Syncro 1600 speedo

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spanishfly
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Syncro 1600 speedo

Post by spanishfly »

Please can anyone tell me the difference (apart from the face) between a syncro mph 1600 and a 2wd mph 805 speedo?
 
1987 Westy Joker 1.6TD
1987 Dehler Profi 2+2
1988 Syncro RHD panel
 

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Aidan
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Re: Syncro 1600 speedo

Post by Aidan »

the speedo drive is calibrated to half the revs on the 2wd one, if you fit one to a Syncro it will display double speed, ie. indicate 60 at 30mph
the Syncro speedo drive is gear driven from the front differential and runs at approximately twice the speed of the road wheel , or is it half the speed, I am not sure :D (and speedo drive is dependent on wheel size and final drive ratio fitted), 2wd speedo cable is direct driven at wheel speed and is only calibrated to standard tyre 185R14C; 205/70/14 is close enough not to worry about the difference, it is within permissible error standard for speedos of that era)
the figure 805 is the number of rotations (x100) of the speedo cable required to measure vehicle travel 1/100th of a mile
Last edited by Aidan on 27 Nov 2021, 04:37, edited 1 time in total.

spanishfly
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Joined: 09 May 2013, 14:43
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Location: Launceston, Cornwall

Re: Syncro 1600 speedo

Post by spanishfly »

Thanks for the reply Aidan.

What I'm trying to work out is how that happens?

From my investigations so far comparing 805 with 1600 speedos the cog and worm drives under the magnet appear to be the same. 93 +/_ rotations of the cable by hand appear to equate to about 1 revolution of the post that drives the odometer, this wheel has 16 teeth so more or less 1600 revolutions would click over a number but that is true of both speedos.

I was perhaps expecting a difference of 2 times somewhere by different numbers of teeth reflecting the different circumferences of the driven wheel versus diff.

What does appear different is the thickness of the magnet on the drive platter. Could it be that the size of the magnet is the mechanism that controls the calibration? Or I guess more likely the hair spring?

Perhaps I'm over thinking this? Or missing the blindingly obvious? 

Not just idle curiosity ultimately I'm trying to understand if I can use an 805 rotor/platter to repair the 1600...... :roll:
1987 Westy Joker 1.6TD
1987 Dehler Profi 2+2
1988 Syncro RHD panel
 

spanishfly
Registered user
Posts: 305
Joined: 09 May 2013, 14:43
80-90 Mem No: 12044
Location: Launceston, Cornwall

Re: Syncro 1600 speedo

Post by spanishfly »

Have tried rebuilding many times using parts from a donated 2wd kmh speedo 500 (thanks!), a 2wd MPH speedo 805 and the remains of the original I have realised, a bit late in the day perhaps, that the crucial elements are the strength of the magnet and of the spring. Using parts from a combination of these and a golf mk2 1540 speedo I now have a fully functioning and reasonably accurate 1600 syncro speedo again... fiddly but doable..
Success!
1987 Westy Joker 1.6TD
1987 Dehler Profi 2+2
1988 Syncro RHD panel
 

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