Went out to start the Z this afternoon and noticed that after start tach needle was high and then slowly buried itself at 8 grand. I checked all the visible wiring under the hood and found nothing out of place.

Any ideas? Tach dead? Silly thing worked fine yesterday. Maybe it's just old and tired like me.

Any input appreciated

HCH

Ballast Resistor

Sorry MOM, the Ballast Resistor wouldn't cause those problems.

HCH, sounds as though it is dead or in the process of dying. Was it extremely warm that day? Heat has been shown to be one of the tell-tale events/causes of tach failure before it actually dies.

I had heard Arne had a dead tach for me to take to a friend to see if it could be repaired and hence have a repair procedure. But in the fun over Canby, we never got around to talking about it.

FWIW

E

Yup, I forgot to load it in the car prior to Canby. The dead one I have sometimes works, sometimes is intermittent, and has been known to snap all the way to 8000 when the ignition is switched on. Very warm days make it worse, it actually worked fine for several months - the cool winter months.

I'll try to remember to bring it next time I come North.

I was actually going to put in my original post that it has been unseasonably warm here, but in relation to other places like phx. I didnt Think it was relevant, but maybe thats it. I'll take it out this evening in the cool and see if its working.

I do have an extra tach I can install, I just dread dealing with anything under the dash, no room. Also any repair info would be much appreciated as I do like to keep spares of most anything.

Thanks all,

HCH

Sure enough, I waited until 11 PM tonight when things cooled down and went for a drive and the quirky little thing worked fine! But... does this mean that this tach is beginning its journey south?? Is there a time prognosis? I just hate working under that dash.

Thanks again,

HCH

Sure enough, I waited until 11 PM tonight when things cooled down and went for a drive and the quirky little thing worked fine! But... does this mean that this tach is beginning its journey south?? Is there a time prognosis? I just hate working under that dash.

Thanks again,

HCH

Answers to your questions:1) It's been an indicator in other failures. Not every heat flaw has been re-reported as an eventual tach failure, nor has every tach failure been reported as a result of the heat flaw.2) No. Not enough people have noted it and reported it with the timelines involved to be able to give anything more than a shrug as an answer.It's just one of those common things. The fix has generally been to replace the tach. Since most people don't attempt to fix the tach afterward (which is a shame as they CAN be repaired (or so I've been told)), the supply of these is slowly dwindling.

FWIW

E

A fault like you describe may be due to a dry joint on the circuit board.

Hot weather may cause the wire/joint to expand and not make contact:cross-eye

The chances of having a bad component are rare I would say, more likely a bad joint due to vibration.

I had a tach in my P510 which exhibited random not working sessions.

Eventually got sick of it and pulled it out.

Using a fine tipped low wattage soldering iron I re-soldered all the joints I could find.

[There is not much inside an impulse tachometer.]

Hasn't missed a beat since:)

The tachs are flaky on all 3 of our 280z's and two of them have been replaced with known good units that failed within 6 months. That's 5 bad tachs!

I read somewhere that it is commonly a mechanical failure, not electrical. Heat causing parts to bind that are already dragging due to wear or contamination. From what I think I remember, the mechanism has to be treated like a clock: checked and cleaned, but no lubricant to attract dust. I haven't tried fixing one yet but I'm refurbing a dash for mw wife's Z and will try to get the tach working.

I read somewhere that it is commonly a mechanical failure, not electrical. Heat causing parts to bind that are already dragging due to wear or contamination.

I'd buy that theory as a possibility for some types of failures, like bouncy needles, or needles that stick at 3500 RPM, and suchlike.

But for tachs that immediately snap to the peg at 8000 when the ignition is switched on, it has to be electrical.

E, let's try to make plans to get my dead one to you. Maybe use Bryan Parcel Service?

what about the tach only revving to about 3k?

Jason:

I'd make a smart-a.. remark about only running on 3 cylinders...or not using the accelerator pedal and just the choke.....or that you're only using the + side of the wire and not the - side.....but that's all they would be.

Smart A.. Replies and not very good ones either.

The only thought that comes to mind is that maybe you have some form of gunk in there that's stopping the needle from rotating.

How does it operate at Idle or barely revving, does it follow the perceived speed of the engine until you get past 3k RPM? What happens at 3k, does it stop suddenly or does it seem that it just hasn't got the "strength" to go past 3k?

Sorry, this one isn't even 2¢ ....

E