speedometer

[dazole]

i had an irregular reading on my speedometer which i traced back to broken wires going to the final drive sender unit.
i have cut back and replaced the wiring and even fitted a new sender unit but the speedometer now reads at approx 20mph slower than it should ????
could anyone help me with this ?

its a 1994 318i touring

[Brianmoooore]

Nothing you have done with the repair should cause your problem.
Are you sure it was't this far out before it went wrong? The purpose of a speedo. (the only instrument you are legally obliged to have) is NOT to tell you what speed you are going, but to provide the driver with the data he needs to be able to avoid breaking speed limits. Consequently, all speedos are designed to over read, but yours does sound excessive.
Do you have the correct sized tyres?

[dazole]

yes the tyres are fine they are the same ones when the speedometer was working.
the orignal reading was very good then the needle started to bounce intermittently which i assume was caused by the broken wire.
now i have repaired it will not read correctly.i have contacted bmw to confirm i have the correct part and other than the possiibilty of a faulty part i am stumped.
i know the clusters can fail but all the other dials work ok its just the lag on the speedometer...........

also i have checked the mileage counter and that is still working correctly its just the needle that seems to be miss-reading ?!?

[Brianmoooore]

Clutching at straws, but the best I can come up with is maybe the needle falling back and bouncing off its stop while it had the intermittent feed has moved it around a bit on its shaft.

[dazole]

i have had a look at the cluster and the needle is very light and moves freely so i thought that it was controlled by magnets ??? or am i completely wrong?......

would a diagnostic check pick up what the problem is ????

[Brianmoooore]

The movement that controls the needle is essentially controlled by electric magnets, but the needle is a push taper fit on its spindle, and can be pulled off and relocated.
Diagnostics on an E30 are extremely primitive, and won't even really show up anything of use even in diagnosing engine problems. Not a chance with your problem.

[kam-325i]

is the amount that the speedo is out constant, or does it increase/decrease (the amont of error) as the road speed increases ?

[dazole]

its seems to be constant, it will not move till approx 20mph then will sit at approx 20mph slower than the car is moving....

[kam-325i]

sounds like the needle has moved on the shaft, like brian mentioned.

[dazole]

ok i will take at look at that guys and let you know how i get on,thanks alot for your advice it is very much appreciated

p.s. is it an easy job? do i have to take the cluster out?......

[kam-325i]

yes, cluster out job.

[Brianmoooore]

While you have the cluster out, check that both of the small brass screws on the back of the case are tight, the solder joints to a large resistor near the temperature gauge are sound (they won't be if they've never been attended to), and that the batteries on the SI circuit board (in the front half of the case) are good if they are NiCd cells.
Probably a good idea to change the two larger 3W bulbs that illuminate the cluster, and to replace any of the 1.2W bulbs that are blackened.

[dazole]

ok will do, thank you brian, thats my job for today...........