Noisy speedometer, 88 5kq - Update

[S. Jaworski]

>     Speedo makes intermittant noise when cold. Sounds like a spinning
> bushing. Noise comes and goes in colder weather. . . . .
>  . . . . .    Before I tear it all apart, does anyone have BTDT on this?
What's the
> theory of operation for this type speedometer? . . . . ..


Well, I didnt get any how-to info.
Chris Semple form Force 5 sent me an email offering an instrument cluster
assy for $75. Will keep that in mind for the future.

I took the speedo apart this weekend. The only delicate operations are
removing the indicator needle, and removing the return spring from the same
shaft.
Once those are removed, remove the 3 screws holding the speedo cover on.

Lift out the metal cup/shaft assy(speedo indicator dial is attached to this)
Next, remove the cover with magnet and shaft assy.

What I found is that the magnet and shaft assy had end play. It was kinda
loose in the cover bushing.
On one side of the cover is the round magnet pressed on the shaft. A plastic
pinion gear is mounted on the other side of the cover. There is a thrust
washer between gear and bushing, and also between magnet and bushing. There
was about .030 end play on the shaft.
I carefully pried off the plastic pinion gear off the shaft using a wide
bladed screwdriver. After cleaning off the old grease, I applied some high
temp brake grease to bushing and shaft. Then I made a jig and used a socket
and drill press to press the pinion gear back onto the shaft, till there was
no end play.
I tested the assy and it worked smoothly with no binding and no end play.
Put everything back together and took it for a ride. No noise so far, but it
wasnt cold. The noise only occurs when its cold. Will test it again when the
temp drops.

Principle of Operation:
1. speedo cable turns the shaft with pinion gear and rotating magnet
attached.
2. pinion gear operates the odometer gears
3. rotating magnet field moves the cup/shaft assy  . . .there is no physical
contact between the cup and magnet.
4. the cup/shaft assy is attached to indicator needle.
5. a small spring (looks like a watch spring) is press fit onto the
cup/shaft and brings needle back to the peg. The magnetic force on cup works
against this spring.
6. the faster the rotation of magnet, the more force applied to cup and it
moves more against the spring thus indicating higher speed.

Note: Previously I had repaired the famous odometer problem.
I dont know how the turbo odometers work. But on the non turbo odometer,
there is another ring and pinion gear that drives the odo. The gears are
plastic with very little resistance. But, there is enough resistance that
over time the ring gear and its attached shaft will be moved by the pinion
gear and become disengaged from the pinion gear.

The fix is to prevent the ring-gear/shaft from moving. I epoxied a piece of
metal to the plastic case. The shaft contacts this piece of metal and is
prevented from moving.
Its been working fine the whole summer so far. When I took it all apart this
weekend, it looked fine.

oh yes, I removed and junked all the wacky stuff associated with the oxygen
sensor maintenance interval light when I did my fix. That stuff is ok for
the life-skilled impaired, but us audi gurus dont need that funky stuff.

Syl
88 5kq
90 100q