Speedbrake issues in 737 and 747

Hi all,

I was flying a 737 the other day and a 747 today and I noticed some problems:

On the 737, the speedbrake, though armed using the command Shift+/, it does not engage and work after touchdown at destination. The speedbrake panels do not rise.

On the 747, the speedbrake, though armed using the command Shift+/, works, however, only after the aircraft has almost come to a complete halt and awaiting instructions to taxi to gate. Its no use now!

I arm the speedbrake well in time, on vectors-to-final into the ILS runway, once the aircraft has stabilised and lined up.

I also set the autobrake to 3 for both the 737 and 747.

Please help me.

Thank you!