Topic: Odometer Repair Details
Although it's been covered before, we still see folk who find their fuel mileage seems low, or find their odometer is inaccurate (which is often the reason the mileage seems low). In the 70s VW used a press-on plastic drive gear on the odometer that shrinks and cracks given enough ttime and heat. I had put a 70s NOS speedometer in my wife's Mexi to replace the metric unit, and last week I noticed the symptoms of the cracked-gear problem. I found just what I expected:
As the gear ages and shrinks, it cracks between two teeth. This opens up the gap wider between these teeth, so as the gear rotates to where this cracked area has to mesh with the drive gear, it jams because of the wider gap, and the odometer stops moving for a bit until it catches the next tooth and moves on normally. If you aren't looking at it when it has stopped, you won't notice the problem, except for mileage reading low. You can see the rubbing marks on the teeth beside the crack, showing where it was jamming.
Some time back I bought some replacement brass gears from http://www.speedometerplus.com/ - so I slipped the cracked gear off and pressed one of these on:
An of course greased it up well since the brass isn't "self-lubricating" like they claim of the plastic.
The odometer design changed several times during the Beetle production, with some using brass gears and some plastic, and the number of teeth changed as well. The 70s cars that had this problem generally have a plastic gear with 11 teeth, and that's the replacement brass gear from the above source.
Getting at the gear is easy. Disconnect the Battery ground strap (working near live wires behind the dash), take a photo of the back of the speedometer or label the wires with tape so they can be returned to the right place, remove the speedometer cable, various light wires, and the two mounting bolts holding the speedometer to the dash. Pull out the speedometer. Carefully pry off the lens/bezel, remove the gas gauge from the back, and remove the two screws that hold the "works" in the case. The gear is easy to see on the back of the "works." The brass gear fits a bit tight, so support the far end of the shaft against a solid surface (vise or metal block) when tapping the gear in place.