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MG MGA - mgb tach

Will an electric tach from an MGB work with the Metropolitan motor? Would you need to convert the car to negative earth for this change?

Yes and yes. You could have the tach rebuilt to make it work on a pos earth system, but it's easier to just convert the car to neg earth.
Bill Young

Yes. You can remain positive earth. See what Barney has to say:

However, the instrument will be labelled Smiths instead of Jaegar that is standard on the MGA.

Steve Gyles

Or I have a couple of Jaeger +ve earth tachos for sale off board
dominic clancy

You can also swap the faces over!
Neil McGurk


Any -ve ones?

Neil, swapping the dials over is not that straight forward. The screw holes do not line up on the one I have.

Steve Gyles

Thank you for the info. I was hoping that would work. I have access to a tach out of a 73 mgb gt. I guess that model is to small to fit in my dash.
Barney's site is great!

When you source the large diameter MGB tach, make sure you find one with the white wire loop attached on the back. The wire loop and nylon block are actually part of the car's harness, so it would have to have been cut out. They used to be available to buy, but I heard they are N/A. From examining mine it looks like it would be a pretty simple piece to make yourself. Your tach won't work without it.
Mark J Michalak

Steve, you can just drill two new holes, question is whether the new screw position is more obvious than the Jaeger/Smiths logo (one is in the "orange band" if I remember correctly). I suspect not because no-one looks for that! (The old screw holes are not that obvious)

Neil McGurk

I've never had anyone comment on the "Smiths" logo on mine. The most conspicuous difference is the trim disk on the needle hub. (See picture.) My car is positive earth.

David Breneman

Oh dear................

For MGA tacho conversions with MGB 5 main bearing motors use the 2401/ tacho can make this either +ve or negative

We can reprint dials to Jaeger so no hole alignment problems but you must supply a Jaeger pointer to make it look original and match your speedo
Ron Edmond

Also, if you want to put a pointer from the Jaeger mechanical tach onto the electric tach you need a bush or shim of some kind. The shaft on the electric tach is smaller in diameter. Did mine a long time ago and remember using some kind of shim but don't remember exactly what I used.

Jeff Schultz


I use the RVC 2415/OOAF with my MGB 5 bearing engine. I could be interested in the reprint you mention. Do you do the rebush that Jeff mentions?

Unfortunately, my Jaegar instrument is packed away for a house move and it may be several months before I see it again. Nevertheless, could you email me your contact details.

stephen dot gyles at virgin dot net

Steve Gyles

"You can also swap the faces over!"

Neil, I would really be interested in with your solution
I own both tachos and I would like yo keep on the original jaeger look on my electronic one. But I guess, it's not that straigh forward, am i right?

Guy, it's really quite straight forward. Remove the chrome bezel and glass by twisting until the tabs in the bezel line up with the slots in the case. Mark the position of the needle relative to the balance weight. The needle is removed by pulling (I use two screwdrivers on opposite sides under the flange levering on the edge of the casing) The face is then removed with two small screws. You can use the new face as a template for drilling new holes in the old face. Voila!
Neil McGurk

Hmm... I thought I just looked at this last month. It seemed to me that the scales on the Jager and Smiths tachs were not exactly identical which would lead to a slight miscalibration when the faces were swapped. Am I correct or did I drink too much craft beer this weekend?
Mark J Michalak

This thread was discussed between 27/05/2010 and 31/05/2010

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