VW/VDO Odometer Repair

Visitor # 57502 since 19.SEP.2001

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Overview:

Introduction:

Does your Odometer click every mile? If so, chances are you have a very common problem with VW odometers. Look for a detailed writeup on this fix on "Jan's VW page". There are detailed instructions on a fix there. Howeve, lets for the sake of this discuussion, assume that the problem is with the main spur gear that is driven by the worm gear that is cracked. It is a press-fit nylon gear on a 3mm shaft, over time, the plastic fatigue and crack from the press-fit. As the worm teeth passed the crack, the crack will expand, allowing the worm gear to slip past the spur tooth (i.e. click!). One might be tempted to pull the spur gear off the shaft, ream out the hole to 1/8" (a shade over 3mm) to relieve the stress, then used some activated/catalyzed super glue to glue the gear back onto the shaft. With the larger hole, stress of the press fit is relieved allowing the crack to remain closed and the glue now holds the gear to the shaft instead of the press fit (which led to the crack in the first place).

Repair

You can see the steps involved in the images below. The speedometer can be removed from the instrument cluster by removing the screws that hold it in place. Then, remove the two screws that hold the back plastic cover and look for the worm gear/spur gear combination that drives the odometer. If the spur gear has a crack, that is the source of the skipping.

Broken odometer drive gear

1/8" drill bit to enlarge the 3mm press fit hole

Odometer gear reattached with plastic cyanoacrylic glue

Notes:

Several points are key in this repair procedure:
1. The hole in the gear is reamed out to release the stress of the press-fit.
2. A plastic-rated adhesive is used to glue the cracked gear back together as well as to hold the gear to the shaft of the odometer.
It is fairly easy to remove the instrument cluster after removing the dash panel, pressing the headlight switch release button, disconnecting the speedometer cable and finally disconnecting the electical connector. The the cluster may be tilted forward and removed. It is not necessary to remove the steering wheel but doing so will give you more room to work.
Since it seems to work for the Snake Oil Vendors, I figured I might as well hype the MPG improvement of this fix. This simple fix will gain you 5-10% (or more) MPG. Why you ask? The gear in question has 20 teeth. It rotates once per mile. Every click is 1/20th of a mile (or 5%). Mine seemed to click one or two times per mile, on average, so I think you'll see a 5-10% MPG improvement (measured not actual).
Tampering with the odometer may have legal implications, so proceed with caution, YMMV, yada-yada-yada...
Other folks have reported that wrapping a fine copper wire around the hub of the gear along with some good epoxy glue can help to keep the gear from re-splitting. Another option is to find a small washer that can be press-fit over the gear hub and then glued in place. In any even, both these techniques strengthen the gear to resist the force of the press fit.
Some later model A2 and A3 vehicles may bave a metal drive gear instead of the plastic one. In this case, the likely cause of the problem is that the gear is slipping on the shaft. You can either try using an exopy glue to lock the gear in place, or try roughening up the shaft, after carefully pulling the gear off, and then carefully reinstall it or try shrinking the hub of the gear a bit with a small nail set punch around the circumference.

Cost:

       $3 for some plastic-compatible super glue

Rating:

   --  (it depends on how hard you need to work to get to the odometer)

VW/VDO Odometer Repair

Overview:

Introduction:

Repair

Notes:

Links: