to determine. On most vehicles, it’s a relatively simple matter to reach
up behind the instrument panel and unscrew the speedometer drive
cable nut (or collar) from the back of the speedometer head. It’s a good
idea to disconnect the vehicle’s battery first, because the ammeter
terminals are always live. Often, this nut is only finger tight, but you can
use pliers if you have to — just be sure to disconnect the battery. With
the drive cable off, feel for the little drive shaft within the speedometer
head and spin it with your fingers while watching the speedometer
needle. You might have to use a mirror on vehicles where it’s necessary
to get way down behind the instrument panel. Naturally, you’ll spin the
shaft in the direction of speedometer needle travel, although it won’t
hurt anything if you accidentally spin it backwards.
If the speedometer head is in good condition, the needle will instantly
flick up to 20 mph or more and then bounce right back to zero. Do this
several times. Both the needle and the little drive shaft should move
freely and smoothly, and the needle itself should flick and bounce
energetically. (This is also a good way to check out any speedometer or
mechanical tachometer at a flea-market or swap-meet.) If the needle
flicks and bounces freely, always returning immediately to zero, and the
little drive shaft rotates freely, then there’s usually nothing wrong with
the speedometer, and the problem is most likely a broken drive cable.
On the other hand, if the little drive shaft is difficult to turn and feels
as if it’s binding, and the speedometer needle is sluggish and only sort of
drifts back to zero, then the head may be worn out or simply needs to be
cleaned and lubricated (this is usually the case). In most of these
instances, the drive cable is also broken, because of the stress of trying to
turn a dirty or worn-out speedometer head.
On many vehicles, the drive cable’s inner core can be pulled out with
your fingers from the top (or speedometer) end, though on other
vehicles, it will have to be pulled out from the bottom (or transmission/
transfer case) end.
Most of the time in these situations, you will find that the cable’s inner
core is broken. This core will generally break at points where the drive
cable bends, often near the transmission/transfer case, or sometimes up
near the speedometer head.
This is not the best fix: A common mistake is to go to the nearest auto
parts store and buy one of those universal speedometer cable repair kits
singke
(singke)
#1