The Stovebolt Site Forums The Shop Area The Electrical Bay GMC sun tach

I have found and installed an original Sun Tach in my 59 GMC with the original 235 I6.

The tach is electronic, and came with the EB7A tranmitter.

I followed the original installation instructions with the tach and the tach needle operates up and down with engine RPM, but I think it is reading to high, ie. more rpm on the tach than on the engine. At idle the tach reads 1100 rpm and driving down the highway at 55 mph (original drivetrain, 235 I6, 3 speed manual, and 3.90 rear end) the tach reads anywhere from 2500 rom to 4200 rpm. When driving at 55 rpm the tach reads fairly consistant, but different each time I drive it.

There does not seem to be much for adjustment on it, just a screw to turn to steady the needle, which I have done.

One problem with the tach is it requires a 1.35 volt mercury battery, which I can not find. So it now has a 1.5 volt battery.

Any ideas?

http://www.google.com/search?hl=en&ie=ISO-8859-1&q=1.35+volt.
Will an Eveready 1N work?

k10,
$12 for a 1.35 button cell batt???. I'm in the consumer electronic business selling wrist instruments (altimeter watches) and bicycle speedometers. All our of meters were originally designed using the infamous 1.35 mercuric oxide battery. Once it was outlawed, we tried the zinc air cell which averages 1.4+ volts, but the consumer had problems remembering to peel the sticker off in order to activate the cell. We finally switched the the silver oxide #357 which has shown no side affects on our power sensitivity units. I cannot imagine that the increase of .15 volts would have any affect of a sun tac.

A watch battery won't work. I bought some Duracell copper top equivelent from eBay that works OK.

Back to the original question, there are a few people that advertise in Hemmings to fix these. And some will convert the sender to electronics for about $250. My own experience with a box full of tachs and senders I bought over a couple of years is that 2/3 of them don't work, or work inacurately or meander. I've noticed that even the length and gauge of wire seems to affect their accuracy.

If you want accuracy, I'd get a modern tach.

Also, isn't the EB7A for a V8? You need a transmitter that's 6 cyl, 12V for a 235.

Jim

I have a 6 cylinder transmitter.

I find it curious that 2/3 of these never works right to begin with?

I want the tach more for a factory option than a working tach so maybe I will have to live with it.

Ya know, Radio Shack has just about every kind of screwball battery made and will order what they don't have in stock.

Take the spec by your local Radio Shack store and see if they can cough up the 1.35 in the size and spec you need.

I meant that 2/3 of the ones you find now on eBay and swap meets that are 20-30+ years old don't work. Even ones that look NOS in the box. The people who service them ask that you tape the needle before shipping...

Interestingly, two I have stamped '1946' seem to work the best...

Jim

Anybody know of some retired tach fixer now worker from his/her home that might try fixing my problem?

The only sure fix for these old GMC tachs is to send them to Williamson\'s and have it converted to solid state. Cost about $150. That's why they're so cheap at swap meets.

Thanks, I have contacted Williamson's through their web page and I am seriously considering this.

As for cheap tach's at swap meet's, well I have yet to find a Sun tach with the correct GMC face go cheap, but maybe i'm in the wrong places.