Well I've finally got round to taking my existing clocks apart after mucking about with a set of turbo clocks for a while.
I'm sure everyone here knows the problem. You fit some nice new blue LEDs and you can't see squat anymore unless it's pitch black outside. You try one in the mileage display and suddenly it dissapears even when it's dark. Want to know why? well so did I so I decided to compare a set of turbo clocks that seemed to be ok against a set of 140mph clocks from a 52 plated Mk4.
Are they different? yes by very small amounts but it's these that cause the problem. I'd noticed when I removed the existing 140mph clocks that the mileage display seemed to have an orange edge just behind the metal framework. However at the time I couldn't figure out how to remove the needles to get to it. Even put a post up on the forum to see if the needles came off and no one at that time knew.
So I put a blue LED in the mileage display, it was CRAP with a capitol C. It was so bad I had to put the white bulb back in. I'd tried the same blue LED in the mileage display of the turbo clocks and it worked fine. So what's the difference, well the difference is that the later clocks have had a small yellow filter installed between the glass display and the bulb. You can put a 100w blue bulb in that sucker and it's just coming out green if your lucky. Solution!! take it out, is it easy?, erm not really. I can describe how to do it if you wish but it's complicated but it's doable if your willing to try it.
This is the little sucker that causes the problem
It's the middle piece in case your colour blind the left hand one is the glass of the display, the right hand piece is actually a small piece of hardish rubber that connects the glass to the circuit board. The bottom piece is the frame the mileage display sits in.
So mystery solved for the mileage display. So why are the clocks so bad at lighting up blue. I was convinced it was the light prism that causes the problem, it has changed between the 2 models, the turbo clocks have a frosted light prism, the 140 clocks have a clear prism with small light bands running through it. Comparing the 2 lit up with the same blue LEDs shows the turbo one allowing a better spread of light but it's not the problem. So what's the answer, well I was stumped for a while until I looked at the dial facings. There are markedly different. The turbo clocks are almost transparent, the 140 clock facings aren't. They are multi layed and one of the layers is our friend the yellow one. So any blue light trying to get through that is going to have a hard time, here's what it looks like.
That's the reverse side, it's quite clear when you see it isn't it. It appears that Vx changed the facia around 2000 so if you can find an old set of clocks nick the facia plate.
I dismantled both sets of clocks and made a set of clocks that was a mix of the turbo and 140 clocks, they light up a nice shade of blue, it's nice to be able to see what speed I'm doing at night, the mileage display is also blue and I can see it in daylight
Well that's it, I've talked enough.