[Healeys] Lempert Gears

Bob Spidell bspidell at comcast.net
Wed Feb 22 21:26:34 MST 2017

The odometer and trip meter gears are driven by a worm gear driven 
directly by the speedo cable.   These have to be changed if the diff 
ratio is changed (well, if you want the odometer and trip meter to be 
accurate).  These gears are known to crack and can produce a speed 
indicator that 'jumps' in proportion to speed.

Thanks for the info on the speed indicator adjustment; always wondered 
how that was done.  I thought they might change the 'watch' spring that 
resists the magnets.


On 2/22/2017 8:10 PM, WILLIAM B LAWRENCE wrote:
> Actually it is simpler than that. The speedometer is trimmed by 
> varying the amount of magnetic flux in the permanent magnets in 
> the speedometer head. This is accomplished by placing the gauge in a 
> machine that can adjust the magnet's strength. A good gauge shop can 
> do this if they know the number of turns the cable makes when it runs 
> over a set distance. Usually they ask you to count the number of turns 
> the cable makes as the car is moved 53 feet. Multiplying by 1000 gives 
> the number of turns per mile and the gaussing/degaussing machine does 
> the rest.
> Bill Lawrence
> BN1 #554
> ------------------------------------------------------------------------
> *From:* Healeys <healeys-bounces at autox.team.net> on behalf of Bob 
> Spidell <bspidell at comcast.net>
> *Sent:* Wednesday, February 22, 2017 2:29:54 AM
> *To:* healeys at autox.team.net
> *Subject:* Re: [Healeys] Lempert Gears
> Yep.  Going from 3.9:1, for instance, to 3.54:1 will cause your speedo,
> odometer and trip meter to indicate about 11% low; e.g. if you're
> indicating 60MPH you'll be doing about 67.
> You can:
> 1) get new gears for the odometer/trip meter and get the speedo 
> calibrated,
> 2) get an inline ratio adapter,
> 3) get a GPS with real-time speed readout
> 4) get good at multiplying by 1.11 in your head
> Bob
> On 2/21/2017 5:37 PM, 1 2 wrote:
> > Sorry if this has been asked and answered.  Will the Lempert gears
> > change how the speedometer reads? Or is it independent?
> >
> > Thank you
> >

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