Overview. You are here because your odometer has stopped registering mileage. It is a common failure of the marque, and happens to just about everyone. Make yourself familiar with the procedure in the Clarks garage on the removal of the instrument cluster from the car. There are a few details that we have to deal with, primarily the airbag, but other than that, the Clarks garage writeup will suffice.
Tools: Phillips and flat blade screwdrivers, Torx T-6 bit and 1/4 drive ratchet, common kitchen towel(dry).
WARNING: You will be working with lethal explosives with the airbag. Failure to follow instructions could result in serious injury or death. Do NOT skip this safety warning. Follow instructions on page 968 Workshop manual pages 68-53/54 for removal of the drivers airbag. You MUST first disconnect the battery negative terminal and wait 30 minutes before beginning work.
Take the two Torx T-6 bolts out from the recess on the back of the steering wheel hub.
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Once you have those two screws out. Gently pry the airbag toward you. You will see the wire from the hub to the ignition pill on the back of the airbag. It is a red connector. You can disconnect this connector if you wish, and set the airbag aside, but I left it connected. At this point, refer to steps in the Clarks garage writeup to remove the steering wheel, or as I did, just take the nut off, and move the steering wheel forward on the shaft a bit so the instrument cluster can slide out the right side.
One more deviation from Clarks that I found, in step 9 where he says to remove all four screws from the cluster, you can leave the left screws in, but loosen them about 2-3 turns. The cluster housing is slotted, so it will slide to the right as you move it. Once you have access to the back, in step 10 of Clarks, be very careful of those three cable connectors. The plastic connector housing is very fragile and they crack easily. If you break the connector housing, prepare to do some repair with JB Weld.
Refer to Clarks volume on 'Odometer repair' for the removal of the cluster from the housing. Do NOT remove the needle from the speedometer! At this point, you should have your instrument cluster and housing out in your hand. CAUTION. Do not touch any of the instrument pointers.They are fragile, and you can easily damage them. Remove the four slotted screws on the back of the cluster holding the speedometer(refer to Clarks Odometer repair). When you take the speedometer out of the housing, grasp it with your thumb at the lower, and fingers at the upper section and rock it top to bottom to get it to disconnect from the elect pins at the back.
Now, go do the dishes, and prepare a spot on the kitchen table. Borrow a medium size kitchen towel and fold it once lengthwise, then several times widthwise so that you have a green vagina shape, about 6" square. This is the work surface for your instrument. (see pic)
Set the speedometer down in your towel-vagina with the needle in the gap so that the face is supported and the needle is not touching anything. Do not remove the needle from the instrument as said in other references, this is only for the 944 process, and we do not do that here.
Now, looking at the back, you will see the electronic board, held on to a plastic housing with three studs and there should be a rubber bushing around each of the studs. I have only two bushings on my instrument. Gently pry those bushings off, and set them aside. Now work the electric board off the studs and lay it over on its back, allowing the wires to just fold open. (the board and wires are in the very bottom of the second pic)
In the next pic, I have put the elect board back on the studs for ease of visibility, you want to leave the board off and hanging by the wires. Look at the side of the instrument where the small motor is held on by two screws. Remove these two phillips screws identified by the red arrows.
Now, the fun part begins. The motor board and the motor will come off as a unit. However, there are two small blue wires(yellow arrow) at the bottom which go into the speedometer unit, and they must be left connected. To take the motor out, pull it straight back and out of the assembly, allowing the wires to flex with the motor and board. As you pull the motor off, the gear inside may fall out. Don't panic. You now have the speedo assembly, with the motor laying next to it, attached by the two blue wires, and the elect board laying next that, connected to the motor board by a few wires, with the odo gear and pod exposed.
The amber colored gear is the one that breaks, and the gear pod is the one behind it in white with a blue side. Your colors may vary. If the gear pod didn't fall out, you can now remove it from the housing. The amber gear is the planet, and the white/blue gear is the sun in the planetary gear arrangement. It is driven by the gear on the motor, and the whole thing is aligned by that extended shaft of the motor, sticking up past the gear.
Once you have the pod in your hand, flip it over, and count the teeth on the pod. I'm guessing for MPH cars it is 16 teeth, and for KPH cars it is 12. Now, go to www.odometergears.com, click on Porsche, click on 968 at the bottom of the list, and select the correct pod gear tooth count, and add it to the cart. Add the odometer gear, and then check out, using whatever payment and shipping options you like.
You are now ready to reassemble. There are a few tricks to getting things back together right. First, it's important to work cleanly, and one or more of the teeth have come off that amber gear. Try to locate where they went and get them out of there. If you look in my speedometer housing, just on the left side of the round flange, you will see a speck of amber. That is the old tooth off my speedometer gear. I used a dental tool to remove it.
Next, when you put the speedometer gear on the pod, it tends to slip off. I'm not sure what kind of lube is good or bad, but I used a small touch of white lithium grease to get it to stick to the pod. <edit: I have my new gears. The odo gear fits on the pod gear with the small chamfer going away from the pod gear, and toward the motor. Also, I was having trouble getting the pod gear to stay in the housing well, so I stuck the odo gear to the pod, then I mounted the pod gear on the extended shaft of the motor sitting there, then I fitted the whole motor and cluster of gears into the side of the assembly. This may be easier that sticking the pod gear in first, then guiding the motor in.>
Now, when you put the pod, and the speedometer gear back in the housing, it must engage the two black gears behind it. Tip the speedometer carefully on it's side a bit to get the pod to sit in the housing perfectly centered. This will tell you that the gears on the pod have aligned with the black gears in the housing. The motor and board will not go on smoothly if the pod is not perfectly centered. Once the pod is centered, push the motor on perfectly straight, insuring that the centering pin on the shaft aligns with the hole in the pod. It can only go on one way, so don't force it.
Hold the motor and board on with your thumb, and put the two screws back in the motor and board assembly. Set the instrument back down in the vagina.
Now, roll the elect board back over onto the studs of the top plastic housing. Put the two/three rubber bushings back on those studs. The instrument is ready to go back in the housing.
When you put it in the housing, hold it again by the MPH at the bottom and the 80-100MPH area at the top. Guide that stupid and annoying little reset slug back into the solenoid hole first(below my thumb), then go straight down into the well, so that the pins in the back, align with the receptacles in the speedo assembly. It's a tight fit in there, but make sure you go straight down so that the pins hit the holes.
Once it's down firm in the well, compare the face alignment with the tach next to it, they should be the same level. Then, put the slotted screws back in the instrument housing in back, and put the cluster back in the housing using the 9 phillips screws.
At this point, follow Clarks write up for returning the cluster to the car. Be careful again with the connectors, and insure they are down tight into the snaps before closing things up.
A bonus WYAIT job, is to renew the backing of the light guides on the bottom of the cluster housing. There are three bulbs that provide front lighting to the instruments, and they are notoriously dim. If you use some 400 grit wet on the light guides, then put aluminum foil over the guides, and use super glue on it, that will bring much more light back to the instruments. Others have used a custom made reflector, and used LEDs, etc but this is a low cost, low tech solution for the poor lighting of the instruments. I plan to cover the Alum foil on the bottom when I install the cluster with a piece of folded newspaper held on with tape that I can remove once the cluster is past the instrument binnacle and safely inside the dash. (yes I trimmed the excess Alum foil before installing)
One more WYAIT job. Kind of important. Note the condition of the three ribbon connectors on the instrument cluster. If they are like mine, they have a dull gray appearance with some oxidation that will cause a bit of resistance between the connector slotted socket and the ribbon connector. I took some 400 grit and gently cleaned the silver part of the connector(circled in red). Don't put much force on it. the middle one is kind of hard to get the inside of the connector but if you take your time it will come out nice and shiny. This may improve any gauge issues or lamp issues you've had in the past.