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914World.com _ 914World Garage _ Calibration of tach for V8 use

Posted by: dlee1967 Nov 22 2004, 08:05 PM

I have a couple of V8 cars and have been lucky that they both use late model tachometers (one signal indicator). These tachs can be converted to V8 use by adding a 15K ohm resistor in parallel with an existing resistor and then making a slight adjustment to a potentiometer to calibrate them.

The early (two signal indicator) tachs are a mystery to me. They don't have a potentiometer and I am not sure if adding a resisitor will do the trick. Is there anyone out there on the board who knows how to do the home garage fix without sending the early units off to an instrument shop and paying the big bucks?

Late units cost me about 20 cents to convert. The later models have to be sent out for $75 to $160. Hmmmm???

David Lee in Houston.

Posted by: BIGKAT_83 Nov 22 2004, 08:33 PM

David did you get that info from the old porschev group on Yahoo. I did that file about 2 years ago and have had 3 or 4 people email me about it.
http://f3.grp.yahoofs.com/v1/oJmiQa6hnRuz4tDNFOtiPoBp5mow_oiY037ExidS1ji6A5YGIYgkoK8rguNFDUDOVwTu76TSqo-B9TQHWzJJQXzyXqw4LUE/Tach_cal_small.doc

Bob

Posted by: dlee1967 Nov 22 2004, 08:36 PM

Bob, that's the one! Thanks for sharing. It seems to work well, but doesn't help me on the early cars. Maybe someone has the "trick" for earlies. DLee

Posted by: MarkV Nov 22 2004, 08:42 PM

Maybe you could just put the guts out of a late tach in a early housing.

Posted by: BIGKAT_83 Nov 22 2004, 08:47 PM

I did a early tach and it was alot of trouble. I see now that a member is selling a new calibration board on Ebay with jumpers to set for 4/6/8 cyl engines. I think that these are for both the old and newer tachs. This looks like a good fix for the older tachs.

Bob

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&item=7936642447&category=6763

Posted by: dlee1967 Nov 22 2004, 09:09 PM

Mark, I have put the new tach guts in an early housing, but you also have to change the gauge face. My 72 is running that setup at the moment. That meant pointer needle removal, which is a pain. I am looking for a better way. David Lee

Posted by: dlee1967 Nov 22 2004, 09:12 PM

Bob, I notice that adbuch (Desert Hybrids) is high bidder at the moment on that tach. He must be interested in an breaking it down to get a look at how it is done. Way to go! DLee

Posted by: smrz914 Nov 22 2004, 11:08 PM

Here you are:

http://www.pelicanparts.com/MotorCity/smrz914/electricalupgrades.htm

Posted by: dlee1967 Nov 23 2004, 07:22 AM

Thanks Paul......Great work........DLee