Mine does the stop and start thing too even after the replacement. My feeling is that the entire rack get's laterally loose and that is what chews up the gears anyway. A "reputable" VDO shop should have addressed that. I didn't and sorta learned about it after I did mine.

Bottom line is NEVER EVER use the button on the dash PERIOD for ANY REASON!!!!!

What happens is the gears deflect and push apart under the tiny load they see and then they are only partially meshed chipping off the corners of the inner gear. Once is starts they mesh and unmesh randomly unless you are a racer and you can watch it happen in only like left hand .75 G turns :) But bottom line is the gear is already damaged. I ain't going in there to fix mine till it completely stops or I completely lose my fuel gauge.

Jay K.
79 (clocking miles at the moment)


I really don't like the thought of replacing a known weak component with another one like it, so I went with the brass replacement odometer gear. I've seen plenty of clocks and other instruments with brass gears that are over 100 years old and are still working. Using self destructing plastic doesn't seem like the best idea to me. The place that I went to put in the brass gear, repaired and adjusted another gear that was slipping on it's shaft, and checked everything for $75. That was done by:

Speedometer & Clock Company
2337 S. Michigan Ave.
Chicago, IL 60616
(312) 842-6378

Brass replacement gears are available from there, or complete speedometers can be shipped to them for repair.

I also found another source for plastic replacement gears. The web page is at:


In case you're wondering how the Porsche dealership repairs a gauge when it doesn't work anymore, they don't. When your plastic odometer gear self destructs, you're buying a brand new speedometer as far as they're concerned.

Mike Schmidt


I have replaced the double worm/spur gear in my odo with Levy's beautiful product and the speedo works absolutely perfectamento! The trip reset button works so well I sometimes just tap out a rythmic beat with it (but this phase will probably pass). This is an excellent fix and Levy has provided a beautifully pictured guide to doing the job (not the pod removal, but the odo gear R&R.
83S A/T
PS: Hey! Maybe we can get into long boring diatribes about who can replace that gear the quickest? You know, I mean, in case those other two finally get tired of entertaining us.



20x21 MPH gear                                                                                                                                20x31 KM/H gear



Porsche Euro and US
Each gear is $25 plus $4 Priority Mail USPS(2-3 day)
Last updated 05/29/2004



20 outside x 21 inside tooth count  20 outside x 30 inside tooth count



WPO shop also has them:

Passend für alle:

Porsche 928 mit KM/h-Tachometer
vereinzelt ist im 928 auch das 20x29 verbaut. Suchen Sie dazu einfach im Shop nach "20x29"

Modelle mit Meilentacho haben immer das 20x21 verbaut!

Wir können zwar mit großer Gewissheit, aber nicht zu 100%iger Sicherheit sagen, welches Modell welche Zahnradgröße verbaut hat. Hier spielen zu viele Einflussfaktoren (Motortyp/Getriebetyp/Übersetzung/Differentialtyp/Baujahr/Modell) mit ein. Sollten Sie wider Erwarten ein anderes Zahnrad benötigen, bieten wir einen kostenlosen Tauschservice an: Senden Sie uns dazu einfach Ihr Zahnrad mit einem Hinweis zurück. Gern können Sie auch die Reste des Originals der Briefsendung beilegen.

Die folgenden Daten helfen jedoch zuverlässig bei der Ermittlung des richtigen Zahnrads:

Alle Varianten dieses Doppelzahnrads für VDO-Tachos:

20x21 (17,60mm/9,00mm) Zähnezahl gegenüberliegendes Partnerzahnrad: 49 Zähne 911/928Mph/944
20x22 (17,60mm/9,40mm) Zähnezahl gegenüberliegendes Partnerzahnrad: 48 Zähne 911/944Mph
20x23 (17,60mm/9,65mm) Zähnezahl gegenüberliegendes Partnerzahnrad: 47 Zähne 944 (S2)
20x29 (17,60mm/12,05mm) Zähnezahl gegenüberliegendes Partnerzahnrad: 41 Zähne 928Km/h
20x30 (17,60mm/12,55mm) Zähnezahl gegenüberliegendes Partnerzahnrad: 40 Zähne 911/944
20x32 (17,60mm/13,40mm) Zähnezahl gegenüberliegendes Partnerzahnrad: 38 Zähne 928Km/h

Zählen Sie einfach die Zähne des Zahnrads, in welches dieses Zahnrad eingreift und/oder nehmen Sie die Maße zur Hilfe.

Gesamt-Durchmesser = 17,60mm (20 Zähne)
Durchmesser kleineres Zahnrad = 13,40 mm (32 Zähne)
Gemessen von Zahnspitze zu Zahnspitze



One source for the gear is KLA Industries at www.klaindustries.net or you can call them at 918-409-4011. Instructions are on their web too.

Normal disclaimers apply. Just saw their products at a recent PCA Tech Session.



Porsche Odometer Speedometer Repair Gears



Kilometerzähler funktionieren nicht mehr. Ursache Zahnausfall beim Zahnrad, welches in Schneckenwelle vom Elektroantriebsmotor greift. Bei Ausfall von mehr als 1 Zahn gibt’s keinen Eingriff mehr.

Tachousbau ging mit Thommys Beschreibung ganz gut, für Einbau ist Hilfe von 2. Person über ein paar Minuten von Vorteil.

Fa. HAVLIK - INSTRUMENTS Tachometerreparatur Siebenbrunnengasse 55 - 57 A - 1050 Wien +43 1 544 13 24 wird am 12. 1. 07 konsultiert, kriegt aber keine VDO Ersatzteile, könnte Zahnrad aber einbauen. Havlik hat mich an Fa. VDO Siemens in Flachgasse 54-58 01/981270 verwiesen, macht aber nur Generalüberholung um ca. 170 Euro.

Tacho aus Ersatzwagen ausgebaut, detto Zahnausfall.

In USA (rennbay) ist Zahnrad um 27$/Stk erhältlich...Zähnezahl am Tacho ermittelt Z Schneckenrad=20, Z Zahnrad=32 Zahnrad 2 Stk bestellt bei Ka-ja Tachodienst. 12 Euro/Stk plus 7 Euro Versand. Bestellnr.: 5583/2 auf Zähnezahl und Steigung achten!
Eingebaut. Tacho funktioniert wieder.


Porsche 928 euro (KM teller) has 20x32 gear
Porsche 928 US (MPH teller) has 20x21 gear
Porsche 944 US (MPH teller) has 20x21 of 20x22 gear
Porsche 911 has 20x30 of 20x23 gear

Careful, this is still not 100% sure !!!....   Theo




A brand new replacement gear for your broken VDO odometer / speedometer / tacho.

You can also find other gear versions in my store!

approx. dimensions:
diameter (large gear): 17,5 mm
tooth count: (large gear): 20
diameter (small gear): 9,6 mm
tooth count: (small gear): 23
bore: 3 mm

This odometer/gear can be found in a number of vehicles from around late '80-s and the '90-s.
Some of these were:

?BMW 7 E23 77-86
?Porsche 911 76-89
?Porsche 911-930 86-88
?Porsche 912E 76
?Porsche 928 77-95
?Porsche 944 82-91
?Renault Alpine 310
?Renault R5 Turbo
?Vixen Motor Home

The list is incomplete, there are other cars that were also fitted with these.
Also, if your car is on the list, that does not mean 100% sure that it has the same part gear in it, due to manufacturing variations and aftermarket repairs.
The only way to tell is to pull the odometer apart.
If the original gear is damaged and it is impossible to tell the original tooth count, you may also count the teeth on the neighboring gear:

49 teeth: 20x21
48 teeth: 20x22
47 teeth: 20x23
41 teeth: 20x29
40 teeth: 20x30
38 teeth: 20x32

All these other versions are available in my store!

This part is _not_ a factory original, it was precision made from durable plastic, it will not break like the original one.
Good luck for the replacement!
Should you have any questions, don't hesitate to contact me...


And here it comes.... the gear combination mystery:

There are multiple tooth count options that can and will be installed in this odometer. You will need to count the teeth on the old gear before ordering. The outside gear will have 20 teeth, the smaller inner gear between 21 and 29.{If you cannot count the teeth on the main gear then count the teeth of the next gear that it meshes with.

If your tooth count is   49: 20x21

                                        48: 20x22

                                        47: 20x23

                                        41: 20x29

                                        40: 20x30

                                        38: 20x32

The euro S4 GT and GTS likely have 20x32 as a setup. This gear is also often shown as 944 gear.

The US version with km/h gear may look like this (obviously that does not work):

Possible explanation is that there are differences in the face plate which are matched by a different gear setup.

You will find a good working instruction here: http://dwaynesgarage.norcal928.org/1984%20Odometer%20Repair%20Procedure.htm


Reparatur Ihres defekten km Zählers für das Kombiinstrument Porsche 928 bis MJ 1988.pdf




Guten Tag,

Wir sind dabei die Website zu überarbeiten, einige Auflistungen sind nicht korrekt.

Wir haben die 20x32 Zahnräder auf Lager.

Sie können auch die Zähne vom nächsten eingreifenden Zahnrad abzählen und so feststellen ob ein 20x32 Zahnrad benötigt wird.

Wenn das nächste eingreifende Zahnrad 38 Zähne hat wird das 20x32 benötigt.