My 77 has a lazy speedometer

[Keith77]

My speedo bounced while driving and then stopped working. I have replaced the lower cable which was not broken, but did it anyway since I bought one. I tested the upper cable by turning and watching the speedo needle move. I have replaced the cruise control transducer with a rebuilt unit.

The problem - none of the above seemed to work. Last weekend I backed out of the garage and it magically worked until I got to highway speed - never got about 50 then slowly went to -0- and stopped. Figuring motion could have played a role I went to a parking lot and backed up several times - it did work again for about 1/2 block then stopped. Today it jiggled a bit getting on the highway and went dead.

I took the old cable and connected to the transducer so that I could watch for movement while driving - nothing.

It seems if it moves on occasion the cables should be OK. Anyone have any ideas. Can't figure out the eratic behavior. It does not look like there is anything in the speedometer itself to replace. Tach works perfect.

 

[Artsvette73]

Have you checked the speedo gear in the trans? 1 bolt and the housing will pull out. Look at the teeth they maybe chewed up.

 

[bmotojoe]

Unhook the lower cable at the transmission. There is a 1/4x20 (7/16” head)(may be metric 10mmI don't remember now) lock bolt securing the speedo gear sleeve bracket to the transmission. Remove the bolt and the little flat bracket. Pull the sleeve from the transmission the speedo gear should be with the sleeve. The speedo gear is plastic and where the square end of the speedo cable goes into the speedo gear it may be worn out, also check the gears. If bad take the speedo gear to your local Chevrolet stealer and have them match it up to the correct color as the original one your replacing. They should stock this part and if not there is no shipping charges like aftermarket vendors charge. When you have it out check to see if the shaft of the speedo gear fits nice inside the speedo gear sleeve with no wobble. These do wear out also over time and you will have a dip of transmission fluid coming out of the speedo cable no matter how tight you make the cable connection to speedo gear sleeve.
If that doesn’t solve the problem then your going to have to remove the speedometer assembly and have the speedometer head rebuilt.
Brian

 

[Bob Chadwick]

You can start by removing the trans side cable from the transducer. if it turns when the other end is pushed all the way into the transmission, the gear is toast.

 

[Scott Winebarger]

Mine did the same thing coming back from Bowling Green. I have not addressed it yet . Does yours ever look like this? :L

or this....

I just smiled and made the best of it by snapping a couple of photos.

 

[Keith77]

Great picture, but I would need a video camera to do justice to increaseing speed and decreasing speedo.

Keith

 

[Dream Ride]

Keith, if you're still out there what did your problem end up being? Mine did the same thing on the day I bought it. I have access to a rack but it would be nice to already have everything on hand parts wise once I get it up in the air. Thanks

 

[Keith77]

Keith, if you're still out there what did your problem end up being? Mine did the same thing on the day I bought it. I have access to a rack but it would be nice to already have everything on hand parts wise once I get it up in the air. Thanks

The problem started to be intermitant with the speedo working then stopping, then showing a much slower speed that actual, then it stopped all together.

I replaced the speedo transducer (to hopefully fix my cruise control as well) and the speedo cable, tested the speedometer by turning the cable by hand a watching the speedo move. None of these fixed the problem. My next step was to replace the gear that the speedo cable goes into in the transmission. Someone sent me instructions on replacing but lost access to a lift before I got that done. The gears are cheap you just need to know what color gear you have to replace it.

I took mine to a transmission shop that wanted $350 to fix it - figured they were just ripping me off so have just used my GPS as the speedo ever since. May never fix it now unless you find the solution to be an easy fix.

Let me know how yours turns out.

 

[Dream Ride]

^^^^^I'll have mine on the rack within the next few days. I'll keep you posted. I'm doing away with my cruise and going to a 1 piece cable. I have 3 other vehicles with cruise and have never used it. Lot of winding back roads around here so there's not much use for it. But I'll still know why it's not working.