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Discussion Starter · #1 ·
Greetings all. This weekend I got my car out on the road for the first time after its seven-ish year restoration. I did a few shake down drives and put in maybe 75 miles total and, for the most part, they were trouble free. I've got a few odds and ends that I need to chase down, one of them being that the speedo reads about 10mph too fast. From what I can tell, it's not reading (for example) 10% too high, rather it's a constant 10-ish mph higher than actual. In other words, I'm guessing this is not an issue of incorrect gearing, as this was not something I changed during the resto. Any ideas what could be causing this and how to address? My car is a '65 Giulia Sprint GT. Thanks in advance.
 

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Oh man, killer shot! Where is that?

10mph over? No worries. That's a typical Porsche trick. What are you using to verify it?
 

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Tom, Great to hear that you’ve got your car in the road! Calibrated speedo or not, I expect to see you Saturday for One Lap Marin.
Ken
 

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Greetings all. This weekend I got my car out on the road for the first time after its seven-ish year restoration. I did a few shake down drives and put in maybe 75 miles total and, for the most part, they were trouble free. I've got a few odds and ends that I need to chase down, one of them being that the speedo reads about 10mph too fast. From what I can tell, it's not reading (for example) 10% too high, rather it's a constant 10-ish mph higher than actual. In other words, I'm guessing this is not an issue of incorrect gearing, as this was not something I changed during the resto. Any ideas what could be causing this and how to address? My car is a '65 Giulia Sprint GT. Thanks in advance.

Hallo,

About speedometer reading, I'll try to give you my contribution.
The speedometer reading is a result of a cinematic chain from posterior wheels speed (ground velocity) to the gauge. Between these elements you have some reductions (posterior bridge, gearbox exit etc.) that if are not all aligned you will have a wrong indication on the gauge. Always a Veglia speedometer 1960 reads:

1 TURN=1 METER in metric unit (Km/h)
1.610 TURN=1 METER in English unit (MPH)

Attached there is a simplified layout of Giulietta 101 type, but your 105 type has almost the same concept
Why don't you read the correct MPH?
I could suggest a troubleshooting in this order:

1) Have you installed on the car the correct wheel diameter or not?
2) perform a bench test of speedometer that have to give the correct speed indication with 1.610 TURN=1 METER;
3) if the bech test is ok, check the reduction of the posterior bridge and the reduction of the exit of the gearbox.

My last opinion is that a comparison between a 1965 speedometer and a nowaday GPS is not applicable, we are comparing 2 different geological eras so we should try to as much as possible but in my experience the error on the speedometer is between 5 to 10% (depending on the range).
Let us update!
Regards

Massimo

P.S. great restoration!
1685214
 

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Discussion Starter · #6 ·
Thanks all. AlfaJP105, the photo was taken up near Guerneville in Northern California. Lots of great roads out that way. I could be wrong but I just don't think it's the gear in the transmission. My assumption, but it is just that, is that this would translate to a percentage gain at a given speed, meaning the gap between indicated and actual would increase with speed. In my case that doesn't seem to be happening (based on using a GPS-based speedometer App on my phone), rather, it just stays as reading 10mph-ish too high at all times.
 
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But Mad North-Northwest
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Tom Sahines did an article in the ARA magazine about speedometer calibration. If my memory isn't going, I think he said the way to fix a constant offset was to remove and replace the needle in the correct location. But I could be wrong.

Don't try this at home because you will break the thing. Personally a 10 MPH delta is easy to remember and I'd just live with it.
 
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Trich - I'm planning a trip down that way sometime and I'll certainly look for those roads!

I use Waze a lot and I find that my car speedo is typically 5-10 km over the Waze reading, so I follow the Waze reading. :)

Which is more accurate? I'd hate to pulled over following the Waze...
 

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Greetings all. This weekend I got my car out on the road for the first time after its seven-ish year restoration. I did a few shake down drives and put in maybe 75 miles total and, for the most part, they were trouble free. I've got a few odds and ends that I need to chase down, one of them being that the speedo reads about 10mph too fast. From what I can tell, it's not reading (for example) 10% too high, rather it's a constant 10-ish mph higher than actual. In other words, I'm guessing this is not an issue of incorrect gearing, as this was not something I changed during the resto. Any ideas what could be causing this and how to address? My car is a '65 Giulia Sprint GT. Thanks in advance.
Is it just the speedometer that inaccurate?
Have you checked the odometer? Ten miles or more on an interstate with mileage markers will do. Also a stopwatch adds info. On the bench, a reversible drill and a stopwatch can tell you a lot your speedometer.
Jim
60 spider
64 Sprint GT
 

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But Mad North-Northwest
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Have you checked the odometer? Ten miles or more on an interstate with mileage markers will do. Also a stopwatch adds info. On the bench, a reversible drill and a stopwatch can tell you a lot your speedometer.
So, uh, Jim...we've got this thing called "GPS" now... :)
 

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Just think of the technology that was around when these cars were made. Actual maps, payphones, hand brakes, no cruise control, etc... Refreshingly simple.
 

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Mine is the opposite, shows 10km slower than the actual speed I'm going. I still haven't gotten used to it and have gotten around 9 speeding tickets in a year because of it.
 

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Mine is the opposite, shows 10km slower than the actual speed I'm going. I still haven't gotten used to it and have gotten around 9 speeding tickets in a year because of it.
9 speeding tickets? Bro - respect! I think I'd lose my license here with those kinds of stats. I'm liking Kuwait more and more! :cool:
 

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9 speeding tickets? Bro - respect! I think I'd lose my license here with those kinds of stats. I'm liking Kuwait more and more! :cool:
lol yeah we don't get points deducted but the tickets aren't cheap here. On the other hand, I accidentally got 8 speeding tickets in South Africa on one 6 hour drive. I thought I was gonna get screwed but turned out to be just 60$ for all 8!
 
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Discussion Starter · #16 ·
I'm curious to meeting the person who doesn't "accidentally" get speeding tickets, but rather does it on purpose ;)

Joking aside, thanks all for the tips, I'll see if I can make some progress on it this weekend and report back if I find a solution.
 
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lol yeah we don't get points deducted but the tickets aren't cheap here. On the other hand, I accidentally got 8 speeding tickets in South Africa on one 6 hour drive. I thought I was gonna get screwed but turned out to be just 60$ for all 8!
Off topic, but were you driving around the garden route by any chance? 😬
 
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