard. Worked great! I've tried this with the 80 CDL swich, it works the same. Remember, the motor has a spring tension load on the dog clutch, it's just waiting for no-load equal driveshaft rotation. Hence the warning not to engage while wheels are slipping.

I think you need to re-write this. First you say you use it for the rear diff, with the center diff always locked. Then go on to talk about locking and unlocking the center diff, which you just told us you always had locked. Are you talking about locking and unlocking the CDL, or the rear locker? As it is, it really is confusing.

Specific to low mu, I think the CDL on is going to give better control - that's even what most folks here agree with....

I agree with firetruck41, speak for yourself. Toyota disagrees, and says that unlocked gives "BETTER VEHICLE CONTROL".

In an open diff, 50% of the power goes to the front wheels all the time.

Huh? Open diff the power is going to go to the wheel with the least traction. If your front diff is open, center diff is completely open (no viscous coupling), and rear diff is open, and you raise one tire off the ground - the vehicle isn't moving.

A locked Center diff will run 50% of power front and rear. Then you have to raise one front tire and one rear tire off the ground to stop movement.

please, someone other than me correct this.....

Car & Driver - July 1986

"The VW system, which is now in production in the Vanagon Syncro, incorporates a multiplate viscous coupling instead of a center differential. The coupling automatically distributes torque to the front and rear as needed, like a limited-slip differential. Nearly all of the torque goes to the front wheels if the rears are on glare ice, for instance. On dry surfaces, only about three percent of the torque gets mailed tip front.

In contrast, the Audi system tends to send the torque toward the end of the car with less traction-unless the center differential is manually locked, forcing a 50/50 split. VW engineers prefer their simpler (and probably less expensive) system and will use it with future 4wd models."

Car & Driver seem to understand.

Sorry Sumo, this isn't a matter of opinion, it's a matter of fact. This

In an open diff, 50% of the power goes to the front wheels all the time.

Is an incorrect statement, in fact, it's 100% backwards.

 

[Romer]

I have temporarily closed this thread.

I have asked nicely to stop the pissing contest.

 

[Romer]

Now that we hav had a cooling off period. The argument back and forth is OVER. It detracts from the thread.

SUMOTOY has expressed his opinion for all to read

Walking Eagle has expressed his opinion for all to read.

I would like to opportunity for others to post to this thread without worrying about getting between folks in a very old argument.

 

[IdahoDoug]

Wow.....

I'd like to state for the record that this thread started as "use CDL in high range on ice and snow - yes or no?" and that I feel the answer should be no. Anytime you cause the front and rear axles to fight each other on a slippery surface due to the different rotational speeds they must have when the vehicle is turning, you are reducing available traction for directional stability. Sure, if you're in competition, are driving like a maniac or otherwise not subject to the standard of safe operation on the public roadway there may be a use for it. But when driving around on snowy conditions with the intention merely to get somewhere and home safely - don't use the CDL. The 80s ability to be driving all 4 wheels yet allow for different axle speeds is a safety advantage on slippery roads that part time traditional 4wd systems do not have. They use a transfer case that's essentially a locked diff and exhibit all manner of handling ills on slippery roads. Giving this advantage away doesn't make sense.

DougM

 

[lovetoski]

Wow.....

I'd like to state for the record that this thread started as "use CDL in high range on ice and snow - yes or no?" and that I feel the answer should be no. Anytime you cause the front and rear axles to fight each other on a slippery surface due to the different rotational speeds they must have when the vehicle is turning, you are reducing available traction for directional stability. Sure, if you're in competition, are driving like a maniac or otherwise not subject to the standard of safe operation on the public roadway there may be a use for it. But when driving around on snowy conditions with the intention merely to get somewhere and home safely - don't use the CDL. The 80s ability to be driving all 4 wheels yet allow for different axle speeds is a safety advantage on slippery roads that part time traditional 4wd systems do not have. They use a transfer case that's essentially a locked diff and exhibit all manner of handling ills on slippery roads. Giving this advantage away doesn't make sense.

DougM

When I posted up the initial question, I didn't realize I would cause such a stir. I learned a bit though, only some of it about my 80 and a CDL!

Doug - your summary makes sense to me, especially in the context of all the other posts - thanks.

Peace.

 

[Klunky Chris]

…..really what it boils down to is this:
the great thing about your 80 is that you can buy the CDL switch for not too much money (it's good to have for a number of reasons that have nothing to do with this thread ) and it's super easy for you to install.

As with any vehicle, I'm a believer in the school of thought that *any* vehicle you drive in bad weather/ snow should be put through its paces by YOU. Get in a safe parking lot etc and throw the truck around so you can get the feel of it. This is good to do with any vehicle. Try it with and w/o the CDL. Then get on some safe back roads and try it there while being very careful.

If you install the CDL, you can try it both ways and make up your own mind.
I really don't recommend learning how your truck reacts with CDL when taking the kids to school though!!

 

[Walking Eagle]

SUMOTOY has expressed his opinion for all to read

Walking Eagle has expressed his opinion for all to read.

and 92LC_good2go has expressed Toyota's opinion via owners manual.

 

[92LC_good2go]

and Steph (Stephanie) has expressed Toyota's opinion via owners manual.

fixed it ^ for ya




I agree with Klunky Chris that one should endeavour to test out one's own vehicle and one's own response(s) in a safe manner and place/time.

 

[landtank]

I use the CDL on occasion. That occasion is usually when I'm driving on covered roads in the 8 - 10" of snow range at slow speeds. I feel I have more control.

Now that's not to say that someone else in that same situation would have more control with the CDL off but since I'm behind the wheel I have better control with it on and that's all that counts.

All this theoretical talk is BS as far as I'm concerned. While it's a good guide line, do whatever makes you more competent behind the wheel. That's your best chance of getting yourself to where ever it is your going safely.

If you can pilot these 6,000 pound machines more safely with the CDL on then do it. But since some feel that having it off is better you might go down to that vacant lot and give it a go.

 

[CoveredInRedMud]

...you might go down to that vacant lot and give it a go.

Hard to argue there. The best thing I ever got from K-Mart was their empty parking lot after a Salt Lake 24" overnight snowfall, just after I had gotten my 80. Hidden parking space concrete stoppers and all, I learned a lot more in half an hour than reading for half a day...

 

[Walking Eagle]

Hey all - One last post on this thread for me. The FAQ has some great links on this stuff, if your interested in facts.

http://www.safari4x4.com.au/80scool/george_couyant/diffs/diffs.html

http://auto.howstuffworks.com/differential2.htm

 

[92LC_good2go]

Hard to argue there. The best thing I ever got from K-Mart was their empty parking lot after a Salt Lake 24" overnight snowfall, just after I had gotten my 80. Hidden parking space concrete stoppers and all, I learned a lot more in half an hour than reading for half a day...

Me too!


How funny is that. We both did the same thing... at the same chain. (that's all they're good for?)



We got snow overnight, too, and I just came back from our local K-Mart. I went back to playing in the snow pre-plow, with my 80 early this morning.

I won't start the argument again, but I did "play" with CDL and turns, short stops, starts from dead stops, etc.

And I wasn't the only one out there -- doing the exact same thing, I noticed.

 

[Tym@work]

Okay... this has gotten my curiosity up. Not sure how many of you guys own cruisers other than an 80, but it seems to me that the CDL on position is just like a 40 or a 60 series in 4x4, right? I have each of those and can tell no steering or cornering difference when in 4x4 as opposed to 2wd (no locker in front). The tire slippage in turns should be in the front and rear diffs, thus without either of those diffs locked it's still open and tires left and right of each other can turn at different speeds. So IMHO the CDL makes no difference in turning much like a classic cruiser in 4wd sans lockers.

Am I totally off base??

 

[SUMOTOY]

A couple comments from me here.... There seems to be some confusion on my position of CDL. *IN MY OPINION* there is no reason CDL can't be run in the on position. I've attempted to explain vehicle dynamics and experiences/documentation to support that opinion. I understand it's not popular, and many folks don't agree with it. I'm quite fine with that actually. IF all these threads do is make folks try it, I've already done more than I expected!

Do what you are comfortable doing. If CDL confuses you, or makes you uncomfortable, don't touch it. AWD in the 80 works really well. In fact, IMO, get a set of Blizzacks for the winter, and you will have more winter traction than CDL with a lot of other tires.

Regarding differential operation, I look at Post 122 and have the *opinion* that how differentials work isn't understood by many. An open differential always allocates engine torque 50/50, that is just a fact.

A locked differential differs in that it allocates torque such that either axle is *capable* of supporting up to 100% of engine torque. In a straight line with a center diff locked, engine torque allocation will follow vehicle weight transfer up to wheel spin. That is also a fact.

What gets confusing, IMO, is that the marketing boys have done a lot of crossbleeding of terms, concepts and wording to support a chassis dynamic statement. Audi (thank you) is one of the worst violators. A lot of this has to do with the torsen differential, which is a very complicated differential in dynamic operation. It shares some characteristics with an open diff (allows wheel speed differences) and a locked diff (torque follows weight transfer in a straight line). The Haldex (4motion) coupler also has a unique set of dynamic characteristics for the marketing boys to spin.

Add in traction control, stability control, Select Low/Select High ABS, throttle control to a variety of differentials, it's a free for all in the marketing (and quite often: engineering) departments, IMO. I see it all the time in print, many rags and websites buy into some of this as well.

What's the answer? IMO, it's getting the basics down, and then applying all this to YOUR skilset level. IMO, Electronics can be helpful, but we must understand that most of the electronics are designed to account for flaws in hardware and driver. I always advocate that if the hardware is given, reduce the flaws in the driver by education.

That said, I'm off to Steamboat Center for Driving Sciences Ice track next week to work on some chassis dynamics on ice. I look forward to the break, and will post up some pics and vids when I can.

ST

 

[Walking Eagle]

Regarding differential operation, I look at Post 122 and have the *opinion* that how differentials work isn't understood by many. An open differential always allocates engine torque 50/50, that is just a fact.

ST

I'll concied that the common terminology of a locked center diff giving 50/50 split is confusing. I say common terminology cause magazines have refered to it in that manner for years. Seems like you're willing to buy that.

The part that is missleading when you just flat state the engine torque is split 50/50 and end it at that, is that it gives the reader (me) the impression that the available engine torque (say engine generates 100 ft*lbs for easy math), is applied 50/50 (50ft*lbs each side, or front rear depending on which diff your talking about). In reality, it's not necessarily 50/50 of what the engine can make. It's 50/50 of the engine torque UP to the point that a tire slips, in which case they are both equal to what the tire has the least traction.

Here, from the how it works site I linked earlier, and you subsiquently pm'd me:

"Remember that the open differential always applies the same torque to both wheels, and the maximum amount of torque is limited to the greatest amount that will not make the wheels slip. "

and from Diffs for dummies link:

"An undesirable phenomenon with diffs is that the drive exerted on both shafts is the same amount as that of the shaft (wheel) with the least traction. "


So, if one of the tires is in the air, and it only takes 1 ft*lbs to spin that tire, then the opposing tire is also only getting 1 ft*lbs, which isn't enough to move the vehicle.

I'll admit I was off on terminology. The EFFECT that the driver sees is still the same.

Open front and rear diffs, with an open center diff (we have Viscous Couplers on 80's, so we don't really have an open center diff). Lift one tire off the ground. If it takes 1ft*lb to spin that tire, then all the torque the other three tires see is 1ft*lb. The vehicle doesn't move.

Lock the center diff. Lift one rear tire, and one front tire. We can see that with 80 series either with the CDL switch, or by putting in low range CDL. Classic ditch crossing, or ramping on RTI ramp in loose ground. It takes 1 ft*lb to spin the rear tire in the air, and opposite rear tire gets 1 ft*lb. It takes 1 ft*lb to spin the front tire in the air, and opposite front tire gets 1 ft*lb. The vehicle doesn't move.

So, when you're saying that the front always gets 50% of the torque, what it's really getting in mixed mu (I hate that term, how about in an unequal traction surface?), or really anything but dry pavement, is torque equal to the torque required to spin the tire with the least traction, unless of course that required torque is more than the engine can apply (which is where we are on dry pavement with only 275ft*lbs of torque available, and more than enough traction to support it).

Can we aggree on this?

 

[Walking Eagle]

More interesting links

This has a need little annimation showing exactly what I described:

http://www.howstuffworks.com/four-wheel-drive1.htm


and the previous page has a nice little animation too....

http://www.howstuffworks.com/four-wheel-drive.htm

and this interesting statement

"As soon as they start to slip, the torque drops down to almost zero."

So I'll admit that the torque is equal, but it is almost equal to zero. And as far as accomplishing anything, like work (work requires not only a force, but movement), or moving the car, it might as well be zero.

 

[SUMOTOY]

The part that is missleading when you just flat state the engine torque is split 50/50 and end it at that, is that it gives the reader (me) the impression that the available engine torque (say engine generates 100 ft*lbs for easy math), is applied 50/50 (50ft*lbs each side, or front rear depending on which diff your talking about). In reality, it's not necessarily 50/50 of what the engine can make. It's 50/50 of what the tires can support.

That's not a correct statement. In my PM, I gave the formula for the open diff as
T1 + T2 = Trg
T1 = Torque axle 1
T2 = Torque axle 2
Trg = Torque ring gear

I always use Torque RING GEAR because we have a variety of variables that affect what constitutes T1/T2 and Trg, specifically, engine output, throttle position, gearing, friction, traction, and recently "equivelent traction" (ABS and/or Traction control). So a statement that it's 50% of what the *tires* can support isn't correct. You can have an open diff, with two tires in the air, apply the brakes (defines EDL) and increase Trg with the slipping tire supporting the exact same tractive torque.

Here, from the how it works site I linked earlier, and you subsiquently pm'd me:

"Remember that the open differential always applies the same torque to both wheels, and the maximum amount of torque is limited to the greatest amount that will not make the wheels slip. "

and from Diffs for dummies link:

"An undesirable phenomenon with diffs is that the drive exerted on both shafts is the same amount as that of the shaft (wheel) with the least traction. "

Neither is technically correct to an open diff vehicle Heath. I might rephrase #1 to read:
"Remember that the open differential always applies the same engine torque to both driveshafts, and the maximum amount of torque to both axles is limited to 2 times the axle with the lower supported torque"(sic)

In Diffs for dummies:
"An undesireable phenomenon with open diffs is that the drive exerted on both shafts is the same amount of that of the shaft (axle) with the least amount of total supported torque." (sic)

The terminology is off, and those definitions can't account for an EDL open diff or you putting your foot on the brake when a wheel spins. We could go further and explore over the center axle EDL, but I believe the Torque Ring Gear is correct terminology, and T1 and T2 can include EDL, friction, gearing, traction and all the other variables to TOTAL AXLE SUPPORTED TORQUE.

It is incorrect to claim Tire or traction, as EDL or braking intervention is not a dependent variable to *traction* or *tire*.

I'll admit I was off on terminology. The EFFECT that the driver sees is still the same.

I don't believe the terminology is correct, nor is the effect that the driver sees is the same. EDL dictates that torque generation isn't a tire or traction variable in an open diff.

Open front and rear diffs, with an open center diff (we have Viscous Couplers on 80's, so we don't really have an open center diff). Lift one tire off the ground. If it takes 1ft*lb to spin that tire, then all the torque the other three tires see is 1ft*lb. The vehicle doesn't move.

Agree

Lock the center diff. Lift one rear tire, and one front tire. We can see that with 80 series either with the CDL switch, or by putting in low range CDL. Classic ditch crossing, or ramping on RTI ramp in loose ground. It takes 1 ft*lb to spin the rear tire in the air, and opposite rear tire gets 1 ft*lb. It takes 1 ft*lb to spin the front tire in the air, and opposite front tire gets 1 ft*lb. The vehicle doesn't move.

Rephrased in the formula for an open center diff and open front and rear diffs....
T1 = (Tright front axle + T left front axle)
T1 = (1lb/ft + 1lb/ft)
T1 = 2lb/ft
T2 = (T right rear axle + T left rear axle)
T2 = (1lb/ft + 1lb/ft)
T2 = 2 lb/ft
T1 + T2 = Trg
2 + 2 = Trg
Trg = 4

Trg is exactly allocated 50% T1 and 50% T2 ALWAYS

So, when you're saying that the front always gets 50% of the torque, what it's really getting in mixed mu (I hate that term, how about in an unequal traction surface?), or really anything but dry pavement, is torque equal to the torque required to spin the tire with the least traction, unless of course that required torque is more than the engine can apply (which is where we are on dry pavement with only 275ft*lbs of torque available, and more than enough traction to support it).

Can we aggree on this?

No. The definitions need to be changed, specifically TRACTION is not necessarily a variable to an open diff. Total supported axle torque is.

Heath, if take and open diff axle and put one axle in the air with available engine torque at 260lb/ft, and you can generate 130lb with brake force, the torque to the other axle is 130lb/ft, even in mixed mu! The tire has the same *traction* and Trg = Teng!

This is how these concepts are presented in SAE papers. IMO, you have not presented an open diff concept correctly. Traction can be a variable to Trg. This concept doesn't require EDL, only putting your foot on the brake when you have a wheel in the air. BTDT many times in my 4R when wheeling.

Edit: I recently had a dyno run on a hub mounted dyno. No wheels or tires attached, and both the front and rear axles are in the air. 350RWHP on an audi quattro with open center diff. Heath, the using your terminology, that couldn't be done!

HTH


ST

 

[Romer]

This thread is about the CDL on ice and snow. An old argument has appeared in this thread and other threads and I am done with it.

I have instructed the participants to PM their arguments back and forth or start their own thread and keep the name calling out of it. I have no issue with the back and forth discussion as long as it is civil.

WHAT I HAVE ISSUES WITH IS DRAGGING THIS INTO OTHER PEOPLES THREADS TIME AND TIME AGAIN.

 

[Walking Eagle]

Sorry All

Sorry guys, I thought we were real close to getting consensus on it.


Sorry for the continued sideline, just really wanted to get consensus I guess.