help! speedo stopped working?

[Fred R.]

i was driving back from getting the correct intake manifold installed and all of sudden the speedo stopped working? If I disconnect from the distributor and turn the cable by hand, the needle on the speedo moves? the cable is only about two years old and the speedo was rebuilt about two years ago - any ideas?

[Dennis O.]

Re: help! speedo stopped working?

The cable from the distributor drives the tachometer, not the speedometer. It would also help to know some more specific information about your car.

[Robert S.]

Re: help! speedo stopped working?

I will assume we are talking about the tachometer and not the speedometer. The tachometer cable is connected to a short cross shaft within the distributor. The teeth on the cross shaft mate with teeth on the main distributor shaft. A common failure mode is for the teeth on both the cross shaft and main shaft to become damaged to the point where they will no longer drive the tachometer cable. This failure will occur quite suddenly. If this is the failure mode more damage within the distributor can occur if you continue to operate the engine from the bits and pieces of damaged teeth within the distributor even though the engine will run normally with the damaged teeth. The cross shaft can be removed with the distributor in the car to see if the teeth are damaged however do not replace the cross shaft and assume all is well. The teeth on the main shaft are probably damaged and will just chew up the new cross shaft in a relatively short period of time. Bottom line: You will likely need to remove the distributor and have it disassembled to inspect the main shaft and cross shaft teeth for damage and have either or both shafts replaced as required. There is a lot of information on this failure mode and associated issues (cross shaft wear buttons etc.) in the archives that will help you make an informed decision on how to proceed.

[Fred R.]

Re: help! speedo stopped working?

hey guys thanks for the replys, it is definitely the speedometer that is not working, the tachometer works fine. The transmission was also rebuilt about two years ago, 327/300 -close ratio 4 speed

[Edward J.]

Re: help! speedo stopped working?

Fred, About the only things left are the driven gear and the drive gear.( Which is metal). next step would be to remove the housing on tail shaft and check the driven gear, which is plastic and does wear out. once the driven gear is out, inspect for uneven wear, sometimes during the rebuild of trans. the drive gear inside the tailshaft housing is set to a preditermed deep, and if not correct it will accelarate the wear on the plastic driven. generally the drive gear is centered in the housing of the driven gear.

[Fred R.]

Re: help! speedo stopped working?

hey -thanks! I would never have thought to check those gears..