[Shotimes] Is the speedo servicable?

[Leigh Smith]

Yes!
For James, and George and others:
If you have changed the cable and that didn't help, and you really believe
it is the head unit, take it to a speedometer calibration shop. They used to
be commonplace, you should still be able to find one. Or you can test it
yourself. Failing that, I would get a yard unit and install that. You should
be able to find a whole SHO guage cluster very easily. You could just swap
out the bad speedo head unit. Speedo head unit calibration is very touchy,
and I do not recommend fooling with it. If you are worried about the mileage
odo, that part is pretty easily reset or swapped between head units to keep
your original. All you need is a set of jewelers micro-sized screwdrivers.
Reset the mileage back to the original setting, or you are looking at a
felony offense. Or you could put a door sticker on it saying the odometer
has been replaced. There are several pics of gauge clusters on the net, most
cars are fairly simlar, and fooling with the gauge cluster is pretty common
these days with all the white-faced guages, etc.
TEST: I would run a simple test first to test the calibration of both the
odo and the speedo independently, see if the speedo head unit went bad. The
speed and the odo are connected mechanically and magnetically and should
both read correctly at the same time. If they are both "high" by the same
amount it is probably just a low-profile tire size issue. If they have
separate error rates they must be re-calibrated separately. Find a several
mile stretch of road with mile markers. The odo has a direct mechanical
connection, so it is the most important. It should read exactly 1 mile
between mile markers, to better than 1 tenth. You should do the odo part for
at least 5 miles to get really good answers, 10 is better. 1 tenth mile
marker error at ten miles is one percent odo error. Should be 2-3% or less.
If that reads OK, proceed to step 2, check the speedo. It has a magnetic
connection, which can get fouled up., relative to the odo. Drive exactly 60
mph. You must be within 1 mph at all times, and this will take some
practice. If you are 1 mph over for 4 seconds you must correct by going 1
mph under for 4 seconds.  Stopwatch between mile markers. It should read
exactly 60 sec, within 1 second.  2 or 3 miles of this should suffice, if
you are steady.  If the speedo is off, but not the odo, then the magnetic
drive is "off", change the head unit, period. It's even hard for a speedo
shop to fix. And costly. But it is not usually bad, although it can happen
(right, George?) If the odo is off, fix the mechanical gearing / tire sizes
first. I doubt if you can get get different Ford trans speedo gears to
correct this, if you have an non-stock tire size, so find a speed shop and
they can set up a speedo gear ratio reduction box for you. It goes in the
speedo cable line. Had one on my 70 Z28 from the factory (w/4.11s) and I had
to change the reduction box every time we switched the rear axle ratio.
The shops are still around somewhere, cause the cop cars have to get theirs
re-checked all the time. The difference between a new tire and a worn-out
one is at least 1-2 mph.

Lee
----- Original Message ----- 
From: "James B." <silver1995mtxsho@sbcglobal.net>
To: <shotimes@autox.team.net>
Sent: Monday, March 28, 2005 5:16 AM
Subject: [Shotimes] Is the speedo servicable?


> I have a speedometer issue, not the common cable issue, I believe the
> bearing in the back of the speedometer is bad or the magnetic induction is
> severely off.
>
> Is there anything back there that is serviceable or swappable between
> clusters? I would rather "rebuild" the one I have rather than replace it.
I
> do not want to take all the time to take it apart and have to put it all
> back together without having a game plan, as it's my daily driver. I am
just
> looking for a heads-up. If anyone has a cluster out of the car and can
take
> a couple pictures of the back of a cluster for me to get an idea what is
all
> hidden in my dash that would be great, e-mail me off-list.
>
> James B.
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