speedo and diff calculations

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speedo and diff calculations

Postby Hans Efde » Mon Sep 07, 2009 10:07 pm

As mentioned in my topic on the problem I am having with my speedometer:
http://www.ime.org.uk/ime/s/speedo.html
http://www.ime.org.uk/ime/f/final_drive.html
Interesting if you want to finetune your speedometer after a tyre or diff change.
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Re: speedo and diff calculations

Postby Rich » Mon Sep 07, 2009 11:09 pm

Don't know about fine tuning, but my speedo is showing 90mph when the GPS tells me I'm doing 60mph.

Considering the speedo drive was apparently chosen professionally to match the diff etc I'm wondering if there's anything else that could cause the speedo to over-read so much? The needle bounces a lot at around an indicated 30mph.

Rich
;)
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Re: speedo and diff calculations

Postby Hans Efde » Tue Sep 08, 2009 7:23 am

Needle bounce is usually caused by a worn out cable. But this would cause the needle to lag behind. It seems they made an error with the speed gears in your car. Perhaps due to the speedo itself. Not all speedo's require the same revolutions. What I understand from the Dutch Mini forum is that a figure is printed on the speedometer housing. This is the basis for the gear calculation as on the referred websites.
My speedo is 12,5% too low, but with the present available sets it's difficult to get close.
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Re: speedo and diff calculations

Postby Alan D. » Tue Sep 08, 2009 8:34 pm

Hello All,

Been a bit busy.

My speedo often reads 90mph on my 998cc convertible. All I can say is I'm very flattered and will leave the speedo telling lies. It would probable cost me a lot of money to get it to tell the truth! This is the answer, don't spend all of your money building flash engines, just get your speedo to read high!

Just my strange sense of humour.

Alan D.
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Re: speedo and diff calculations

Postby Hans Efde » Tue Sep 08, 2009 9:12 pm

Hi Alan,
I prefer to get it a) working and b) right. The a) bit is a pain in the butt. I am going to take the spindle out in the weekend to see if it has a problem. I checked the plastic wheel and it seems okay. The only problem, reported in an earlier TGT, is that the hole in the drive shaft is 3,4 mm square, but the cable is 2,7 mm square. It may be possible that the speedo gear worked, but was spinning around the cable. There seem to be drive shafts with the correct smaller hole (later Metro engines). I am into contact with my Mini garage to see what he has in stock or on old engines. I'll see if I can get a 16 teeth gear work with a 5 teeth spline. That would be my perfect combination. Else I have to go to 17/6 which will give a too high reading.
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Re: speedo and diff calculations

Postby Hans Efde » Mon Oct 05, 2009 4:27 pm

My speedo is working again. It seems the problem is in the square hole in the shaft with the colored gear that is driven by the engine (and where you stick the cable in). The Mini one is bigger than the Metro hole, so if you have an engine from a Mini and don't upgrade the drive shaft in your Gold, the cable won't fit properly. So my speedo drive gear was working, but hardly rotated the cable. Sort of chap with a small dick in a big mama.
At a Mini specialist we tested all possible varieties. We found out every combination works and you don't need to stick to the manual. I ended up with a 5 teeth spline shaft that drives a 17 teeth plastic gear. Better for me would have been a 16 teeth gear but that one seems rare. Never mind, when I switch to bigger tyres this one should be perfect.
Cheers, Hans
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