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MG MGB Technical - MGB GT Speedometer
|Please can anyone tell me the number that should be on a 1967 MGBGT 3schcro speedometer as the one I have in the car was replaced by the original owner and does not read correctly. I was told it was replace just in order to sell the car|
|Overdrive or non-Overdrive? A UK 67 without OD would originally have had a 1060tpm Jaeger or a 1040tpm Smiths, and one with OD a 1040tpm Jaeger or a 1020tpm Smiths, although the differences between them as far as readings go is obviously minimal.|
If you have a 1280tpm as for 4-synch chrome bumper cars (as in the attached, reference number and tpm under the odometer) it will be way out. The originals are likely to be rare and expensive. Rubber bumper cars used a 1000tpm speed, which is close but will under-read by a few percent, however as most are calibrated to over-read by a few percent it should be close enough. However the speedo size on UK rubber bumper cars went down to 80mm from 4" so a UK one will not fit. Paradoxically USA speedos went back to 4" from 80mm with the change to 1000tpm, so that's a possibility.
I had a similar problem with my 1970 GT when I bought it, and needed to go from 1280TPM to 1000TPM. I bought a 1000TPM speedo from the internet and it was 80mm. (Both Smiths). You can remove the needle and face and swap the 80mm movement into the 4". The zeroing cable on the 80mm is on the back and the 4" is on the bottom. You need to drill one small hole in the movement from the 80" to fit the 4" one. The small black screwdriver is through the drilled hole in the photo.
|"with my 1970 GT when I bought it, and needed to go from 1280TPM to 1000TPM. I bought a 1000TPM speedo ..."|
I take the point of using the guts of one in the case of the other to retain the appearance. But just to be clear, a 1970 should have a 1280tpm, not a 1000tpm. Unless that was a typo, it sounds like your 1970 had a rubber-bumper gearbox.
|All very interesting, as I am intending to convert my car to overdrive when it goes back together.|
One of the gearboxes that I have came from a low mileage R/B car. I will have to change my speedo anyway, so it doesn't really matter which gearbox I fit.
|Dave O'Neill 2|
When I bought the car the speedometer was very far out. I cant remember how much but it was in the region of 12 MPH. I think the OD was from a different model, as the 1000tpm corrected it and the GPS and the speedometer are now within 1 MPH of each other. I was only trying to indicate that it was possible to use the inside of the small one in the large case. I did put a label on the casing for the benefit of any future owner as the dial obviously still states 1280tpm.
|I needed a 100mm (4") 1000tpm for my 67GT because it has a late RB 4 sync o/d.|
If you want one that is direct fit without having to swap internals, do like I did and purchase an MG Midget 100mm 1000tpm speedo.
|Here's a photo with the serial numbers.|
That would have been an easier way, but I never thought of using one from a Midget. I also did not know I was buying a 80mm speedometer until it arrived !!!!.
|BTW, don't type 'Midget speedo' into Google ...|
This thread was discussed between 19/07/2014 and 22/07/2014
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