Speedo Problem

[Jamo]

Well this is nice, my car for no reason devolped another fault today.

The speedo stopped working, but then it does work, and it doesn't work

Tapping on the speedo has no effect so what could it be?

any ideas?

Thanks

[charlie]

Check where speedo cable joins gearbox.
Sounds like it's come loose/popped out.

[tekkno435]

Check where speedo cable joins gearbox.

graham.

[charlie]

graham.

I thought that speed was picked from tranny.
unless someone is willing to correct me.

[4WheelDrifter]

Maybe he means the connection with the reed switch on the gearbox?

[s2driveruk]

yeah sensor plugs into the box. I have a spare kicking around somewhere if you need one let me know

[martinjs]

I have the same problem but with my rev counter instead. Where does that get its signal from?
Thread hijack

[rotoryboy]

Well this is nice, my car for no reason devolped another fault today.

The speedo stopped working, but then it does work, and it doesn't work

Tapping on the speedo has no effect so what could it be?

any ideas?

Thanks

Mine does this when I've driven through a lot of water, large puddle etc.....

[T2Andy]

Stop start traffic can cause this annomaly.

[~Delta]

... Magnetic pick up causes intermittent operation of the speedo. It is a circular magnet fitted to the crownwheel. I have had a couple, thought it may be the pick up, turned out the magnetic disc had a hairline crack. Centrifugal force cause the crack to widen, and speedo would not work, slowing down normally caused the crack to "momentarily" join, and speedo became operational.

Try replacing the pick up with a known working one, same part fitted to all type 89 cars and type 8D A4's, so no shortage of these from wreckers. If problem persists, you'll have to replace the magnetic rotor within the differential housing. It is accessible from the left hand side if the box.

Remove S8 alloy centre cap
Loosen hub bolt on L/H driveshaft
Loosen wheel nuts
Jack up L/H front of car and secure with axle stands
Remove wheel
Remove hub bolt
Unbolt pinch bolt on lower ball joint
Knock / lever lower arm downwards to free ball joint from bearing carrier
Undo 6 splined bolts securing inner CV joint to drive flange
Remove drive shaft complete
Lever drive flange out of differential, taking care not to nip the oil seal in diff cover
Disconnect wiring plug from speedo sender
Remove speedo sender by pressing tag downwards and swiveling sender and pull out
Undo 17mm plug from lower differential housing and drain oil, replace plug and tighten
remove bolts from differential cover, and carefully lever cover off. Do not pinch seal
Magnetic ring can now be removed. Pull off from crownwheel and examine for cracks
Replace magnetic wheel, making sure tags engage with cutouts in crownwheel shaft
Replace all parts in reverse order, remembering to refill differential with correct grade of oil
Finally, road test

[Jamo]

I took car to a mate at a garage and apparently sensor contacts were dirty.

Cleaned out and it's fine.

Haven't had any problems since last weeks so i'll jiust have to keep my eye on it.

[dan_b]

Mine starts to stick after driving for about 2hours.

[4WheelDrifter]

Peeling dials Dan?

[Bibby]

I took car to a mate at a garage and apparently sensor contacts were dirty.

Cleaned out and it's fine.

Haven't had any problems since last weeks so i'll jiust have to keep my eye on it.

Jamo, did this reappear? Can you explain where the contacts are?

Mine has just been doing this the last 2 days. Suddenly dropped to zero, then popped back up again.

[Jamo]

I wasn't there when he did it, but he said the contacts on the sensor on the gearbox were iffy.

It cleared for a while, then i had a reoccurance on the motorway and a swift whack to the speedo made it work

Makes me think its a dodgy connection in the dash.