Speed Sensor

[Diesel Max]

On a 93 F250 with the ZF5 and sterling 10.25, is the speed sensor on the diff tied into the speedometer ? Every once in a while my speedometer will bounce up and down for a few seconds and then return to normal. It reads the speeds accuratley, just bounces up and down every so often. Or.... is there a speed sensor or cable that is tied into the transmission or some where else that controls the speedometer function ???

 

[LCAM-01XA]

'92-newer trucks use the axle VSS only, they have no transmission or transfer case VSS or speedometer cable. The same VSS also feeds signal to the TECA and the RABS brain. When your speedometer starts bouncing, do you feel the torque converter locking and unlocking?

 

[Diesel Max]

'92-newer trucks use the axle VSS only, they have no transmission or transfer case VSS or speedometer cable. The same VSS also feeds signal to the TECA and the RABS brain. When your speedometer starts bouncing, do you feel the torque converter locking and unlocking?

No. It's got the ZF5 -- manual transmission, it's not an automatic. The truck doesn't feel or drive any different when the speedo bounces.

But now that you mention it my ABS light is on as well but the brakes work fine and stop great. Sound like maybe a bad speed sensor ????

 

[LCAM-01XA]

Haha, well you can tell I didn't pay enough attention to your signature, it says ZF5 right here! But yes, a bad VSS can cause ABS light to come on - the light tells you there is a problem with the system, which means all power is cut to the HCU and you're defaulting to non-ABS brakes, which makes for lots of fun when trying to do an emergency stop on the freeway after it's just rained or snowed.

 

[Diesel Max]

Haha, well you can tell I didn't pay enough attention to your signature, it says ZF5 right here! But yes, a bad VSS can cause ABS light to come on - the light tells you there is a problem with the system, which means all power is cut to the HCU and you're defaulting to non-ABS brakes, which makes for lots of fun when trying to do an emergency stop on the freeway after it's just rained or snowed.

So if I understand you, that speed sendor controls the ABS function as well as the speedometer ?? Sounds like a new one is in the future.

On a side note, how do you reset the ABS light ? Disconnect the battery for 10-15 minutes ???

 

[LCAM-01XA]

Yes, the VSS feeds signal to the speedometer, the ABS brain, and (in case of an E4OD transmission) the TECA. One size fits all kinda thing, I guess. The ABS light will go off on its own once the problem within the ABS system is resolved - the ABS brain does not store codes like the PCMs do, so no need for disconnecting the batteries, you will only wipe out your radio presets with that

 

[RLDSL]

Before you replace the sensor, take the plug out and hit the connectors on both sides with electric cleaner and check the wiring for breaks and weak spots. Usually an intermittant like that is in the plug of wiring, mostly wiring, the wire has been bending up and down with the axle all these years, you bend a wire enough times, it breaks. I've had to rewire those suckers on vehicles on family vacations in campgrounds and all kinds of interesting places

 

[mankypro]

both sensor wires shorted out on the knuckle on mine and fried the controller...

Need a new controller now. fun, fun...