factory tach install will it work?

Hey guys I see LMC truck now offers a factory tach for the 73-87 pickups. The two available list either points or HEI. Is there any way this tach could be used with a 6.2? Want to keep my dash looking original. Any ideas?
John

http://www.lmctruck.com/newparts/cc/ccrpt.htm

I was going to use one of LMCs smaller fuel gauges and move it to one of the smaller pods.

Well .. they're gasser tachs so straight up they won't work without a mod to feed them the proper signal.
Other's have used dakota digital/tiny tach/keltec converter etc. Basically you can convert a signal then feed it to a 'normal' tach. (for a price)

The real issue that jumps out at me is compatability with the dash circuit board.
Those factory gauges plug into the the slot where your fuel gauge is now.
The pins supplied through the printed circuit that you have are for the fuel gauge.
I don't know how much rewiring you want to get into to make that work.

I could be wrong, but that's what jumps out at me anyway.

So...
Short answer, no.
Long answer, you could 'make' it work. You would have to set up your own sensor to get the signal, then convert it to output through a gasser tach. You would also need to rewire and relocate your fuel gauge (perhaps from the sender before it plugs into the printed circuit).
Idealy (if it were that easy) the tach might use the same plug style. For fuel gauge you have (IIRC) power/ground/sender feed. If the heavens align and the tach uses the same pin for it's feed as the fuel gauge uses for the sender feed it could be as simple as swapping the fuel level sender feed wire at the circuit board plug for your new tach feed wire. (you would still need a converter to achieve this tach feed though), then wire a new fuel gauge.

The drivers side alt ( GEN 1 ) has a tach output on it, that feeds a tach buffer under the dash that is wired to the STE/ICE port on the bottom of the dash. There was at least one member here who was able to get an aftermarket tach to work with the alternator tach output, though I think he bypassed the existing tach buffer.

I don't know what the factory tach expects for its input. Perhaps someone has wiring diagrams for a civi k5 6.2 with factory tach? Also, I thought the factory tach also had a small fuel gauge in the bottom portion of the gauge. As mentioned above, the printed circuit will be a problem. Assuming the factory tach could be made to work, I'd expect you'd have to use a different printed circuit, or hand wire all the connections. At best maybe an adapter could be made to go between the existing harness and the connectors on the printed circuit to route signals properly and add in what ever else is needed.

Good luck and post pictures!

Do a search here for tiny tach and it might lead you to some help. I've always been curious about my rpm's, not like it would change my driving, but still.

The Factory GM Tachs have their own harness and do not use the printed circuit overlay on the back. The Tach Cluster housing is also different and does not have the provisions for the fuel gauge prongs that snap in the cluster and tap into the overlay. I think you would have to cut the housing back itself for the factory GM Tach to clear in a right hand fuel gauge cluster.

The Medium Duty GM Trucks had the 4000 Rpm Tach with the fuel gauge in the bottom. I just bought one off a Truck Forum to eventually experiment this. I've read in other forums that the Calif Emission 6.2s had a signal tap in the rear vacuum pump assembly simular to the Hummer but with the vacuum can on them like CUCVs and Civy J code 6.2s but they are rare and hard to find.

Sorry for the double post -got click happy and now can't delete it...

Was looking at this as well as it would be nice to have a tach in the trucks.

Found this thread from another forum which has a bit of info: http://67-72chevytrucks.com/vboard/showthread.php?t=371045

48cj2a - would you happen to have the GM part number of that 4000 rpm tach with fuel gauge? I have a long-distance source for a few NOS tachs but he doesn't know what they fit and doesn't want to open the boxes.

Thanks in advance.

Sharecropper said:

48cj2a - would you happen to have the GM part number of that 4000 rpm tach with fuel gauge? I have a long-distance source for a few NOS tachs but he doesn't know what they fit and doesn't want to open the boxes.

Click to expand...

Here you go...pictures I kept from an ad I found on eBay for reference, I do not have any or know a source.

THAT would be cool!

THAT would be cool! I want one.

It appears that LMC also sells the correct printed circuit board for the CUCV gauge cluster. LMC part 38-8036. $79.95

richingalveston said:

It appears that LMC also sells the correct printed circuit board for the CUCV gauge cluster. LMC part 38-8036. $79.95

Click to expand...

Ok, this got me curious... per the -34p, the part number for the printed circuit is 25053623. Searching for that number came up with this: http://www.classicindustries.com/truck/parts/25053623.html .

So, as it appears these can be bought from fairly common sources, has anyone tried one? Mine works fine now, but I'd love to know that a new replacement part is available! Why does everyone seem to think they can't be found? Or is it just that they are a bit pricey?

Alternator 'R' and 'W' terminal tachometer feed

cpf240 said:

The drivers side alt ( GEN 1 ) has a tach output on it, that feeds a tach buffer under the dash that is wired to the STE/ICE port on the bottom of the dash.

Click to expand...

This is correct. Inet search for 'R' and 'W' alternator terminals. They are tied in to a single pole of the rectifier bridge and produce approximately 7 volts AC unregulated output. There are multiple uses for these terminals including the production of a tachometer signal.

If you have a multimeter with a counting or frequency function you can check this for yourself and validate the AC frequency.

As there are variables, pulley size etc, that need to be accounted for, most tachometers designed to work off of these signals need to be calibrated. You will need a known good external tachometer in order to set it properly. Fortunately a decent unit can be had at locations like http://www.harborfreight.com/digital-photo-sensor-tachometer-66632.html

I have not added a tachometer to my trucks yet but do plan on it. I have done enough research to know that the tachometers that utilize these signals are "reasonably" priced IMO. Now, all I need is that time dilation machine that will add 6 hours to each day .... where did I put that darn thing?

scottladdy said:

Now, all I need is that time dilation machine that will add 6 hours to each day .... where did I put that darn thing?

Click to expand...

Don't look at me! I don't have it!

Very cool. I like the look of the OE gauge

48cj2a said:

Here you go...pictures I kept from an ad I found on eBay for reference, I do not have any or know a source.

View attachment 399254 View attachment 399255

Click to expand...

One thing to note on the Big Truck style Tach that I posted the pic of...you loose the warning/info lamps in the window at the base of the fuel gauge for the (left) Seat Belt Indicator Light and (right) Brake Warning System Light because the little fuel gauge now takes up that space. (not that those are drastic to have but something to know)

I'm thinking a HUMV dash panel mounted Brake Warning Lamp could easily be modified into the dash bezel trim with a 12v bulb.

Does anyone know of a simular Seat Belt Lamp in newer models?

48cj2a - I just scored on one of those 4000 RPM Medium Duty Truck tachs with the small fuel gauge. Not NOS, but a nice clean used unit from an '84 Chevy C6500. The numbers and needle match my M1028 gauges perfectly.

Now I need to figure out how to make it work. The first thing to determine is how to cut out the back of the housing to accomodate the tach. I will abandon the seat belt and brake warning lights, and will need to figure out how to wire the new smaller fuel gauge.

I will post photos and more information when I get into the project.

I just received this from LMC, it is a new item. It matches good, the black is a little darker most likely due to age of other gages. It was $129 and needs something to drive it. I am using a Dakato digital ds1 module. I have installed it in the cluster but not into the truck yet. I am waiting on the small fuel gauge from LMC.
With this unit, dont get the wiring harness unless you want to cut the back of the housing out. Cutting the housing out in this area will create problems with the circuit board. There are three square holes that held the clips that the fuel gauge connected to. I removed those clips and will be using these holes to run the wires through.
I have put some documentation on the 'gauge cluster conversion question' thread in the cucv hotrod mod section. you can see what I have done so far.
I should have the cluster complete and in the truck in another week or two.

Sharecropper said:

48cj2a - I just scored on one of those 4000 RPM Medium Duty Truck tachs with the small fuel gauge. Not NOS, but a nice clean used unit from an '84 Chevy C6500. The numbers and needle match my M1028 gauges perfectly.

Now I need to figure out how to make it work. The first thing to determine is how to cut out the back of the housing to accomodate the tach. I will abandon the seat belt and brake warning lights, and will need to figure out how to wire the new smaller fuel gauge.

I will post photos and more information when I get into the project.

Click to expand...

If you do not use the cluster housing and all the mounting tabs for the scews are all good I may be interested in the housing. The one I bought is broken.