Wobbly tachometer needle.

WarrenL

WarrenL

Active Member
I've searched the threads with little success, so it's time to start a thread. I apologise if I'm retreading old ground.

My problem is, as you've correctly guessed, a wobbling tacho needle. The other week I was driving ghce's car and marvelling at the steady tacho needle. I want this for my car! From what I have been able to dredge up from the depths of the forum, I can supply you with two pertinent facts: I have an RVI-type tacho; and I have a Pertronix ignition system installed. However, I do believe that the needle bounced around a bit even prior to that.

What can I do? I can't shoot a decent ZF-in-action video with a wobbly tacho needle!
 
I have never looked at the insides of the Rover Tachometer however I have looked at quite a few faulty tacho's in the past and have usually found an assortment of dry joints and loose connection.
I really cant see that it is a wiring problem as were that the case you would be seeing erratic spark as well.
It could come down to something as simple as an unlubricated needle pivot bearing or a changed component value or dry joint , given the age all of these are possible.

Graeme
 
Maybe you're right, Graeme. A dozen or so years ago I had the instruments overhauled by a certain local instrumentation firm who shall remain nameless due to the rules of the forum (but you know to whom I refer), and whilst they sorted a couple of problems out, the tacho remained somewhat bouncy, so far as I can remember. And this was long before the Pertronix, which I installed in 2009. This particular firm ballsed up the latest little job I took to them, and I've subsequently heard iffy reports from several sources, so maybe it's time to pull the damn thing out and look at it myself.
 
why not remove remove facia and try 1-2 drops of 3 in 1 oil on needle spindle------it worked on mine and my car live outside 24/7 all year round
 
I think that's a very good piece of advice, symes. It's worth a crack before I go in search of other solutions, such as an RVC tachometer. To be clear, I have to access the spindle from the back of the cluster?
 
Hi Warren Had this very same problem myself. I had bouncing and under reading needle (not much maybe 400 revs) Fault traced to bad earth on tachco. Cleaned terminal on back of rev counter (not too bad) but other end was obviously corroded. Bit of emert and now tacho reads correct and smooth, maybe you have this issue also? Ian
 
Sounds like the second thing to try, after a spot of oil on the spindle. Thanks Ian. I know the terminals in the instrument panel are good, but I'll check the other end. Got all the other jobs sorted (apart from the fuel pump) so it's time to tackle the tacho, methinks.
 
Well fellas, I dropped a bit of sewing machine oil on the spindle, removing the rev counter so I could tilt it back and make the oil run down the shaft. I also checked the connection at the coil, but I still have a slightly stuttering tachometer. I didn't think until later to check the connections at the ballast resistor, so will do that next time I'm out in the garage. What I'm not sure about is where the tachometer earth is run to. Is it in the back of the instrument panel, or elsewhere?
 
In a recent thread on converting the taco from I to V operation I noted in the photos the use of electronic components any of which maybe subject to dry joints.

Graeme
 
This is just a comment as I'm definitely no expert, but I was under the impression that ballast resistors become redundant when electronic ignition is fitted?
John
 
I'm no expert either, John, but there was no clear indication one way or the other whether the ballast resistor should be removed when I fitted the Pertronix. Additionally, it sits in series between the coil and the tachometer, and must therefore influence the current through the tachometer. Removing it might have consequences in that department.
 
UPDATE: I was on a test drive today for other reasons and I noticed that since lubricating the spindle and cleaning up the coil contact there was much less twitch in the tachometer. Not quite cured, but it was noticeably better than the last time I drove the car. Might be on the right track! Will check the other contacts and the ballast resistor.
 
Nah, maybe not. Here's summat to chew on: Today I drove over some long high speed undulations that set the car pitching, and the needles (tachometer and speedo) were both dancing in time to the car's movement.
 
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