When I put in my speedometer cable, it makes a good "buzzing" noise at times and runs about 30 mph faster than actual speed.

The cable is new condition and the transmission is all rebuilt.

is there an issue with the transmission gear or in the instrument panel?

Do you have a light grease coating on the entire length of the speedo cable, such as a white lithium grease?

I second the idea to lubricate the flexible inner cable with white lithium.

If the bushing in the head becomes dry or worn you can get squeaks and or a jumpy needle.

Use an oil to lubricate the bushing. Not wd-40! This is should help, but if the needle is jumpy or not reading the correct speed it is time to have the speedometer head rebuilt. This usually involves recharging the magnet and a new bushing. Once it is reassembled it is usually bench tested for proper operation.

In my opinion this is worth what ever the cost may be.

When I finished my 67 coronet 440/727, with a rebuilt dash and new speedo cable, the speedo needle whacked away until Redline gauges informed me that my CHEAPO speedo cable was already worn out.. The inside nylon lining had melted next to the exhaust pipe/manifold. I purchased a GOOD cable from Redline, mounted it a little different, than the last one, and it works perfectly...

the speed cup in the speedo head may be going bad.... i work in a speedo shop, i see almost all mech speedo heads wear this way and make the sound you are describing... beeps A+Speedos 904.642.8120, 8:30 to 5 eastern

Looks like Ihave some things to trouble shoot. It was a new cable back when I got the drivetrain rebuilt and did it immediatly. I do recall it was melted a little, from the exhaust pipe, but I think I replaced that one with a Napa cable.

I did a search and on an older post, the person said he also "reset the index of the cable in the transmission" anyone know what he was referring to?