One of the first things I noticed on the Corvette, was that the gauge cluster wasn’t working. When the car was running, the cluster would light up like a Christmas tree in lots of bright colours, but the actual gauges wouldn’t work.
I figured that this was going to be an expensive fix that would require the replacement of the entire cluster, but after a bit of research I discovered that it was easily DIY repairable.
What typically happens with C4 gauges, is there polarised coating on the outside of the gauges fades over time with sun exposure. This causes everything to light up and the LCD indicators to become unreadable.
I promptly pulled the gauge cluster out of the car, by undoing the screws around the faceplate (not forgetting the ones near the door opening) and the visible screws for the top of the dashboard. There were then 4x 7mm screws to pull the cluster out – 1 in each top corner, and 1 on the bottom on either side of the steering column. I was then able to use a screwdriver to get under the clips for the wiring harness and pull the 2 plugs out.
It’s worth noting that you need to tilt the steering wheel down and unscrew the tilt lever to be able to access the bottom 2 screws and manipulate the face plate and cluster out of the dashboard.
Once it was out of the car, I started dismantling it. Unfortunately, I once again forgot to photograph the steps to dismantle it, but there were 5x 7mm screws on the back plate which gave access to the top circuit board. Then there were another 7 screws (estimating) to remove the top circuit board including 2 screws at the harness connector. It’s then possible to gently, but firmly, pull the top board out of the cluster. There is a multi-pin connector that connects the 2 boards together (did they have ribbon cables in 1986??) that needs to be pried apart.
With the top circuit board out, there’s then 16 more screws needed to take out the lower circuit board. It then just lifts out without any effort.
Once the bottom circuit board is out, there’s then 3 layers that comprising of light diffusers, brackets for the light diffusers and the elastomeric zebra connectors then a colour diffuser that gives the gauges their unique appearance.
If it sounds like a lot, it is!
Finally after removing all of that, there is access to the glass LCD panels.
The image above is after I scraped off the old polarising filter. To remove the polarising filter, you need to scrape it off with a razor blade. It comes off fairly easily, but has 2 layers that may or may not come off together. Then there is the adhesive that needs to be scraped off with a razor blade. Just a note, it does give off a strong acetone-type odour when you peel it off. To remove the adhesive, I found it came off quite well with some window cleaner and a razor blade.
Everything up to this point was relatively easy. The next step was to sort out the back of my gauge. As far as I understand it, the OEM LCD panel is screen printed with the numbers and the cool column chart display, but mine looks like it was applied as a sticker of some sort and it was peeling and cracking.
Fortunately I had a plan for this, although I was unsure if it would actually work. A friend of my wife has a Cricut vinyl cutter. If I could draw the graphics, I should be able to print it on the Cricut and stick it to the glass. How hard could it be?
I was able to put these 2 images together in a couple of hours. The fonts are not perfect, but you’d need to be a real Corvette aficionado to pick it. I didn’t produce one for the trip computer LCD as that one was OK.
Note that when printing these on the Cricut, they must be mirrored so that the graphics are pack to front. This allows the decals to be stuck on the underside of the glass and in the correct orientation when viewed from the front.
That was the easy bit. The tricky bit was getting it onto the glass. The first issue I ran into was that when removing the vinyl for the numbers – particularly the hollow numbers like 4, 6, 8 – it was very difficult to not remove the hole in the middle too. It took several attempts but I found a method that seemed to work.
Firstly, I peel the main part of the vinyl from the backing paper. Ignoring the numbers etc. I spray some soapy water on to the glass and position the vinyl. I then use a credit card or similar to squeegee the soapy water off the glass as much as possible. Once I’m satisfied there’s no bubbles and it’s positioned OK, I set it aside for 10-20 minutes to dry.
This gives me 90% of the graphic on the glass. I then use the left over bits fill in the hollow sections on the 4, 6, 8, 0 numerics and letter P. I place them on the glass one by one using a pick, tweezers or whatever it takes to put them in place.
Once I completed all of this, and was satisfied with the position, I then moved to the front of the glass to stick the polarising film on.
A note about the polarising film
There’s several suppliers selling “C4 Corvette” polarising film that’s cut to size for this job. The truth is, this is just ordinary polarising film that can be bought online for a quarter of the price. I will say however, that I inadvertently bought glossy film instead of matte. It’s not original, but I personally really like the look of it. It may not be the best in bright sunlight though.
Polarising film alignment
There is a right and a wrong way to align / orient the film on the glass. Before removing the backing film, place the film on top of the gauge, then rotate it 90 degrees and take another look. Whatever orientation appears darker is the correct orientation as the gauges should be completely black with and not visible with the ignition off.
Sticking the polarising film to the glass
This step drove me nuts! In theory if you get it wrong you can peel the film off and try again, but in reality if it’s peeled of it introduces wrinkles and other imperfection. It must be laid down perfectly the first time. I originally tried with a credit car to smooth it out as I was going but this ALWAYS resulted in bubbles. I then purchased a Cricut rubber roller and it immediately stuck with no bubbles, but the is a technique to it.
Cut the film quite a bit larger than the glass, noting the orientation as mentioned above, remove the entire backing film and stick one corner down. Starting at this corner, use the roller to stick film to the glass with a firm press. It should stick perfectly with no bubbles providing the glass was free from and old adhesive and dust.
Then just trim the excess with a razor blade. It’s important when cutting the excess to not scrape the side of the glass. There is an epoxy here that keeps the LCD sealed and it’s imperative not to damage this. Scrape at a 45 degree angle to the surface being trimmed to avoid this.
There’s a little more to it
I repeated the process for the polarising film on the tachometer and trip computer displays. With the polarising film on, I then noticed that my speedo wasn’t quite as dark as the others. It turns out that the polarising film needed to go on the front and back of the display.
I scraped of the vinyl that I so painstakingly applied just a few hours earlier and applied another sheet of polarising film. I then repeated the process described above to put the graphics back on.
Next time
I wasn’t totally happy with the results of the Cricut vinyl. While it did cut it exactly as I had specified, the issue with the hollow digits is too much of a compromise for me. Next time instead of using the Cricut, I will use those same images to laser print the graphics onto clear adhesive vinyl and stick this over the polarising film. This will eliminate the issue with the hollow digits, but I am concerned that laser printing may not blackout the numerals as much as I need it to.
Reassembly and testing
I put everything back together and tested it out in the car. Success! Well mostly. Some of the LCD digits didn’t work. I stripped it again, cleaned the edge of the LCD’s thoroughly and cleaned the edges of the elastomeric connectors. Re-assembled and tried again. I had to do this several times, each time, getting a little bit more working than the previous time. Finally I gave up when the speedo wouldn’t light up all of the digits in the speed display. I believe the LCD is OK, but the elastomeric connectors maybe to blame. After sitting in the car for 40 years, they were a bit misshaped and I believe this is providing a poor connection.
I’ll order new connectors and at the same time, clear adhesive film for my laser printer experiment. I think if I print in the highest quality setting it should put down enough toner to do the trick.
