smongiovi

For the last several months my 1991 911C2 has had eratic speedo sysmtoms. The needle will often not register any speed, then suddenly start working, then just as suddenly dies, then comes back to life fluctuating wildly. Any combination of those three symptoms happens at any time. Sometimes it works fine for hours, sometimes not at all.

Since I'm almost always driving over the limit, my true speed is not really that important. However since the darn thing is often not registering a speed at all, the rear wing doesn't auto deploy and of course the odometer is not registering the miles properly. So, I'd like to get this fixed without replacing the gauge.

My research on this indicates the problem may be with 'Relay 52' which apparently has something to do with the speedo operation.

Anyone else encounter this problem?
Is there a way to determine if 'Relay 52' is funtioning properly?

wellcraft290

Not sure on these if cable driven and sounds more like a connection issue or bad cable. Have you pulled the dial to see if anything is lose behind the speedo?

John Boggiano

Agreed - try pulling the dial and unplugging the conector, then reconnecting it.

jimq

clean the connector pins with a pencil eraser

smongiovi

Will pull the gage and inspect and clean it up...My understanding is that to remove the guage I simply pry it out gently with a flat head screwdriver...anything else I need to know about removing the guage? I deff don't want to break anything else...

Thanks for the feedback folks!
Steve

martin964

just pull it out using the srewdriver. it is held in with the neoprene ring an that is it. Mine is out and away for repair for the third time (my issue was the odometer not the speedo) they fixed the cogs, but it still occaisionally would not work for about 10 miles on start up. As I am not really interested in keeping miles off the clock, I want them to fix it! (fingers crossed this time it is sorted)

wellcraft290

also on the screwdrive use tape on the tip not to gauge the dial or dash.

altarchsa

I had the exact same experience with my 89 C4. Still unresolved as the engine is now out of the car for repair. I couldn't decide if it was a bad speedo or sending unit. I know the tolerance on the flywheel-to-sending unit is critical. If cleaning the contacts doesn't work, you might try pulling the sender, located on the driver side of the bell housing, and cleaning/readjusting it. I will be able to check mine while the engine's out, but will remember the advice on cleaning the contacts if that doesn't work.

Speedo does play havoc with the spoiler.

John Boggiano

You can probably pull it just using your fingers - I find it's one of those jobs that's all in the mind - if you know it can be done that way then you just do it and it works, if you're not sure then it won't budge.

evoderby

Had the same problems, I pulled the relay and cleaned the contacts.....haven't had any problems since (10K km).

The relay itself is quite expensive at around 180 Euro.

smongiovi

Well I pulled the speedo, cleaned the contacts, pulled the relay and also cleaned that up too - sadly, no luck with this. Still eratic action on the dial. Unless there are any other suggestions, I think a trip to the repair shop is next for this particular problem.

Thanks for the advise, I really do appreciate it, this is a great place to share thoughts on these magnificent cars.

craig001

Sending unit?

smongiovi

Looks like the possible sources of the problem are either the sending unit, the relay or the speedo itself.

Anyone know how I can get at that sending unit and what I can check for when I get at it?

altarchsa

If you'll PM me with a phone number, I'll send you a phone pic or two of my '89 C4 sending unit. I think yours is the same. I have the engine out and the transmission removed, so you can clearly see how the sending unit relates to the flywheel.

It's on the driver side, between 2 and 3 o'clock when viewed from the front (transmission) end of the motor. It's attached to the case with a 2 bolt bracket just in front of and above #3 cylinder. Setting is by loosening a third bolt that holds it in the bracket and with feeler gauge measurement to the flywheel rear teeth. These are the larger teeth, not the starter teeth.

altarchsa

Here are a couple of snapshots. You'll have to imagine the trans in place.

You can access this from underneath the car, but I'm sure it will be a little tedious because it is "up in there".

Good luck.