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1984 Spider. I checked my Speedo this morning against a GPS and it is off across the spectrum. For example when my speedo reads 67 I am actually doing 60! Any ideas gentlemen? Stock size tires BTW.
 

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Do you think that your original 4.1 axle may have been swapped for a 4.55? That would account for the 10% error.
 

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they are never deadly accurate at the best of times.

reading 67 at 60 is not bad tbh! (think of all the speeding tickets it will save you from;))
 

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Think it that STUPID DOT box under the hood. Gonna order a regular speedo cable and bypass that POS. My 82 is bad as well. It's doing the same exact thing.
 

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Discussion Starter #6
Do you think that your original 4.1 axle may have been swapped for a 4.55? That would account for the 10% error.
Pretty sure it has not, it is a low mile unmolested car and it revs a lot lower at speed than my 4.55 1978 did~

they are never deadly accurate at the best of times.

reading 67 at 60 is not bad tbh! (think of all the speeding tickets it will save you from;))
True~!!! But now I KNOW so the equation has changed!

Think it that STUPID DOT box under the hood. Gonna order a regular speedo cable and bypass that POS. My 82 is bad as well. It's doing the same exact thing.
Might be!~~!

Leave it alone. You'll impress your friends, and it'll keep you out of trouble.0:)

I just might if there is no fix. I do not want to change the speedo/odo out so if it cannot be fixed it is staying where it is!
 

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The speedometer in my 79 spider is as accurate as the ones in my Acura and my Wife's Toyota. I think that 11% error is excessive for an Alfa.
 

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10% ish is acceptable - even my DD's read fast, manufacturers always fit speedos that read fast within the regs so I'd say an old Alfa at 10% is doing well
 

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Has the gear box been changed? It could be the drive unit and rear unit that holds the rubber guibo. If they are miss matched you could have a huge speedometer error.
 

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my speedo reads 67 I am actually doing 60!
Spot on for an old Italian car. Mine too is off by about the same amount. I had a Fiat Spider that would read 70 MPH when doing 55 MPH. Only my modern cars are accurate, but they are digital.
 

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Had the same problem with my 84 Veloce. Son is a very competent watch repairman, so we disassembled speedo, repositioned needle, reassembled, not a problem since - this was @ 2 yrs ago. Simple enough that even I (old eyes, loss of fine motor skills) could have done it. Reads zero at rest, very accurate at all speeds. Good opportunity to clean lens and dial.
 

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I need a speedo that reads a little high to keep my license. I wouldn't fix this myself. Actually what I do now is I use a GPS and the speed it is saying and set the cruise control ... oops yeah my GTV does not have that.

To me speedo's are always a rough idea thing ... but then I've had lots of tickets :(
Pete
 

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I need a speedo that reads a little high to keep my license. I wouldn't fix this myself. Actually what I do now is I use a GPS and the speed it is saying and set the cruise control ... oops yeah my GTV does not have that.

To me speedo's are always a rough idea thing ... but then I've had lots of tickets :(
Pete
I have a 1600 diff in my 1750 spider...it's not even close to being correct, but it looks like I'm flying even at 60mph:)

Makes a great highclimb car with the 1600 diff, but revs a touch high at a true 60mph {around 3300rpm}
 
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