I just had one of those breakthrough moments driving home, where you're like "wait a...hmm....wait....OHHH.....GOT IT!" Ok...the Vehicle Speed Sensor is what gives your speed output to your speedometer right? Now, is this sensor linked to the torque converter clutch? My speedometer only starts to work after I really slam the gas around for a few minutes..otherwise it stays at 0. Then it's really jumpy until the car warms up. I noticed today while driving home that the torque converter was locked as long as the needle shook over 40 mph. I was actually doing 45.. The second the needle dropped below 40 though, the converter unlocked...so there's a connection here. My question...does the TCC get its lock/unlock signal dealing with the vehicle speed from the VSS directly, or does it get routed through the speedometer? Basically, I'm asking if my suspicions are possible and whether the problem lies in the sensor or the gauge cluster.

 

I don't know if you have a cable drive VSS or an electronic VSS. My '87 is cable drive speedo and it has no effect if I disable it when it comes to shifting or convertor lockup. I do get a VSS fault code if not hooked up though.

However, both of my 700r4's are not stock. One of them I don't even have to run 12 volts to it. That one has an elec. VSS but also has a non-lockup overdrive.

 

As long as it is the '91 in your sig. . . The VSS is mounted in the transmission tailshaft. The signal from the VSS goes directly to the ECM (1227730), the ECM then controls the TCC through a signal to the transmission. And yes, vehicle speed is tied into the ECM TCC logic.

The TCC lock/unlock at ~40 mph is controlled by the ECM.

The ECM outputs two pulse trains derived from the VSS signal. One goes to the speedometer to operate it and the other goes to the cruise control. There are no mechanical speedo cables anywhere in the system.

Check the wires/connector at the trans first. It is a 2-wire twisted pair for the VSS.

RBob.

 

Even a cable driven speedo (with VSS in rear of speedometer) will send the computer a signal to engage the TCC... TCC's mainly driven by road speed, so that might be your problem!!

 

I'm not really sure on what the input for the VSS is, but I had a problem with one on my old 83 Caprice. It used to give me a code 24 but would not afftect driveability. Is your SES light on? Have you had a code 24 in the past?

 

If you speedo is reading less then what it should or not working you need a new magnetic pickup sensor on the tranny. THE TCC is also controled by engine load bassed on TPS also.

 

Ok, I've never gotten a code 24.... Also, my speed is displayed accurately once I get the needle to move. It'll sit still at 0 until either I've driven the car for around 15-20 mins, depending on various things...or until I mash the gas pedal excessively at several stop lights for as long as possible...the acceleration kicks the needle up and it jumps around BELOW my actual speed. Example: If I'm actually doing 45, the needle jumps between 35 and 45..never over. There's a few things that SEEM to affect the needle's operation..such as outside air temp, etc..but I don't see how they would, so it might just be in my head.

 

You need a new pick up speed sensor. Borg Warner part, I think it's the cheapest one at O'Raily, $50 bucks

 

Could it just be the speedo and not the VSS? If you built that scanner cable for a laptop, you could drive and notice the VSS reading...

 

doubt it, the way it's reacting it seems to be the sensor.

 

Wow...sensors REALLY suck. I swear, I could type a post for almost ANY problem and the reply would be "check your sensors"... Either that or vacuum or EGR. I'm sick of these damn sensors!

I've got all these sneaking suspicions about them..I'll probably end up replacing every last one...