Diagnosing a non-functioning Speedometer on a R-154 Transmission
Before you get started doing this, you may want to drain your transmission. I am not sure whether or not removing the drive gear would make transmission fluid come out or not but you should do it to be safe.
There are a few components that work together to make your speedometer function. There is the actual speedometer in the cluster, the speedometer cable which is two parts, and the drive gear which is inside the transmission. If there is a problem with any of these it will cause your speedometer to no longer function.
The first component to check is the speedometer itself, located in the cluster. There are two ways to do this, both involve removing the cluster. Disconnect the center console radio bracket, and kick panel screws and remove the cluster connecters. When the cluster is out, drive the car. If the square ended metal piece that is in the green housing does not turn that means there is a problem with either the drive gear or the cable. If it does spin it means the problem is your speedometer. I have found that typically the cable and or drive gear fails. You can test the speedometer by sticking a drill with a screw bit in it and stick it in the back of the speedometer. At full drill speed I got the speedometer up to 20mph.
The speedometer cable is broken up into two parts, the lower and uppersides. The Upperside connects the speedometer with the middle and the lower side connects the drive gear with the middle. Check the drive gear. Put the car up on jacks and get under it. The drive gear is on the passenger side and slightly protrudes. You can see the cable going to it, unscrew the retaining cap that holds the end of the cable into the drive gear. Mine was only on finger tight. With the cap loose, pull the cable from the transmission. It should come out easily and have a 2-3 inch keyed hard metal end. This metal end matches up with the drive gear. If you pull it off and there’s no hard piece attached, it should still be in the drive gear.
Remove the bolt holding the drive gear in and pull the drive gear out. Inspect the plastic drive gear for signs of wear and tear, they should be fairly obvious. The gear either looks good, or it looks like a shredded up limb.
At this point if it isn’t the top cable, bottom cable, speedometer or drive gear, the only thing left for it to be is the connection between the top and bottom cables.
