Tach a little lazy

Mattlock18 · Mattlock18's Garage

About every other drive the tach in my SC takes a nap for the first few miles, slowly creeping up to the 3000 rpm mark and then after that operating properly. When I say slowly creeping up, I mean it will take about 1 mile to even move to the 1000 rpm mark and then about 3 miles to move to 3000. After that it usually kicks in and works, but it is fairly annoying and I don't want it to go out completely. Any thoughts on the cause/solution?

Targa4now · 06-08-2007, 06:05 AM

A recent Tach issue on my 81 SC led to the real problem.... the battery and charging system. Check your battery, voltage regulator, and alternator. Related searches will provide sufficient info.

Just a hunch....

________________
Targa4now
1981 911SC Targa

Mattlock18 · Mattlock18's Garage

Will do. If that's the answer, you probably just saved me a couple of wasted hours.

Porsche_monkey · 06-08-2007, 06:11 AM

The voltage/charging solution is usually offered up to solve the 'foating tach' where it oscillates, and over shoots. It;s easy to check the rnning voltage so do that first.

Your symptoms sound more like an issue with the tach's mechanical movement, it sounds like it loosens up and then starts to work.

You might end up taking the cover off and checking the mechanics of the movement. You should be able to blow on the needle and move it.

CAPierce · 06-08-2007, 09:14 AM

I have the EXACT same issue with my 82SC tach. First I had the bouncing tach so the Alt was checked, new regulator installed, new battery installed and that problem went away (also installed cockpit voltage guage). I have assumed my lazy tach was a mechanical issue and if it gets to anoying, I'll pull it and check it out... Keep us posted on your progress!

dweymer · dweymer's Garage

I opened one up, and don't see any place to DIY any type of fix/adjust. I'll see if I can find it for pics, might be packed already though-moving.

Tim Hancock · 06-08-2007, 09:49 AM

Quote:

Originally posted by Mattlock18
About every other drive the tach in my SC takes a nap for the first few miles, slowly creeping up to the 3000 rpm mark and then after that operating properly. When I say slowly creeping up, I mean it will take about 1 mile to even move to the 1000 rpm mark and then about 3 miles to move to 3000. After that it usually kicks in and works, but it is fairly annoying and I don't want it to go out completely. Any thoughts on the cause/solution?

Mine does the exact same thing, but only after sitting out in the sun in the parking lot at work. It NEVER does it when parked overnight in my shop. Obviously heat related mechanical issue on mine, but it has done this for a year with no other ill effects.

Porsche_monkey · 06-08-2007, 10:17 AM

A drop of light machine oil? Or a drop of WD-40 on the bearing?

Mattlock18 · Mattlock18's Garage

I should note that mine also really only does this after sitting out in the sun. Generally it happens when making trips out to get lunch or when heading home from the office, but there must be a heat issue there somewhere. First thing the next morning it seems fine again. Since I know others have this issue I'll be sure to post any solution (if one can be found).

dweymer · dweymer's Garage

heat expands, so it may be the shaft inside the bearings expanding just a little. After looking at the insides...it seems to be a very delicate piece.

Try a sun visor on the windshield as a test

Tom '74 911 · 07-02-2007, 08:01 PM

I was doing some searching, found this thread and since it's not too old thought I'd add another response.

My search was for "lazy tach" as that's what I've experienced a few times. It's been seemingly out of the blue and on very hot days too, as others above have posted. My symptoms are exactly the same as in the original post, although it's only happened to me a few times - today being the first in a while. My tach needle was very sleepy when I started up during lunch time - It was hot today. I didn't take too long, but over the course of about 3-5 minutes, it came to life and then worked fine. I never got any wild oscillations or crazy readings - it didn't budge when I first started the car, and then after 3-5 minutes, everything was working fine.

I thought for sure I'd be in for a new alternator/regulator - maybe I still am, but I'm glad I found this thread. It makes me feel a little less nervous about the impending doom. A voltmeter is in my future!

Tom