Speedometer problem

[alpine318]

I've not had my e30 long but it has strange problem with the speedometer.

Firing up from cold and driving away, the speedo doesn't work at all. After 5 minutes or so, the needle comes to life and goes up and down quite quickly, a bit like a tachometer when someone revs on and off. After another few minutes, the speedo then works fine for the rest of the journey.

Any idea what's going on?
Also is the speedo cable driven or electronic?

[Brianmoooore]

Speedo. is electronic, with the signal being derived from a sensor on the back plate of the diff.
Two common faults: The copper in the wire leading from the plug to the diff. sensor hardens as a result of vibration, and eventually breaks inside the cable. Cure is to replace (not repair) at least the last 300mm of the lead and plug.
Other fault is a dry joint on the pins where the speedo. unit plugs into the rest of the instruments. Easily cured with a soldering iron. If a good thump on top of the dash affects the fault, then this is usually the problem.

[alpine318]

Cheers for the reply, I'll have a look at it when the weather gets a little better. I've got a handy speedo app on my phone which is helping me in the short term.

[alpine318]

I've gave the dash a slap a few times when driving the speedo needle does jump into life a little when I do that, so it would suggest the dry joint problem on the back of the cluster.

[ChrisHC]

The first part of an article on replacing the dashboard is a helpful description of how to remove the instrument cluster. Here- http://www.e30zone.net/e30zonewiki/imag ... d_Swap.pdf
I took mine out without removing the steering wheel, though.

[Brianmoooore]

Definitely no need to remove the steering wheel. Lay the luster face down on top of the column shroud, disconnect the plugs, and it'll slide out to the left.

[alpine318]

That's a nice little write up, looks easy enough to do.

Does anyone know it the back of the clock unit is easy to remove? I was hoping to try touching each joint with a soldering iron to get it back to life.

[Brianmoooore]

Does anyone know it the back of the clock unit is easy to remove?

Place the cluster face down, remove all the cross head screws on the back except the slightly smaller ones on the raised areas behind the speedo. and tacho., then carefully pull the two halves apart. The SI board will remain in the front section, while the main circuit board and the instruments will stay with the rear.
The speedo. and tacho. are retained by the smaller self tappers on the raised area, so remove the ones behind the speedo. in your case, and pull it out.
Fuel gauge and temp. gauge are held by the single brass nuts behind them. Check that these nuts are tight before refitting the cluster - they are known to come loose and cause the gauges to flicker between the correct position and a slightly higher one.
To remove the SI board,first pull out the coding plug from the front lower right face of the cluster, then remove the single self tapper inside the front of the cluster that holds the plastic retaining bracket in place. Note that this bracket also holds the little plastic mask with the legend 'check' on it for 6 pot cars or the opaque mask on 4 pot cars, so check that this is in place when reassembling, and don't lose it in the meantime.
Things you should do with the cluster out:
1/ Check the brass nuts are tight (already mentioned above.)
2/ Place the SI board in the freezer for ten minutes, then measure the voltage on each battery. Replace batteries if seriously low.
3/ Check all the little warning lights and panel illumination lights for blackening of their glass. Replace any that are black and have a mirrored appearance.
4/ Do the same with the three bulbs on the SI board's daughter board.
5/Remove the speedo. and check the soldering of the pins that connect it to the main circuit board
6/ There is a raised rectangular area on the back of the cluster, near the temp. gauge. This contains a large resistor, whose soldered connections can be found near the temp. gauge on the main circuit board. These will have deteriorated and need resoldering, unless they've been attended to before.
7/ Check the soldering on the pins for the white and blue sockets on the back. They are not a weak point, but can sometimes suffer at the hands of someone in the past that doesn't realise how to release the plugs.

[alpine318]

Thanks Brian, that's a good thorough write up.