Classic Mustangs List Archive

This read-only message was archived from a public mail list.
Mail From: Rick Rickert (email redacted)

Just to brag on my usually unreliable car, my 69 Mustang made it from
Washington DC to Philadelphia this past weekend (170 miles each way),
surprisingly without any problems. The vibrations, however, confirm my
needs for a rebuilt front end.

The point of this mail however, is to find out how to calibrate a
speedometer, if thats possible. I was cruising along all weekend at about
60Mph (or at least thats what the gauge read). Gee, I thought it was odd
that I was going faster than most people on the road at 60Mph. Later in
the trip, I stopped off to get a friend who followed me in his car. On
this short stretch of my drive, I kept my speedometer reading 62Mph. When
I arrived home, my friend told me that we were doing 80Mph the whole way.
I had replaced my C4 transmission last summer with another C4. Could it
have different gears? I also went from 14" wheels, to 15" wheels, yet my
tires are lower profile, so I think the outside circumference of my tires
are roughly the same. Is there anyway to fix this?

Thanks,


-Rick
69 Convertible (302/4bbl/C4)

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This read-only message was archived from a public mail list.
Mail From: Mark Dixon (email redacted)

When Ford produced your car, the speedo drive installed was the correct
drive to match your tyre size, wheel size and differential ratio. Any
changes over the yeras on any or all these parts can result in serious
discrepancies between actual and indicated speed. Ford make (distribute ?)
a variety of different speedo drives. They are the plastic spiral
attachments which fit onto the end of the speedo cable where it enters the
grearbox. You'll need to calculate the following - diff ratio (if altered
since new), tyre size/wheel size (if altered since new) - and either talk
to a "guru" Ford partsman or similar transmission partsman about the drive
ratio you need. Alternatively, as they are cheap, but a variety of ratios
and test drive until you find the most accurate. Good Luck. Mark, Capital
Classics.

----------
> From: Rick Rickert <(email redacted)>
> To: (email redacted)
> Subject: [CM:12516] new tranny and off-set speedometer
> Date: 23 July, 1998 2:50 AM
>
> Just to brag on my usually unreliable car, my 69 Mustang made it from
> Washington DC to Philadelphia this past weekend (170 miles each way),
> surprisingly without any problems. The vibrations, however, confirm my
> needs for a rebuilt front end.
>
> The point of this mail however, is to find out how to calibrate a
> speedometer, if thats possible. I was cruising along all weekend at
about
> 60Mph (or at least thats what the gauge read). Gee, I thought it was odd
> that I was going faster than most people on the road at 60Mph. Later in
> the trip, I stopped off to get a friend who followed me in his car. On
> this short stretch of my drive, I kept my speedometer reading 62Mph.
When
> I arrived home, my friend told me that we were doing 80Mph the whole way.
> I had replaced my C4 transmission last summer with another C4. Could it
> have different gears? I also went from 14" wheels, to 15" wheels, yet
my
> tires are lower profile, so I think the outside circumference of my tires
> are roughly the same. Is there anyway to fix this?
>
> Thanks,
>
>
> -Rick
> 69 Convertible (302/4bbl/C4)
>
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This read-only message was archived from a public mail list.
Mail From: Mr Fomoco (email redacted)

Mark Dixon wrote:
>
> When Ford produced your car, the speedo drive installed was the correct
> drive to match your tyre size, wheel size and differential ratio. Any
> changes over the yeras on any or all these parts can result in serious
> discrepancies between actual and indicated speed. Ford make (distribute ?)
> a variety of different speedo drives.

[....]

Mark is correct, of course...so I'll just point out
a few related things:

- Odds are it was the tire/wheel change that screwed
up the speedo readout.

- In a C-4, the "drive" gear is part of the output
shaft. To my knowledge, they are interchangable
and could not cause this readout disparity.

- You can try doing a simple mathmatical calculation
to figure how many teeth your cable's driven gear
should have, but you're still subject to what gears
are available from Ford - some never existed and
several are obsolete.

- The Ford parts catalog has scrupulously detailed
entries - if your mix of equipment duplicates (or
even nearly does) an original setup, its easy to
match it up to the proper gear.

Hope this helps.
--
MrF
Allen Cross
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voicenet.com/~fomoco
Your online source for 1960-1973 Ford & L-M info

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This read-only message was archived from a public mail list.
Mail From: Rick Rickert (email redacted)

>a variety of different speedo drives. They are the plastic spiral
>attachments which fit onto the end of the speedo cable where it enters the
>grearbox.

I'm pretty sure I know the part you're talking about. If I remember
correcltly, its a white plastic piece about the size and shape of about 10
quarters stacked. ??

>You'll need to calculate the following - diff ratio (if altered
>since new), tyre size/wheel size (if altered since new) - and either talk
>to a "guru" Ford partsman or similar transmission partsman about the drive
>ratio you need.

I've been followed by friends now a total of 3 times, and each time I've
calculated that my speed is ~1.282x what the needle reads. Now all I have
to do is figure out what gear is in there (the gear is from a stock 1969,
250-6cyl motor, C4, 5-bolt hubs (in case that helps determine the rear)),
so that I can figure out what to replace it with.

>Alternatively, as they are cheap, but a variety of ratios
>and test drive until you find the most accurate. Good Luck. Mark, Capital
>Classics.

Does anyone know a good source for these? Is the dealership a good place
to start?

__________________________________________________
James "Rick" Rickert 1.800.488.6384 x5382
UUNET Technologies 703.645.4505 fax
Http://www.us.uu.net (email redacted)


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This read-only message was archived from a public mail list.
Mail From: Mark Dixon (email redacted)

Yeah, that stack sounds about right. All the ones I've seen have been
either light brown or light green in colour. However, a simple check for
the gear you have is this. Measure off a set distance using a tape, a
friends car or a known accurate distance between 2 points. Drive your car
that distance and record the shown on YOUR speedo. Comparison with the
known distance will give you the error factor. Now, remove your speedo
gear and count the teeth - as what you have is wrong, you can then
calculate whether you need a gear with more or less teeth. Then try your
tranny shop for the likely gears needed.
Alternatively, fit thecar with the same size wheels and tyres that it had
originally. If you have a friendly wrecker nearby, try scavenging gears
from "Ford" transmissions. Mark Capital Classics, Canberra.

----------
> From: Rick Rickert <(email redacted)>
> To: (email redacted)
> Subject: [CM:12541] new tranny and off-set speedometer
> Date: 24 July, 1998 6:31 AM
>
> >a variety of different speedo drives. They are the plastic spiral
> >attachments which fit onto the end of the speedo cable where it enters
the
> >grearbox.
>
> I'm pretty sure I know the part you're talking about. If I remember
> correcltly, its a white plastic piece about the size and shape of about
10
> quarters stacked. ??
>
> >You'll need to calculate the following - diff ratio (if altered
> >since new), tyre size/wheel size (if altered since new) - and either
talk
> >to a "guru" Ford partsman or similar transmission partsman about the
drive
> >ratio you need.
>
> I've been followed by friends now a total of 3 times, and each time I've
> calculated that my speed is ~1.282x what the needle reads. Now all I
have
> to do is figure out what gear is in there (the gear is from a stock 1969,
> 250-6cyl motor, C4, 5-bolt hubs (in case that helps determine the rear)),
> so that I can figure out what to replace it with.
>
> >Alternatively, as they are cheap, but a variety of ratios
> >and test drive until you find the most accurate. Good Luck. Mark,
Capital
> >Classics.
>
> Does anyone know a good source for these? Is the dealership a good
place
> to start?
>
> __________________________________________________
> James "Rick" Rickert 1.800.488.6384 x5382
> UUNET Technologies 703.645.4505 fax
> Http://www.us.uu.net (email redacted)
>
>
> ------------------------------------------------------------------------
> All the list info you'll ever want: antler.moose.to/~server/cm

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