speedometer not working where to start?
 

1980 sc targa, speedo moves around from time to time but has never worked I picked up the car for a person who had no Idea what a porsche was. so it is needs of some major overhaulin I would like a starting point on the speedo, I read the post about getting the odometer working I will look to get the gear replaced also because the odometer no worky either. anyway can anyone tell me if the speedo has a electrical sending unit and where it is located? Any help is great, I am new to Porsche I am eager to learn all about my new 911.

Hi, Welcome to the Board. Mark

Mark,

let me welcome you as well!

Maybe you have already look at this but, check the wire connections at the speedo itself. I had a speedo that stopped working and it was simply the connectors on the back of the speedo were loose.

If that doesn't fix it - I would bit the speedo is the problem. But don't rely on my opinion. Hopefully others who are much more versed in the issue will post here!

Good luck,

earl

The speedometer is run by a sensor on the outside of the transaxle case, above the right axle on your car--a round unit about the size of a quarter and half an inch or so deep. It's very easy to remove and replace--simply held in place by a spring clip, as I remember, and there are two wires going to it.

When You put it back in, be sure to replace it in the correct orientation. It's a bit counterintuitive, since the potted part faces outward and the metal "can" of the unit faces in, toward the transmission.

The sensor counts the number of times magnetic stations mounted on the ring gear pass the sensor and thus calculates speed. If the sensor's tits-up, the speedo won't work. It sounds to me like that might be your problem, if the speedo works only occasionally.

it is on the passenger side of your tranny. (i think) but it is a round disc with a wire running out of it. the disc simply sets inside of a indentions and is basically a magnetic pickup. there is a wire running out of it, and it will go into a hole near the front nose of the tranny. if you take the access panel off at the floor section between the foot areas of the rear seat, you will see where it connects to. it runs to the speedo from there. the switch at the tranny is held on with a small wire brace, secured with a small 10mm bolt.

i agree with earl, yank the speedo out. you may need to use something like a plastic spatula to pry it started. see if there is a wire disconnected or something.

You should check the sensor FIRST, before pulling anything off or out!

1. Put the back end up on jack stands, remove rear passenger-side wheel.

2. Find the two wires out of the sensor and trace forward to 2-pole connector. Disconnect wiring harness and connect multimeter set to low Ohms or continuity function.

3. Rotate rear hub exactly one turn and count number of low Ohms readings during one revolution ... it should be eight. If no continuity or low Ohms readings are found, remove sensor and test again away from car with known good magnet. The magnet rings are known to occasionally shed the magnets.

4. If test good at transaxle, reconnect 2-pole connector and proceed to pulling speedometer.

5. Connect multimeter test leads to speedometer terminals 31b and '-' [ground] ... and repeat the test performed at transaxle.

6. Check for 12 Volts at speedometer '+12 V' terminal when ignition switch on.

http://www.pelicanparts.com/911/911_...SC_Part5-2.jpg

Before you dig too deeply into this thing first pull the inspection cover located on the hump by the back seat and make sure the two wire connection for the speedo is firmly seated...4 phillips head screws hold that cover on. If someone has been in there futzing with the shift coupler they could have easily disturbed the two spade connectors.

wow thank you all for the helpful hints I will be checking them out tomorrow after work. This web site is awesome I have never had so many people be so freindly on line before. so thanks Mark, ecm911, Steve, earlsman, motorhead 45, vash ,

All the above is great advice. If it happens to be the unit itself you can pry the whole thing out. The ring around the unit is rubber and holds it in the dash. I used a 1" paint scraper/mud knife to slowly pry it out. Take good notes of where each and every wire goes and carfully disconnect the speedo cable from the unit. Pack it carefully and send it to North Hollywood Speedometer in CA. They will fix it for a little over 100 bucks if I remember corectly. There is also a company called speedometergears.com who will sell you the little odometer gear, if that is what is needed, it gets a bit complicated from there.. Wayne writes well about it in his book "101 Projects for your Porsche" available from the host of this site. This is a good thing to fix right away on a new/used car..

Where are you? I have an Extra Speedo I bought. To try it out if you are local . Thanks Mark

Nobody's said it yet so I will. You're new to the forum therefore the unwritten rule (though many have written it:D ) is to post pics of your car as all proud P-car owners love to do. We do love pictures, you'll see;)SmileWavy Welcome.

Mark thanks for the welcome. I will post pics but my Sc is not as nice as the P cars on this site it needs retoration bad and I live in Colorad so it will be snowing here soon and thats when I will pull it into the garage and start my winter long tear down and rebiuld I can't wait to get the car done It will be so fun.
Jason

Welcome to this great resource. It'll save you time and money. Buy Wayne's "101 Project's for your 911" book to give you an idea of what some common upgrades and fixes are for your car.

My car had to same jumpy speedo syndrome, and the sensor wires were unplugged. Unscrew the floor plate to check, like others have mentioned.

There are lots of Colorado Pelicans, so someone is usually close to your city if you need a second opinion before you dive into a major project.