cold speedometer problem

[jwex2]

the speedometer in my 87 cab doesn't work when the car is cold and the outside temp is below 45 to 50 degrees. After running for 5-10 minutes the thing will come alive and keep working fine.

If the temp is above 45-50 there is never a problem even when the engine is cold. I have checked the connections on the back of the speedo . Any ideas??

Thanks

[JDaniel]

I had a similar problem 2 years ago. The speedo would not work when car was really cold (ie. less than 40f). The tach always worked. Sometimes the speedo would catch when shifting through the gears, but it would usually stay dead until car warmed up... I noticed this for several weeks, and then as I decided to fix the problem, it went away.

This fall it returned.

Since shifting has a tendency to cure the problem, I think it might be a loose connection or wires touching. I put the car away for the winter and will tackle the failing speedo in the spring when I drop the motor for the "Top-End".

Sorry I couldn' t be more help. If you solve the problem let me know the solution.

[nhromyak]

I tend to think it would be the sender in the tail housing of the transmission.

I suppose it could be a loose connection. Maybe a bad transmission ground?

Not sure though.

Good luck.

[ChrisL]

Does the odometer work while the speedometer is acting up? If so, it's probably not the sending unit. My speedometer will 'stick' at zero until I get over 25 mph or so, then it acts normally. I need to send it in to be rebuilt for $100 or so.

Chris.

[jamesiii]

nhromyak,
Nice post-script!

[Early_S_Man]

Sounds like a problem with the magnetic-reed switch 'sensor' bolted to the transaxle. Either a dirty/loose connection at the two-wire connection to the body wiring harness, or a bad, sticking reed that has to be warmed up and vibrated a bit before it 'wakes up' and starts working.

As stated above ... if the odometer works while speedo doesn't it isn't a sensor problem!

If you have an oscilloscope and jack stands, put the car up on stands, and monitor the two sensor leads while still attached to the body wiring harness. With the engine in 1st or 2nd gear and the rear wheels turning ... you should see a 6-Volt peak-to-peak pulse train ... eight pulses per ring gear rotation.

[jwex2]

when the speedometer is dead so are the odometer and the cruise control. when one works they all work. I'll look at transmission connection but don't see how temperature could effect it

[avi8torny]

It's the pickup at the transmission. Your's is on the left side. Access for the wire connector is under the access hole on the tunnel behind the seats. I have the same problem...sometimes it works, sometimes it doesn't.

tdowling
87 Targa