Sluggish Speedometer

[Zoso]

I noticed something new on my drive into work today. A few times I thought I saw a blip on the speedometer out of the corner of my eye.

I concentrated on it and felt like the speedometer was slow or sluggish to respond. I downshifted at one point and the speedometer fell to 0 MPH when the clutch was engaged and then went back up to the correct value. I couldn't get it to do this again.

I'm assuming the sensor in the rear diff has something to do with speedo operation but the sluggish response and the clutch engagement leads me to believe that there is some vacuum lines in play. Also, my SI lights are operating fine so that would probably rule out an SI battery issue (if they are related).

Can anyone speak definitely on how the speedo works?

[tim_s]

Speedo sensor is on the back of the diff housing. Check the wires going down to it on the diff from the car floor, often they become brittle and break/get damaged - this is very common over here in the uk, i guess because of our weather.

[Zoso]

It gets pretty cold and nasty here in Massachusetts too. This winter has been really weak though. It has only gone below the freezing mark a few times so far and we haven't gotten any snow yet. We've typically had a few deep snow storms by this time in the winter. I remember last year around this time we had a storm that dumped around 20" of snow. At this rate I won't have to break out my studded snow tires this year!

I had thought about the wiring on the diff housing but wrote it off because my odometer works fine.


Also, I was able to recreate the circumstance where the needle drops to 0. It happens when I down shift and at the moment when I disengage the clutch in the new gear.

[Zoso]

Update:

This condition got worse and worse until the speedometer just stopped working. Naturally the weather turned foul and it's been under 30 degrees for the past few weeks.

I just got a chance to climb under the car and look around. Just as Tim said, the wires leading to the diff became very brittle. When I touched the wire, it broke where the wire connects to the 90 degree connector. As a temporary fix until I get a new one, I was able to take the connector apart and get at the 90 degree connector. I then took a knife and whittled away at the plastic strain relief part until I got to fresh wiring. I soldered in a new wire and taped it all back up.