9 replies to this topic

[Moon_bear]

Good morning, would any body be able to tell me the correct speedo for a 78 1275gt? 
 

I have to tried to google it, however have found different answers. Some have said the ones that go to 120mph, others 130. I have even found a site that has said 90mph, I am so confused.

[Spider]

Here's a few sets I have to hand

 

 

 

The top 2 sets are early sets and were also fitted to our locally assembled Clubman GT, which was essentially a Cooper S in a Clumban Body shell, quite different to the (UK) 1275GT, though these were fitted to the 1275GT to (as best I can determine) 1975.

 

The lower set was fitted to the 1275GT from 1975 to (as best I can determine) the end of their production.

 

The speedos were 120 MPH / 200 kph. As far as I know, they were all dual scale.

 

The Tachos from 1969 to 75 were redlined at 6500 RPM however from 1975 on, this was reduced to 6000 RPM as per this lower set. Note too, the Fuel and Temp Gauges have 'red' zones on these later gauges.

 

Other differences are the early types had a screw on speedo cable, and later they changed to a clip on type.

 

Also around 1974 - 75 (?) the Tachos were changed from an RVI to a RVC type.

[Chris1275gt]

Good morning, would any body be able to tell me the correct speedo for a 78 1275gt? 
 
I have to tried to google it, however have found different answers. Some have said the ones that go to 120mph, others 130. I have even found a site that has said 90mph, I am so confused.

These are off my 75 gt the tacho is a rvl with bullet connections. The speedo is the clip on type cable. They are all the same as my 80 gt had except for the tacho wiring.

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[slidehammer]

I am sure my old 1978 1275GT had red zones in the temp and fuel, speedo went up to 120mph with kph in the middle and red lined at 6,000 rpm (the only way you would get a standard engine there would be down hill in second gear, I think they ran out of puff really around 5,000 rpm) Edges of the round bezels where painted silver. So looks like the bottom ones to me.

[Moon_bear]

Thank you all so much! The previous owner has changed the clock and it’s out by around 15mph :/ so I’ll need to track down a 120mph one.

[Matt Halsey]

Can I simply swap out a 120kph speedo for 90mph for 90 Mini Mayfair or is there more to it?

Also, if I have a 3 gauge, it looks like the taco is separate so can I just replace the speedo and center dial?

[Chris1275gt]

The tacho was always an add on to the Speedo and centre dial as far as I'm aware so I would say yes.

Edited by Chris1275gt, 08 March 2021 - 06:50 PM.

[Spider]

Can I simply swap out a 120kph speedo for 90mph for 90 Mini Mayfair or is there more to it?

Also, if I have a 3 gauge, it looks like the taco is separate so can I just replace the speedo and center dial?

 

You need to check and convert the TPM and TPKM numbers of the Speedos and then possibly change the Speedo Drive Gears in the Gearbox (which are accessible with the engine in, but a fiddle), or, fit it, go for a drive with a GPS, and at a true higher speed (say 50 MPH / 80 KPH) note the error, then remove the Speedo Drive Gears to see what you currently have and then work out what you need.

[Matt Halsey]

I have the Haynes manual but dont see this quoted.  Where can I find out the TPM and TPKM ratios?

[Spider]

I have the Haynes manual but dont see this quoted.  Where can I find out the TPM and TPKM ratios?

 

They are usually on the face of the speedo, in very small numbers. Some of the late Gauges don't have them printed on them, for these you need a felt tip marker, a bench type magnifying glass and lots of patience to count the gear teeth in the Speedo itself. For these, I don't bother working that out, I just use the trial and calculation method that I suggested, using a GPS. It's much more accurate too.