Speedometer for '87 4kq quattro

[Scott]

 The W- 1xxx has to be a pulse(s) per something as a calibration.

Hence the question from the speedo shop.

http://auto.howstuffworks.com/car-driving-safety/safety-regulatory-devices/speedometer3.htm
"	The Electronic Speedometer
		
An electronic speedometer receives its data from a vehicle speed sensor (VSS), not a drive cable. The VSS is mounted to the transmission output shaft or to the crankshaft and consists of a toothed metal disk and a stationary detector that covers a magnetic coil. As the teeth move past the coil, they "interrupt" the magnetic field, creating a series of pulses that are sent to a computer. For each 40,000 pulses from the VSS, the trip and total odometers increase by one mile. Speed is also determined from the input pulse frequency. Circuit electronics in the car are designed to display the speed either on a digital screen or on a typical analog system with a needle and dial."


http://auto.howstuffworks.com/car-driving-safety/safety-regulatory-devices/speedometer4.htm



"All speedometers must be calibrated to make sure the torque created by the magnetic field accurately reflects the speed of the car. This calibration must take into account several factors, including the ratios of the gears in the drive cable, the final drive ratio in the differential and the diameter of the tires. All of these factors affect the overall speed of the vehicle. Take tire size, for example. When an axle makes one complete turn, the tire it's connected to makes one complete revolution. But a tire with a larger diameter will travel farther than a wheel with a smaller diameter. That's because the distance a tire covers in one revolution is equal to its circumference. So a tire with a diameter of 20 inches will cover about 62.8 inches of ground in one revolution. A tire with a diameter of 30 inches will cover more ground -- about 94.2 inches."


"Calibration adjusts for these variances and is done by the manufacturer, which sets up the speedometer gear to correspond with the factory-installed ring and pinion ratio and tire size. A car owner may have to recalibrate his speedometer if he makes changes that make his vehicle fall out of factory specifications (see the sidebar below). Recalibrating a speedometer can be done by manipulating the hairspring, the permanent magnet or both. Generally, the strength of the magnetic field is the easiest variable to change. This requires a powerful electromagnet, which can be used to adjust the strength of the permanent magnet in the speedometer until the needle matches the input from the rotating drive cable."


	

- Scott by BOSTON
quattro123.com
SuffolkD at aol.com

 

 

-----Original Message-----
From: vittorio <vittorio at mybares.com>
To: Tony Hoffman <auditony at gmail.com>; Chris Semple <chris at force5auto.com>
Cc: Scott <suffolkd at aol.com>; quattro <quattro at audifans.com>
Sent: Wed, Jul 25, 2012 11:13 am
Subject: RE: Speedometer for '87 4kq quattro


"The only difference in gear ratios is actually the fifth gear. In the 84's,
it's a .83 to one, in the 85-87's it's a .79 to one. The official Audi
literature shows otherwise, but I've hand them apart, counted teeth, done
the math. As have others. Go figure."


Further confirmation of what I thought to be true...to be true...


Thanks for doing the math Tony. As I swapped 84 tranny's w/85-87's I really wasn't feeling the difference on the rally stages. I rarely get into 5th, but my A$$ math matches your real math.


And to stay on topic, I believe the gear that drives the cable on these transmissions essentially runs off the drivers side half shaft so wouldn't be affected by gear ratio's...


V-