Problem with the tacho, it is the original tacho on my 78LS, when the car is idling it sometimes doesn’t move as if its not working then when I accelerate it fluctuates all over the place, then when I have it idling or say driving along at 2500 or 3000 rpm’s for example it eventually stops bouncing up and down and then will become steady on the rpm that I’m doing. Ive been told that maybe an earth problem.

ANY IDEAS

Definitely sounds like a dodgy earth to me...

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Simon

The adventures of an owner builder in the Tallarook Ranges

Not just the earth, it can be on either side of the circuit. get out your diagram and follow the wires back to any connection point you can see and check that they are nice clean and firm connections. It may also be the tacho itself or the backplane, but check these first.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

So by diagram you mean the electrical diagram or just trace back from the behind the dash to where ever the wires will take me or i suppose yoou mean both. Sounds like fun. And, what is "the backplane" excuse my ignorance.

yeah you will need to do both. Look at the diagram, trace the wire, check, clean and reconnect nice and firm. Do clean them though when you are there, don't rely on firm on it's own.

Sorry by backplane I mean the flexible printed circuit behind the tacho and speedo attached to the cluster. All copper connections come in on a plug and are distributed there to each of the instruments. It avoids the messiness of a wired instrument like earlier minis. You can run the engine with this out, and prod and poke around. if the needle goes steady at any point, you have probably found a cracked copper track. Not so bad if it is, you can solder a wire around it.

But don't get confused, do the simple stuff first, start at the distributor and work backwards.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

Mine does it, clubmans does it but not so bad.

I think in my case it's just a crapped old tacho. My car does it at high rpm and sudden rpm changes, like going down a gear, not really when going up a gear though.

I'd recommend checking all your electrical circuitry though.

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1964 Morris 850, 1330 Supercharged - 81.8hp atws.
1975 Leyland Mini S 1100S powered - Nice and reliable.
1977 Leyland Mini LS - Project LS-T

I was thinking that could be a possiblity, cause when i was looking at it (now i know what its called) the backplane, it has a twist in it ( but its not kinked). Say from the center gauge to the tacho it dosn't run flat is that how it is ment to be cause i pulled off the little clip that hold it in place and went twist it back so it would be flat and then the hole didn't line up.

Slight twists aren't so bad, but get rid of any twist that isn't needed and look carefully at any creases, they will probably disguise cracked copper tracks.

Try bypassing the flexible printed circuit card by using a jumper wire to go from where it comes in from the loom to the connection on the back of the tacho. This will tell you straight away if it is the printed circuit that is giving you the problems.

Double and Triple check the path to get the jumpers correct though, it's not hard to see where it is coming and going from. It really is just a cheap and simple version of a copper wire, nothing more.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

try eating these, then..

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NO MANUEL THEY GIV'ET ME DA S***

It's the beans! Not bouncing beans, Mexican jumping beans, in your tacho?

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1964 Morris 850, 1330 Supercharged - 81.8hp atws.
1975 Leyland Mini S 1100S powered - Nice and reliable.
1977 Leyland Mini LS - Project LS-T

I don't understand it, but from the tone I reckon you are having a lot of fun and that things are coming along just swimmingly.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

Most Clubbie tacho's "fall asleep" when you first start-up
But anything over 6500rpm and it just goes insane...

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Most Clubby tachos have very poor damping, and bounce around with vibration. Hey, it's a Smiths...... (maybe related to Lucas?)

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

I agree with both LS1380 and the Doc on that stuff. Dodgy! But mine si worse than it should but my guages are dodgy, the printed circuit bopard is dead and has solderings all over it, it was fixed than my tacho fell out while driving in behind the dash once. And ripped all the new soldering out. Dodgy clip snapped. All fixed now though.

Ahhh, good mini stories....

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1964 Morris 850, 1330 Supercharged - 81.8hp atws.
1975 Leyland Mini S 1100S powered - Nice and reliable.
1977 Leyland Mini LS - Project LS-T