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914World.com _ 914World Garage _ Hyfire and silver dot tach - Working!

Posted by: agrump Apr 10 2005, 05:31 AM

My early silver dot tach did not work at all once I installed a hyfire ignition box. This is caused by the fact that the stock tack is looking for a high voltage signal that no longer exist. I was able to modify the tach to run off of the Hyfire's tach port by placing a jumper over the initial signal resister. As a side note I experimented with the hyfire's tach testor and found that the stock tach is pretty acurate.

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Posted by: synthesisdv Apr 10 2005, 06:21 AM

that's great.

I could never get mine to work and just went with an autometer. Does the old tach still bounce around alot? I kind of got used to the dead steady new tach but I would go back to the original unit if it worked OK.

Posted by: Aaron Cox Apr 10 2005, 10:26 AM

my hero!!!!

need to do tis ASAP

Posted by: Aaron Cox Apr 10 2005, 02:55 PM

hmmm... mine looks different....
could be because it is a 912 tach

ill open up a 914 one too...

Posted by: agrump Apr 11 2005, 05:39 AM

synthesisdv, it still bounces around like a squirrel in the middle of the road. That could probably be cured by place a capacitor across the needle leads but I didn't think to try it. It's kind of tough to see what is happening on the circuit board because it wraps around the needle mechanism.

Posted by: synthesisdv Apr 11 2005, 05:46 AM

hey dean,

you seem to know your way around a circuit board. How hard do you think it would be to transplant the guts of my autometer into the silver dot porsche tach?

I wouldn't want to do it if I couldn't use the silver dot needle.

Posted by: Joe Ricard Apr 11 2005, 10:31 AM

I don't think I will ever go back to stock tach. Love my Autometer and the shift light.
I can see the light out of the corner of my peripherial vision while screaming though the cones. set it go go on at 5800 RPM I find I am staying off the rev limiter and shifting to 3rd earlier pulling WAY harder to the next feature.
Pretty cool to be able to fix the stock one though

Posted by: Aaron Cox Apr 11 2005, 10:39 AM

ill be doing this on friday.

i didnt know the hyfire had a tach testor....

Posted by: maf914 Apr 11 2005, 11:05 AM

Okay, for the benefit of those of us who have never disassembled gauges, could someone describe how to disassemble a VDO tach. I assume disassembly is from the gauge face side?

I think I could handle soldering the jumper around the resistor, but I just don't want to ruin the gauge taking it apart. Thanks.

Posted by: Aaron Cox Apr 11 2005, 11:07 AM

QUOTE (maf914 @ Apr 11 2005, 10:05 AM)
Okay, for the benefit of those of us who have never disassembled gauges, could someone describe how to disassemble a VDO tach. I assume disassembly is from the gauge face side?

I think I could handle soldering the jumper around the resistor, but I just don't want to ruin the gauge taking it apart. Thanks.

uncrimp the bezel...a royal PITA.

then take the 3 or 4 screws out from the back. voila..... done.