Miata Mailing List: September 1993, Message #57
sponsored by



     


   From: Jim Dobbins 
Subject: Flakey Speedometer Fix
   Date: Tue, 7 Sep 1993 13:05:57 -0400


    For several months I have been experiencing problems with the speedometer
on my 1990 Miata (mileage = ~45K). Lately the problem had become worse and
I was seeing indicated speeds in excess of 120mph as I traveled to and from
work. The odometer readings were normal.

    A local speedometer repair place suggested that this could be caused by
lubricant leaking from the drive cable into the innards of the speedometer.
They had seen three other Miatas with this problem.

    This weekend I dis-assembled the instrument panel and found that there
was some heavy oil in the drive cable to speedometer needle coupling.
This coupling consists of a magnetic disk that is directly driven by the
speedometer cable. The magnetic disk interfaces with a steel disk and
magnetically couples the drive cable rotation to the speedometer needle. There
is no direct mechanical connection between the needle disk and the cable magnet.
The oil that had collected between the magnet and the speedo disk was causing
greater than normal coupling.

    I had to dis-assemble the speedometer to clean things off but the job was
straightforward. The illustrations in the shop manual were instrumental in
helping to discern how things come apart/go together. Caution: there is a return 
spring on the speedo needle that is very delicate and care should be taken
when removing the indicator needle from the face of the speedometer. The job
took about 2 hours and all the swiss watchmaker skills I could muster. This
approach seems a better alternative than the "replace the speedometer"  
fix (~ $140) suggested in the shop manual.
-Jim