Possibilities:
...by reusing the original speedo cable instead of the longer OD cable, it
now has tight bends which cause friction...
... Or the cable is worn and needs replacing...
... Or the right-angle adapter (if present) is worn...
... Or the speedo itself needs cleaning (probably least likely).
I doubt that merely lubing the cable will make much difference. BTW the
speedo shop which sold me a new cable for my other car told me to use the
least amount of lubricant possible.
I would be almost certain that you have the "wrong" pinion for your
speedometer, but in certain cases a speedometer swap might be a solution
(for some applications no appropriate one is available). The problem is
that, depending on the year of vehicle, speedo, OD, and size of tire fitted,
there may not be a pinion available, either, which will give a perfect
reading. I am living with about a 6% low reading right now.
This is with a 66 MGB with a 1977 OD tranny, and 175R14 tires.
on 11/22/04 7:49 AM, Derek Vandivere at derek@vandivere.net wrote:
> So my mechanic, about a year ago, converted my 78 B to overdrive.
> Hooray! I now have two problems with it: the speedo is now very jerky,
> tending to settle down a bit more at speed (around 20 mph, it jerks
> between 0 and 40, but only oscillates by 10 mph or so at 70 mph).
> Second, it consistently reads about 10 mph (maybe 10%, actually) lower
> than my actual speed (as measured with a GPS).
>
> For the first problem, do I correctly remember that powdered graphite
> is a good lubricant for the cable? Funnily enough, Dad still had the
> tube left over from a Pinewood Derby, so I'm set there.
>
> For the second problem, my best guess is that the OD has the wrong
> speedo pinion on it (Moss parts 462-610 or 462-615 for OD, but I
> suspect he may have just left the original non-OD pinion on, if that's
> possible). Would that be at all consistent with reading low all the
> time? And am I correct in thinking that which pinion you use depends
> on the marking of the OD unit itself?
>
> (or should I just give up and go back to my mechanic and tell him it
> just don't work and he should fix it? it's been a bit of a saga with
> this speedo...)
>
> Thanks,
> Derek (78 B in Amsterdam, and now a 2002 Saab 93 diesel for the commute)
>
--
Max Heim
'66 MGB GHN3L76149
If you're near Mountain View, CA,
it's the primer red one with chrome wires
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