Brake Shudder

New pads??
Youve got to wear them in for a few hundred kms ie normal city type driveing before you "break quickly" or heavily. Otherwise you may glaze the pads and discs, one of the symptoms of which is shudder. Quick fix for this is remove pads and deglaze them on a flat surface with some 80 grit wet or dry and refit.
Conversely the discs may not have been machined correctly or one of them may have distorted due to heavy brakeing or it may be incorrectly tensioned wheel bearings.
Take it back and get it checked out.

Take it back to whoever serviced it pronto and get it checked out.

CRUISER DISCS SHOULD ONLY EVER BE MACHINED ON CAR

do you have any pulsation through the pedal???

if your game you can clamp off either frt or rear brake hoses and go around the block, ( slowly!!!!!!!! ) if the front is clamped and you have a pulse through the pedal, problem is in thee rear and vise versa. this will give you a starting point.

if it seems like wheel brgs, jack it up and hold wheel frt and rear and shake side to side. movement will confirm wheel brgs not adjusted correctly

If you have had the discs machined they have obviously machined a shudder into it. If they didn't check the runout before machining they haven't done it right.
You can machine them off the car OK but the cruiser's don't have much meat to play with.
Never deglaze the pads with wet and dry.
They also need to check the wheel bearing adjustment.
Try my site HERE and you may pick up some usefull information.
Brake shudder is a major drama these days and is dependant on lots of factors. It sounds as though the rears are the problem if it is coming through the car. It could have happened when they put the wheels on and the discs on the rear haven't seated on the flange properly. The rears are slip off top hat style rotors where the fronts are bearing mounted hub type.
It is a good idea to machine every time prior to installing new pads these days. We strongly promote this in my workshop and even though it is more expensive we don't have any come backs. It pays to have it done properly in the first place.
We like off car machining them because the wheel bearings get a clean, inspect and grease repack at the same time.

Your drama is they have either machined a shudder into it or they have overtightened the rear wheels whilst the discs haven't seated correctly.
Some times with the top hat style rotors when the wheel is removed the disc moves on the hub and rust and scale can fall down behind the seating position causing the disc not to seat properly but this is very rare on Landruisers.

Hope this helps and if you have any dramas you can contact me on Monday at my workshop via my web page
120scruiser