TOD and no rear driveshaft....

Last year I felt my VX was pretty spooky on ice, but part of that was getting on roads with a good "dome". I was about to slide sideways into the curb so I had to stay centered on the crest. I don't have ABS and the rear end tried to swing around on me at the slightest touch of the brakes. It was bad enough that it made me reconsider my position on fixing my ABS. Acceleration seemed fine though.

On snow, I was simply amazed and never experienced anything that could be considered surging. I drive cautiously and the only time I pukered was when I tried to stop where some ice had formed. As I became more adventurous, I got to a point where I crawled through snow that was deep enough that I left two tire ruts with a perfectly flat snowplowed area in between. (That section was about 30' long.)

I'm looking forward to hearing what you think about TOD after you drive it on snow in WA. :) Since the VX is my first 4WD, I have nothing to compare it to other than FWD & RWD vehicles.

Oh yeah... and I found references that say the computer reads the sensors every 20 milliseconds.

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Originally Posted by RickOKC

Oh yeah... and I found references that say the computer reads the sensors every 20 milliseconds.

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I agree, but that does not mean it can analyze, react, actuate the electric clutch in the transfer case and send power to the front that fast. That would take much longer, even with a fast processor, needless to say I doubt early-mid 90s technology was up to the task on a passenger vehicle.

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Originally Posted by Marlin

I agree, except that its not moot. TOD should sense the rear wheels slipping (no drive shaft, the puter thinks it is, so it senses slipping, no different than it would be on snow) and subsequently sends power to the front. That was the problem, it doesn't take the slipping input and then transfer power at a rate fast enough to make it doable,hence the jerky responses, then it seemed to reset and start the process over, giving it that bouncy jerky effect. Having said that, imagine the effects of the delay on snow or ice.

If I had to drive this way, it would be in 4low only, to remove TOD from the picture and have the straight mechanical drive engaged.

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Where does the tod computer get its wheel speed input from? Maybe I am missing something but, if the VX is moving, with or without a driveshaft all four tires are spinning at the same rate so why would the tod send power to the front? Sounds like it is doing what it is supposed to.

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Originally Posted by Marlin

. That pulsing power transfer sounds like a recipe for disaster.

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This is actually my first 4WD so I am no expert, but I did grow up in Michigan and learned how to drive in the stuff and I found the Vehicross to be EXCELLENT in the snow, even this wet crap they call snow here in western Washington

You guys really need to check out that new Ferrari FF Shooting Brake model, I mentioned earlier on. It takes it's power directly off the front and the back of the engine, itself. Both ends of the car are driven independently but guided by computer sensors. No transfer anything! I've driven everything from Blazers to Commandtrak Jeeps and M and G class Mercedes, and unless you go to the top of the line G class in multilock-up 4 Low they are not as good as VX "fulltime TOD" in my estimation on snow and ice, maybe this new Ferrari can out do it but it costs $300K. Also, you wheelers types are running larger than spec tires and that may throw off your TOD a bit, it's very tire size sensitive.

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Originally Posted by Triathlete

Where does the tod computer get its wheel speed input from? Maybe I am missing something but, if the VX is moving, with or without a driveshaft all four tires are spinning at the same rate so why would the tod send power to the front? Sounds like it is doing what it is supposed to.

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With no driveshaft,the vehicle is not moving at the calculated speed that it should be. I am not sure where all the sensors are, but I know there are front and rear. It basis the wheel speed off of the calculated speed based on RPM and gear. At 2000 RPMs, I was not moving, so it transferred power to the front, assuming the rear wheels were spinning out for some reason (rear tires on ice, spinning at 20mph, front tires only spinning at 5mph, therefore shifts power to front)? I don't know what it uses as a reference for the speed.
All I am saying, if the rear tires were on ice, as simulated by removing the drive shaft, I would think the power transfer to the front should be smooth.

I learned to drive in a 1978 volvo wagon, rwd, in Ohio. I prefer RWD cars in the snow, and anticipate the fish tale and prefer to drive based on my own predicted path, not a path that is determined by some computer.

I got it! The TOD sensors are in the transfer case! When the drive shaft begins to spin faster than the prop shaft,that is considered wheel slip in the rear and power is transferred to the front. That is why TOD goes crazy. It sees the rear shaft spinning fast(even thought the shaft isn't there, the sensor is in the transfer case), the prop shaft isn't spinning at all. It then shifts power to the front, giving me the jerking as the clutch tries to engage at a few thousand RPMS and a higher gear, which gives the tranny a bitch of a workout.

One more experiment. Disengage my hubs, no wheels are connected to the driveline. Then I can watch the TOD lights disco it up on the dash without fear of hurting something.

Without the fear of hurting something" Ah ah including yourself.....:bwgy:

sorry I couldn't resist. :happyface

Hey I'm sorry but I'm thinking right now of a story I heard which emphasizes the great care and common sense that we all must use when fooling around under our vehicles. A man wanted to see where a problem was along his drivetrain so he slung a rope from side to side cross ways under the vehicle perpendicular to the drive shaft. Then he slung himself in the rope I guess kind of like a hammock in the rope and had his buddy take the vehicle for a spin. The buddy didn't get far and thump thump thump. The man's clothing got caught on the driveshaft and instantly spun his body around the shaft. He was history. Some of you may have heard this and this is my rendition of the story. I also know of a man killed when the car fell off a jack. And then there is the guy we all heard of that was working on his roof, tied a rope around himself then tied himself off to the bumper of his wifes car. :) The wife went shopping. but he survived to tell his story.

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Originally Posted by Marlin

I agree, but that does not mean it can analyze, react, actuate the electric clutch in the transfer case and send power to the front that fast. That would take much longer, even with a fast processor, needless to say I doubt early-mid 90s technology was up to the task on a passenger vehicle.

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Oh, sure enough... the number was just thrown out because it was the the only one I found that mentioned computer speed (Hopefully that was actually released by Isuzu and isn't some "friend of a friend who works for an Isuzu dealership" thing.) I was also thinking, "but what is the final reaction time?" the instant I saw it.

And, like I said, I'm very much looking forward to the opinion of first hand experience from someone who has lotsa more time on snow in various 4x4 vehicles. All I know is I was hoping I could get out of my driveway... then down the street... then up the hill to the main road... then to work... then it was 5 hours later and I'd had a blast! ;Dy; All the while, TOD seemed smooth to me. The only reason I went (rushed!) home is because the crazies came out en mass and I became afraid the probability of someone bouncing off my cladding had become very, very high. :(

Hey, I keep seeing references to "12 sensors" that control TOD - would all of them be within the transfer case? I wish I had bookmarked more items when I first started researching the VX. I could have sworn that also included the ABS sensors, but I've read messages here that make it sound like TOD is unaffected by a dead ABS sensor.

Those 12 sensors would have to be somewhere in the transfer case. I cut the wires and pulled the fuse for my ABS, TOD works fine when I have my hubs locked in. Its not in the tranny, I did a tranny swap, JoeD did a tranny swap with a tranny from an OLD rodeo, it was old enough it still had the dipstick. No problems. I have had the front axle off, no plugs there.

My experience with TOD is limited to gravel. It would not let me drift, which made for slow going. Instead of allowing the rear end to kick out so you can power through a turn, it forced the front tires to spin, which in turn drove the front to slide as power was shifted to the front wheels, which of course is disaster in a corner.

The factory literature mentions the throttle and brakes as sensor spots, as well. Maybe it's just at the pedal itself??

I'm sure there are RPM sensors, TPS sensors etc.

I was under the impression that the ABS sensors are used too - as well as others within the transfer case and gear box -
My TOD is superbe - Mud , snow , ice never got stuck yet - maybe i haven't been trying but beleive me i have been
cheers
Steve

Well, out of all the vehicles I have ever owned, my VX is easily the best on snow and ice.

I knew someone who drove their 1st gen Trooper around with no rear drive shaft for several weeks, just using 4HI. Kinda funny.

Bart