[xk] speedometer calibration

My recently purchased 1953 XK-120 shows a much faster speedometer
reading that acutal speed. How would one begin to calibrate the
speedometer with acutal speed? The maintance manual that came with
the car doesn’t address this issue.–
Carl Myatt
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

Smith made speedometers with a variety of ratios to be compatible with the
differential ratios. There should be a number on the face of the speedometer
that identifies which one you have. It’s possible that your speedometer has
been replaced with one that looks the same as the original but is for a
differential with a lower ratio.

Carl,
Also, your wheel and/or tire size will also affect the speedometer reading.
Likely at least the tires have been replaced and are of a slightly different
overall size. Most people simply have someone follow them at highway speeds
and make the mental adjustment required to travel at, say 60 mph, etc.While
our Jaguar instruments by Smiths are relatively better than most of the 50s,
speedometers etc. of the period are not known for there accuracy. And the
amount of discrepancy varies at different speeds, due to the nature of the
construction. Your speedo and/or cable might also need refurbishing. I’ve
used “MoMa” in Albuquerque, New Mexico (no affiliation) several times with
success.
Or, if you have an OTS, use my method by judging how fast you’re going by
the wind in your face. (;-).
Jerry Oliver
Olympia WA----- Original Message -----
From: “newhouse” cmyatt3363@aol.com
To: xk@jag-lovers.org
Sent: Saturday, September 13, 2003 5:14 AM
Subject: [xk] speedometer calibration

My recently purchased 1953 XK-120 shows a much faster speedometer
reading that acutal speed. How would one begin to calibrate the
speedometer with acutal speed? The maintance manual that came with
the car doesn’t address this issue.

Carl Myatt
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

In reply to a message from Jerry Oliver sent Sat 13 Sep 2003:

Jerry.The 4 digit no. near the centre of the speedo is the number
of turns per mile that the speedo is calibrated for.
You could do a calculation… diameter of the out side of the tyre,
as measured, by pi divided into a mile and see how it compares with
the number on the speedo.
If it reads fast , it may be that you have a speedo from a saloon.
Is it a 0-140 mph speedo?
Depending on what diff ratio you have, it may be from a a car with
a different final drive ratio.
Or your CW&P may have been changed to a different ratio.–
Ed Nantes SS
Melbourne, Australia
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

In reply to a message from newhouse sent Sat 13 Sep 2003:

Carl;
The wonderful truth is that your XK 120 Jaguar is SO sleek, fast
and powerful that it feels to be going slowly when in fact it is
traveling far faster than it seems. (This is especially true when
the 120 is a Drop Head Coupe.) When it feels like a nice sedate
(legal) 55 mph, you are actually streaking over the land at
aproximately 70 mph’s, or MORE! This is how you get to meet so
many nice police officers that really love your beautiful cat.

Well, you’ve heard the story from the knowledgable folks on this
board. Who do you want to believe? :-^

Roger :-^–
Roger, 1954 120 DHC BRG, S678300
Tamarac, South Fla., United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

Hi Guys
I have had all my instruments rebuilt for my 140 and a set of
instrutions came with the speedometer. I do not have the papers with me.
Basicaly it says to remove the speedo drive cable from the rear of the
speedo, fix a pointer pointer on the square part of the cable. Put a mark on
the side wall of a tyre and the floor then push the car back or forward for
2 revolutions of the tyre and count the turns of the speedo cable, the
number of turns of the cable will give you a reference point to adjust your
speedo head. This will also allow for tyre/wheel changes from original. I
should be back home in about 2-3 weeks and will look out the paperwork and
send a PDF so you can follow the instructions to correct your speedo
Cheers Ian>From: “Jerry Oliver” slantws@comcast.net

Reply-To: xk@jag-lovers.org
To: xk@jag-lovers.org
Subject: Re: [xk] speedometer calibration
Date: Sat, 13 Sep 2003 08:42:07 -0700

Carl,
Also, your wheel and/or tire size will also affect the speedometer reading.
Likely at least the tires have been replaced and are of a slightly
different
overall size. Most people simply have someone follow them at highway speeds
and make the mental adjustment required to travel at, say 60 mph, etc.While
our Jaguar instruments by Smiths are relatively better than most of the
50s,
speedometers etc. of the period are not known for there accuracy. And the
amount of discrepancy varies at different speeds, due to the nature of the
construction. Your speedo and/or cable might also need refurbishing. I’ve
used “MoMa” in Albuquerque, New Mexico (no affiliation) several times with
success.
Or, if you have an OTS, use my method by judging how fast you’re going by
the wind in your face. (;-).
Jerry Oliver
Olympia WA
----- Original Message -----
From: “newhouse” cmyatt3363@aol.com
To: xk@jag-lovers.org
Sent: Saturday, September 13, 2003 5:14 AM
Subject: [xk] speedometer calibration

My recently purchased 1953 XK-120 shows a much faster speedometer
reading that acutal speed. How would one begin to calibrate the
speedometer with acutal speed? The maintance manual that came with
the car doesn’t address this issue.

Carl Myatt
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–


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Hello

I too have an inaccurate speedo. Were you ever able to locate the instructions about how to adjust the speedo?

Thanks

They are not adjustable in the sense you mean.
They operate by proximity, a magnetic disc rotating near a springy disc with the needle attached to it.
The calibration is by selecting the tension of the return spring on the needle, and by the gearing in the gearbox, e.g. straight or 90 degree.
Nisonger Instruments in Mamaroneck New York nisonger.com and Palo Alto Speedometer in Calif paspeedo.com can do it.

My speedo is relatively accurate but I drive by the tachometer. In 4th gear if the tach reads 3500 I’m doing 70 mph in my 140 with a Moss box and original (3.45) rear.

as \Rob said…go to the Nisonger web pages…they rebuild to suit…and provide the measurments of rolling distance you need…and they need. Of course it would need to be with the wheels/tires you intend to use…and keeping same diff ratio. There are several archive posts listing the Smiths numbers on the face referenced to which cars/diff ratio etc.
Nick

The Nisonger web page says that due to extensive damage to their facilities from Hurricane Ida, they are exiting the business of repair of Smiths instruments. I plan to send mine out soon for testing and repair and refurbishment as needed. Are there other reputable providers of this service?

[quote=“avd5613, post:11, topic:288644”]
Nisonger web page exiting the business of repair of Smiths instruments
[/quote]wow…that is a loss of a needed resource
Nick

Nisonger was good. I have not tried Palo Alto.