Tach Bounce Between Shifts

[deputydog95]

When I shift up or down, the tach tends to bounce up 500 to 1k rpm higher than it should, and then immediately settle to the correct rpm.

Any idea what causes that and how I can fix it?

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[DRACO A5OG]

If the 3.2, obtain ohm readings on the Speed and Reference Sensors.

[deputydog95]

Yeah, it's the 3.2 liter. Sorry I forgot to post that.

So this isn't normal?

Odd the way it only jumps up when you're shifting. Within a half second of engaging a gear, up or down, it holds a steady reading.

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[Uncle Enzo]

My 2.7 does the same thing. Ive tried to track down the cause but have not had any luck. I guess I have just gotten used to it.

[deputydog95]

Still freaking me out... When you downshift it looks like you're going to zing it the way the needle swings lol.

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[tshebib]

I had the same issue when I had my 3.0l in the car. I ended up sending it to North Hollywood to be rebuilt. They told me there are damping springs that stop the needle from "bouncing around". They fixed it but then the tach seems to be sluggish as if the engine is spinning up faster than the tach. That was 6 years ago and now I don't notice the sluggishness so I think it was just in my head.

[deputydog95]

My tach has already been to them to be resealed. Sigh... Would have thought they would have addressed this.

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[DRACO A5OG]

Unfortunately NOHO SPEEDO, will only do work as requested. I had an issue with my speedo, it was clocking too slow, but luckily they warranted it but when the odo failed they charged me for it. WTD?

Is not a refurb a whole refurb?

[RMG001]

And I thought my clutch was slipping!!

[75 911s]

mine does it too, join the club. Just some of the patina of our worn out damping springs.

[Otter74]

In the club of those glad to know what is behind this. My SC's tach does this and at first I thought my clutch was slipping, but it was obvious from the feel and performance of the clutch that it wasn't. But I didn't know what the hell was behind it.

[pampadori]

Can anyone confirm these springs exist with a pic or two? I've been told it's a thick oil that "dampens" the movement.

[lateapex911]

The guys at Nichols in NC are super fast, and reasonable, and can answer the question(s) on the phone, but it sounds like it needs to go in for a service.
Nichols Speedometer & Instruments - Speedometers, Tachographs, Service and Repair North Carolina

[kevbo]

I put up with a jumpy tach for about 2 years. It would also jump on bumps (sometimes), spike to 9k then to 0 after turning on the headlights. I finally brought it in and they said it was the headlight switch 940$. Instead I found another tach for my 86 and now everything works. I just need to send my original tach off to get fixed.

Buy another one and see what happens.

Good luck!

[jbell959]

There are no damping springs in any of the tachs. There are recoil springs to bring the needle back to it's resting position but don't do anything to smooth the needle movement. As the years went on the tach design improved and the bouncing is the most noticeable improvement. I believe it was improved by increasing the strength of the permanent and electro magnets that make up the movement.

The only thing that dampens these tachs is a few drops of a thick oil in the plastic "bushing" that supports the bottom of the needle shaft. If the oil isn't there the needle bounces more and if the oil gets thick and sticky the needle gets sluggish. I've played around with the oil and it doesn't make a lot of difference. I've opened up a couple of tachs that were previously at other shops for the same issue and in most cases wasn't able to improve them. I'm starting to think that the permanent magnet may lose strength over time. It's on my list to do more testing but just haven't had the time yet.

I can post pictures if anyone is interested.