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Old 23-03-2018, 02:56 PM   #1
niannorth
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Default Speedo Correction

I'm running Rover clocks in a K series mini and according to the GPS speedo they are reading about 15% high at all speeds. Does anyone know an easy way to reduce the frequency of the signal from the sender to the speedo by that amount? Any circuit diagrams or off the shelf solutions that don't cost the earth?
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Old 23-03-2018, 03:22 PM   #2
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Default speedograph recalibration

speedograph charge 43 if I remember when they did mine.
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Old 23-03-2018, 09:57 PM   #3
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Mine does exactly the same (mg tf clocks) I've been told by Agoaty that you can pull the speedo needle off drive at say 50 mph (use gps or something) and get a passenager to push the needle back on at the speed your doing and hay presto your speedo will now read the correct speed
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Old 24-03-2018, 01:12 AM   #4
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Mine does exactly the same (mg tf clocks) I've been told by Agoaty that you can pull the speedo needle off drive at say 50 mph (use gps or something) and get a passenager to push the needle back on at the speed your doing and hay presto your speedo will now read the correct speed
Well mine is bang on at 50 doing that! It's only 3 mph out at 100mph. That's better than most cars to be honest.

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Old 24-03-2018, 10:35 AM   #5
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Might give this a try: https://www.jaycar.co.uk/corrector-s...utm_medium=web

Just need to identify the signal wire.

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Old 24-03-2018, 09:18 PM   #6
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Might give this a try: https://www.jaycar.co.uk/corrector-s...utm_medium=web

Just need to identify the signal wire.

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Looks a good price. Signal wire is easy to find as i ran a new section of wiring in when ruling out the speedo issue

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Old 24-03-2018, 09:20 PM   #7
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Looks a good price. Signal wire is easy to find as i ran a new section of wiring in when ruling out the speedo issue

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Great, might end up being a simple fix.

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Old 26-03-2018, 11:22 AM   #8
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Being a bit of a tight ar#e and considering the unit is quoted as being 23 I thought 20 shipping was a bit steep. So I have found a circuit diagram and it looks like the parts should come to less than a tenner. So when I get time I might try making one myself.
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Old 26-03-2018, 01:12 PM   #9
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Being a bit of a tight ar#e and considering the unit is quoted as being 23 I thought 20 shipping was a bit steep. So I have found a circuit diagram and it looks like the parts should come to less than a tenner. So when I get time I might try making one myself.
Sounds an interesting circuit, so share it if it works. In principal its probably a similar principal to the fuel gauge wizard from spiyda that i fitted to the fuel gauge.

I still think the goaty method of popping the needle back on at 50mph is worth a try first though

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Old 26-03-2018, 01:26 PM   #10
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Originally Posted by niannorth View Post
Being a bit of a tight ar#e and considering the unit is quoted as being 23 I thought 20 shipping was a bit steep. So I have found a circuit diagram and it looks like the parts should come to less than a tenner. So when I get time I might try making one myself.
I cannot believe you are quoting yourself as tight and then paying for an item that you are trying to get to work, when I offered a free solution to the problem.

I don't know what the fuel sender issue was but this is a simple resistor across the terminals of either the sender or gauge. Somewhere between 100 and 60 ohms. If you bought both sizes a quid would be over priced.
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Old 26-03-2018, 01:36 PM   #11
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I cannot believe you are quoting yourself as tight and then paying for an item that you are trying to get to work, when I offered a free solution to the problem.

I don't know what the fuel sender issue was but this is a simple resistor across the terminals of either the sender or gauge. Somewhere between 100 and 60 ohms. If you bought both sizes a quid would be over priced.
Yes but changing the needle position makes it less wrong rather than correct. The speedo is about 15% out so the faster you go the more it's out. But moving the needle as suggested would at least mean the Speedo was only about 5 or 6 out at 70.
So I'll have to see how challenging putting the circuit together is.

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Old 26-03-2018, 01:52 PM   #12
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Yes but changing the needle position makes it less wrong rather than correct. The speedo is about 15% out so the faster you go the more it's out. But moving the needle as suggested would at least mean the Speedo was only about 5 or 6 out at 70.
So I'll have to see how challenging putting the circuit together is.

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My speedo is bang on at 50. At 100 it's about 3-4 mph out. I very much doubt you can better that.

All the cars I drive are out. My Honda Civic reads 10% over, Audi TT 7% over, MG ZS 5% over, Audi A4 5% over. It's not something manufactures seem keen to make correct. All these are standard cars.
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Old 26-03-2018, 02:12 PM   #13
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Manufacturers deliberately make speedometers read under to cover their ass.
Removing the needle and putting it back on is fine, my only query would be what has that done to the readings under 50mph?
I ended up using a GPS speedo because I wanted to use the Mini gauges but finding a cable was a nuisance and then the gauge would need recalibration too.
The little box of tricks to recalibrate the speedo seems a good idea to me.


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Old 26-03-2018, 02:16 PM   #14
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Well for me moving the speedo would mean this:

actual, reading, corrected reading
10 , 11.5, 4
15 , 17.25, 9.75
20 , 23 , 15.5
25 , 28.75, 21.25
30 , 34.5 , 27
35 , 40.25, 32.75
40 , 46 , 38.5
45 , 51.75, 44.25
50 , 57.5 , 50
55 , 63.25, 55.75
60 , 69 , 61.5
65 , 74.75, 67.25
70 , 80.5 , 73
75 , 86.25, 78.75
80 , 92 , 84.5
85 , 97.75, 90.25
90 , 103.5, 96
95 , 109.25, 101.75
100, 115 , 107.5

Because you are making a linear correction to an exponential error.

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Old 26-03-2018, 07:50 PM   #15
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I fitted my satnav to the car yesterday to get a true'er speed reading and found out the same as Niannorth in that the higher the speed the further out the error gets, 30, 40 & 50 the speedo is 5-6 mph fast, 70 and its 8-9mph and at 3 figures it's more like 12-13mph fast. So the little box of tricks or circuit that Ninnorth is about to make could be the answer into getting a more accurate speedo reading, although I havent tied the remove and refit the needle fix as yet, I think I'll wait to see how Niannorth gets on making his box of tricks. On the fuel gauge Inaccuracy I have got my gauge reading pretty much bang on with a little playing around with some resistors, first of all you will need a 100ohm 3w resistor and a 30ohm 3w resistor, soldering iron & sharp snips. Tacke your dash out and unscrew your fuel gauge out of the facia, you will see it has 2 resistors on it (75ohn + 62ohm) now this is the brave bit, cut both resistors off (you will see where the standard resistors are crimped/soldered to the underside of the gauge) cut just at the end of this, then tin the ends of the little tabs that are left. Take your 100ohm resistor and put a little flux on the ends and some solder on your iron (I used a 50w iron) solder the ends of the resistor to the lefthand tabs, the do the same with the 30ohm resistor and solder it to the righthand tabs it doesn't matter which way round the orentation of the resistors go they will work both way round. After you have soldered them on gently bend them up the side of the casing so that you can refit the gauge to the dash and hay presto your gauge will now read empty when it's empty and between 3/4 & full when full, I can live with it not showing full, I just needed to know that the gauge was showing empty when it is actually empty in the tank. I had drained the tank dry and then refilled it measuring how much I put back in, 5L and it just starts lifting the needle off empty, 35L and it reads the best part of the full mark. I hope this helps in getting a more accurate fuel gauge when using the zr, mgf or mg tf clocks. Niannorth if you could let me know how you get on with your speedo box of tricks I'd be greatful.

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