Cost: $25 (plus shipping) each gear, $3.00 for the bulbs
Pros: Fairly easy repair, Working odometer, Easier to see instruments
Cons: Delicate job, Working odometer (for areas where insurance cost is based in part on mileage)
Time: ~3 hours
A very common problem in the BMW 635CSi is the breaking of the plastic gears in the instrument cluster causing the trip meter/odometer to stop incrementing miles. The most likely culprit of this would be gears made of a material not able to hold up to the temperature changes the poorly-insulated instrument pod might be subjected. After 15 plus years, the gears can become brittle. Most owners report their odometer fails after they reset the trip meter – particularly if the car is moving. Both of these actions – and in particular the latter – put a greater amount of stress on the gears than any other time, thus causing the brittle gears to break.
After determining which gear I needed, I ordered the replacement gear Odometer Gears LTD (please tell them Z3Bimmer.com sent you). They have reproduced gears made from a stronger, more heat tolerant resin material. The gears are produced using molds cast from OEM gears. I only ordered the one smaller gear (called E1). One of these days I may buy and replace the other 2 gears just so I won’t have to worry about them breaking.
These procedures are based on my 1985 635CSiA with an ///M style steering wheel and no airbag. I don’t have enough experience with other years and variations of the 635 to determine how many variances you might experience applying these procedures to your car.
If you have the original dim 3w instrument cluster light bulbs, replacing them with a set of 5w bulb will make the instruments much easier to read at night. I used a pair of Sylvania 2825 European Lamps. I understand the Sylvania 168 will also work.