<VV> slow speedo

[Tony Underwood]

At 11:44 AM 5/25/2010, ncoonen at fastbears.com wrote:
>Tires: 185/80-13 KingStar radials from Les Schwab in Winnemucca, NV 
>(good story here)
>Speedo gear: seems unlikely the gears have been changed but I am not 
>the original owner; it is definitely an original three-speed car.
>Speed test: has been timed using mile markers and paced by known 
>good speedo cars
>
>Yup, it reads low...ned.




Not unusual for an early 'Vair speedo.   They often get "slower" with age.

The pointer of an early (or late for that matter) 'Vair speedo is on 
a meter movement and is "connected" to the speedo cable by a cup and 
armature coupling that uses a magnetized armature inside (but not 
touching) a cup which inductively drags the cup around, moving the 
pointer against a spring.    It's actually a bit more sophisticated 
than that but the explanation is basically how the speedo works.


The place I worked for that did GM (among others) sound system 
warranty and dealer work also repaired and calibrated 
speedometers.     I calibrated several of my own, including my 
brother's Yugo speedo.   Rebuilt the odometer and meter movement of 
my Corsa speedo while working there with existing new (then) stocked 
parts off the shelf which kinda surprised me since much of the 
mechanical speedo and odo stuff was for 1980s and '90s GM vehicles 
and it still fit the Corsa speedo.

It was also reading slow and stuck often, smack the dash to get the 
pointer's worn bushings to allow it to return to zero etc.   Pretty 
much wear and tear, meter movement would rattle in the bushings.


I have about 4 early speedos that all read slow... might someday fix 
them...  just recently redid my '60 speedo that was lying to me 
bigtime but didn't have the right drive specs to correctly calibrate 
it after remagnetizing the armature so now it reads a little high 
instead of really slow...  I'll fix it later but for now it's working 
well enough for me to know that 70 is actually 60 on I-81 on the way 
to work clicking stopwatch on mile marker posts.    I really should 
have nabbed the speedo drive box from the shop when I had the 
chance... they had stopped doing speedos and the drive box with both 
magnets got stuck in the back under a bench, never used again.


Anyone with the right hardware (which includes the drive box and two 
electromagnets, one a filtered DC magnet and the other an AC magnet) 
and some smarts can calibrate a 'Vair speedo.    The trick is the 
hardware and the smarts, as in knowing the right rpm of the 
cup/armature so as to get an accurate calibration.


Talk to Lew, he has the hardware and the smarts.  :)




tony..