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Speedometer issues

Posted: Fri Feb 28, 2014 10:08 am
by uglytruck
Just purchased a 1982 long bed a couple of weeks ago. First thing I noticed when I opened the door is that it smells like transmission fluid in the cabin. I was driving it on the highway a few days after I bought it, and the speedometer just quit on me. Then I noticed that the odometer was just barely crawling forward. I've finally had time to get behind the instrument panel today (my first time there), and I can see why the cab smells like tranny fluid and the speedometer and odometer aren't working and all the problems have the same source. There's tranny fluid leaking out of my speedometer cable. Probably has been for a while. Could it have just been a loose connection? Or do I need to replace the cable? If so, how?

Posted: Fri Feb 28, 2014 9:59 pm
by asavage
Generically, that's a symptom of:
  • A plugged transmission vent (a small plastic fitting at/near the top of the transmission);
  • Overfilling of the transmission, or
  • Incorrect transmission lubricant.
It's unlikely that it's a speedo cable issue.

Posted: Fri Mar 07, 2014 8:43 pm
by uglytruck
Thanks for the response, Al. So, before I got your reply, I went ahead and changed out the speedo cable since I had a spare one and it was a fairly simple procedure. It worked (sort of) for about a day and quit. Next time the weather is decent around here again, I'm going to change out the gear oil in the tranny, make sure it's not overfilled and check on that vent. If the vent is plugged, can it just be cleaned out? And if I get all those things in perfect working order, do you think the speedometer cable will start working again or am I going to have to replace it again?

Posted: Fri Mar 07, 2014 9:14 pm
by asavage
Your speedometer's needle sometimes moves up, and sometimes doesn't, and the odometer similarly doesn't always move right?

That sounds like the nylon speedo drive gear is mashed up. It can be removed and replaced from the outside of the transmission, IIRC. It's the part that the speedo cable screws to on the tailshaft of the trans.

If you drain the trans oil and find small chunks of plastic in the oil, bingo you've found the problem. You won't get all of them out though, because the oil passage between where the drain plug is and where the nylon gear is is small.

All this is just a guess.