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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?
Comments: To: Rich Bennington <rich.bennington@CHARTER.NET>
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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