After checking around I find the image is accurate. The sensors I've seen probably won't fit as is, but I'm goingto bet that they're better than what's in there now.

Once I can get underneath the D1, I'll pull the VSS out and investigate.

 

There can't be that much to it... If it comes apart I'd clean it up..
Maybe run it thru my de-gaussing coil and put it back..

Somewhere there was something about the **** on the flywheel being bent and causing an issue.. You might look while you've got it off..

Good luck

John

 

You probably don't want to degauss it. If it's like the one I have, it's got a magnet built in.

 

I suspect it is basically a spinning magnet in a coil which sends an electrical impulse to the ECU each time the gears in the transfer case spin. That implies a vehicle speed to the computer which does the math.

 

If it was just a coil, I don't see why it would ever fail. I suppose the magnet could weaken, but that seems unlikely.

The sensors I'm looking at are hall effect sensors (semiconductor) with a a built in magnet that detect gear teeth as they pass. I've seen them useds as camshaft & crankshaft sensors in several applications.

 

re: Somewhere there was something about the **** on the flywheel being bent and causing an issue

That would be at the flywheel, rather than past the transmission. The sensor involved with that is the CKP or crank position. And bent tabs or broken off tabs are big problem.

Reluctor sensors for vehicle speed are very common, for instance in Ford vans the ECU has to be programmed to know which rear end ratio is present. Learned that when rear axle in my V-10 E350 was replaced with a junk yard unit, speedo said 65 and GPS was pushing 80 mph. Taxi cab industry has all sorts of converter boxes that change the VSS pulses to a new count that the cab meter can understand (I always think they select a position that counts in their favor).

 

I found the Allmakes after market version of the VSS at RovahFarm for $70.

Even with the new one installed my truck misfires and throughs multiple misfire codes.

Runs great with it unplugged. Looking into other causes.

I have seen similar posts (runs great without VSS, replaced VSS and same issue) on other forums but have never seen a solution posted.

 

I did a bit of looking around, and found the VSS mentioned in a TSB -TEC190397 to be exact. they explain that the VSS is a reed switch.

FOr those of you who don't know, a reed switch is two metal reeds contained in a glass envelope. When in the presesence of a magnetic field, the reeds attract, and a connection is made. But it's only a mechanical switch. You typically see these things inside the pickups for burglar alarms.

They further explain that it makes contact 8000 times per mile. My Disco has about 132,000 miles on it. That means the reed switch has opened and closed 1,056,000,000 times. ONE BILLION TIMES!

I have never seen a reed switch used in this fashion. Try doing one billion cycles on your ignition or window lift switch.

The wonder here is that they don't all screw up.

Why the heck are these so expensive? Reed switches themselves are about a buck!

 

Six pulses per wheel rotation per the RAVE. Reed switch units can make the billion mark, per some producers. But they are also subject to shock, contact pitting from surges, even a time response of how fast it can drop back out. So I guess you could meter one with an ohm meter and turn the wheel to see make/break on the GY and BR wires.

Perhaps with aging the contact bounce changes and that fools the ECU in to thinking you are approaching take off velocity, at which point it steps in to save the truck (and perhaps the teenage son who has sneaked it out for a late night drive).

Good catch, I had thought that it was a Hall Effect switch.

 

I thought so too. Any other manufacturer of the time would have used a hall effect. the same goes for the crankshaft position sensor, but I've seen that that' just a coil.

My guess is that the electronics behind the instrument cluster does one heck of a job of cleaning up the signal.

Considering that the truck has electronic controls for everything, the sensor inputs are....
primitve.