Date:         Fri, 21 May 2004 07:00:39 -0700
Reply-To:     mark drillock <drillock@EARTHLINK.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         mark drillock <drillock@EARTHLINK.NET>
Subject:      Re: Syncro Speedometer
Comments: To: Budd Premack <bpremack@MN.RR.COM>
Content-Type: text/plain; charset=us-ascii

Yes, it is somewhat possible to use SOME Golf/Jetta/Quantum speedos in
the Syncro instrument cluster. Theses vehicle drive the speedo from the
tranny and have speedo cable speeds near the speed needed for Syncros. I
have seen speedos for these vehicles in different cable speeds for
different tranny/tire combinations. In order to fit properly you need to
use the back of a Vanagon type speedo with the G/J/Q instrument.
Sometimes some trimming of the rear part is needed. The face reads to a
higher top speed than Vanagon speedos do.

As for cable speeds, 1540, 1575, 1707 are the ones I know of.

The Syncro speedo cable is turning at a speed that is close to 1600 revs
per mile. If you put in a 1540 speedo it will get more revs than that
per mile and therefore read a HIGHER speed than the 1600 speedo did, all
else being equal.

My experience has been that US Syncro speedos read a little optimistic
in the stock configuration. Syncro speedo readings are slightly
complicated by the fact that the speedo cable is not driven by the left
front wheel like it is in 2wd Vanagons. On 2wd Vanagons the speedo cable
rotates exactly once for each time that the left front wheel rotates
once. Syncros have a small gear set in the front diff housing that is
used to drive the speedo cable. The gear set is driven by the pinion
shaft and this means that when different ratio ring and pinions are
installed in the tranny and front diff the speedo reading will change
unless a different speedo cable drive gear set is installed also. VW
sold several speedo cable drive gear ratios for Syncros to adjust the
cable speed for different tires sizes and r+p ratios. They only made one
speedo for Syncros that reads MPH and it is designed for 1600 cable
revs/mile, as printed on the face of the speedo. 2wd Vanagons here came
with either a 805 cable rev/mile or 820 cable rev/mile, again printed on
the face of the speedo.

Mark



Budd Premack wrote:
>
> Can a Jetta speedometer with the ratio 1540 be substituted for a Syncro speedometer with the standard 1600 ratio?  If so, will the typical 4% low speed reading be altered to about 8% low, or will it tend to correct to close to an accurate reading?
>
> My rusty math and high school physics concepts suggest to me that if the replacement speedometer had a ratio of 1664, the common 4% low error would be corrected.
>
> (1600-1540) / 1600 = 3.75% fewer revolutions (?)
> (1664-1600) / 1600 = 4.00% more revolutions (?)
>
> BTW, does anyone have a spare Syncro speedometer?
>
> Budd Premack
> 86 Syncro, 88 Wolfsburg
> Land of Sky-Blue Waters
> Minneapolis, MN