Mounting Tach Sending Unit

[64Short]

I am trying to add a "factory" tach to my 64 straight 6 and need to know where the sending unit should be mounted to be factory correct. Any help, including photos, will be GREATLY appreciated.

[ray_mcavoy]

I believe the factory correct Sun tach for 63 & 64-66 Chevy trucks is the self contained style where the whole unit is mounted in the instrument cluster. It was only the 1962 & earlier Chevy tachs that used the separate transmitter box. I have no idea how the GMC tachs were set up during these years.

Several years ago I pulled a factory tach instrument cluster out of a 62 C80 farm truck. I remember that one having the tach transmitter box mounted on the inside of the firewall over on the passenger side. If you have a copy of the 60-66 factory assembly manual (the one with the yellow & white cover) it has a crude sketch of this setup about halfway through the book. But doesn't show any details on the transmitter box mounting.

[markeb01]

The only Sun tachometers I've seen from the factory are on GMC's. Tachometers are not mentioned anywhere in either the 1960 Chevy Accessories Pricing Schedule or the 1960 Chevy Accessory Installation Manual. If they were offered in Chevy trucks, it's likely that might only have happened in 1962 same as the high performance passenger cars.

I've also never seen anything in GMC documentation indicating where the transmitter was mounted.

[ray_mcavoy]

Originally Posted by markeb01

The only Sun tachometers I've seen from the factory are on GMC's.

The factory Chevy truck tachs were made by Sun too. It's not marked on the faceplate though ... just on the decal that's on the back of the tach and only visible when it's removed from the rear mounting plate that holds it into the cluster.

[64Short]

Any GMC guys out there? I think Mark is right, tachs are at least more common on GMCs than Chevrolets. Any help, even an educated guess, will be appreciated.

[chevyrestoguy]

Sun made the tachs for GM back in the day. That's a secret for all you guys wanting a tach for your truck that goes beyond 5000 rpm. Once you disassemble the outer cup, they're all identical in the way they bolt up. The issue on most of them is, you have to run the sending unit on the older tachs. Not a game-changer, but a lot of the sending units out there for sale don't work, and Sun used a battery with an odd voltage that isn't available anymore.

There are a few shops put there that restore tachs and update the sending units to electronic guts, but they can be spendy. Most old tachs you see on ebay are a crap-shoot. The seller always says "this unit has been untested", which means there's a good chance it might not work. But, it might work just fine. It's just that some guys ask a lot for the tachs that go 6000 rpm and higher, and you might be buying an unserviceable unit.

[64Short]

Cheyrestoguy, you just told my story. Bought tach on ebay, looks great, in original box, did not work, sending unit needed battery (1.35 v), had it rebuilt to the tune of $300+. It better work now!

FYI - Abbott Instruments in Portland, OR are very good with restoration of old instruments.

[chevyrestoguy]

Originally Posted by 64Short

Cheyrestoguy, you just told my story. Bought tach on ebay, looks great, in original box, did not work, sending unit needed battery (1.35 v), had it rebuilt to the tune of $300+. It better work now!

FYI - Abbott Instruments in Portland, OR are very good with restoration of old instruments.

I see that you had the same episode that I had! It all starts out so innocently. You find a tach for a great deal, then find out it doesn't work, and because we refuse to declare defeat, we do whatever it takes to make it work. In the big picture, it's the right thing to do. You now have an accurate gauge with updated electronic internals that will give you years of great service. I have heard of Abbott before, and they were highly recommended.