Date: Sun, 6 Aug 2006 09:55:04 -0500
Reply-To: Allen Hill <route66rider@KNOLOGY.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Allen Hill <route66rider@KNOLOGY.NET>
Subject: Re: Reasonable cruising speed?
In-Reply-To: <002a01c6b8be$52a3c780$6400a8c0@notebook>
Content-Type: text/plain; charset="iso-8859-1"
SPEEDOMETER REPAIR 101:
Many long years ago when I was just out of high school I had a job in an
auto parts house. One of the things that I learned to do there was rebuild
and calibrate speedometers. Yes, believe it or not, in those days we
actually did rebuild things rather than just replace! The main part of the
rebuild was the "T" shaped magnet (the part that directly connects to the
cable) which was removed and new shaft bushings installed. After the
rebuild, the unit was mounted on a bench calibration tool and the strength
of the magnet was either increased or decreased to adjust the MPH reading.
There was also a small spring on the cup (the cup turns in the center point
of the magnet and has the pointer attached to it) that is also moved to
adjust the speedometer MPH reading.
As to the odometer, it was gear driven directly from the cable via a cross
shaft across the bottom of the housing assembly and a and vertical shaft
mounted on the side of the housing. The two shafts had worm gears and they
could be changed as a pair which would then also affect the odometer (total
miles) reading.
Of course, all of this was also affected by the drive gear and the driven
gears (which also could be changed) that are located in the transmission
tail housing.
Now as Paul Harvey says so well "That is the rest of the story."
Route 66 Rider!
Ramon Hill
Live Long and Be Free
-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Rich Bennington
Sent: Saturday, August 05, 2006 1:38 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Reasonable cruising speed?
<________________________________________
From: Loren Busch [mailto:starwagen@gmail.com]
Sent: Friday, August 04, 2006 8:27 AM
To: Rich Bennington
Cc: vanagon@gerry.vanagon.com
Subject: Re: [VANAGON] Reasonable cruising speed?
RE: The speedometer and odometer are fed separately.
Actually, they are both fed from the same source, the speedometer cable. But
the odometer is a direct physical connection to the cable. The speedometer
dial that you can see is driven/moved by induction through a spinning magnet
inside an aluminum cup, consequently the speedometer can vary, no direct
connection. The odometer is counting the turns of the wheel in the case of
the 2wd Vanagon and the inaccuracy can only come from tire diameter being
different from the factory spec and not turning at 805 revolutions per mile.
I happen to be lucky, my odometer and speedometer are in very close sync,
both read about 2% high based on measured mile courses on the highway. BTW,
although my GPS seems to provide accurate speed, it ends up way off on
distance, usually many miles low over a couple of hundred miles.
>
Oops! Sorry, I was thinking of the place where the oxy sensor mileage
counter splits off of the speedo cable. Of course there is only one
connection to the cluster! Duh!
Still, it’s not uncommon for the ODO and speedo to be different, due to
either an offset on the needle on the speedo, or a weak spring, or both.
Interesting about the GPS – I suspected the GPS update time may affect the
distance measurements, especially when going fast, but I never tested it
like you did.
Rich
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