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Posted by: 23e Heure Dec 8 2016, 06:56 PM

I really fancy fitting a 120mph speedo to the car.
I have a spare '67 one from a 912.
Its needle has faded to a pinkish orange and the numbers are a really tasty old yellowed age.



My car has a 3.0 6 in it... So yes: the car will be capable of a significantly higher top speed, but on the road I should never get near that <ahem>.

But I am likely to use the car in germany on unrestricted routes, and also have plans to do a few track days.

I have googled and got confused about "pegging" mechanical speedos.
Research resuults range from "Exceed the top indicated speed and your speedo is broken forever"..
...through "You can exceed the max, but calibration will subsequently be buggered"...
...all the way to "Only some speedos don't like being max-ed, your one might just bounce at the top and then return to normal when your speed drops".

Can anyone give me accurate experienced advice, hopefully directly related to mechanical VDO speedos for early porsches?

If indeed exceeding the max is a no-no for old speedos, is there any mod available that acts as a protection mechanism?

Posted by: Mark Henry Dec 8 2016, 07:05 PM

I pin the 90 mph speedo in my bug all the time, it has never hurt it.
I mean pinned it, it goes right around to the zero pin

Posted by: mgp4591 Dec 8 2016, 08:20 PM

Is there an actual pin to the limit or is there a restrictive internal device that could ruin the speedo?
I used to peg the 85mph speedo in my old Celica all the time in the desert at 2700rpm. Then I'd wind up to 5300 and burn along the freeway (the desert, remember) well in excess of 120... so you may be okay.

Posted by: RickS Dec 8 2016, 11:31 PM

If you planning on hitting 120 I hope you plan on aero aids to keep it planted and stable.

Posted by: mepstein Dec 9 2016, 06:03 AM

I like the way the numbers are spaced on the 120 speedo. Much more useful to me for daily driving.

Posted by: 6freak Dec 9 2016, 08:49 AM

my same thoughts....weeeeeee pucker factor starts take n place around that speed

Posted by: mepstein Dec 9 2016, 11:45 AM

Timmothy could probably weight in on this. He knows a thing or 2 about our gauges.

Posted by: Mark Henry Dec 9 2016, 12:10 PM

It won't hurt them because they run off of a calibrated magnet(s), there's no mechanical connection between the needle and the drive.

Posted by: JRust Dec 9 2016, 12:27 PM

Any reason you don't like the 150mph speedometer Should solve the problem

Posted by: Mark Henry Dec 9 2016, 12:28 PM

BTW the above reason is why you speedo doesn't get ruined when your back you car up...Kapish.

Posted by: mepstein Dec 9 2016, 12:47 PM

Similar to what Timothy said -
Speedometer is not directly linked from the speedo cable to the needle. There is a magnetic coupling that separates everything, so no issue with pegging the needle.
The return spring for the needle should handle it as well. No issues

Posted by: 23e Heure Dec 10 2016, 11:54 AM

So you guys are saying that if I exceed 120, the needle will just keep going clockwise until I back off?

Posted by: sixnotfour Dec 10 2016, 12:26 PM

just don't try and reset the trip odometer,,

Posted by: McMark Dec 10 2016, 08:59 PM

What Mark said.

Posted by: SirAndy Dec 11 2016, 11:33 AM

Yes, unless there is a physical stop at 120. Some older speedos (not 914 ones i believe) had a physical pin at the end of the range to stop the needle.

If there's no stop, it will just keep going until it hits the stop at the 0 mark ...

Posted by: toolguy Dec 11 2016, 01:56 PM

Even if there is a pin to stop the needle, it won't hurt it. . again, there is no physical connection between the needle and the drive magnet mechanism. . the needle is driven by inductive magnetism. .

Posted by: Mark Henry Dec 11 2016, 02:00 PM

There is a pin at zero so it can't go around twice....just in case you're thinking of puting it in your 917....

Posted by: mbseto Dec 12 2016, 01:55 PM

I've typed and deleted three sarcastic comments, then decided not to be a bully. :-)