How to Repair Your Broken Odometer

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.

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!

Remove the hush panel under the drivers side dash. There are 3 phillips screws on the top

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.

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,

Disconnect the master harness for the gauge cluster. It is usually quite tight so just pull gently straight

Take the cluster and put on a clean towel in an area with good lighting. Then remove

Gently lift out the clock cluster and set aside. Remove the 2 screws holding the speedo to the cluster, but

Remove the 2 screws holding the gauge cluster and the dimmer switch. If your dimmer switch does not

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

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

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.