Speedo showing 10mph faster

Hello guys I need a little help, I replaced my speedo due to the other one having a very bad Mylar and battery not charging due to a tear in the Mylar, now the new speedo is showing 10mph more so if I'm doing 30moh on the speedo on my Garmin sat nav it shows 20mph and this goes like it is until around 50-60 mph, then it goes even more so if I'm doing around 83-85mph on the Sat nav it shows me 70mph, nothing else has changed apart from the clocks, the old clocks were quiet accurate, does anyone know what it could be, I'm sure it can't be the cable, like if I moved the spindle piece that goes In the back of the speedo, just really confused all help is appreciated in advance thank you ………bright side is at least it's not showing under lol 

Speedometer are not all the same.
Speedometers and Transmission gears are a matched set.

Depending on the Transmission that you have you may just need to change the gear in there to accurately determine the speed.  More on that later.

The back side of the speedometer is a stamped number in a box.  


if the one you removed matches the one that you put in no gear changes are usually required.

The size of your tires are also in the equation.  If you installed larger tires, then the speedo and odo will be off equally….

Automatics all used the same drive gear for the speedo.
Manual transmissons all were based on the final drive of the transmission.


From CABBY-INFO.com
The Different Transmission gears over the years
Red Speedometer Gear

No. of teeth: 15
Final drive ratios: 3.65 and 3.67
VW part #171957821B

White Speedometer Gear

No. of teeth: 16
Final drive ratios: 3.89 and 3.94
VW part #171957821A

Green Speedometer Gear

No. of teeth: 17
Final drive ratios: 4.25
VW part #171957821C

Drive gears are sold separately from the speedometer cables.

Drive gear securing ring part number: N 900 154 01

So you need to know the Transmission number you have, for the final drive ratio.

Again from cabby-info.com.
Transmission & Clutch

Gives the Typical tranny to gear required.

Now if your Gear in the Transmission is correct for the transmission installed (unscrewing the speedo cable on the transmission will show you the color of the gear without removing it from the transmission.

Then we can either assume that the incorrect speedo was installed or, that someone remove the needle and repositioned it incorrectly.

You have two options…
Take you car to a Automotive electric shop and have them calibrate the speedo to the car.

or

Carefully remove the speedo needle ( take great care) the center round part is where you need to pry it off, and not the needle itself.

I usually take the needle off and reposition it a little behind the stop about 2 degrees, then carefully lift it back over the stop… This takes the Spring wind load off the needle and then you position the needle back over the stop to get the proper pre-load of the spring to needle.  If some one who owned the car in the past just popped the needle off and then replaced it at the stop, then you could be a little off as the spring pre-load wasn't set, and the needle is out of proper position.

If your odometer is off as well, then I would suspect the transmission mis match as the issue and that a new gear may work without taking the cluster apart.

Thought it would be an easier answer?

In the oldie days I kept getting tickets in my MG.  The speedo was off? or the Radar gun tracking me?

I shelled out 60 pounds back then, and it wasn't a pay pall thing.  I had to get the quote of the part from the Company in the UK.  Then go to the only one of 4 banks that did overseas money orders and shell out at the time about 180USD for a 60pound item, and shipping and customs.  Then wait.

When the new part came (Gordon Spice International Spares) Wow 45 years later and I can still remember the company I ordered from…. I took my car new speedo installed, to a Automotive shop that specialized in Speedo Calibration… They "fixed it" and placed the
speedo calibration sticker on the front of the speedo face……  The next time I got a pulled over for speeding
The Cop asked "Do you know how fast you were going?"
The only answer you give them is "YES", as if you tell them the speed you were doing is an admission of guilt… so say either "yes, I do" Or "No, officer, how fast was I going."  Back to the Story.  all of 18yrs old and full of P&V I went to court, I showed the court that my speedo was calibrated with the papers to prove it, and that at the time of the arrest I was gong below the posted limit.  I also asked to see the Radar guns calibration since the officer didn't have it at court, the ticket was thrown out for lack of evidence…. my Second argument was going to be "Is this the Same gun you used on the date in question, or possibly a different gun".

So, I think I have exhausted the issue….

Check you have correct speedo cable . I think I read somewhere about the cables being colour coded or having a paint mark on them somewhere, like the coil springs markings


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Thanks guys Il have to get the dash out and see what's numbers are stamped on the back, I think the gear clog in the gear box is red, mine is a 1.6 GTI TINTOP, 1982

if it was ok before, then the speedo gear is fine. as mentioned the gear colour is determined by the gearbox you have fitted.

there are 2 speedometer calibrations, one for 1.0-1.3 and another for 1.5-1.8. To know what yours is check the small code printed on the speedometer face

the other thing is if the speedometer has been split for any reason the needle may not have been put back in the right place. you are supposed to remove the unit from the cluster and fit the needle so its pointing at the alignment mark, then lifted up over the stop. Heres mk2 stripdown and rebuild procedure, mk1 is similar:
4130 Products - Step-By-Step

Thanks , where about on the face will the code be or do i have to remove the dash many thanks 

see in the linky above it has the code 1540 just under 'MPH' it'll be similar location on yours

1540 is big block mph, 1505 is smallblock. but having said that I dont think the calibration is that far off, certainly not 10mph different. it sounds more liek needle has been off and put in the wrong place, the alignment mark I mention works out to about '0' if you look closely at the pics. since the stop is set at 10mph, that would explain it…