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MG MGB Technical - Overdrive Speedo

I've just bought a MK1 mgb roadster built in Oct.65.

The car originally did not have overdrive, but a previous owner has installed overdrive. No modifications have been done to the speedo. Will the original speedo work, do I need to re-calibrate this speedo, and how do I recalibrate?
W.D. Lamprecht

Hi:

If the car was built in October of 1965, then the speedo and other gauges are made by Smiths, Previous cars had Jaeger gauges and had different part numbers. The correct speedo for a 1965-67 MGB with a 3 synchro "D" type overdrive is SN6144/02 @ 1020 turns per mile (TPM). The non overdrive part number is SN6144/00 @ 1040 TPM. If your car has an all synchro gearbox with "LH" overdrive then that is another story and more difficult to solve. I have not had any problems finding the SN6144/02 speedos at swap meets or on e-bay or this site in the classified section.
In either case the accuracy of the gauges is not very good. I know some early MGB owners that use the non overdrive speedo with the overdrive face plate. I have one in my 67 B at this time.

Look around, and you will find them. You can have Bob Cassinetta at Nisonger recalibrate your existing speedo for the 1020 TPM. That is for the dial indication, but for the odometer, you need to replace the gears.

Good Luck: Rich Boris.

PS: There are Vendors, like Strictley British in Ohio, who have these gauges NOS, bur expect to pay $ 150 or more.

Rich Boris

WD,
There really is no need to worry with an OD Vs. non-OD Mk I speedo unless you are worried about small details. There is a 2% difference in the two types and the gauges weren't tha accurate when new. I have a '66 that I added overdrive to.
David
David

...which could easily be negated if your running andything besides 155/14 tires. The difference is so minute, not worth the worry. I had a friedly policeman shoot the radar gun at me going 45mph on my speedo (non o/d) with o/d conversion. We both read 45 mph w/ 175/14 tires.

Paul
Paul Hanley

This thread was discussed between 17/01/2004 and 18/01/2004

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