SkinnyG SuperDork
8/20/18 11:10 a.m.

Way back I bought a Tach Adapter off eBay that was programmed to take the 8 pulses of the V8 and turn it into 3 pulses for the stock tach. It was sort of successful, but not something you would rely on.  It kinda fidgeted and floated around.  I contacted them, and they said to put a 100K resistor inline with the input as that would affect the Time Constant of the circuit and smooth it out. Now, I'm not an electrical engineer, but I figured the tach adapter wasn't getting a significant signal, and adding a resistor inline would just make it less significant a signal. And it did.  The tach was lazier and worse.

So, because I didn't want to have to troubleshoot this, I decided to put the Firebird factory tach guts in the Firefly cluster.  Something I should have done back then.  It was actually easier than I feared.

First, pull the tachs out:

Here are the tach guts side by side.  Firebird on left, Firefly on right:

Backside, Firebird on left, Firefly on right. No, I didn't notice any similarities yet:

I sanded down the perimeter of the Firebird tach face (I smoothed it up more later), and drilled two holes so it could line up with the existing holes in the Firefly face. The sweep is different, and the scale is different between the two, so I can't just plunk the 'Bird guts and use the Firefly face:

Then I noticed they were very similar. The Firebird cluster is made by Denso. The guts are super super similar. I bet if I just changed these mounting pins.....

By unsoldering them....

And attaching the Firefly pins to the Firebird tach guts....

It will all fit inside the cluster, and use the existing wiring and everything:

And it did, even using the Firefly needle (though I may change it back to the longer 'Bird needle)!

Trans_Maro PowerDork
8/20/18 12:29 p.m.

Gotta love the GM "lego" engineering mentality.

SkinnyG SuperDork
8/20/18 8:47 p.m.

Looks pretty cool, ammiright?

Except it isn't working properly. It's reading WAY low.

Did the full swap, and then learned that the guts are weighted and stopped according to how the needle needs to sit. 

So I rotated the assembly to make that work, which included disconnecting the circuitry and mounting it separately from the guts.

But it still read low, like half the rpm low.

Then I discovered the Firebird didn't mount the guts straight up, so I had to get in there and rotate it again. which required more holes and more trimming of the cluster plastic inside.

And it still reads way low.

I know I have good positive, a good ground, and a good signal. What the heck.

Perhaps I knackered something in this tach, and could source another.  But the fact that this one is reading weird, and the tach adapter was reading weird, I'm more inclined to think my wiring is weird.

slefain PowerDork
8/21/18 9:17 a.m.
SkinnyG SuperDork
8/21/18 10:02 a.m.

That's freakin' awesome!

SkinnyG SuperDork
8/22/18 10:39 a.m.

Oil Cooler installed.....

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Mezzanine Dork
8/22/18 11:20 a.m.

Love the Foley art in the video. What's the next plan of attack on the cooling issue?


SkinnyG SuperDork
8/22/18 11:57 a.m.

When it gets up to temperature, it will stay there (for the most part) as long as I'm moving.  Once I slow down in traffic, it will start to climb without the fan (obviously), but totally cool right down with the fan.  The fan is only on a toggle right now, so once it's up to temp I just leave the fan on, and it seems to be fine.  I'll run a proper fan switch soon enough.

I keep an evil eye on the temp gauge to make sure it's cooling properly. I haven't driven it a whole lot lately, as it's been really smokey out here in BC, and it hurts my lungs and eyes. Seems to be clearing up recently though.

SkinnyG SuperDork
8/25/18 11:17 p.m.

Started finishing off the interior panels. I need to make this car more "presentable."

First, make a pattern out of cardboard.

Then I transferred the pattern onto 1/8" hardboard, but it turned out I didn't have the right panel clips, so instead I made the panel out of 1/16" ABS.

Then wrapped in gray marine vinyl I picked up at Fabricland, but gluing this down with 3M 77 adhesive was a gooey mess, so I don't have pictures. I didn't like how my panel clips fit under the vinyl, so instead I just poked a hole and ran them through.  You will get over it. Could paint the clips gray if I care enough.

I'm half-way through the passenger side panel pattern right now. Need to remove the residual duct tape up there....

SkinnyG SuperDork
8/26/18 6:15 p.m.

Old and Busted:

New Hotness:

Trial fit driver's side, because I apparently can't measure, and need to buy more vinyl:

Trimmed the speaker covers to finish the cage:

SkinnyG SuperDork
8/26/18 7:56 p.m.

Gray clips ordered, since I can't find any locally.  Should be a couple weeks. I'm not liking the black.

Run_Away HalfDork
8/26/18 10:30 p.m.

Look great! Think it'll do anything for noise levels?


Think that 1/16" abs could be made to fold into fairly sharp 90 deg corners to fabricate heater ducts?

SkinnyG SuperDork
8/27/18 12:03 a.m.

Absolutely.  You can make your own strip bender by finding an old baseboard heater. Careful with plastics, eh? Vacuum forming is the next addiction.

SkinnyG UltraDork
8/28/18 5:39 p.m.

My fourth thread-into-the-engine-block-somewhere-cooling-fan-switch on my '77 Silverado died, so I ordered two of them Hayden adjustable fan switches, one for the '77 and one for the Firefly, as I did not have a fan switch other than a toggle on the dash. Installed both this afternoon.

First switch was from a FWD V6 GM product of some kind, but turned on way too late. Next two switches were from 1990 Ford Escort, had 1/2" pipe thread to fit right into the passenger side head of the 350 in my '77.  First one failed open. Second one failed closed. Third one was relocated to the intake manifold (figured the headers were cooking it). This location made the fan turn on slightly hotter, and just recently failed closed.

Lots of good reviews on the Hayden.  Not removing the toggle switches (both vehicles have 'em) ever.

SkinnyG UltraDork
9/20/18 10:26 p.m.

Interestingly, the Bridgestone RE-71R's aren't quite as grippy at 50°F and light rain.

759NRNG SuperDork
9/21/18 5:08 a.m.
SkinnyG said:

Interestingly, the Bridgestone RE-71R's aren't quite as grippy at 50°F and light rain.

News at

SkinnyG UltraDork
12/15/18 8:10 p.m.

Nothing new to report.  I'm not really motivated to do much of anything with it right now.

A friend informed me there was an '87 Firefly at our local Pick-N-Pull, so I went today to see what I could take.

Not much.  Great shape, though.  Always amazes me the quality of car that people just unload at PnP. 

It was a stick, so I couldn't nab the NSS and Rev. switches for the shifter. The hatch rods were worse than what mine are, but I did snag the plastic bitties to cover the screw holes on the top of the dash (one was missing).

It seems I have a slow leak on a rear tire.  Hopefully just a nail.

SkinnyG UltraDork
1/14/19 9:44 p.m.

Now have a proper sealed & vented battery box in the back.

759NRNG SuperDork
1/15/19 8:30 p.m.

SkinyG is the 'FLY' gonna be in the stable much longer? and have you enjoyed it so far? What's next? 

SkinnyG UltraDork
1/15/19 11:53 p.m.

Come March I want to put plates back on it, and enjoy it a bit.  I'm thinking May or June-ish or so put it up on Bring a Trailer.

It is giggles of fun in its own way, but I don't love it enough for it to be a keeper; I can't keep everything.

I certainly CAN tell you that I totally am going to miss it.

Next is tear into the '61 Chevy Apache (another thread). I'd like to take the money that the Firefly will bring go right into parts for the truck.  When the '61 is done, the '77 Silverado will go away, and Lethal Locost #2 will continue.

SkinnyG UltraDork
3/24/19 11:19 p.m.

Finally built a proper battery box, vented to the underside of the car.

Over this past winter, I started psyching myself up with enthusiasm for driving the car again.  And winter just kept coming, and coming, and coming....

Finally it got warm enough and spring arrived, so I put plates on it to remind myself why I'm not in love with it any more.

The first drive to my work was full of "oh yes, this thing is a riot!" and on the way back I was "yeah, ok, I'm done with it." I want to start the '61 Apache.

Oh, and the battery died at work.  Jumped it off the alternator bolt (it's easy to get to) to get home, and went and bought a new battery, as a result of this:


AngryCorvair MegaDork
3/25/19 9:59 a.m.

dibs on Silverado?

SkinnyG UltraDork
3/25/19 11:11 a.m.

You can have dibs on the Silverado (and its matching trailer) once the '61 Apache is done. :)

AngryCorvair MegaDork
3/25/19 10:15 p.m.

In reply to SkinnyG :


SkinnyG UltraDork
3/25/19 10:37 p.m.

I'll giv'er my best.

Mean-time, the Firefly was giggle squirrely fun today, off to KMS Tools for more Nitrile gloves....

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