Gauge Rebuild

[kjohnson63]

I’m sorry and I’m sure it’s been answered a million times but I looked and couldn’t find the answer I needed. I have a 78 k20 and currently redoing the gauges

My backing plate is busted so order a new one. My truck has gauges but no clock nor tach however don’t see a backing plate that matches this description for 78. However, I was wondering if I need the backing plate for a truck with a tach since that’s where my fuel gauge is.

Second thing order a new lense and it says the same thing so I order the one with a tach. LMC was no help just said order it and send it back if it doesn’t work.

Thanks and sorry if it’s redundant

 

[dvdswan]

You will need to choose. Clock or tach. Technically, you can't have both. There used to be a company that made Tach/fuel gauge in one that looked factory. So you could have the clock too.

IIRC, you can use an 80s camaro/firebird tach/fuel that fits the C/K trucks.

The lens with a clock will have a hole for the adjustment lever.

If you're lucky, you can find a medium duty truck that is not a diesel and it will have the tach/fuel gauge, but the majority are diesels. The diesel tachs go to 4K RPMs and need a different signal than the distributor.

 

[Raider L]

@kjohnson63,

You need to look for a Blazer bezel and circuit board. In my electric schematic for my truck, '74 C10, there is a side diagram for the dash gauges with a tach and it says "Blazer". Same gauge panel just like the one you've got but the big hole on the right would have had a tach in it. Actually, you may only need the circuit board in the back. Then make up the wiring for the tach so you can splice it into where it goes in the bundle. But if you can either find a used tach in good shape, or you may need to buy a tach, it's going to be high. I'd look for a good used one. Then you're fixed up! The circuit board will provide a place for the tach to be made part of the circuitry.

 

[Raider L]

@kjohnson63,

I did a little scrapping around and found: Eckler's '81-'83 Chevy/GMC truck printed circuit board p/n 61-329293-1 factory gauges w/ tach $89.99, '81-'83 Chevy/ GMC truck printed circuit board p/n 61-329271-1 factory gauges w/ tach and A/C $87.99. why it less than the one with just the tach, I don't know, it just is. Classic Industries has the housing for the tach that attaches to the green/white plastic box part behind the bezel that you put all the gauges into, apparently the tach is a separate piece because I know my box thing had a place for one but didn't have the box for the tach, '73-'91 Chevy truck p/n TL3159 $14.99. And lastly, Classic Trucks has the tach '79-'87 Chevy truck 8 cyd. $129.99! I told you I'd be high. It only goes to 5,000 rpm though. If you want a higher rpm one you probably need get a after market one and fit it in the big hole in your dash. There are a bunch of companies that make one that fits that big hole.

 

[75gmck25]

AFAIK, the the base gauge cluster housing and circuit board has the circuit wiring for the clock, so the clock can be added to a base cluster. But I don’t think that is anything you are interested in.

The tach cluster removes the clock wiring and moves the fuel gauge to the lower left pod. The tach wiring is a separate 3 wire plug that connects to power and ground, and has the third wire going through the firewall to the distributor.

Original tachs of this vintage often have electrical problems with the circuit board on the back of the tach. It can be repaired, but most repair places are focused on Corvette tachs, which have a circuit board that is shaped completely different.

 

[kjohnson63]

I’m sorry I guess I didn’t state I would like to go back with the original set up just repair the backing plate and printed circuit board. Right now I have gauges, no clock, and a large fuel gauge where the tach would go.

 

[Raider L]

When my truck was stock, it had the clock in the lower left hole but it didn't work. Like a dummy, amoung many things I did with all the stock parts I removed off the truck getting it ready to rebuild. I chunked the clock! Isn't that terrible? I (dummy) also chunked the stock AM radio. Probably that part I wished I hadn't chunked it more than some of the other parts I chunked. It was perfect and the souind was clear as a bell! I listen to AM radio now but then I didn't, I listened to FM music all the time and thought, "I'm not ever going to need this. It's just AM." Yeah dummy! The cast iron two bbl. intake manifold...gone in the trash! The 2 bbl. carb.!!! Gone!! All the stock gauges that worked and were clean...GONE!! In the trash! DUMMY! The printed circuit board...gone. There wasn't any such thing as Ebay back then in '94 so no one would have bought any of the stuff and I would have been dragging the stuff around with me for years. But looking back it really wasn't that much stuff that a small box would have been all. But the only heavy thing of course, was the intake.

 

[Jacob Miller]

Not sure if you got the money to burn but if so I can recommend going to the Dakota digital cluster, it’s a big chunk of change but it’ll give you a big Speedo & tack, small oil, water, & voltage. You get a small window in each of the big gauges that by default display time and odometer. There’s dual trips and a ton of programmable options also.

 

[dmgr157]

KJpohnson did you ever find a cluster backing plate?? LMC has the correct circuit board (38-8040) but I can not find the correct backing plate for no Tach with huge fuel gauge either. Ordered the 38-8089 with tack, but there are no holes to support the fuel gauge. Wondering if the 1977 will be the one (38-8105)