Tach problems

[Cory Covert]

Hey guys hoping that someone can help me out. My tach seems to be sticking. It wont read over 2, even when I rev. I read some of the articles here and pulled the cable off. The cable rotates but it seems slow to me. How fast should it be spinning. At idle it turns slow and then does go faster when I rev. I have ordered a new cable as I believe it is the original cable. Any ideas?

Thanks
Cory

[SnoBrdr]

Hey guys hoping that someone can help me out. My tach seems to be sticking. It wont read over 2, even when I rev. I read some of the articles here and pulled the cable off. The cable rotates but it seems slow to me. How fast should it be spinning. At idle it turns slow and then does go faster when I rev. I have ordered a new cable as I believe it is the original cable. Any ideas?

Thanks
Cory

Well that's how a tach works.

Never saw the wheel gear or the tach itself go bad but stranger things have happened.

Did you recently take the wheel off?

[Cory Covert]

No only disconnected up by tach. Never did anything else on it

[Cory Covert]

Well replaced the tach cable and still not indicating correctly. I sprayed some WD 40 in the connection port still the same. Any ideas?

[SnoBrdr]

Well replaced the tach cable and still not indicating correctly. I sprayed some WD 40 in the connection port still the same. Any ideas?

How often have I said to you that when you have eliminated the impossible, whatever remains, however improbable, must be the truth?" - Sir Arthur Conan Doyle, Sherlock Holmes: The Sign of Four

So that leaves either the gear or the tach itself.

Is the cable secure in the fuel pump ?

[Cory Covert]

Checked the seating and it was okay. The gear rotates freely. Guess that leaves the tach itself. Took the tach off, used the end from the old cable hooked up to a drill, hardly any movement at all.

[Maz]

Checked the seating and it was okay. The gear rotates freely. Guess that leaves the tach itself. Took the tach off, used the end from the old cable hooked up to a drill, hardly any movement at all.

Silly question, but I assume you were running the drill backwards? (counter-clockwise looking from the back of the Tach).
Maz

[76AuWing]

I just went through something similar. My tach started jumping around and then wound up staying in one place. I bought a cheap set off of Fleabay so that I could take them apart and see how they work. The tach is remarkably simple - the cable goes up into the housing and on the other end is a circular magnet. That magnet sits inside a metal loop frame and, when rotating, must induce a current that is then measured and calibrated onto the needle indicating an rpm. I pulled my tach, and in the process discovered where my problem was as I heard pieces bouncing around inside it. Sent both speedo and tach off to Pistol Pete for rebuild. He sent me a picture back of the magnet - it had broken up into three big pieces and a few smaller ones. Got them rebuilt and had new faces applied as well, they look and work great now.

[Cory Covert]

When I had the tach off it did not make any ratting sounds. I will keep that in mind. As to the drill I ran it both ways just to hedge my bets.

[Maz]

If you've spun it on a drill, counter-clockwise, and it's still not registering, the Tach itself must be faulty. As 76AuWing stated, there's not much inside, apart from a spinning magnet, speed cup (non-ferrous disc/cup connected to the needle) and a hairspring to return the needle to zero. The speed cup/needle may be stuck or, as mentioned, the magnet may have come loose. Either way, you may as well open it up and have a look. Incidentally, WD40 or other oily lubricants shouldn't be used in, or close to, the tacho head. They attract dirt, clog up the internals and eventually find their way onto the face of the meter causing greasy stains. Much better to use a graphite lubricant (the kind locksmiths use) which is dry.

Maz