Back of tachometer OE

[truckin 79]

Does anyone have pictures of the back of stock GM tachometer. I found one out at the local junkyard but I think it is the 76-77 only trucks. The funny thing it came out of a 80’s truck. Does this look like a 1976-77 only tach combo?

[truckin 79]

Originally Posted by truckin 79

Does anyone have pictures of the back of stock GM tachometer. I found one out at the local junkyard but I think it is the 76-77 only trucks. The funny thing it came out of a 80’s truck. Does this look like a 1976-77 only tach combo?

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[truckin 79]

Originally Posted by truckin 79

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The one on top
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[ray_mcavoy]

Yes, the cluster shown at the top of your photo looks like a 76 or 77. It has a mechanical oil pressure gauge and a voltmeter.

The cluster shown at the bottom of your photo looks like a 73 - 75. It also has a mechanical oil pressure gauge but an ammeter instead of a voltmeter (as can be seen from the back by the difference in the terminal orientation).

A 78+ cluster will look very similar from the back, but will have an electric oil pressure gauge. So it will have electrical connections (that look similar to the back of the temp or fuel gauge) on the back of the oil gauge instead of a tube fitting.

The fact that you found a 76-77 cluster in an 80's truck isn't all that uncommon ... the tach clusters seem to be a fairly common swap.

As for the back of the tach itself, they all look very similar as well. Although the 73-75 ones have a different meter movement that uses 4 round studs w/small nuts on the back vs. 3 studs for the later years.

[truckin 79]

Well that won’t work for the 79 will it. Well I just bought a lose OE tach with a gas gauge and I will install in my existing gauge cluster. I have clock where emergency brake light used to sit. Can I splice emergency brake light wiring into the brake light that is under the speedometer?

[ray_mcavoy]

Well, you could use one of those earlier year clusters in your '79 but it wouldn't be a direct plug-in swap like a '78+ cluster would be.

The tach with the fuel gauge at the bottom (originally used in medium duty trucks) is a good option for having both a tach and a clock.

You might want to double check the location of your brake warning light though. Those were usually located at the bottom of the large fuel gauge, not the speedometer. Although it probably would be possible to swap the colored plastic filter to re-locate it there. And follow the traces on the printed circuit back from that bulb location to the cluster plug to see where you would have to re-locate the wire that activates the light.

[kipps]

Originally Posted by truckin 79

Can I splice emergency brake light wiring into the brake light that is under the speedometer?

The late 80's squarebody's did this. The brake warning light was supplied with 12v when the key was on. It could be grounded, thus illuminating the light, by three different methods.

#1, the e-brake lever had a switch that would ground out that circuit.

#2, the brake proportioning valve had an internal switch that would ground out the circuit if there was a pressure differential between the front and rear brakes.

#3, when the key switch was in the crank position, it would supply a ground to that circuit as a bulb test.

[Pontiac1976]

Pretty Kool Tach been thinking if I add a factory one it would be one of them.
Because I got ride of the clocks prefer the VACCUME - Gauge so that style of factory Tach would work better for my gauge style set up would like.
You got a head start with the to tach cluster most of the parts are there the rest on you truck cluster.

[truckin 79]

I just tested my new tachometer and movement of needle seems slow. Can I just pull needle off and add some lube or will this screw up the tachometer. I already pulled needle off to reposition because RPMs we’re off. I put needle back on and it seemed to correct RPMs, I just didn’t add lubricant

[Pontiac1976]

A broken lager needle @ the eye let pressed against the shaft(just hold there not to hard) few drips on the needle will run down the needle shaft on the pointer needle shaft to lube it.( the broken needle eye let or cut should be all most the same size as 1/2 the shaft of the pointer shaft to work best.)

[Pontiac1976]

Question: these styles of tach if it had 4000 rpm this would have been out of a Disel right.

[ray_mcavoy]

Originally Posted by Pontiac1976

Question: these styles of tach if it had 4000 rpm this would have been out of a Disel right.

Yes, a 4000 rpm tach would be from a diesel. Some diesel tachs use the alternator windings as their signal source, but the diesel tachs used in the 70's/80's medium duty GM trucks were hooked up to a magnetic pickup in the bellhousing that senses the flywheel teeth. As a result, they use a different circuit board (on the back of the tach) as compared to the gas engine tachometers. And the diesel version has calibration jumpers to configure it for the different engine / transmission combos.

[Hart_Rod]

What year and model had the tach as well as a trip odometer?

[Pontiac1976]

88-91 burb

[truckin 79]

Well sent tachometer off to have fixed with new circuit board. It cost 125.00 so now it works great but the gas gauge is stuck on 1/2 full. I used jumper wires to attach to my non-tach cluster. I need to check connections, hopefully that is the problem