Intermittent or non functional speedometer repair.
My 1984 325e speedometer unit was working and then eventually it became
intermittent and eventually died. Driving over bumps and hitting the dash
would revive it occasionally. It stayed this way until I was motivated to
begin the diagnostic procedure.
Symptoms are that the speedo works when it was warm, like in the late afternoon
after sitting in the sun all day or being blasted with the heater on for
a long drive in cold weather.
Of course, some of the first things to check are the fuse for the instrument cluster
and to remove the rubber boot from the speed sensor on the differential and remove the connectors, clean them, make sure the connection
is tight and re-connect them and replace the boot.
Detailed Diagnosis is on a different page for those who are interested,
and so we could get to the fix!
The basic problem appears to be the material that the speedo electronics board
is made from. My theory is that this material is severely affected by temperature
( expanding and contracting ) and leads to failure of the speedo unit by
creating highly stressed solder joints leading to a cracks in the joints.
The board then, under temperature, will move enough to re-create the contact
allowing the speedo to function.
The solution is to re-flow all the solder joints on the board on the back of the Speedo unit.
I did this to my speedo mostly on a whim and it caused the speedo to work.
I worked on this solution with Bryon Pinkston (firstname.lastname@example.org) and the
same procedure brought his speedo back to life also. At the time, I didn't
know which joint in particular was the problem, so I did them all.
The speedo was re-assembled into the instrument cluster with only a fraction
of the hardware to facilitate an easy removal if need be. After several
hundred miles of driving in all conditions, the speedo still works and is
Remove the instrument cluster as described below ( valid for early E30's,
not guaranteed for all).
Read these over carefully beforehand to familiarize yourself with the procedure.
Its not as bad as these paragraphs look. Also remember that this applies
to an 1984 325e and if your car is newer, it might be a little different.
First. Remove the lower dash panel under the steering wheel. There are three
half-turn type fasteners. Lower this panel while sitting in the car. Reach
under the opening and behind the black panel under the instrument cluster
there are two thumbscrews, one at each end. To remove the thumbscrews, push
the black panel into the dash, relieving the tension on the screw and unscrew
the thumbscrew. Set these aside and remove the black panel by lifting it
out from above with the top edge coming out first to clear the molded in
screws. This part has a couple of plastic snap pins that can break
Second, there are two phillips screws under the shroud of the instrument
cluster holding the black plastic cover along with some screws along the
bottom face exposed by removing the black panel. Remove all these screws
and save. Remove the black shroud by pulling the top forward and gently
removing the bottom part. . There may be a couple of screws holding the
top of the instrument cluster by these two 'wings' on the upper left and
right. Remove these also. ( mine doesn't have screws there, maybe because
I didn't put them back in at one point. )
Third, Remove the instrument cluster by pulling these 'wings' down and rotating
the instrument cluster top towards you. Now with the back side of the cluster
facing upwards, remove the connectors on the back. There are three colored
connectors ( blue, white, and yellow), and if you have cruise, a fourth
connector for that. To remove the three colored connectors, use a small
flat head screwdriver to pull up a black 'strap' and then remove the connector.
I don't really know about the fourth connector as it is the lead for the
cruise input and I don't have cruise, but it should be fairly straightforward.
Fourth, now tilt the instrument cluster back upright and slide it out towards
the passenger side between the dash and the steering wheel.
Fifth, on the back of the instrument cluster there are about 12 funny looking
phillips screws with hex-heads. Remove all these screws only. Gently lift
the back panel and instruments away from the front section. This will separate
the two halves of the instrument cluster.
Instrument cluster showing colored connectors. Note the two screws of four
holding in the speedo unit. (red arrows) And the hex-head phillips screws
holding the instrument cluster together. ( teal arrows)
To remove the Speedo unit without cruise control, remove the four phillips
head screws from the back side and gently pull the unit forward out of the
instrument cluster. If you have cruise control, you will have to remove
the cruise control connector from the rear of the instrument cluster at
the rear and bottom of the speedometer unit first.
Then place the speedo unit down without damaging the needle and re-flow
all the solder joints. use a good soldering iron and some new solder. Touch
the solder joint with the iron and apply a little new solder to help build
a new joint. Do this with all the solder joints. Also you may want to try
to create more contact between the speedo unit and the instrument cluster
by pressing closed the spring-style contact on the speedo unit.
Front of instrument cluster. Speedo Spring type connectors are to the right
of the speedo unit.
Hint: The orange lenses and lamps underneath are what light the dash. Gently
pry them from the cluster and clean the inside. The lamps can be removed
from the other side with a quarter turn. Also try replacing the alternator
warning lamp with one of the backlights to add more brightness.
Reassemble the unit following the above procedure in reverse.
Happy motoring ! ( especially with a working speedo !)
And many thanks to Bryon pinkston_at_aros_dot_net for his help.