Oh ****e, I need help with a Tachometer issue! HELP!

paitken76 · 10-18-2004, 11:43 AM

Please help! Driving into work this morning I stared down at my dash while sitting in the usual highway rush hour stand still. I noticed the mileage and then again a few minutes later. Nothing unusual. About five minutes later after moving some distance and bored again I noticed it once more. Only this time nothing was different. And then two miles later when I arrived at work still no change. The damn thing just stopped somethere along the way, both the tachometer and odometer. The speedometer works just lovely but I'm apparently just not going anywhere. Any ideas? Fixes? I have no idea where to start and this is a bad bad thing.....

seaboltman · 10-18-2004, 01:44 PM

If im correct, the tach and the odo are run off gears, and it appares yours have broken. I beg someone to correct me if i am wrong about the gears because it sounds right in my head, but i very well may be making this up.

paitken76 · 10-18-2004, 03:04 PM

Well I drove home hoping that is was some sort of fluke this morning but no, its broken. I didnt travel a fragment of a mile according to my 944. So you think its gears? I thought is might have been magnets on the drive shaft or something like that... I have no clue. My old Honda (same year as the Porsche) uses the old cable that nicely plugs in to the back on the instrument. Since our cars have a digital computer cable type attachment and the spedomter portion of the instrument works I was thinking maybe theirs a sending unit or something.... Anyone, anyone?

For sure someone has had this problem before and can fix it? (I hope)

AFJuvat · 10-18-2004, 04:02 PM

Check the fuse and the the grounds behind the instrument cluster

AFJuvat

paitken76 · 10-18-2004, 05:53 PM

Thanks for the input. I already checked the fuse, it was fine. After all I didnt lose the instruments just the tach / odometer. Has to be something more specific dont you think? As far as the grounds...what should I be looking for? Behind the unit there are only the four circuit connections which I know are seated well and locked. Is there something else bacl there I'm not aware of? Thanks again.

livewirevoodoo · livewirevoodoo's Garage

I think the two main causes of odometer failure are 1) the odometer drive gear sliding down the shaft it is mounted on and disengaging from the other gears, or 2) the gear (cheap plastic) corroding over time, missing teeth, etc..

I took my instrument cluster out this weekend to refurb my instrument light cluster and noticed both symptoms with my gear (odometer stopped worked 1500 miles after purschasing car). After sliding the gear back down the shaft to engage it and the worm gear, I got about 4/10ths of a mile before the trip meter stopped working again

Looks like the gear is missing some teeth, time to replace it. I've seen them offered online for ~25 or so.

Zero10 · 10-19-2004, 02:38 PM

If both the odometer and the tach are out, and went out at the same time, it's electrical.
The tach is impulse driven by the DME.
I had my instrument cluster out a few times, and once I got a bit of dust/dirt on one of the connectors when I re-connected it. After about 500km's, the odo stopped working, and about 3 days later, the speedo and tach as well.
Cleaned up the connectors, and all is well.

SlowToady · 10-20-2004, 04:50 PM

/*Thread-jack*/

Being that the tach is driven by the DME, I'm assuming something is getting wet and that is why my tach usually won't work when it's raining? Any ideas on what to check first?

paitken76 · 10-20-2004, 07:44 PM

Thanks to all for the feedback so far and I empathise with those sharing my agony. Special thanks to "livewirevoodoo" for added info. I'm trying to wait until this weekend to give all the suggestions a go. Work ahs been crazy and the rain has hampered things a bit since I work on my car on the driveway. Hopefully I'll have some good news Saturday or Sunday evening for the forum.