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'79 620 Speedo Problem


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Replaced the broken speedo cable. Then the speedometer started acting erratic. Very shortly thereafter the gauge started squawking and then spinning like the clock on a time machine. Disconnected the cable from the back, wrapped the end in some clean cloth and zip tied a small plastic bag over that. Starting to drip tranny fluid on my pant leg. Gotta do something to fix or replace the speedometer. Where to source a replacement is my question.

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How could the speedometer drip trans fluid???

 

As far as the speedo dancing and squealing, I had the same issue in my 521. Not sure about the 620, but the 521 speedometer came apart extremely easily. I pulled mine apart, and applied a very light coat of grease to the bearing for the magnet, and for good measure, shoved some grease in the input hole as well. I've been driving on it for about 2 months now without issue.

 

If you do this, I will say this. It will continue to bounce around a little bit at first, but as the grease wears in, it will subside and act normal afterwards.

 

I know the 620 is a bit different, but I can't imagine it would be much more difficult.

 

As far as leading tranny fluid? Unless your trans is somehow putting fluid into your speedo cable line, you might have a completely separate issue. One that I can't even begin to explain.

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There is a seal in the speedo drive unit that when it fails, it allows trans fluid to come into contact with the cable. As the cable rotates, the oil wicks up the cable until it reaches the dash. Then it drips out of the dash onto your pants.

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  • 2 weeks later...

The speedo cable is delivering a very small amount of tranny fluid to my little cloth and very small plastic wrap job. Did it to keep the disconnected cable end clean till I can find a replacement speedometer. It is dripping so it must not be sealed at the tranny. I hope you can help me by describing the seal at the lower drive end of the cable. I bought this new cable at NAPA. I hope I would have made sure to include any seal that was included. Do you think a new replacement cable would have the needed seal or would that be something that I might have tossed out with my bad, original old cable? Thanks!

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