Dont know if anyone else has had this problem.
My tacho,an old analogue,pull down front card type is playing up when the vehicle is cold.The speedo will not remain steady and the speed will go to maximum.After about ten minutes it will work perfectly,unless its been parked,like on a break, then it will pay up again but will work ok after it has warmed up.The sender has been changed.The voltage is ok as well.Dont know if anyone has any ideas ?
Lot of drivers put a blank one,in the part where you would put a second drivers chart,it is legal.
what truck is it in??
when you say “pull down front” type, do you meant he one with the key in the top of the clock and pull the whole clock forwards or the later CD drawer type?
if it is the pull the clock forwards type, it sounds like the head unit is faulty
Thanks for the replies,it is the one with the key and pull the whole lot forward.It is a DAF 55 180.
I’d agree that it’s probably the head unit that’s gone. I had it a few years ago in an old Merc, they replaced the whole unit, eventually…
Another common fault(especially on Daf) are the wires between the gearbox sender unit and the tachograph head(yellow plug marked ‘B’)
From the top of the yellow plug B behind your tachograph;
B1 = +ve supply from tachograph to sender unit,noramlly 8~12volts…(+24 volts on some Volvos)
B2 = -ve supply from tachograph to sender unit.
B3 = Main signal from sender unit to tachograph head(above baseline)
B4 = Secondary signal from sender unit to tachograph head(below baseline)
Just before you go to the expense of replacing your tachograph head,it wouldn’t do any harm to check the continuity and integrity of these four wires.
Just as another thing to check, the 6s180/220 box had a habit of loosening the rear flange, would be worth checking it for any lift, his would cause that problem.
ALso, can you check what make the tacho is? The Veeder root 1318.24, doesnt really have that issue but the VDO 8456 HAS to have a chart in the second man position to work properly, preferably a clear plastic one.