Chevy & GMC Vans

timelessbeing wrote:or going somewhere else.

well what fun would that be.
on a serious note how often do you here of the clutches failing in these TC's i never thought about it until someone mentioned it recently

Well, I don't see myself doing a lot it.

Come to think of it-how often I am supposed to change it...and is the ALL trac the best stuff?

You'll know because the van will start to bind and hop in tight turns. You could always take a fluid sample. If it looks like coffee, it's time to change it.

I use GM Autotrak II. It costs $5/quart.

Check out the inferior AWD systems on these SUV's from off-shore companies.
http://www.youtube.com/watch?v=t09ExAUgtyE

It seems odd to me that they created a large hump of several inches for the rear wheels to drive over, just as the fronts reach the low traction area...

john

It should be no problem for an AWD vehicle. Roads in the real world aren't perfectly smooth.

Being in the science community myself, I like looking at the way experiments are set up and the biases that are inherent to each experiment...
Considering that the hump is unnecessary, and that they attempt to keep it off camera makes me suspicious. It makes me think they are purposely trying to bias the results

john

It looks like the hump is there to keep the vehicle from rolling off backwards, and I don't think it's being intentionally hidden. The only significance is that a bit more torque is required in the rear wheels to overcome the hump. A bias would be something that specifically favours one vehicle over another, but since they all have to get over it, it's a level playing field. It's just a little hump, and it shouldn't pose an unfair problem.

I still felt like they were doing something to make the subies do it better. That being said. I would have liked to see more vehicles on the "ramp" for comparison. Like say a "real" 4wd with manual TC and lockers front and rear. But then there would have been a different winner ... eh..

but it does make one wonder about those active systems and how much they really help.

I think the idea was not to find a "winner" of who can get up the ramp, but rather to compare how different AWD systems work, and observe the effects they have. For example, I really don't like the electronic traction control that makes the asian vehicles go side to side. The VW didn't do badIy. In my opinion, 4WD is in a category of its own and cannot be compared, although it seems the distinction in contemporary vehicles is being blurred more and more.

I would also like to see them test more different systems. There are quite a few out there. A Quattro may have even matched the Legacy.

One interesting point the video brings up, is how manufacturers don't disclose technical details any more. They hide behind catch phrases and buzz words, that don't actually MEAN anything, but to someone who isn't mechanically inclined they sound really high tech. And every manufacturer has their own proprietary names, so it's impossible to compare them. For example, see if you can find detailed information on the Chevy Express 1500 AWD.

It was also interesting how important weight distribution is, and I think it speaks to the advantage that Astros have. Namely, a longitudinally oriented engine, and lots of weight over each wheel. (something pickups don't share). That's what makes vans sure-footed like a goat. However, if only one front wheel has traction it still won't go anywhere.

I have a driveway with a hump at the the street. The hump is the height of a normal curb but rounded so the city didn't have to build driveway entrances for every house.

Anyway, I have tried it with the rear on snow or the front on snow, one axle gets me over the "hump".

It' isn't a Subaru..but I will take it for less money and tire wear. Oh, and quieter.

timelessbeing wrote:The encoder motor isn't an ordinary motor like in a cordless drill. It's not driven by steady current.

Your transfer case isn't part-time 4WD. It's an active on-demand unit, that automatically sends just the right amount of power, at the right time, to the front wheels through a clutch. The clutch is actuated by the encoder motor, but a simple on/off switch is not precise enough to deliver little bits of torque. Instead, the motor is regulated by the transfer case control module (TCCM) which sends a pulse width modulated (PWM) signal thousands of times per second (think ABS). Putting a steady current to the encoder motor would be like pulling the trigger on your cordless and then stopping it from turning.

More sophisticated transfer cases like the NV236 do allow you to switch to 4WD. To do this, the encoder motor closes the clutch and then locks. Current to the motor can then be turned off.

I had to rebuild my NV136, ordered new clutch assembly, seals, etc and have the job done.
Working on it I noticed that it would be fairly easy to replace input shaft, add planet, linkage and encoder motor from NV236. So it would be effectively NV236 swap which gives me, if I understand correctly, additionally 4WD mode to the existing AWD mode.
The question is: how to plug it into my Astro ? Is it enough to replace TCCM and add a switch ?
Has anybody done this maybe ?

I think a clutch locking mechanism is needed for 4WD. The encoder motor can't run all the time.

Yes, I know - the encoder motor has to be replaced for the two way one from NV236. And internal linkage has to be changed to allow locking. I have verified that everything needed fits from 236.
I am worried about TCCM which has to be taken from another car (Blazer ?) and how it would work in Astro.

timelessbeing wrote:Check out the inferior AWD systems on these SUV's from off-shore companies.
http://www.youtube.com/watch?v=t09ExAUgtyE

Not sure how I missed this post way back when... although I think a defeat switch doesn't provide any real benefits so probably wasn't following it... but I did find this video interesting.

But after the video concluded, this one popped up.

[youtube]http://www.youtube.com/watch?v=X3i9_m5vGGI&noredirect=1[/youtube]

Granted, it is a different generation CR-V, and may or may not be the same as the like-year U.S. model, but it shows the system worked. (I've actually been looking for this generation CR-V to possible tow behind our motorhome, hence my interest in whether the AWD system really works.)