My speedometer doesn't work. If I separate the two cable pieces and spin the bottom of the upper piece (the piece that goes to the speedo head), the speedometer needle responds. So, I decided that this was the lower cable - when I pulled the lower cable core out, it spun freely. So, I tried to pull it complete out and it "stuck" just when I assume I was at the end.

1) Should it normally be possible to pull the cable core out from the bottom on the lower cable? THe top part of the lower cable is a female receptical to mate to the male portion from the upper cable.

2) Is it possible/plausible that the gear that the lower cable threads up to is broken on the tranny end?

3) If you have had a speedo failure, what was the ultimate cause?

Thanks

 

1. Yes

2. Yes

3. I have had them fail for: (a)cable end where it goes into the cruise coming loose from the cable, (b)broken cable, (c)driven gear stripped on the inside where the cable goes in, (d)driven gear teeth stripped, (e)drive gear teeth stripped, (f)gear housing not holding the driven gear up against the drive gear, (g)drive gear stripped, (h)clip that holds the drive gear on broken. (I've had lots of cars) Most common proximate causes are a, b, & d. Most common root cause is cruise regulator binding and putting too much stress on the whole arrangement.

Plug your upper cable back in, and undo the lower cable. The bronze collar on the very outside edge of where it plugs in (1/8" or so) turns with the cable. See if it turns smoothly.

 

When you say the lower cable spins freely, did you just spin the cable, or did you check and see if the speedometer is turning also? I had my lower cable break in the middle. It spun freely but the speedometer wouldn't move. You can check this by putting the end of the cable into a drill and then spin the drill. That shoud tell you if the cable is broken. What year is your car? I don't know about later models but on my 82 the lower cable goes into the cruise control thing (real technical I know) then the upper one comes out of it and goes to the speedometer. It's possible that there might be a problem in there if the lower cable doesn't spin the speedo when hooked up to the drill. You can check the speedometer by spinning the upper cable the same way as you did the lower. This shoudl tell you if it's the speedo, cables, or cruise control unit. If everything there checks out, which I bet probably will, it's the crappy plastic gear in the tranny that broke. Hope this helps.

 

Very good information, guys. Thanks.

First, on my 88 IROC, the speedo cable does not go to the cruise control unit. ..no mention of this in my Haynes or Chilton's manuals, but it's true. However, it does have a break where the upper and lower cables would normally plug into the cruise unit - only the two cables plug in together. The union is incenvenient UNDER the master cylinder and it was a real bear to get uncoupled. Sometimes I wonder about GM engineers...

Anyway, I made the above post in between letting to car off the jack and going to my nephew's birthday party. So, I had to stop in mid-stream. Unfortunately, I wasn't smart enough to spin the lower cable and have my wife check the speedometer. But I like the drill idea - excellent.

Once I check the entire cable assembly, and since I already know the head and upper cable is OK, then I'll simply have to deal with the lower cable or the gear on the tranny...

How hard is it to find those plastic gears on the tranny? Getting parts for this car has been a nightmare! (9-bolt rear, speedo head, etc are all "unavailable")

Thanks. II'll let you all know what I find today.