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E30 Speedometer Reading High

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MICK View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MICK Quote  Post ReplyReply Direct Link To This Post Topic: E30 Speedometer Reading High
    Posted: 25 Feb 2016 at 12:49pm
My 1984 E30 1.8i  speedo is indicating 37 mph at a true 30 mph.  Any ideas as to what might be the likely  cause. The dial is steady reading with no fluctuations.

Edited by MICK - 25 Feb 2016 at 12:51pm
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RParkinson View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RParkinson Quote  Post ReplyReply Direct Link To This Post Posted: 25 Feb 2016 at 1:50pm
Tyres with smaller rolling radius than they should be, although 20% out is pretty excessive.

What wheels and tyres do you have on it?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote NickDE Quote  Post ReplyReply Direct Link To This Post Posted: 25 Feb 2016 at 6:03pm
Differential has been changed to one with the wrong ratio ?
Is the speedo wrong at all speeds ? Try comparing speedo speeds to GPS speeds.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MICK Quote  Post ReplyReply Direct Link To This Post Posted: 26 Feb 2016 at 2:35pm
Thanks for your replies. 
      I have owned the car since 1987 and the diff. has never been changed. The wheels and tyres are of original spec. Steel wheels with recommended tyre sizes fitted. Don't know when this started to occur. It's not my every day car so doesn't get used regularly.( E46 2.8 coupe is normal transport ) Have checked with Gps and the error seems to be constant across the range of speeds.
 I started to think that it was the sensor on the diff. but that would probably make it read lower rather than higher I would guess. Maybe there is something I can do at the speedometer end ( like move the needle back )
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RParkinson Quote  Post ReplyReply Direct Link To This Post Posted: 26 Feb 2016 at 5:00pm
So is the error a fixed 7mph regardless of speed or is the error a percentage of the actual speed (about 23%)?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lokoktentek Quote  Post ReplyReply Direct Link To This Post Posted: 26 Feb 2016 at 9:49pm
Hi,
Differential ratio has nothing to do with speedo reading.
I wouldn't worry about the differnce. From my point of view it is normal.

Don't worry :)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Robert Quote  Post ReplyReply Direct Link To This Post Posted: 27 Feb 2016 at 9:47am
The Speedo reading can be altered but it is an instrument cluster out jobby. There is a small white adjuster screw on the back of the instrument cluster. I wish I had fixed up mine last time I had the cluster out. Not an easy job but driving up and down the road a couple of hundred times to see if the adjustment is right is a bit of a hassle.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MICK Quote  Post ReplyReply Direct Link To This Post Posted: 27 Feb 2016 at 5:38pm
RPARKINSON.  The error is constant right across the range of speeds that I have driven . (  up to about 65 mph )

Robert.  I have had the speedo cluster  out of the dashboard  many years ago as there was a dry solder joint on one of the multi-plugs which stopped the speedo working and it is quite a fiddly job I agree . Found the fault by driving with the speedo lying on the dashboard and fiddling with it until it worked , then soldered the offending connector. Maybe that is the way forward,adjust it a little then try it. Thanks ,I didn't remember seeing an adjuster before.

LOKOKTENTEC. I am just concerned that I am holding up the traffic by driving too slowly in 30 mph areas.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lokoktentek Quote  Post ReplyReply Direct Link To This Post Posted: 27 Feb 2016 at 8:52pm
Yeah, you're right, it shouldn't be constant difference... Sorry i didn't read carefully :(
Maybe the easiest way is to borrow a cluster from someone and test it before doing any search... Of course if you can borrow it...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MICK Quote  Post ReplyReply Direct Link To This Post Posted: 28 Feb 2016 at 12:24am
Lokoktentec.   I'll have a crack at it when I can devote some time to it. Thanks for your responses.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote thechef Quote  Post ReplyReply Direct Link To This Post Posted: 02 Mar 2016 at 1:34pm
I have same on my cars Confused I have two E30's at the mo, a 318is and a 316i, both have 14" wheels with 195/65/14 tyres, and when I go through any speed traps - the one ones you get when you're coming into a town / village, and both my speedo's are 6/7 mph out, so speedo reading, 30mph, will get me a 23/24mph reading on the speed trap thing !!
I thought it would be something to do with tyre / wheel size, but I haven't changed the tyres sizes, although I did replace all 4 tyres on the i S, but they are same size as what was on it when I bought it !
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MICK Quote  Post ReplyReply Direct Link To This Post Posted: 02 Mar 2016 at 11:25pm
Thanks for that reply. I suppose all those years of driving mine I didn't check the speedo for accuracy until I borrowed an GPS speedo which warns you when you exceed the speed limits.I'll have to look to see if there is any adjuster,if not I'll just live with it. Thanks again for your interest.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ZGreen Quote  Post ReplyReply Direct Link To This Post Posted: 01 Nov 2016 at 4:58pm
Just a warning some of these road side speed indicators are not correct, I used to go through one regularly that showed my speed at 30 mph as being around 24-5 mph. But I went through a Mobile
Speed camera and did not panic as my speedo showed i was doing about 34mph I got done for doing 36mph, and like you I found cars backing up behind me and usually about 33 indicated mph seemed to cause less concern to those following. I went on a driver training option rather than get a fine and explained what happened but no comment was made as you might expect.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ZGreen Quote  Post ReplyReply Direct Link To This Post Posted: 01 Nov 2016 at 5:02pm
My speedo did fail once but it was the electronic connector plug on the diff that a little soldering put right.
Many speedometers read about 10% out. They say the Police allow for this. No comment.


Edited by ZGreen - 01 Nov 2016 at 5:05pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MICK Quote  Post ReplyReply Direct Link To This Post Posted: 01 Nov 2016 at 5:47pm
Thanks for that information. I'll get under and have a look at it. in the weekend. Have temporarily marked the dial with the correct speed but it would be good to get it right.  Thanks  again.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RParkinson Quote  Post ReplyReply Direct Link To This Post Posted: 01 Nov 2016 at 7:10pm
If it's a constant offset, maybe the needle on the dial has been removed at some point and not be put back in exactly the right place?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MICK Quote  Post ReplyReply Direct Link To This Post Posted: 01 Nov 2016 at 11:02pm
Thanks for your interest and advice. I've had the car since 1987. The dial has never been taken off or moved by me so if this has happened it was done before I had it. I would not attempt to remove the needle as I had a bad experience getting the needles off of my E46 2.8 litre. The guages would not work after being put back on so I must have wrecked the movements in the removal process. Cost me a new instrument cluster. Painful!!
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