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MG MGB Technical - early overdrive speedometer

I know that there's a list on all speedos for all year MGBs but for the life of me can't find it. I have a 67 MGB with a retrofited type D overdrive. My present speedo is 1040 tpm. Before it broke it seemed to keep the right speed. I now need to buy another one so want to make sure I get the right one for the OD gearbox.

Thanks Andy
Andy Preston

Andy,

The 1040 tpm speedo's were fitted to non OD early cars (mine has one). The D type OD cars were 1020 tpm. This is however less than 2% difference, so in reality it'll make no real difference unless you need very accurate mileage for rallying etc. If you are getting a new one you might be as well to get the 1020 tpm one though if you can get hold of one.

Iain
67 BGT
I D Cameron

Andy,
Try going to the North American MGB Register site.Chick on the tech section.It has a article on speedo applications. www.mgcars.org.uk/namgbr/speedo.htm
Tony
Tony Shoviak

It changed in 67, it all depends on whether it is a Mk1 or a Mk2. However if the D-type OD is correct for the rest of the car i.e. a 3-synch it should be a Mk1. The standard speedo is either a Jaeger SN6125/04 @ 1060tpm, SN6124/04A or SN6144/00 both Smiths @ 1040 tpm. OD is a Jaeger SN6125/06 @ 1040, SN6125/06A or SN6144/03 both Smiths @ 1020tpm.

You might like to have a look at http://www.mgb-stuff.org.uk/wn_miscframe.htm and click on 'Speedos'.
Paul Hunt 2

paul the sn6144/03 is kph and the /02 is mph
the others you qoute are mph
Ste Brown

Thanks Paul and everyone else. I now remember where I saw the chart before on Paul's site. I even have it in my favourites.

Mine is a 67 B with the non synchro first, so it should be the 1020 for OD. However there's so little difference between the 1040 and the 1020 I think that either will do. So I've just bought a 1040 on ebay which looks good.

Thanks for your help.

Andy
Andy Preston

Andy

I added the D OD to my 67 GT last year. I am running 175/70 R 14 tires. Prior to the switch I showed 62 mph on my speedo when my GPS said I was doing 60. With the OD and the 1040 speedo, I now show 60 at 60.

BEC Cunha

Thanks Ste - jumped a box when visually copying and typing.
Paul Hunt 2

This thread was discussed between 02/05/2007 and 03/05/2007

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