This article is one in a series that have been released in conjunction with Wayne's book, 101 Projects for Your Porsche 911. The book contains 240 pages of full color projects detailing everything from performance mods to changing your brake pads. With more than 650+ full-color glossy photos accompanying extensive step-by-step procedures, this book is required reading in any Porsche 911 owner's collection. See The Official Book Website for more details.
In the early 1980s, the United States mandated that all cars sold would have their speedometers limited to 85 MPH. While fine for the standard Buick or Toyota, this limitation is somewhat of a pain for Porsche owners. The good news is that this law was changed a few years later, and Porsches were again equipped with a speedometer that could more accurately reflect their performance.
More good news exists for cars equipped with the paltry 85 MPH speedometer. The speedometer can be replaced with either an earlier or later model unit with the higher speed markings. In the same manner, a MPH speedometer can be replaced with a KPH speedometer.
The first step is to find yourself the proper speedometer. There have been different faces and different type styles used on a few of the 911 speedometers, so you should probably take a look at one you are buying very carefully to make sure that it matches the rest of your gauges. Also, the gauges manufactured by VDO for Porsche have a less than desirable life for the odometer (See Pelican Technical Article: Odometer Repair, Odometer Repair), so make sure that any used gauge you purchase is fully tested and working. Otherwise you may have to pay an additional $100 or so to have the gauge repaired.
Replacing the speedometer couldn't be easier. Like the rest of the gauges, the speedometer is held into the dash with a rubber seal. You should be able to grab onto the speedometer and pull it out from the dash. Gently pry on the rim of the speedometer with a stiff putty knife if it doesn't want to come out easily. Work carefully so that you don't ding anything. You can also reach around underneath the dashboard and push it out from behind. Be aware of the wires that are attached to the rear of the unit as you are pulling on it.
Replacement is easy: simply remove the wires from the old one, and plug in the new one. Make sure that you make a note of which wire goes where, as it is easy to get confused, and the speedometers are not well marked. Also make sure that you don't damage any of the small light bulbs or their fixtures when removing them from the rear of the gauge. An additional concern is the glass or plastic face of the gauge. It's easy to scratch it if you leave it hanging near the steering wheel column.
On the very early cars, the gauges were held in using two small clamps behind the gauge. In order to remove the speedometer, you need to remove the two clamps and pull out the gauge. On cars equipped with cable-driven speedometers, you need to unscrew the cable from the back of the unit before you remove it from the dash.
Getting your speedometer out of the dash is the first step in a few projects. Once you have the speedometer out, you can send it in for recalibration, have the odometer repaired, or simply have it cleaned and a new faceplate installed.
The speedometer is held into the dash using a rubber seal. Pulling on the outside of the speedometer should remove it from the dashboard. Make sure that you disconnect the speedometer cable if the unit isn't electronic. Some of the wires attached to the rear of the unit may not be too long, so be careful when pulling on them.