I just recently purchased my first automobile (70 custom) the speedometer does not work at all. what might of happened? how do i fix it

 

The speedometer cable is probably bad or disconnected.

 

Pull it all the way out and inspect it to make sure it's still in one piece and that the ends are rounded off, if all good lube it up and try again. Make sure you clean the flex tube really good with some solvent or something and blow it out with air.

Okie65

1965 F100, 398
1968 F100, 240

 

 

There's a three step process to find your problem.

1. First, check to make sure that the speedometer cable is attached properly to the speedometer. This is the hardest part because it's a pain to get your hand under the dash, through all the cable harness, to the back of the speedometer. However, this is the most likely place for a problem to develop so you need to check it first. The speedometer cable attaches with a nut. If it seems like the nut is more or less tight then it probably is okay. If it is loose, tighten or reattach.

2. Crawl under the truck and detach the speedometer cable from the transmission; it's held in place with a small bolt. On the end of the speedometer cable should be a small plastic gear. Inspect the gear. If it looks like the teeth are mashed, or there is a worn spot, or any other kind of damage, this is your problem. If it looks okay, try to look into the hole in the transmission where the gear was inserted; there is another, larger, plastic gear in there. Try to see if this gear is okay; a small flashlight might help or you can use your finger to feel around. If the gear inside the tranny is damaged (or missing!) this really sucks because you have to disassemble the tranny to change it.

3. If everything so far has checked out have a friend watch your speedometer needle while you spin the gear on the end of the speedometer cable with your fingers. If the needle doesn't move try spinning the gear in the other direction. You're not looking for a lot of movement on the speedometer needle, just a bump. If the needle doesn't move then your cable is broken or stripped and needs to be changed.

 

The plastic speedometer DRIVEN gears at the end of the cable are still available from Ford. The same ones used today have been used since 1960.

These gears come with either: 16, 17, 18, 19, 20 or 21 teeth.

These DRIVEN gears range in price from $2.02 to $3.47 each.
-----------------------------------------------------------
Inside the speedometer cable's housing is a woven steel core.

It was lubed at the factory, and was supposed to be lubed every so often, but prolly 99% of them were never lubed again.

After so many years, the lube dries up, causing the core to bind up in the housing and snap.

Every autoparts store sells a universal woven core kit.

Cut it to the correct length, crimp on the squared ends (come with the kit), lube it with graphite or a thin coating of white lithium grease, install in the housing.

 

Actually there is a fourth step- make sure the thread is fairly recent, not seven years old.