tach cluster

[79 blue monster]

i have 3 tach clusters, and their all different?? some have more lights than others, differtent colors, amps volts, etc. could someone tell me what these are out off?? 4x4? years? thanks

i'll post pics

[79 blue monster]

cluster #1

[79 blue monster]

cluster #2

[79 blue monster]

cluster #3

[ray_mcavoy]

Ammeter = 73-75, Voltmeter = 76-up
Mechanical oil gauge = 73-77, Electric oil gauge = 78-up

The warning lights at the bottoms of the speedometer & tach are another thing that changed over the years. Some of the very early ones didn't have any lights down there. And they made the change from the narrow "window" for one light to the wider "window" for two lights late in the 76 model run. I believe this was the same time they started adding the yellow/red line markings on the tachs as well.

So with that in mind, it looks like your clusters are:

#1 = 1977 (or late 1976) because it has a voltmeter, what appears to be a mechanical oil gauge, and the wide double warning light "windows" at the bottoms of the speedometer & tach.

#2 = 1973 - 1975 because it has an ammeter and mechanical oil gauge. The speedometer/tach faces with just the "tick marks" and no circular line inside of them is also characteristic of the 73-75 clusters.

#3 = 1976 because it has a voltmeter, mechanical oil gauge, and the narrow single warning light "windows" at the bottoms of the speedometer & tach.

[79 blue monster]

Originally Posted by ray_mcavoy

Ammeter = 73-75, Voltmeter = 76-up
Mechanical oil gauge = 73-77, Electric oil gauge = 78-up

The warning lights at the bottoms of the speedometer & tach are another thing that changed over the years. Some of the very early ones didn't have any lights down there. And they made the change from the narrow "window" for one light to the wider "window" for two lights late in the 76 model run. I believe this was the same time they started adding the yellow/red line markings on the tachs as well.

So with that in mind, it looks like your clusters are:

#1 = 1977 (or late 1976) because it has a voltmeter, what appears to be a mechanical oil gauge, and the wide double warning light "windows" at the bottoms of the speedometer & tach.

#2 = 1973 - 1975 because it has an ammeter and mechanical oil gauge. The speedometer/tach faces with just the "tick marks" and no circular line inside of them is also characteristic of the 73-75 clusters.

#3 = 1976 because it has a voltmeter, mechanical oil gauge, and the narrow single warning light "windows" at the bottoms of the speedometer & tach.

wow thats a crazy awsome response! thanks so much you summed it all up!

[Duncan and son]

Originally Posted by ray_mcavoy

Ammeter = 73-75, Voltmeter = 76-up
Mechanical oil gauge = 73-77, Electric oil gauge = 78-up

The warning lights at the bottoms of the speedometer & tach are another thing that changed over the years. Some of the very early ones didn't have any lights down there. And they made the change from the narrow "window" for one light to the wider "window" for two lights late in the 76 model run. I believe this was the same time they started adding the yellow/red line markings on the tachs as well.

So with that in mind, it looks like your clusters are:

#1 = 1977 (or late 1976) because it has a voltmeter, what appears to be a mechanical oil gauge, and the wide double warning light "windows" at the bottoms of the speedometer & tach.

#2 = 1973 - 1975 because it has an ammeter and mechanical oil gauge. The speedometer/tach faces with just the "tick marks" and no circular line inside of them is also characteristic of the 73-75 clusters.

#3 = 1976 because it has a voltmeter, mechanical oil gauge, and the narrow single warning light "windows" at the bottoms of the speedometer & tach.

Hey Ray thanks for the info. Jason and I have been doing 67-72 for years but just bought a 75 crew cab 454 dually and are looking for a tach but did not know exactly what we were looking for..you must have been taking your smart pills LOL
Thank you again Paul

[ray_mcavoy]

You guys are welcome!

Although I do have some first hand experience working with various year GM truck tach clusters I can't take full credit for all of that info. A lot of it came from this page --> http://www.73-87.com/7387garage/inte...achometers.htm

About the only thing not mentioned on that page is the subtle difference in the warning lights. I noticed the photo example of a "1977 cluster" shown on that page is actually from a 76. The 76/77 clusters are otherwise identical and the ones I've seen have even had the same printed circuit on the back. The only difference being the 76 plastic housing only having holes & baffling to accept 2 warning lights even though the printed circuit could operate 4.

Originally Posted by Duncan and son

...just bought a 75 crew cab 454 dually and are looking for a tach but did not know exactly what we were looking for.

As it says on that page I linked to above, 73-75 are not serviceable since they are completely sealed. What he is talking about there is the little control circuit board for the tach, not the larger flexible printed circuit that covers the back of the cluster. The components on those 73-75 tach boards are sealed in some sort of epoxy type coating.

So in your search for a 73-75 tach cluster, look for one that has been tested/verified to work correctly. But if you find a good deal on a cluster with a dead tach that's otherwise in good condition, there are a couple of options now available:

(1) Willcox Corvette offers a replacement tach board for about $90 --> http://willcoxcorvette.com/product_i...ducts_id=27330 But notice that it says it only works on 3-terminal tachs. Some of these tachs (particularly the 73-75 ones) have 4-terminals and won't work with that board. Note that they're talking about the threaded stud terminals that connect the tach's meter movement to the circuit board, not the flat bladed terminals where the wiring harness plugs into the tach.

(2) LMC is now offering complete reproduction tachometer assemblies for about $130. Although they have all the different font/face styles to match the originals, they all have the wider window at the bottom for the warning lights which technically isn't 100% correct for the early years.


And while we're on the subject of factory tachometers, there's a good write-up on how to easily repair a 78-up tach that's working but reading too high at: http://www.howtoalmanac.com/kevin/pr...chfixtruck.htm

I just did this repair on a 77 tach. It had the same circuit board as shown on that site so GM either changed to the new tach circuit design in 77 instead of 78. Or this particular one I have had been swapped to the newer style board sometime in the past.