Permission to publish this article is provided generously by Robin Sun at www.p-car.com. Be sure to visit his site for loads of 993 info!
After way too long of not having a working odometer and not wanting to shell out around $200 bucks for someone else to do a simple job, I finally got around to fixing my speedo/odomoter unit.
DIFFICULTY: ~3 on a scale of 1 to 10. (Easier than an oil change on a 993.)
TIME to COMPLETE: ~2 hours
COST: $25 + $4 USPS shipping (As of 6/2005)
RISK: Cost of new or used speedo if you break this one.
DOWNTIME: You can drive your car without speedo. No cruise control or speed controlled wing. (I think.)
TOOLS REQUIRED: Small (jewelers) regular screwdriver, small phillips screwdriver, small to medium regular screwdriver.
BEERS REQUIRED: I drank 3... but was regulating a new keg... Old Dominion Ale. Very nice.
Your speedometer works, your odometer quit. Chances are, your drive gear has given up. The popular story is that you hit the trip meter reset while the car was in motion. While it is entirely possible that that particular event was the event that caused the actual failure, the root cause lies at the VDO factory. The tiny, little, 15 tooth planetary gear that drives the odometer and trip meter from the speedo sensor has turned into a soft jello like rubber over the years due to excessive heat and a corrosive oil lubricant that has turned that essential gear into mush. The separation of a couple teeth from that gear has been inevitable.
Your repair choices consist of sending it to a reputable speedo shop and dump a couple hundred bucks into a rebuild and be sans speedo for at least a week, or give it a run yourself. Replacing the gear is NOT that difficult. No crazy tools are needed. No special skills are needed. But it is risky. The most finnicky point of the rebuild is dealing with removal and reinstall of the needle pointer onto its shaft. The shaft of the needle is tiny... very tiny. Break that and you are looking at replacing your speedo. These aren't cheap speedo's... the broken gear is.
NOTICE: This DIY procedure will NOT help you change the mileage on your odometer. The main assembly holding the numerical wheels in place is not easily opened. You will not be able to roll your odometer forward OR back. Trust me... I tried. I wanted to add a bunch of miles to get back to reality, but there is no easy way to get the numbers free wheeling. Furthermore, tampering with the mileage on your odometer is illegal... or something like that.
Anyway, I did this on my first attempt with relative ease and great success. Your results may vary. Don't attempt at home... unless you are willing to accept the risk of ruining your gauge.
STEP 1: Odometer Removal.
Using a cloth covered screwdriver, gently pry the speedometer out from your dashboard. The rubber ring around the edge comes out too so get under that with the flat screwdriver and pry out. Do NOT use the neighboring gauge as a leverage point. The black trim ring is very easily scratched. Once you get it started you should be able to get your hands on it and pull it out. Unplug the connector and head to a clean work area.
STEP 2: Disassembly
TRIM RING: Remove the rubber grippy retainer ring. Remove the 4 screws from the back of the unit.
Now the soft metal trim ring needs removed by gently prying around the entire edge of the assembly to bend/lift the edge over the lip of the outside housing. This isn't pretty, but go slow. Be careful not to scratch the ring beyond the lip. You won't see what you have done to it once the rubber retainer goes back on so don't worry about chewing it up a little bit. Keep slowly prying around the edge until it can be pulled out.
STEP 3: Trip meter reset button removal
There is a thick post over the thin post of the reset button. Support the button assembly below and pull the top off. This will take some pressure, but be sure to brace the assembly from below so you don't pull too hard on the lever where it clips to the drive gears.
Note where the shaft gets thinner... that is where it separates.
STEP 4: Speedometer needle removal
This is the trickiest part of the job. The needle is pressed onto a shaft that is extremely thin. It feels like a pretty tough metal, but you HAVE to be careful here. Do not pull straight up. Do not put any torque on the shaft. Rotate the speedometer needle clockwise until it hits a stop point. Gently continue to rotate the needle whil lifting up gently at the same time. The friction is all that is holding the needle to the shaft. Keep turning and prying until the needle comes off. Do not force it. I don't know that that shaft assembly is user replaceable.
Note: See how small the shaft is:
STEP 5: Disassembly
You've come this far, there is nothing stopping you now. Take the two screws out of the faceplate.
Remove the circuit board.
Remove the motor.
STEP 6: The guts
Once the motor comes out, you will get to the drive gear and pod. Inside the pod is going to be your broken gear. Replace it with your new gear.
See the broken gear - and its yellow decay - compared to the new gear.
STEP 7: Reassembly
This is completely reverse of everything else. Nothing is too tricky. Continue to take your time paying particular attention to the needle shaft. When reinstalling the speedo needle, make sure you rotate while gently pushing down. Never simply compress the needle onto the shaft. Once it is in firm enough, use the stop points at max speed and 0 mph/kph to realign the needle with 0. Once everything is back together, also gently recompress the trim ring around the back of the speedo housing. You could use a black permanent marker to cover any scratches. Plug the unit back into the dash and reinsert into your gauge opening. Hopefully all is now re-recording miles.
PARTS and BACKGROUND INFO:
The new gear cost me $25 as of this writing in June, 2005. I found the gear at http://www.odometergears.com/. Jeff Caplan at Odometer Gears is a top notch, class act. I called there looking for help in isolating the part and he gave me spot on directions on how to get into the speedo, what to watch out for, andPaul
United Kingdom. what to do once in there. Once I got things figured out, he had a new part in the mail that same day. You can call him at 757-593-3478 or email him at firstname.lastname@example.org. My car is a '95 993 but I think all 964's, 968's and 993's will use the same 15 pin gear found when you hit the "Porsche" link at their website at http://www.odometergears.com/. Check with him first if you aren't sure.
Again, this is a VERY easy job. Not easy like a tire change - but only because you are dealing with a delicate instrument. If you have big, clumsy hands, you might want to forego this exercise and send it to a pro. If you can be gentle with this, you should be ok.
Additional helpful tips!
Firstly let me thank you for such a great site. It's a great contribution to 993 aficionado owners.
I have just successfully completed doing the odometer DIY repair following your instructions and I have a couple of contributions that I'd like to submit to you.
Firstly, I suggest that rather than assembling the speedometer completely and reinstalling it in the car after replacing the gears, do a partial assembly and connect it to their car to ensure its working properly. I completed the repair, I put the speedometer back together and when I installed it on the car, it didn't work. I had to disassemble it again right down to the gears and put it back together. The second time, I didn't install the needle or the trim ring/crystal and held it to the case with only one screw. I connected it to the car and drove for 4 miles to ensure it worked and then completed the assembly. This is a tedious job and it sucks finding out that it doesn't work after you've put the whole thing back together.
Secondly, my trim ring got somewhat lopsided during the prying stage. Not too much but I am a bit of a perfectionist and the speedo is something you look at constantly. I corrected 90% of the problem by gently rotating the outer edge of the trim ring against a hard surface while applying pressure. I did this after the trim ring was reinstalled on the unit and I used the edge of a table covered with a towel so as to not damage or scratch either the trim ring or the table; I gently applied pressure on the speedo unit against the table while rotating, effectively ironing out the kinks. After doing this the trim ring looks almost as though the unit was never opened.
I just finished replacing the gears ("pod" and little gear") - the following may be helpful:
1. to verify that all is well when you reassemble, use a pin, or a jewler's screwdriver to turn the stepper motor clockwise. you can touch the back of the armature through the laticework at the back of the motor, and you can turn it enough to move it to the next step - you should be able to see the counters move after turning it just 3 or 4 steps
2. to re-roll the bezel, use the round shank of a screwdriver. Press the assembled gauge, bezel down, against a flat surface - press hard (remember to have the odometer reset button located off the edge of the surface so you don't break it) and then pressing down hard on the screwdriver shank, slide it around the back side of the bezel holding the shank tangential to the case. this will make a reasonable rolling force on the bezel and will close it back up much more aesthetically than trying to crimp it back with pliers or something.
----- Original Message -----
From: "Bill Noble"
Sent: Tuesday, May 26, 2009 8:28 AM
Subject: addendum to 993 odometer article
Robin - an addendum to http://p-car.com/diy/odometer/
my 993's "pod" - the assembly that holds the small gear - measured 15.93mm diameter, which is a bit larger than the "small pod" listed at http://www.odometergears.com/porsche.html- I talked to the guys there, very helpful - and they assured me that the "small pod" will work for this application.
On my car, the small 15 tooth gear was actually stuck to the pod - the oil had become glue - that contributed, at least, to the failure of the gear - the odometergears,com folks said that the rubber VDO used for the gears is attacked by the oil they used, and so they recommended replacing both the pod and the small gear - at $25 each, that's not too much investment, even though it's a pretty easy job to get at the gears in the 993 - at least you don't have to pull the whole dash like some other cars.
One more hint to help separate the bezel from the gage- once you get the bezel lifted slightly, you can put a (dull) jewler's screwdriver under the edge, and holding the handle tangential to the bezel, slide it around the gauge - this will roll the edge upward smoothly and greatly reduce the risk of distorting the soft aluminum bezel.