The speedometer needle sweeps like it always did, and the odometer just sits there. A small amber plastic gear inside the speedometer has gone brittle and let go. Open the thing up and it's usually not one clean break. It's sticky amber crumbs floating around inside the housing.
Before You Start
First, check you're in the right place. Look at your dash: if the gauge binnacle is the rounded oval one, you've got a late car, 1985.5 through 1991, and this guide is yours. If it's the angular early dash carried over from the 924, stop here. Early cars run a cable-driven mechanical speedometer with a single 17-tooth gear. That is a different part, a different teardown, and our kit does not contain a gear that will fit it. Nothing below applies to you, and we'd rather tell you now than after you've bought something.
Then do the diagnosis, because it takes about ten seconds and it can save you the whole afternoon.
The late 944 speedometer is electronic. A speed sensor at the transaxle feeds a signal up to the cluster, and there's no cable anywhere in the system. So it's one of two things:
- Speedometer works, odometer doesn't. The sensor and the wiring are proven good, so the fault is inside the speedometer head. That's this job.
- Both are dead. Stop. The problem is upstream at the sensor, the wiring, or the cluster connectors, and pulling the cluster apart to change a gear won't fix a thing.
The gear doesn't always break. Sometimes it just slides along its shaft and comes out of mesh with the worm gear that drives it, and that's a five-minute fix with a screwdriver and a drop of glue rather than a full teardown. You won't know which one you've got until the cluster is open.
Worth knowing before you start: Porsche never sold this gear on its own. The factory answer to a dead odometer was a whole new speedometer head, so there's no dealer number to chase and no factory procedure for swapping the gear.
WARNING: Never reset the trip odometer while the car is moving. That's the single most common way these gears get destroyed in the first place, and it will kill your new one just as fast. Come to a complete stop first.
What You're Replacing
Hold the speedometer with the face pointing away from you. Every left and right in this guide assumes that orientation, so if you turn the unit around, turn the instructions around with it.
Inside the speedometer, behind the number drums, is a short train of small plastic gears. At the left end of that train sits a white plastic worm gear (it looks like a plastic screw), and the gear that meshes with it is the one that drives the odometer. That leftmost gear is the part that fails. It's the original amber-colored plastic, it ages badly, and between three decades of heat cycles and the occasional trip-meter reset at 70 mph, the teeth round off or the whole thing crumbles.
You'll hear it called a few things: the odometer gear, the odometer drive gear, the speedo gear, the trip gear, or "that little plastic gear in the 944 speedo that always breaks." Same part.
If yours is gray rather than translucent amber, somebody has already been in there and fitted a replacement. That's worth knowing, because a gray gear means the tooth count in there was somebody else's guess, not the factory's. Count it anyway before you pick a replacement.
| Part | Part Number | Notes |
|---|---|---|
| Odometer Gear Repair Kit | No OEM part number, never sold separately by Porsche | Three gears, 20x21, 20x22 and 20x23, embossed 1, 2 and 3 so you can match on the bench. MPH clusters only. Porsche 944 928 911 Odometer Gear Repair Kit. Porsche only ever supplied this gear inside a complete speedometer head, so there's no dealer number to cross-reference. |
| Speedometer Head, Electronic (If Yours Is Beyond Repair) | Varies, check by VIN | Splits by year, transmission, market and mph vs km/h, and no single suffix covers the range. Have your VIN read at a dealer or a Porsche parts specialist. The wrong one is an expensive mistake. |
| Instrument Cluster Lens Assembly (If The Bulb-Holder Coating Is Peeling) | 944 641 941 01 | Late oval-dash cluster only. It's the part the nine Phillips screws hold on. You'd buy it if the silver reflective coating on the bulb holders is too far gone to refurbish. |
| Crazy Glue (Cyanoacrylate) | n/a | One drop on the shaft where it passes through the gear, only if your old gear simply slid out of mesh instead of breaking. |
| Adhesive Remover (Goo Gone, Goof-Off Or Similar) | n/a | For the gummy amber residue the old gear leaves on the post. Isopropyl and a rag gets most of it, the sticky stuff needs the solvent. |
What this guide does not cover: speedometer calibration, the transaxle speed sender, the cluster bulbs, or the tachometer. Those are separate jobs with separate failure modes.
Which Gear Do I Need? Count The Teeth
This is the one decision that can waste the whole job, so read it before you order anything.
The gear is a two-stage type, described by two numbers: 20x21, 20x22 and so on. Most 1985.5-on US-market cars use the 20x21, and a minority use the 20x22. But "most" isn't "yours," and nothing in the VIN or the build year tells you which gear is actually in your speedometer. The kit ships a 20x23 as well, so you've got a third option to match against on the bench with the speedometer already open.
Count the teeth on your old gear before you decide which one to fit. That's not us hedging. It's the only way to be sure. Here's why:
- Early square-dash cars (1982 through early 1985) are not this job. They have a cable-driven mechanical speedometer with a single 17-tooth gear, and the teardown is different too: the speedometer pushes out the front of the cluster and the bezel pries off. This kit isn't for them.
- Non-US and rest-of-world cars need checking, whatever the year. The published year-to-tooth-count mappings are all US-market, and ROW cars used different speedometer hardware. Don't assume a US model year tells you what's in your car.
- 1991 cars need checking too. Open the speedometer and look at what's actually in there before you order.
- 968 (1992-1995) uses a 15-tooth gear. Different part, not covered here.
- 924S (1987-88) is a separate fitment question. Don't assume it folds into the 944 answer.
- MPH clusters only. The kit is not for km/h clusters. The gearing is different.
Don't bother looking for a number on the gear you pull out. The 1, 2 and 3 are ours, embossed on the replacements so you can tell them apart in the box. The original carries no marking at all, so counting its teeth is the only read you get.
If your old gear has crumbled past the point where you can count anything, mark tooth one with a fine paint marker, photograph the gear, and count on the zoomed photo. You're trying to tell 21 from 22, and that's not an eyeball job.
WARNING: Spinning the train on the bench only proves the gears mesh. It can't tell you the ratio is right. All three kit gears will mesh and turn the drums. To confirm the ratio, drive a measured 10 miles on GPS or highway mile markers and compare. Right gear reads 10.0. One tooth off reads about 9.5. Two teeth off reads about 9.1. If it's short, go back in and try the next gear.
What You'll Need
### Parts
- Porsche 944 928 911 Odometer Gear Repair Kit, which is three resin gears (20x21, 20x22, 20x23) embossed 1, 2 and 3. MPH clusters only.
- A drop of cyanoacrylate glue, only if your gear turns out to have slid out of mesh instead of breaking.
- Adhesive remover, for cleaning the gummy residue the old gear leaves on its post.
### Tools
| Tool | For |
|---|---|
| 24mm Socket and Breaker Bar | Steering wheel retaining nut |
| Torque Wrench | The wheel nut goes back at 45 Nm (33 ft-lb) |
| T30 Torx Driver | The two recessed screws on the back of an airbag steering wheel |
| Phillips Screwdriver | Nine cluster front-cover screws, cluster trim screws |
| Straight-Slot (Flat Blade) Screwdriver | The four screws behind the speedometer, trim levers |
| Trim Removal Pliers | Pulling the speedometer needle without bending it. Get the one with the thinnest notch so it engages the base of the needle. |
| Small Jeweler's / Eyeglass Screwdriver | Dislodging the odometer gear c-clips |
| Small Needle-Nose Pliers | Getting those c-clips back on |
| Drill Bit or Awl | Pushing the dually gear axle out of the plastic carrier |
| Painter's Tape | Protecting the gauge face while the needle comes off |
| Very Fine Emery Cloth | Polishing amber residue off the gear post |
| Soft Brush and Compressed Air | Clearing amber crumbs out of the housing |
| Paint Pen or Nail Polish | Marking the steering wheel splines |
| Camera or Phone | Photographing the needle rest position before you touch it. Not optional. |
Fitment Notes
Oval dash means late car. 1985.5 through 1991, electronic speedometer, and that's what this guide covers. Square dash means an early car with a cable-driven speedometer, and neither the kit nor the teardown applies.
MPH clusters only. The kit's gearing is wrong for a km/h cluster.
Airbag or not changes the front end of the job. Look at the center of the steering wheel. A horn pad that pulls off by hand means no airbag. An airbag wheel has two recessed T30 Torx screws in the back of the hub. Step 1 splits by variant.
Step 1: Battery, Airbag And Steering Wheel
Disconnect the battery ground lead first. It's going to be off for a few hours, so if your radio is coded, dig the code out before you pull the lead, and expect to reset the clock at the end.
You can technically do this job with the wheel in place, but you'll hate every minute of it and the cluster is far more likely to get dragged across something on its way out.
Non-airbag cars. Pull the horn pad off firmly (it's tougher than you expect, and you're not going to break it), disconnect the spade connector on the back, then take the retaining nut and washer off with a 24mm or 15/16" socket. Keep the washer, it goes back behind the nut. Mark the wheel-to-shaft splines with a paint pen or nail polish, then pull the wheel straight off.
Airbag cars. Leave the battery disconnected for at least 30 minutes before you touch the airbag. The two screws holding it are recessed T30 Torx on the back side of the wheel. Take those out, slide the airbag off the front, unplug it, and set it aside face up where it can't get knocked around. Then the nut and washer, the spline mark, and the wheel.
WARNING: An airbag that's been unplugged and plugged back in can fire on the first key-on. When you get to that point in Step 10, stand outside the car and reach in through the open door to turn the key. Don't sit in front of it.
Last thing before the cluster: the dash reset switch sits to the right of the cluster and pulls straight out of the dash. Pop it out and slip it behind the dash so it isn't fighting you.
Step 2: Get The Cluster Out Of The Dash
With the wheel off, work the cluster trim surround free:
1. Three Phillips screws across the top of the trim piece. A stubby Phillips driver earns its keep here. 2. Two Phillips screws that thread up into the trim from underneath, one either side of the steering column. 3. Three more in the vents, because the center vents are part of the same trim piece: one in the vent area furthest right of the cluster, two in the vent area nearest the cluster. 4. Lift the bottom edge of the trim right behind the column shroud, pull down slightly on the top to clear the dash, and slide the trim piece out.
That exposes four Phillips screws holding the cluster itself. Take those out and slide the cluster forward far enough to reach the three electrical connectors on the back. Each one has locking levers. Push outward on the levers to release each connector, and label them as they come off so reassembly isn't a guessing game.
WARNING: There's a flexible ribbon circuit board on the back of the cluster and it tears easily. It catches on the edges of the dash opening if you rush, and it will tear if you pull the cluster before all three connector levers are fully released. Tilt the cluster back, bring one end out first, and push up on the dash opening for clearance if you need it. Be patient here.
Step 3: Split The Cluster And Free The Speedometer
Get the cluster on a clean bench with something soft under the face.
Remove the nine Phillips screws around the back edge of the cluster. That releases the clear plastic front cover, which lifts straight off. Set it somewhere it can't get scratched or sat on.
WARNING: With the front cover off, the needles and gauge faces are completely exposed. The needles are extremely delicate and the faces scratch if you look at them wrong. Don't rest anything on them, and don't set the cluster face-down on a bare bench.
Now turn the cluster over and take out the four slotted screws directly behind the speedometer. Support the speedometer with your other hand as the last screw comes out, because if it drops it takes the needle with it. Then lay the cluster face up and lift the speedometer straight up and out of the housing.
Three rubber spacer feet live under the speedometer. Some come out with it, some stay stuck in the cluster housing. Find all three and put them somewhere you won't lose them. The speedometer doesn't go back together without them.
Check their condition while they're out. These feet are what clamp the circuit board tight enough for the speedometer's electrical pins to seat, so a torn or flattened foot is why a rebuilt speedo comes back dead. Thirty-year-old rubber often is. Sort a replacement before you reassemble, not after.
Step 4: Look Before You Go Further
Everything past this point is irreversible, so check now whether you actually need to go there.
Hold the speedometer with the face pointing away from you and look at the left side for the white plastic worm gear. Find the gear that meshes with it.
If that gear is intact and has simply slid along its shaft out of mesh, push it back into engagement with a small flat-tip screwdriver and put one drop of cyanoacrylate on the shaft where it passes through the gear so it can't wander again. You're done. Reassemble from Step 9, and the needle never came off.
If the gear is broken, worn or crumbled, carry on.
Step 5: Pull The Needle And The Gauge Face
Photograph where the needle is resting before you touch it. Get a straight-on shot, close enough to see exactly which mark it sits against. This is the most important thirty seconds of the whole job.
Then mask the gauge face with painter's tape so nothing you do next can scratch it.
The needle is just pressed onto a tiny splined post. Whichever method you use, lift it. Don't squeeze it and don't bend it, because it won't survive either. Three ways to get it off, best first:
1. Trim removal pliers. Slide the tool all the way under the base of the needle and squeeze the tool to apply even upward pressure. The needle pops off without drama. 2. A wide screwdriver bridging both sides of the center post, prying up evenly. 3. Turn the needle counter-clockwise to its stop, then keep turning gently while pulling up at the center.
With the needle off, remove the two screws holding the gauge face and lift the face away.
WARNING: If the needle goes back on a spline or two off from where it started, your indicated speed is permanently wrong by exactly that amount. Late speedometers don't have a mechanical stop pin to index against, so your photo of the rest position is the only reference you get.
Step 6: Separate The Speedometer Halves
Before you split anything, photograph the trip reset assembly. There's a black plunger that passes between the two halves, sitting in a solenoid at the bottom and in a white plastic reset mechanism on top. It can fall out when the halves come apart and there's no obvious right way up when it goes back. Take the picture now.
Four screws under the face plate hold the two halves together. Take them out and lift the top half, the half carrying the gears and the number drums, straight up off the bottom half.
This is where you find out how bad it is. Look at the leftmost gear in the train, the one meshing with the white worm gear. Translucent amber means original. Gray means someone has been here before you.
Whatever you find, clear every amber crumb out of that housing before you go a step further. Soft brush and low-pressure compressed air, working over the bench rather than over the open bottom half. Check inside and behind the number drums specifically, because that's where the crumbs settle and that's what jams the train later.
WARNING: Keep adhesive remover and every other solvent away from the gauge face and the printed number drums. Solvent is for the gear post only, applied on a rag, never sprayed.
Step 7: Strip The Gear Train, Right To Left
You can't just pull the failed gear out. It's buried at the left end of the train and everything to its right has to come off first. Face still pointing away from you.
Start at the right end:
1. The dually gear. Use a drill bit, an awl, or any similar punch to slide the axle out of the plastic carrier and lift the dually gear off. If it separates into two gears, note exactly how they were stacked. They go back together the same way. 2. The c-clips. The remaining two gears are each held by a tiny c-clip. Insert a jeweler's screwdriver into the clip's recess and twist to dislodge it. Keep your thumb over the clip while you do this. 3. The gears. With the clips off, the remaining gears slide straight off their posts. Note the orientation of each one as it comes off.
WARNING: Lose a c-clip and the job stops until you find it or source another. They're tiny, they're springy, and they clear a workbench in one hop. Thumb over the clip, work over a tray or a towel, and don't do this step over a floor drain. They're sold as e-clips, c-clips or circlips. Measure the shaft before you go looking and buy an assortment rather than one. They cost almost nothing and you'll lose another.
Step 8: Fit The New Gear And Rebuild The Train, Left To Right
The new odometer gear goes on first, then you build back out to the right in reverse order.
Before it goes on, clean the post properly. The old amber gear leaves a gummy, sap-like film behind, and a new gear on a contaminated post drags. Adhesive remover on a rag usually handles it. If it doesn't, polish the post with a piece of very fine emery cloth.
Slide the new gear on and spin-test it with a fingertip. Compare it against the feel of the middle gear if you're not sure what "free" should feel like. Do not assemble a draggy gear and hope. The whole train is driven by very little torque, and drag is how you end up doing this job twice.
Then rebuild:
1. Remaining gears back on their posts in the orientation you noted. 2. C-clips back on. Small needle-nose pliers make this manageable. 3. The dually gear back into its carrier, and the axle pin slides back in by hand. No tools needed for that pin.
Your mileage lives in the number drums themselves and it doesn't reset when the gears come out. Whatever it read going in is what it reads coming out. Spinning the train to test it will tick over a tenth or two, which is normal. What you don't do is turn the drums by hand to change the reading. That's odometer tampering, it's a federal offence, and it wrecks the car's value on top.
Last check before you close anything up: turn the new odometer gear with your finger and watch the whole train. Every gear should mesh and turn freely, and you should see both the odometer drums and the trip meter advance. If either one doesn't move, sort it out now while everything is still open. Remember this proves mesh, not ratio. The ratio gets confirmed on the road in Step 10.
Step 9: Reassemble The Speedometer And Cluster
Reassembly is the reverse of what you just did. But three things break on the way back in that didn't break on the way out, so work in this order:
1. Gauge face back on with its two screws. 2. Needle back on the same spline you photographed. Check it against the photo before you go further, not after. 3. Circuit board back against the speedometer. It hangs off the bottom on three thin wires, and those three wires are the whole electrical connection. Use the three rubber feet to hold the board tight against the speedometer, and route the wires so they aren't pinched between the board and the housing. 4. Speedometer into the cluster housing. The four electrical pins at its base have to seat in their sockets, and they'll push out the bottom instead if you're not careful. Press on the back side of the cluster while you seat the speedometer to hold them in place. 5. Trip reset plunger checked. The black plunger goes into the solenoid hole at the bottom and seats up into the white plastic reset mechanism on top. If it isn't in both, the trip reset won't work. Match it to the photo you took in Step 6. 6. Four slotted screws, then the clear front cover, then the nine Phillips screws.
Step 10: Refit The Cluster, The Wheel, And Test It
Slide the cluster into the dash opening the same careful way it came out, watching that ribbon board again. Plug in the three connectors, going by the labels you made, and make sure every locking lever clicks home. Four Phillips screws hold the cluster.
Then, in this order:
1. Push the dash reset switch back into its opening to the right of the cluster. 2. Steering wheel onto the marked splines. Washer behind the nut, and torque the nut to 45 Nm (33 ft-lb). 3. Reconnect the horn wire and press the horn pad in, or on an airbag car plug the airbag back in and secure it with the two T30 Torx screws. 4. Reconnect the battery. 5. Standing outside the car, reach in and turn the ignition on. Then start it.
The trim is the only thing that stays off for the test drive. The wheel and the airbag go back first, every time.
Now drive it. Confirm both the odometer and the trip meter are counting, and run the measured 10 miles to check the ratio before you close the dash up. Once you're happy, the trim goes back: vent screws, bottom screws, top screws.
Airbag light on afterwards? That's expected once the system's been disturbed. On most airbag 944s it resets with two jumper wires and a watch: ground pin 2 of the white three-pin Molex connector under the passenger side of the dash in a timed five-second sequence with the ignition on. If it won't clear after three attempts, there's a real fault in the airbag system. On the later cars, the 944 S2 and the 968, the reset has to be done at a dealer with their diagnostic tool.
Troubleshooting
The new gear turns but the numbers still don't roll. Something in the train isn't meshed. Open it back up and turn the new gear by hand while you watch each gear in sequence to find where the motion stops. Check the dually gear went back together in the correct stack, and check that no amber crumb is jammed between teeth.
The odometer counts, but ten measured miles came up short. Wrong ratio, and it's exactly why you check on the road. About 9.5 miles means you're one tooth off. About 9.1 means two. Go back in and fit the next gear in the kit.
The speedometer now reads high or low by a consistent amount. The needle went back on a spline or two off. It won't correct itself and it isn't a calibration issue. Pull the needle again and re-index it to your photo. This is why the photo matters.
The gear feels tight or notchy on its post. Amber residue. The old gear leaves a sticky film that new resin doesn't slide on. Take it off, clean the post with adhesive remover, polish with very fine emery cloth if needed, and try again.
A c-clip launched itself across the shop. Stop and find it before you do anything else. Kill the shop lights and run a flashlight flat along the floor. The clip throws a shadow you can see from across the room.
The odometer worked for a week and then stopped again. The gear probably slid along its shaft and out of mesh with the worm gear rather than breaking. Push it back into engagement with a small flat-tip screwdriver, then put one drop of cyanoacrylate on the shaft where it passes through the gear so it can't wander again.
Both the speedometer and the odometer are dead after reassembly. Almost always the four electrical pins at the base of the speedometer pushed out the bottom instead of seating in their sockets. Open the cluster back up, re-seat the speedometer while pressing on the back of the cluster, and check the three thin circuit-board wires weren't pinched or pulled loose. A perished rubber foot does the same thing by letting the board sit loose.
The gears you got don't match your old one. Count the teeth again, and check whether your car is a ROW-market or a km/h car. Those use different counts entirely.
A Note On Parts Porsche Never Sold
Open the Porsche parts catalog and you'll find the speedometer head, the cluster housing, the lens carrier, even the bulbs. What you won't find is the little amber gear that's the actual reason your odometer stopped. It was never a serviceable part. Your factory options were a whole new speedometer head, which is a serious four-figure conversation if you can even source the right suffix for your car, or shipping the gauge off to a VDO-authorized rebuilder and waiting.
That's the entire reason aftermarket gears exist. Ours is printed in glass-filled resin instead of the plastic that failed the first time around. The original plastic had 30 years to go brittle and gummy, and yours has had them. The point of the swap is that you do it once.
Wrap-Up
You've got a counting odometer again, and you didn't have to buy a speedometer head to get it.
The cluster's already on the bench, which makes right now the cheapest the dash lighting will ever be to fix. The dim-instruments problem is usually the silver reflective coating flaking off the bulb holders, not the bulbs. The coating strips with a non-acetone solvent and gets replaced with aluminium foil and clear double-sided tape. Don't sand it, and don't try to pull the reflective assemblies out of the lens housing. If you're changing bulbs while you're in there, stay in the 3 to 4 watt range. Go bigger and you'll melt the holders.
Related: the Porsche 944 rear hatch drain pan guide covers the other 944 failure nobody catches until the rear carpet is soaked. Torque figures for the rest of the car live in the Porsche 944 torque specifications reference. And if there's an E30 in the garage too, the BMW E30 odometer gear replacement guide is the same failure with the same fix.
Got questions? Tag us on socials or hit us at info@treedylabs.com. Show us the build when it's done. We actually want to see it.