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Speedo Seal. What is it?

I am slowly making progress on my project trooper and next on the list is another leak. I think my mechanic said that the transmission was leaking at the speedo seal and that the seal needed to be replaced.

Can anyone tell me what the repair job is going to be like and any advice?

There’s an O-ring at the speedometer cable where it enters the transmission. When this O-ring fails, it leaks transmission fluid where the cable enters the transmission. Or worse yet, the transmission fluid gets pulled up the speedometer cable jacket and starts dripping on your shoes from behind the speedometer.

The fix is to remove the speedometer cable from the transmission and install a new O-ring.


my experience is with a 60’s GM car so it may not apply to you specifically, but perhaps the general concepts are similar. in older cars with mechanical speedometers a cable runs from the final drive area (rear) of the transmission, under the floor, through the firewall, and into the back of the dashboard. inside the outer sleeve of this cable is a metal wire which spins as the vehicle moves, proportional to vehicle speed, which in turn move the speedo needle. where this cable plugs into the transmission there will be some type of cap or plug assembly behind which is the speedometer drive gear. the mechanism itself is very simple and to replace the seal, which could be a rubber o-ring or a gasket should not be complicated. the job still could be very hard because the location may be very difficult to access. crawl under there and see if you can find the cable end. if you can get your hands on it, the job shouldn’t be too hard. be aware that there’s a seal there because the drive mechanism operates in a fluid-bathed environment so when you take things apart, fluid will run out, possibly a lot. you will also need to refill with the proper lubricant as a last step.