| I've been seeing more and more 1990-1991 gauge clusters come in for the same problem. The speedometer reading will start acting erratic and then continue to climb all the way as far as it can go. Example.
 Two things need to be done in order to fix this problem. First, the mechanical gauge needs to be removed. The mechanical gauge is held to the circuit board with a sort of riveted screw (4ea). Here is a picture of the back of the speedometer showing the riveted screws.
 To remove the gauge from the board the screw rivet collars need to be removed. Here I've started grinding them away using a dremel grinding stone.
 In this picture I lifted the collars and started removing them.  The collars removed.
 Then unsolder the pins to the gauge.
 The gauge seperated from the board.
 Closeup of the gauge.
 Closeup of the bottom of the board.
 On the top of the board are metal shims that sit between the washers that surround the gauge rivet screws and the copper contact pads on the board. Over time, the shims and copper pads become corroded and cause bad connections to the gauge.
 The shims removed exposing the corroded copper pads.
 I found that the shims are not necessary and can be discarded. A closeup view of the copper pads.
 The bottom of the board cleaned up and ready for resolder.
 The copper pads cleaned up.
 The next thing to do is remove the speed processing IC. All old solder must be removed. First remove the interference shield.
 Then remove the IC and clean all pin connections on both the top and bottom of the board.
 Top.
 Bottom.
 Remove all old solder from the IC pins and clean the IC pins prior to reinstalling the IC.
 The revit screw collars are not necessary when reinstalling the gauge to the board. The gauge pins will hold the gauge to the board and the gauge is held firmly in place once the speedometer board is reinstalled into the gauge cluster. Even when the gauge was not installed into the gauge cluster the electrical contact between the gauge and board was good enough for the gauge to operate properly. Before installing the speedometer board it's a good idea to resolder as many connections on the board as you can. There are many connections that are failing on these old boards. Many of the connections are what are called feed through holes. These are holes that do not have component leads through them. They are just connecting points that connect the top layer of circuits to the bottom layer of circuits in certain locations throughout the board. This info is for those who feel they might like to give repairing their gauge cluster a try. If it's something you'd like me to do then please send me an email. Thanks!
 
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