Date: Wed, 12 Sep 2001 03:13:43 +0100
From: "Lineone" <adriannopsamone.org>
Subject: Re: Wacky speedometer


Greg I had very similar once with a Vauxhall (GM in UK). Quantitatively, the figures were just about the same (115 indicated at about 65). Turned out to be a distorted drag-cup, which is the magnetic device in the speedo housing which couples the rotating drive cable to the speedo needle assembly. Key symptom of this was that the needle would occasionally stick at about 10 to 20 mph, when at rest. I learned the cost of a new speedo (silly price), and decided a home-repair was worth trying - nothing to loose. As I remember, it came apart quite easily and needed a little tidying up with a warding file where the driven plate was contacting the cup. Reassembly was easy, and as far as I'm aware, calibration was good if not perfect after the repair. I had had some training as an instrumentation engineer, but in the overall scheme of things, the speedo was quite simple to work on. Trust me, there's MUCH trickier stuff out there. All this only applies if your speedo is mechanical, though I'm fairly certain that in '86, the whole Saab range had mechanicals. And I can't guarantee that the Saab unit is as accessible as the Vauxhall's, but the technology should be just about identical. If the speedo is indeed mechanical, then I think that your odometer inaccuracy is a separate problem. If electronic, then the two could be related, though I doubt it - more like tyre (US tire) size. I like Wysiwyg's fuzz ball theory. I've not heard of this before, though it sounds entirely feasible (and Wysiwyg is speaking from personal experience so we know it can happen). Whatever the final diagnosis, I think you must get the speedo out and take a look inside. Go with the fuzz ball theory first, as it's a lot simpler. Be careful and good luck. Adrian F, Hampshire, England '92 9000 CS 2.3 16i, 105k, Cirrus White. <wysiwyg.docnopsamspring.com> wrote in message news:3B9CD583.40BC1FE2nopsamspring.com... > you'd have to pull the speedo and know what you're doing, like be an > instrument technician type person. these are delicate devices and you'll mess > it up if you have a slip of the fingers. what has happened is a fuzz ball > (lint) has developed in the mechanical actuator or if it's an electro drivin > device several of the windins have shorted on the coil of the meter. i had a > similat problem and found the lint. mine was mechanical. i used canned air > like you blow out a computer with to clean it. do not try to lubricate the > device you'll cause yourself more problems. > also that vintage speedo had an inhereint problem with one of the little > numbers on the odometer cracking at the shaft. when that happens it will stop > clicking miles but the speedo will still work. > hope this helps > > Greg Youngen wrote: > > > The speedometer in my '86 900 8v (115k mi) is registering ~30-40 mph more > > than the actual speed at 65 mph. > > > > This is the second speedometer in the car (original replaced at 25k mi). > > Soon after it turned 100k mi, the speedo needle started bouncing > > erratically. It still bounces at low speed and stabilizes above 50 mph. > > However it's reading 100-115 mph when I'm actually going 65. > > > > The odometer is also running fast, though not as much as the speedo might > > indicate. It clocks up 20 mi. for every 19 actually driven. > > > > Any suggestions for fixing this? Is it a sign of impending failure on the > > speedo? > > ____________________________________________________________________ > > Greg Youngen > > youngennopsam.edu >

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