crazy speedo

john freedman · 12:22 AM

My speedo went crazy today at 60mph quickly fluctuating from 60 to 20 and then at 30mph fluctuating and sometimes sticking at 0.

I've also heard a "grinding" noise coming from the dash when it's cold out which I assume is the odometer. I assume I'll need to check the all the electrical contacts, etc.

Any suggestions/tips would be appreciated.

idopps · 03-14-2002, 07:01 PM

those speedometers and odometers are not powered by cable like the 944. They have a motor that turn them. I have heard of one of the gears in them going bad. It is sort of a red colored gear, not the white ones. I suppose it could be electrical, but grinding makes me think it is mechanical. Let me know if you need any advice opening it up.

Joe Ricard · Joe Ricard's Garage

However, I could be wrong and it is easy to verifiy the sending unit. Located at the back of the transmission read continuity across both leads as you move car back and forth. You can see the switch operate.
the grinding would definatley lead me to the Speedo gear. BTW it is a real pain.

Wayne 962 · Wayne 962's Garage

Our speedo repair article has a bunch of info on this:

http://www.pelicanparts.com/techarticles/Mult_gauge_repair/mult_gauge_repair.htm

-Wayne

john freedman · 03-14-2002, 09:32 PM

Thanks everybody.

As usual when looking for a problem everything worked fine today: speedo operating normally and no noise from dash.

It was 70 and sunny today in Virginia so who knows? We'll see what happens when it's cold and wet.

I've heard the dash noise ever since I had the car serviced for a head gasket. The noise sounds just like an unlubricated cable and gets louder the faster I go. Since the 928 has an electronic speedo I chalked it up to odometer/tripometer gears. Of course the Porsche people didn't want to touch it and recommended shipping the entire dash off for overhaul.

I'm still concerned about the speedo going crazy - is there a spring that holds the needle back? Can a faulty/dirty sensor or a bad motor cause the wild fluctuations?

Looks like a tough job for a do-it-yourselfer.

Wayne 962 · Wayne 962's Garage

WD-40 behind the dash...

-Wayne

idopps · 03-14-2002, 10:27 PM

Does your odometer act up at the same time as the rest?

john freedman · 03-14-2002, 10:57 PM

Wayne - do I spray all over or just in the general direction of the speedo? The WD-40 won't interfere with any electronics or gunk up the assembly?

The odometer/tripometer seem to work fine.

What do you think the problem is - dry/broken worm drives?

BTW my gas gauge is screwed up too. Doesn't read full and drops real fast. This doesn't concern me too much as I fill up based on mileage.

Wayne, if you redo dashes/gauges please send me an email with estimated cost (ballpark).

This is a new car to me <6 months. Thanks again...John

Wayne 962 · Wayne 962's Garage

Speedos run around $85-120 depending upon what's wrong with them. The little gear replacement is $85. You can send it in to us for evaluation (we send it to a gauge guy - all he does is VDOs...)

Use WD-40 if there is a cable, if not, use some model train oil on the internals...

-Wayne