ST185 Speedo conversion

[LEAKER]

Just got hold of a NZ New st18x 240 kph speedo cluster ans i want to replace my old 180 kph one. I removed the old speedo from the cluster and fitted the new one in however i'm not getting any reading. has anyone done this or have any idea what i'm doing wrong.
The "new" speedo has done 315000km so i suspect it's possible it doesn't work. How do you test them?
Cheers

[RunningRich]

I have done this to a few ST185 and a SW20. The speedos are plug and play. Did you install all the screws back in the same place? They act as earths.

The only difference between the 240kph and the 180 kph speedo is the face (well duh ) and the solder bridges on the circuit board.

If it is kaput not all is lost. The circuit board pulls off the rear and if you copy the solder bridge positions using a soldering iron and sucker (you will see the jumpers) you can swap your working board over.

Don't pull the circuit board off too often as you can muck up the free movement of the needle.

Other option is to clamp the needle shaft firmly and pull off the needle (if you don't clamp the shaft you wreck the return spring). Then you can swap the face. You still need to solder the bridges obviously but you know the speedo works.

You can also flick the odometer easily but you can figure that out for yourself.

[LEAKER]

I may have pulled the needle off......

The kms tick over but the needle doesn't move I've just noticed. Maybe I've over tensioned the needle.

[RunningRich]

Does the needle move freely if you spin it to 240kph and let go? It should glide back to zero smoothly in about a second. If it grabs on the way or stops it means the disk is jamming in the gel.

The stepper motor on the circuit board seems to have a disk inside encased in damping gel. I think the needle presses through the disk and the disk is spun by the stepper motor drive (not too sure on that, never pulled one apart). If the needle doesn't quite sit right the disk sits either eccentric or against the housing, causing a sticky needle.

I had one speedo that no amount of arseing around would fix. I had to swap the circuit board (and stepper motor).

[BlakeNZ]

Dang you know lots, Richard! Am impressed.

[RunningRich]

Continued Celica ownership since 1994. Learnt a few things