Previously I posted a post about Fuel gauge decreasing at higher revs. I have made up a new voltage regulator using an IC voltage regulator, it is controlling at 10 volts. I have run another earth lead from the speedo to the body. I have earthed the return wire at the sender- the gauge goes to full. When I rev the car when it is parked the gauge acts as expected. It is only when I drive it does the gauge to 1/2 full from full. I may have to take it to an auto electrician as I am stumped as to what the problem maybe.

Cheers' Scott.

Is the back of the speedo open to the engine bay? Airflow has been known to effect gauges.
viewtopic.php?t=91462

Have you removed the sender and checked it's resistance from full to empty positions? With wear the wiper arm can get loose against the resistor winding.

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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.

The speedo is not open to air flow. I haven't had the sender out because it seems to work, because it is ok at idle. When I rev the car when it is standing still the gauge stays where it should, only goes to half when I drive it.

I am no expert, but I would imagine the motion of the car actually moving is enough to upset the sender unit.

I will purchase a new sender as I am at my wits end to what the problem is. Thanks for all the comments.

lol - my car does the same - went through the same, voltage reg, airflow, earthing, different gauge etc. etc. I still think airflow is the cause, as per the thread Dr Mini linked above...




I just ignore it. I usually know how much fuel the car has in it. If I stop and it's below the E mark, I find a servo and put some in.

Does your temp gauge do the same thing? It used to do it for my temp gauge too, but when I injected the car I needed a different type of sender so I made a servo driven gauge

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did I tell you that I won a trophy?

Thanks Simon for the reply.

yes my temperature gauge does the same thing. I have the MK2/MIni k setup. I have the mat which has sponge on the back of it with vinyl on top of it which covers the firewall speedo area. I thought this would stop airflow around the speedo area- maybe not?. I mention the problem to an auto electrician today and he said it was an odd one which he could not give a solution to.

One thing I forgot to mention was that I did notice was I took a resistance measurement between the back of the speedo and the body with the engine off and it was approx. 6 ohms. I ten started the engine 2000 rpm and te resistance was a lot higher. That is when I added another earth lead- I thought it may have fixed the problem, but it didn't. My blinkers seem to be flashing faster though.

there's gotta be something in that... what about at 4000rpm? what about testing how much current flows from the regulator to the temp gauge at RPM steps... ?



did you remove the old earth lead? shouldn't make a difference (path of least resistance) but it's possible to get a loop going.

the back of a mini engine bay does get a lot of air pressure going, so any way for air to get from there to behind the speedo housing will be taken... I wonder what would happen if you put the temp gauge in a plastic bag and hung it out of the speedo housing so there was no chance of air rushing past it

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did I tell you that I won a trophy?

No I didn't remove the earth. Its part of the loom and screws on the back of the speedo where the regulator bolts to. I ran another wire from there to the body. More investigative work required.

keep me posted

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did I tell you that I won a trophy?

Careful you don't introduce an earth loop with unintended consequences

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"Show me the Mini!"

Just something simple to try which helped mine. Cut a square of underfelt and fit/tuck it in the hole behind the speedo then the firewall blanket over that. That was me with the gauge that reacted to window up or down.

I reckon though it's a loose connection somewhere or a fault made worse with vibration.


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68 Morris Cooper S Mk1 (*ex 78 1275 LS 4th last built, 70 Morris 1500 OHC & 70 MiniMatic)