When i was driving a Saturday I noticed the speedometer bouncing around 30 t0 40 mph when i was going around 70 mph on the highway. It did this for a while and then died. It now sits at zero at any speed. Any idea what is involved with fixing this?

Thanks, Mike

 

Depends on the problem:

1) Bad metal drive gear in transmission - remove transmission and replace gear

2) Bad plastic driven gear in side of transmission - remove plastic gear and replace

3) Bad speedometer cable - replace cable

4) Bad speedometer head - remove instrument cluster, remove speedometer, repair, install

 

WOW!! Thanks

 

Sorry for the short reply the first time. Here's some diagnostic ideas.

1) Bad metal drive gear in transmission - These rarely go bad, but they can be mismatched to the plastic driven gear in which case the metal gear eats the plastic gear in short order. To determine the state of the metal gear: a) disconnect speedo cable from tranny. b) remove driven gear housing (held on with a small bolt/clip). c) peer inside of transmission to see if the metal gear is in place and not chewed up. In general the metal gears are a press fit, so it is unlikely that it has come loose. I believe there was one year (66, 67?) that the gear was plastic and held in place with a clip of some sort.

2) Bad plastic driven gear in side of transmission - remove plastic gear and replace. To check this out: a) disconnect speedo cable from tranny. b) remove driven gear housing (held on with a small bolt/clip) and inspect gear. If chewed up, replace but be aware that it got chewed up for a reason - either because it was mismatched to the metal gear, or because the speedo or cable locked up. Mismatched to metal gear: What this means, is that there are just a few metal "drive" gears, and bunches of different plastic "driven" gears, and a combination of drive/driven is used to satisfy the calibration requirements for the rear end ratio that is in your car. With only a few metal gears, but lots of plastic gears, you can end up with drive/driven combinations that are NOT meant to go together and when this happens, the drive gear eats the driven gear. On my 62, this usually took only 20 or 30 miles to happen so chances are if this problem is brand new, then mismatched gears is not the issue for you.

3) Bad speedometer cable - replace cable. To check this out: a) disconnect speedo cable from tranny. b) connect an electric drill to end of speedo cable. c) turn drill on in COUNTER clockwise direction and see if speedometer reacts. If the speedo does not react then either the cable or the speedo is bad. d) Disconnect cable from speedometer. e) Check cable for continuity from end to end and if the cable is solid, then the speedo is bad, otherwise the cable is toast.

4) Bad speedometer head - remove instrument cluster, remove speedometer, repair, install. To check this out, repeat steps from item 3 - and if the cable is intact in step e, then your speedo is at fault.

 

Thanks again Jeff, I guess i'll start with 3 and 4 and hopefully this is were the problem is.