So on my 84 berlinetta the digital dash tops out at 85 mph at which point it just blinks 85. i have a small block 350 in it. it’s been passed down 4 generations and now i plan on LS swapping it. But does anyone know how to “fix” this problem. i cant find any similar threads on here so i’m wondering if it’s a common problem. i took her out on the freeway for the first time in 5 years the other day and was easily going 100+ but only got the flashing 85. there are 3 digits on the dash (obviously) so it has to be able to show above 99mph i just don’t know how. any help would be much appreciated, thanks

 

Hi, This is a normal behaviour from those dashboard, I never found a way to solve this but I found a work around.
the buffer box under the dash (yellow box) sends speed signal to the dashboard and it got 4 output 2 normal and 2 half.
Dashboard is using an normal one so on mine I switched it to half output
so the reading is half the speed, to make it flash it would need to get to 170mph...
I'm using it this way for five years now, no pain there and no more blinking

 

From 74ish until about 86 or 87, speedometers in cars sold to the public could not indicate above 85, by law. It was part of the 55 mph speed limit deal.

So yeah, it is what it is. Gonna come down to whether you can reprogram the "chip" that works the whole thing. Not a trivial matter even when that sort of "chip" was the latest & greatest; even less likely now, that those things are mostly museum exhibits.