Coasting speed OK; Accell Speed Not

[HOTLNC]

Ok, guys. Here’s a strange one. The speedometer only reads while the car is coasting. If you apply the slightest amount of acceleration, the reading goes to zero. This continues until the motor gets up to operating temperature. Then it more or less works. Although every time you accelerate, the indicated speed glitches, changes.

I’ve disconnected the speed sensor and measured its frequency. Under acceleration, it falls like a rock. Coasting, it works fine.

I’ve installed a brand new speed sensor. I’ve tested the EIC (Electronics Instrument Cluster) by replacing it with a unit I got out of the junk yard I had to replace all the lamps to get it to display, but the same thing happens. I’ve replaced the speed sensor connector and cleaned all other connectors.

I’ve eliminated all things electric causing this. It’s got to be mechanical, inside the tranny. When I put the new sensor in I reached in and rotated the drive gear that is connected to the driven gear on the speed sensor. Should it rotate?

Jacking up the car and allowing the wheels to speed under power indicates the speed coasting or accelerating.

Tomorrow I’m going to check tranny (trans-axle) fluid.

 

[sleeper]

could be something in the tranny. i don't think the gear that drives teh speedo is supposed to rotate at all unless the wheels are rotating. kinda weird that it would work when coasting but not when accelerating.

 

[HOTLNC]

Yeah, it was in the tranny. The driving gear is plastic on a metal shaft. Yes, it is NOT suppose to turn -- it should be locked to the output shaft. The plastic was worn so badly that just the small amount of play that happened when the output shafts were loaded (accelerating) or not loaded (coasting) was enough to disengage and engage the speed sensor gear.

Boy that was one for the books.