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404 Speedo drama

1435 Views 3 Replies 3 Participants Last post by  Two Tone
A couple of weeks ago on the way home from a really fun trip, my speedo needle got all jittery and then just fell to zero. This on a speedo with only a bit over 11,000 km on it.

Assuming that the cable had broken from extreme speed (NOT) I ordered another from Expediton Imports and carried on. I installed the new cable today and it broke immediately. At first I was disgusted that the new cable was defective but that was not the case.

It turns out that the input shaft in the speedo itself had seized up solid. I couldn't move it at all with an appropriately sized flat screwdriver stuck into the square hole where the cable enters.

So I popped out the speedo and took it apart. The thing looked pristine, no rust, dirt or moisture, inside or out. I guess the lube on the shaft just dried up between 1969 and now.

Anyway, it wasn't too tricky to disassemble the drive after looking at it for a while. I already knew how to get the guts out of the body from having to take apart the electronic VDO speedo in my 911. It was nice to see all steel and brass gears in this unit.

I was able to take it apart, clean and lube it and reassemble it without wrecking it. I am amazed at how tightly seized the shaft was. I couldn't get it to move until I got into some pretty serious prying.

I was still left with no cable. The new one broke about 2mm from the transmission end but the old one had failed in a different way. It had become detached within the socket of the drive fitting and hadn't actually broken. So, believe it or not, I pulled the cable out of the cover and I cleaned and lubed it. I then inserted the cable back into the cover and degreased the transmission end. I degreased the socket on the drive fitting, put some Krazy Glue in the socket and stuck it back onto the cable. I let it sit while I reinstalled the speedo.

So far, so good, its working perfectly. It will be interesting to see how long this cable lasts. I might as well order another new cable now I suppose.

It would have been useful if I had documented the disassembly with photos but I regret I did not have my camera handy today. Sorry.

Be sure to check that the speedo is still free if you break a speedo cable. Its easy to do and it might save you some frustration.
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You have to pry up the lip of the bezel that is pressed over the rim of the instrument body.

With the speedo laying face down on a flat surface you take a small screwdriver and pry up small sections of the lip and work your way around the rim. Once you've done about three quarters of it you'll be able to pop the bezel off. The bezel holds the lens and sealing ring in place on the instrument face. Now you can spin off the 22mm nut on the back of the speedo and push the guts out through the face. There's a worm gear shaft on the side of the speedo drive that drives the odo. Theres a screw that secures it in place and if the screw is loosened the worm gear can be moved up so as not to engage the odo. gear. Maybe yours slipped a bit.

Upon reassembly you have to press the lip of the bezel that was bent up back down firmly to hold everything in place.

If you want to lube the shaft while you have it apart, first you must remove the drive from the back of the odometer cluster and dial face. Its secured with 2 screws. Then you must tap the worm drive that sticks out the side into the body of speedo drive. This pushes a steel ball out the other side and the worm shaft slides out through. With this shaft removed you can now pull or pry up on the magenetic wheel and pull the input shaft out for cleaning and lubing. There are a couple of spacers and lock rings in there so just pay attention as you take it apart. Its a nicely constructed piece of kit.

The process of removing the bezel is similar to the one described here:

Pelican Technical Article: Porsche Dashboard Gauge Repair and Refurbishment

Good luck.
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