The speedometer in my 55 Olds hung at about 40 mph, but the odometer was still working. The shop manual says to grease only the lower 2/3 to prevent grease from getting into the speedo head. However, someone in the past put too much grease in the casing and when I took the cable aloose from the head the needle dropped to 0 as it should. I've tried several things to correct; cleaned the casing and cable, tried a new cable, put the old cable back in. With the old cable back in and the cable aloose from trans I can turn the cable by hand and speedo needle moves and drops back to 0. But on reconnecting to trans nothing works except odometer.
Any suggestions as to how the odometer would work, but not the speedo? And how to fix?

 

It sounds like the speedo head needs to be removed and worked on. The odometer is gear driven from the cable. The speedo needle relies on a spinning magnet driven from the cable. When the needle itself is binding, it can stick. Old solidified grease or oil and dirt can cause this. The needle rides on tiny bearings and needs to move very freely. The slightest bind and stall it.

 

Thanks for the info. Can the grease accumulated be cleaned with something like brake cleaner or electronic parts cleaner, or will the head need to be dismantled? I'm a little afraid of loosing the bearings you describe if it's taken apart.

 

The head itself will need to be disassembled. Lots of small parts, so do inside if possible, take lots of pics, and keep an egg carton for inventorying parts.
The old grease and lube will require a solvent to remove it, WD40, PB blaster or paint thinner will work. Apply it on a rag first! Do not spray into the head. Also be very careful with the face as the numbering can probably get smeared with just water.
Upon reassy, use just a tiny tad of 3 in one oil for the speedo needle bearings and wipe away excess. A lighter clock oil would be best.

 

Thanks very much for your help; you've answered all my questions. Now I just have to be very careful with the speedo head.

 

Sure thing... Be very careful and take your time. Do inside in a clean room in case you drop or launch a part...