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MG MGA - speedometer odometer incorrect readings

Both the speedometer and the odometer of my mga 1500 (with early mgb engine, original mga gearbox, correct tyre size) give incorrect information about tempo and covered distance. Driving approx 50 kmh the speedometer reads some 55 mph, driving 70 kmh it reads approx 75 mph. After driving 1 km the odometer shows a covered distance of 2-3 miles.
Where to start to tackle the problem? The dash instrument is new / revised.
jan donders

... of course: my message earlier today deals with a problem many mga owners have (had) and quite a lot of them will feel a bit tired to reply.
... of course: I paid some visits to the pages of Mr. Barney Gaylord, but his explanations and advice go far beyond my technical capabilities.
... so I would appreciate some general advice in terms of what to check step by step in such a way that I can help the guy who takes care of my car following the right track...
jan donders

Jan,
Yes, many of us have had the same problem. Mine were the result of changing the differential gears from 4.3 to 3.9. The early 3 bearing MGB engine is not a factor. Since you, like me, are not wanting to open up the speedometer, I suggest you have the speedometer rebuilt and recalibrated to your car. There are lots of parts (gears, magnets, etc.) that can wear out after 50 years of use.

I used the services of MOMA in Albuquerque, New Mexico, USA. Margaret Lucas is the proprietor of that company and they did an excellent job for (as I remember) about USD$150.

It requires a small amount of work on your part: creating a pointer out of cardboard for your speedometer cable, putting a chalk mark on the rear tire and having someone push the car for a specified number of rear wheel revolutions while you count the full and partial turns of the cardboard pointer. MOMA will send you a form that explains the process; it has places to write in the results and the form is sent back to MoMA with the speedometer.

There are other companies who will do this job as well (Nisonger in New York, and a company in California). The guys on this board on your side of the pond may be able to recommend a company in the UK or Europe. To contact Margaret Lucas: momanm@aol.com.

Frank
Frank Nocera

Jan,

The first questions are;
What is the Smiths Number on the face of your speedometer?
Do you have a copy of the book "Original MGA" by Anders Clausager? If so, have a look at page 51.
Do you know how to measure the rear axle Differential ratio by raising one wheel off the ground and turning the engine in top gear? (If you have not done this there is a trick for new players. See next episode!!).

Mick
Mick Anderson

You can see how to check your speedometer here:

http://www.gaugeguys.com/ratiotest.htm

http://www.speedometershop.com/ratio.html#GEAR
CDD Dewey

Jan

You need to know your rear axle ratio and your tyre size, then send the unit to Keith Swindell in the UK, who can recalibrate it for you.

His address is in the archive

dominic

This thread was discussed on 27/10/2005

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This thread is from the archive. The Live MG MGA BBS is active now.