speedo drive gear ratio question

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sonoramicommando
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speedo drive gear ratio question

Post by sonoramicommando » 04 Oct 2016, 22:11

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
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2006 C6 Exclusive 2.7HDi
1982 GSA Pallas
A couple of bikes
A boyracer car ;)

aerodynamica
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Re: speedo drive gear ratio question

Post by aerodynamica » 06 Oct 2016, 18:51

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?
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Graeme M
1993 Xantia 1.9 TD VSX Mk1 Sinker. 'Old Katy'

sonoramicommando
Posts: 288
Joined: 07 Sep 2011, 11:03
Location: Nouvelle-Zélande
My Cars: GSA & C6
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Re: speedo drive gear ratio question

Post by sonoramicommando » 06 Oct 2016, 20:14

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
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2006 C6 Exclusive 2.7HDi
1982 GSA Pallas
A couple of bikes
A boyracer car ;)

aerodynamica
Posts: 743
Joined: 26 Dec 2007, 19:10
Location: Glasgow
My Cars: 1993 Xantia 1.9 TD VSX Mk1 Sinker A.K.A Slugmobile 13'
'Old Katy'
x 10

Re: speedo drive gear ratio question

Post by aerodynamica » 06 Oct 2016, 22:11

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..
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Graeme M
1993 Xantia 1.9 TD VSX Mk1 Sinker. 'Old Katy'