Tacheometer calibration
 

Does anyone know how to calibrate a 911 Carrera tacheometer?

Any?

On a Carrera, the PROM should shut it down at the preset RPM, 6350?

I mean the speed dial not the rpm one

If you are talking about the speedometer, that can be done by North Hollywood Speedometer in Los Angeles. I don't think there is any access to the electronics from the outside of the housing. They probably have to open up the speedometer.

The gauge has to be opened up. NHS will also need your tire size.

Yes I know they can do that, just a little bit difficult to send it from Italt to US :)
That's why I was asking if someone knows how to do that

Ravenpower asks a great question - does anybody have the schematic for the internals of the carrera speedometer? I'm also curious how NHS or others 'calibrate' them. If not the schematic how about a picture of the internal circuit board?

I'm wild-a$$ guessing that a resistor change in the last stage before the needle swings would affect the movement in a positive or negative direction, but I don't see that affecting the odometer... hmmm.

Chuck.H
'89 TurboLookTarga, 359k miles (or so I think)

A google search turned up a post by emarsh years ago, I think this is the link:

http://forums.pelicanparts.com/porsche-911-technical-forum/116573-vdo-speedometer-calibration-how.html?highlight=vdo+speedometer+calibration

There is already a variable resistor in there it seems, just need to get access to it!

Chuck.H
'89 TurboLookTarga, 359k miles

Well it would be good to have a pic of it :)

Wait a minute, they didn't ask me, maybe that's why my speedo is off by 10 miles throughout the range. Makes sense now.

They have an old solid state machine they hooks up the speedo to read the pulses ergo speed match. I was surprised how analog it was when they had to correct my speed, probably due to the fact I have 17"s

Overall tire height.....you can have the same with 16 and 17s if the 17 inch tire has a lower aspect than the 16. Bill V has the tire chart and can likely quote from memory.

Call them up and say WTF? Act dumb and inqure as to why your newly refurbed speedo is off by 10 mph.

Ravenpower...If you put your location under your name...we would know that you are in Italy

No worries, went back and waited and chatted with the tech while he was correcting it.

He told me normally when conpensating it will throw the range off but it my case it didn't, strange.