Jim Chambers

Speedo was working fine (except trip odo, full odo OK). Then yesterday the speed indicator itself stopped working...needle at zero no matter the road speed.
Where to start? Is it fused? Checked the connector in the spare tire well and all seemed good, though the grommet has pulled out to the exterior. Wire to the transaxle appears connected. Haven't tried the very technical "pound on the pod" remedy yet.

jpitman2

Check that pick up is in place on the diff rear cover. If still no good, do a search here (or somebody will pipe up with the data) for the central board connections involved in the speedo leads to the pod. Best solution is its a connectivity fault rather than the speedo itself. If the odometer still registers distance travelled, but no speed indication, the speedo is at fault, not connections. If neither speed nor distance works, could be either.
Once you know where the leads from the rear meet the central board, jack up one rear wheel, out of gear, handbrake off, put a meter across the leads , showing resistance, turn the free wheel, you should see the circuit go open,close,open,close etc.

hth

jp 83 Euro S AT 56k

vanster

Or you might have lost the gears. Not too difficult to pull it out and buy new gears from Roger
Dwayne has a good write up on doing just this. In my opinion this is why most 928's for sale regardless the year all show around 85k

dr bob

Jim--

Raise the rear of the car and place on safety stands. (Let me know when you want to pick them up and I'll alert Karen... or wait until mid next week.) Use your multimeter set on Ohms, attach the probes to the two wires in the spare wheel area connector, so you can read continuity through the reed switch in the back of the transaxle. Slowly rotate the rear wheels with the gearbox in neutral. One wheel must be stopped or turning in the same direction as the other, so that the ring gear and its attached magnet assembly is turning inside the differential housing. As one of the magnets passes the reed switch, it should close and show continuity on the meter.

I don't have your '78 wiring diagrams handy, so you'll do a little research to find the CE panel connection where the wire from the switch passes through on its way to the instrument cluster. Kinda like the way we isolated and tested the turn signal wiring for continuity and short to ground.

Because you wrere working very recently at the gearbox, I'd be looking in that area first. The reed switch and the connector in the spare wheel well, along with the ground connection for the switch, would get initial focus.

Randy V

Bang on the pod.

Works for me.

Rob Edwards

The 78 speedo sender plugs into pins 3 and 4 of the 7-pin connector in the spare tire area, then travels to pins T1 and T2 of the CE panel, then through and out of the CE panel on pins H1 and H2, to pins 1 and 2 on the left instrument cluster connector (pins 1 and 2 are closest to the steering column). The other brown wire on pin 2 is the ground to the chassis on the left side of the steering column.

Left connector:



Pin numbering, 1-12 from right to left:

Jim Chambers

Thanks to all. I was looking at wiring diagram with no luck. You guys are much better than a diagram! I will report results after testing. Hoping it is electrical rather than mechanical. But if I have to pull the pod I can test the water level warning bulb which is dark.

GuardsTurbo

My speedometer cuts out intermittently, but after a few taps on the dash it pops back to life. I'm sure you are dealing with a ground issue.

Wisconsin Joe

It's not the odo gear. That doesn't affect the speedo. And for "main" odo to work and the trip odo not is a bit unusual. "That Gear" drives both.

If you have signal at the plug by the spare tire and at the CE panel, typical failure mode is corrosion on the rivet connectors from the plastic circuit film to the hard board to the pins that push into the back of the actual speedo.

Dwayne has an excellent writeup on this.

vze2jshn

I have sprayed the connector in the spare area with wd 40 with good results in the past.

LT Texan

What Rob says.

When my speedo went out I cleaned the connectors in the front of the spare tire and voila.

Cleaning grounds and pod connections every year or two is always recommended.

OTR18WHEELER

Sometimes it not just the gear...



Burnt speedometer resistor

Not only was my gear disintegrated, the resistor was fried.

LT Texan

Thats for the fuel gauge?