Toyota Repair: 93 4Runner Erratic Speedometer, speedo gear, toyota 4runner

Question
Good Evening;
I just handed the keys to my 1993 Toyota 4Runner to my 16 year-old son.  Of all the things that I need to function correctly, the speedometer is at the top of the list.  Unfortunately, it works only part of the time.  

The vehicle has 130k miles.  It is a 6 cylinder, 4-wheel drive, with an automatic transmission.  At times the speedometer functions correctly.  At other times, the needle bounces erratically.  I've noticed that when the needle moves back and forth, it doesn't extend beyond what I believe the vehicle speed to be.  Said another way, it does not go from the minimum to the maximum of the gauge.  Rather, it appears to be attempting to jump from zero to the current speed, then rapidly back to zero and so on.  It can begin bouncing at slow speeds or at higher speeds - there doesn't seem to be a pattern or specific condition that causes it to occur.  In fact, a local dealer repair shop could not get the problem to appear, so no work was done.

Your advice on what is causing this problem and what is involved in its repair is greatly appreciated.


Answer
Either a chipped speedo gear or drive gear, or the seal in the trans is leaking and the spiral motion of the cable pulls oil up into the speedo head when it heats up.
Take the cable off the trans and check for an oil leak.
you can replace the drive sleeve and seal if leaking.


I have seen a binding cable also cause this on a few occasions.

Mike