While driving, my speedometer was acting erratically (bouncing quite a bit) while slowing down on a highway exit ramp. When I started moving again, my speedometer never went above zero. My odometer doesn't move either.

I've pulled the speedometer cable (I was able to remove the cable from the speedometer without removing the dash), and it looks practically brand new (I've had the car only 5 months). The red cap on the end (at the speedometer attachment) seems to be firmly attached (it didn't come off when I yanked the cable out of the sleeve).

Following the advice on some of the other speedometer cable threads on this forum, I reattached the speedometer side of the cable and detached the transmission side and proceeded to try and drive it with an electric drill. No movement on the speedometer/odometer (I tried both directions of rotation on the drill). While doing the drill thing, I could hear noise coming from the dash. No clicking, just sort of a high speed droning sound (like you would expect a cable spinning in a sleeve perhaps faster than it should be spinning would sound... my drill was doing 1000rpm or so)

This seems to point to an internal problem in the speedometer itself. I guess I'll have to pull out the dash and extract the speedometer. One quick question though, the red cap appears to be a 4 sided pyramid in shape (with its top chopped off). Is it worn? Or is this supposed to be how it is shaped? (instead of purely rectangular)

This post is my last ditch effort to make sure my diagnosis is basically correct (I'm pretty much an beginner/amature mechanic), as the speedometer side seems to be the expensive side to fix (speedometer cable, $8... speedometer drive gear $8....)!

Alex

 

The ends of the speedometer cable should be squared, pyramid, etc. in shape.

From what you have tested, it could still be the cable. If the cable has worn or broken at the Speedometer part, then the cable will still turn with a drill at the transmission side. It doesnt mean that the speedometer is bad. It may still be the cable.

I had this problem with my tachometer cable, which is really the same as the speedometer cable on my 73, The cable frayed and broke at the connection. It would still spin, but since it is broken in two there is no movement at the other end.

I am not discounting your speedometer, but try the cable first. To get to the speedometer to change it out may require you to drop the steering column.

Lets see if some others say you have to drop the column to get to the speedometer/tachometer gauges.

kdf

 

Before I tried driving the cable from the transmission end, I pulled the cable out of the sleeve from the speedometer end. The cable itself is still in one piece and isn't frayed. The red cap seemed to be very solid on the end of the cable (I found other posts in the forum about the cap coming off the cable). The transmission side of the cable is square (not rounded off) and the red cap seems to have an un-worn pyramid shape.

Inspecting the sleeve itself showed no signs of stress, at least externally.

Prior to the failure, the speedometer was solid (no needle bouncing).

I'll definetly double check this before I dig into the dash, as the double check is trivial by comparison....

This is on a '71, so no cruise control and is a single piece cable.

Thanks,
Alex

 

Is your cruise control still working? The transducer or whatever it is for the cruise may have gone bad. I have read where this will make your speedo bounce around. Mine is to doing it as well, but I just haven't gotten there yet.........

 

So, I've pulled the console out of the car, and now I see what the end red cap of the speedometer cable is supposed to look like. It is a tapered pyramid with a perfectly square extension (about 1" long). When I looked at the speedo cable before, it only had the pyramid section, which means the square extension had broken off! The tach cable looks like it is in perfect shape (pyramid + square extension).

Now I have a situation where the red extension is stuck inside the back of the speedometer and I can't get it out. Ugh. Any suggestions?

What is slightly more alarming though is when I spin the brass end piece on the back end of the speedometer by hand, the needle does bounce (which is great), but then the brass end feels as though it really binds up (which is not so great). The binding is really really tight (the tach side doesn't bind at all). This probably means I'm in for a rebuild.

Any comments on how tight the speedometer end should be? It seems way to heavy right now. Also, any suggestions on removing the red plastic piece that is stuck in the back of the speedometer?

Alex

 

if its plastic you could take a small plastic rod and put a small drop of super glue in the end to glue the rod to the red squar piece to pull it out. anyways good luck

 

Just had this happen to my speedo cable, only it happened to me at the cruise control module up in the engine bay.

I was never able to extract the broken off speedo cable end from the transducer, even with it removed from the car. I tore down the module and still did not get the broken end out of the gear connection. This prevents installing a new cable. Other than that, the cruise module spins OK.

Chances are if your speedo cable end broke off, you may be experiencing some turning resistance and you may need a new speedo assembly.

I am now is search of either a replacement gear assembly or a complete cruise control module for my 82.


Brent...

 

This is very much worth checking. The gears in the transducer are pretty soft.

 

I pulled my speedometer and sent it over to Palo Alto Speedometer (www.paspeedo.com). While I was at it, I gave them my tach as well ("while I'm at it" is a phrase I'm learning quite well, I'm going the change the bulbs, tach & speedo cables, and headlight switch while the panel is off).

My speedometer is completely shredded internally (drive gear that provokes the needle and odometer). My tach appears to be in good shape, but I'm having it rebuilt as well. What is nice is the turn around from drop off (yesterday) to finishing (tomorrow) is 2 days! (I'm only 10 miles from their shop).

What I was hoping would be an $8 fix (cable or transmission gear) is now just north of $150 not counting the extras (tach, cables, and switches). Doh!

Alex

 

Sorry to hear about your speedo misfortune. Did the service person say why the internal gears were shredded? I thought that I was being smart last weekend by putting a new cable into my existing guide since my dash was already apart. Before replacing the cable, the needle bounced all over the place; now, it doesn't move at all. I'm hoping that I haven't damaged the internals of my speedometer somehow. I will put it on jackstands this weekend and use the drill test at the transmission end.

 

I picked up my speedo and tach today. Both were disassembled, suitable parts were replaced, then callibrated.

I asked the guy about the speedo failure and he mentioned two things: speedo cable stretching causing lateral pressure on the unit and plain old age/use. The lateral pressure argument seems like a little wierd to me, as the speedo seems rock solid an pretty immune to lateral pressure like this, but he did say there was a bearing in the assembly that was shot (could this be the culprit?). He rebuilds speedos, I don't, it used to not work, now it does, so I guess I can buy that argument....

I asked him about the drill method of testing too, and he mentioned that it is generally a bad idea as electric drills often spin too fast for the speedo to handle (1000+ rpm), and could lead to premature wear.
Pulling the cable off on the speedo and spinning the extension by hand should show some needle movement without stressing anything.

I'm just waiting for a few more parts for behind the panel so I can put it all back together.

Alex

 

I've replaced the bulbs and headlight switch this weekend and put everything back together (I got my Corvette Central shipment this week...).

Everything appears to be in good shape except for a small electrical problem now. Headlights work fine (high and low beam), headlight vaccume works fine as well. Left turn signal works fine, high beam light works fine as well. Parking break works. Right turn signal does not work (the light turns on, but doesn't blink, taillight blinker doesn't work either). The internal dimmer doesn't work, nor does taillight reverse indication.

Any quick suggestions for the electical issues?

Alex

 

what about your hazard flashers do they work.....i think the blinker may be a bad flasher unit...

 

If your dash light turns on but does not blink, then you probably have a burned out bulb in the front or rear blinker light assembly. This is what mine does when a bulb is burnt out.

I was very happy to discover this was an easy fix when it happened to me.

Brent...

 

Rock on Brent! I remembered that the passenger side front turn signal bulb was out and replaced it today. Now all the electrical gremlins are gone!

I didn't expect the system to work like christmas tree lights. One goes out, they all go out.

Now that everything is working again, I can per the screws back in an go for a real drive!

Alex