Series 3 Speedo speeds

aiskew · Aug 29, 2014

Hi, I have just bought my first Series 3 landy, a 1982 petrol 88"
It's a bit of a project, having been sat for at least 6 months in a Norfolk field, but it's fun doing bits to get it something like
So far I've put a new petrol tank and sender unit, but I'm not sure about the speedo
I know when you're doing 30 in a series it will feel like 90 but I do think it's reading incorrectly
I checked the transmission end and found it was only held in by one screw. I replaced the missing ones which seemed to help but I still think it's about 5mph out
Questions
Is this normal/acceptable for an elderly s3? (tyres are 205/r16)
Could the wrong speedo cable have been installed and would this make a difference anyway (I see there are a couple of alternatives)
Could the speedo worm be faulty?
Thanks in anticipation

jamesmartin · Aug 29, 2014

quite normal , theres only one speedo drive for what you have and cable as long as it fits and turns wouldnt make any difference

dominicbeesley · Aug 29, 2014

You might have a speedo like mine where the needle is on wrong and reads everything out by a few miles an hour...but unlikely

You may have a speedo for smaller tyres there should be a TPM figure in small writing at the bottom that can make a smallish difference.

Alternatively you may have a set of range rover differentials fitted these make the car go 33% quicker (or rev 25% slower) but also make the speed read about 25% low so:

Speedo 20 = 27 mph
Speedo 30 = 40
Speedo 40 = 53
Speedo 50 = 67

Best thing is to measure it with a GPS at different speeds and find out if it's a fixed offset (i.e. 5mph out at all speeds) or a relative error (i.e. 25% too low) and we should be able to deduce from that what's up.

D

aiskew · Aug 29, 2014

Many thanks for the replies, I won't bother changing the cable then. I'll check it with the sat-nav when I've got it a bit further on

ben waine · Aug 29, 2014

Mine is about +2/-5 mph in accuracy, just get used to it I think is the easy answer (usually new cars are about -3mph I think) so not too bad really

nickjaxe · Aug 30, 2014

If anybody has altered gearing diffs ect it will read incorrectly...or the wrong speedo head fitted....mine under reads by around 30%....a dot of white paint on the face of my speedo to match 10-20-30 mph ect does the trick for me.

Nick.

aiskew · Aug 31, 2014

Again many thanks, I like the idea of checking with a Sat Nav and marking the correct speeds accordingly

dominicbeesley · Sep 1, 2014

I've just found my spare head unit and I'm going to send it off to Speedy Cables this week to get it recalibrated...they quoted me £65 when I asked though that was a year ago!

steve2286w · Sep 3, 2014

could be affected by diferent tyre/wheel size too

my other modern car overreads by about 5mph compared with sat nav, at least on the safe side for speeding tickets!

Series 3 Speedo speeds

aiskew

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jamesmartin

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dominicbeesley

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aiskew

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ben waine

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nickjaxe

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aiskew

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dominicbeesley

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steve2286w

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