My speedometer has been strange lately. When I move from a dead stop it doesn't report anything until I get to 20-30 Mph. Even then it isn't very accurate, as I've past signs that report your speed and it seems to be a good 5-7 Mph too fast on the gauge. It's a 1985 928 with an automatic transmission. I'm thinking bad sensor on the transmission? Maybe bad contacts on the gauge cluster? I must have taken that cluster apart four times by now and each time I get more scared touching it because it may fall apart.

 

You can try cleaning the contacts for the sender in the spare tire well.

They are in a molex connector usually behind a cover if it is still there. Takes a few minutes and couldn't hurt anything.

Otherwise it could be the sender itself which isn't exactly cheap.

 

I don't remember seeing much of any wiring in the spare tire area. Where in that area can I find the connection?
That's what I'm afraid of. I've seen them go for $200. Have they been known to go bad? I say this and my 928 has 210,000 miles on it. The sensor is on the diff?
https://www.fvd.net/us-en/9116062090...nsmission.html
I swear the 911 sensor looks the same as the 928 and is cheaper. For reference the part # is 91160620901, same as the 928.
https://www.aasesales.com/products/noloc-b52-112-108706
https://eeuroparts.com/product/genui...LQbtKcgywOFRcc

Found someone who had a similar issue but probably not my problem. I'll check the connection first in the tire sections and clean them. Good chance I haven't done that yet. Otherwise I'll probably remove the sensor off the diff and clean that. From the photos I think the sensor just pulls off? Not sure how that is held on.
https://rennlist.com/forums/928-foru...se-sender.html

 

The connections are in the top right corner of the spare tire well. There is a large bundle of wires with molex connectors there.

The sensor itself is held onto the diff by 1 bolt IIRC. It is just a hall sensor so it rarely fails, but can.

It can get cooked from heat back there. The one on my 81 looks like a toasted marshmallow at this point lol. It also has issues causing it to make the gauges read 10 mph too high at 60+

 

Next time you pull the pod replace the gauge foil with the Lutz Boards upgrade. I'll never install another gauge foil into a 928 after discovering this option in a car I bought.

 

Thanks, I'll look into it.
I did change the diff fluid when I got the car. Not sure if that had to do with anything? If it reads too high is that normal or means it's failing?
I don't see the option for an 85 928. I was planning to remove the pod for a number of reasons, but something I was hoping to tackle later as I have problems with other cars that need addressing. The voltage gauge is wacky, which I'm willing to bet a poor connection as I've battled with it in the past. I put in LEDS to help light better but at night I can barely see it illuminated. I soldered the LED's due to poor connection issues, but I'm not sure if I oriented them properly, or maybe they just don't produce enough light? If cleaning the connection doesn't fix it, as well as removing the sensor and cleaning it then looks like the gauges are coming off sooner than later.

 

Contact them about the 85. I believe they do have a kit, but may not be in the website.

 

Lutz told me a few months ago that he was working on an 85 board, possibly by the end of the year…haven’t heard anything yet