How to Repair Your Broken Odometer
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All parts used in these pictorials are available at the diesel parts for sale page
How to repair your broken odometer
Quite often I either hear about or see another broken odometer on an old Mercedes. Don't lose heart! The repair can be done by you. There are usually one of 3 reasons why they don't work. So follow along with my pictorial and fix it yourself.
Safety and security tips:
Please remember to recycle all your used fluids at an appropriate recycling center. Be mindful to not spill or splash fluids on yourself, others or the ground. Also as a safety tip please remember anytime you are working on, around or under your car, to wear safety glasses and secure the car with wheel stops and approved jack stands!
To learn how to remove the dash cluster via DVD, check out the DIY DVD page.
Remove the hush panel under the drivers side dash. There are 3 phillips screws on the top
and 2 plastic phillips half turn locks, 1 on each lower side.
Reach under the dash and gently pull the odometer cable an inch or 2 through the firewall. This will
give you a little more room to get your hand behind the dash cluster when you loosen the cluster.
Also I like to push on the dash cluster from behind to aid in removal.
This is much easier than using the metal tools on the cluster which
can scratch the cluster and tear the sealing gasket.
This is why you want some slack on the speedo cable. The cluster can move forward allowing you to
get your hand behind. Remove the oil supply to the gauge with a 10mm wrench.
Disconnect the speedo cable and remove the clock connection, the seat belt and glow plug connections,
speedo electrical connection, and tach connection.
Disconnect the master harness for the gauge cluster. It is usually quite tight so just pull gently straight
out, don't rock it side to side. This is the whole harness for the cluster.
Take the cluster and put on a clean towel in an area with good lighting. Then remove
the 4 screws holding the clock cluster.
Gently lift out the clock cluster and set aside. Remove the 2 screws holding the speedo to the cluster, but
do not remove just yet.
Remove the 2 screws holding the gauge cluster and the dimmer switch. If your dimmer switch does not
work, now would be a great time to replace it.
Remove the speedo electrical box. Then the 2 screws holding the rear of the speedo.
Gently lift the edge of the gauge cluster closest to the speedo. Lift out the speedo and pay close attention
to the trip meter reset arm, which is why we lifted up the gauge cluster. This makes it much easier to get the speedo
in and out of the cluster without damaging the reset arm.
I like to leave the speedo in the cluster for much of the work just because I can do all the "rear" work without
it laying face down, and possibly bending the speedo gauge needle. These 2 plastic gears are a common place for failure
of the odo. They will often strip. Inspect them carefully especially the gear closest to the cable housing inlet.
These gears look just fine. The brass gear that rides on the plastic gear can sometimes slip on its shaft, so
gently test it with your finger. The brass gear is ok also so there is one more place to look for trouble.....
Ahhh we found the problem! The pot metal gear that the screwdriver is pointing to should NOT be turnable
without the entire shaft and numbers advancing. This gear in fact does "slip" on the shaft, hence the numbers
will never advance. This is the hardest of all the gears to replace, but will cost you only your patience, some time
and some locktight. Remove the speedo head set with these 2 small screws.
Lift straight up and be careful to grab the vertical plastic gear and set aside. Seen in next pic.
I recommend getting some scotch tape and lay on the numbers so that they don't move.
Very gently remove the pressed on collar that holds the numbers shaft. Actually you can pry it off
or just take some needle nose pliers and pull. To reinstall just take your needle nose pliers and
slowly push back on. It is not on with great force to begin with. Please make sure when you reinstall
that you leave a little room so the shaft does not bind, ie some end play. With the collar on slam
tight it will prevent the shaft from turning properly. I got a drill bit the same diameter
as the shaft (7/64) to slip in behind, as I was removing the shaft. GO SLOW and CAREFUL. Don't let the drill bit
get too far behind the shaft as you are removing, or the gears will get out of phase.
With the shaft removed you can see the shinny spot where the pot metal gear was slipping and spinning.
Take a flat bladed screwdriver and very hard rough up the area. This will give the gear something to bite
This is by far the hardest part! Putting the geared shaft back into the number set and getting the pot metal gear
back into position. It took me about 1 hour to do it. There is very little clearance and the shaft obviously
must be out at the point where is the gear is slid back in. This causes the other numbers to move and often fall out.
Don't loose focus. It can be done but a steady hand is a must. Also the phase gears you see next to the
numbers riding on a second shaft, must also line up in the grooves of the numbers.
I resorted to pulling out the numbers and gave it a try on the towel. After you do get all the gears in place then you must get a drop of locktite on the gear without getting any of it on or between the other numbers. If you do then they will be frozen.
Use a toothpick and put a single drop on the shaft after all gears are on. The locktite will wick inside the gear.
But only do this after all the assembly is in the speedo, not on the towel. The reason is the shaft must be taken out
again if done on the towel. The 2nd pic shows me lightly separating the space between the pot metal gear and
speedo housing. This space is where you must get 1 drop of locktite. Right on the shaft where the pot metal gear rides.
The finished product installed and working great!