speedo drive gear ratio question

[sonoramicommando]

Hi,
A bit of a silly question - I have a spare rolling drum speedo I want to chuck on a non-CX, so wanting to know the speedo gear ratio to see if the speedo reading will work out.
Cheers,
Sam

[aerodynamica]

Tricky question as some different drum speedo CXs actually have different ratios. The early cars with the yellow drum and the black figures -I think- were all the same ratio (whatever it was..) but when the 2.0 litre Douvrin engine (CX Reflex, Athena, 20 Pallas, 20 RE and TRE) came along it had a different ratio. And to complicate matters the speedo drum changed during the Reflex and Athena models so some have the yellow drum and others the later black drum with red/ yellow figures. I think the CX 25, where it had the drum speedo, i.e later mk1 GTi (not turbo) used a different ratio (it might be the same as the early CXs).

One final thing is that the speedometer drive on CXs goes into a splitter unit forst to send a second speedo drive to the DIRAVI steering speed controller. However, on 'C-Matic' semi-automatic CXs this isn't used - there are simply two speedo cables coming out the transmission (though on the C-matic I think the ratio is the same as other first type CXs with the yellow drum).

I might be able to look up the CX service manuals I have if the info is there but I am not sure that it is. There might be a way of working it out though using a drill to drive the speedo at full drill speed and see what speed comes up then do the same for the speedo you're replacing and compare?

[sonoramicommando]

Oh that is a bit tricky - it is black-on-yellow but not sure the exact spec of the car it's from.
Too hard basket it goes. It's a groovy looking thing but can't say it's particularly functional from my experience...
Thanks!
Sam

[aerodynamica]

Ha don't give up if you've got a plan! If it's the black-on-yellow then it's a series one and I reckon they are all the same speed. They're meant to work behind a magnifying lens too, the lens vanished with the yellow drums around 1981 when the later ones came alog with the black drum and no lens. The early ones are my faves..