Don't necessarily assume that it would be only a front brake issue. You
didn't mention whether you've checked both ends.
Tyre pressures OK?
I'd expect one or more sticky caliper pistons. Start by removing the
pads a caliper at a time, insert a substitute wooden spacer (About 10mm
thick initially. You're safe down to about 3mm in the later stages once
you've got piston movement under control.) to prevent the pistons
being forced out all the way. Stroke the pistons in and out. Force them
out with the brake hydraulics and back with a lever taking care not to
damage the pistons. You'll probably need to do this several times
gaining a little more movement on each occasion, hopefully. Take care
not to allow the piston to cock in the bore. Clean the piston as much as
possible (string wrapped round the piston can work well) every time
before forcing it back into the caliper. Remember that the outside
diameter of the piston is the surface on which the piston seal slides.
Some brake fluid as lubricant can help. You need to use common sense on
how you do this: I can't cover all potential problems.
If you can get all pistons moving freely you've probably solved your
problem. (Note that if you need to replace the pads with new, the piston
will have to retract fully.) Don't be too surprised if a piston won't
move at all! You may have to sacrifice the piston (it'll be scrap
anyway) and use sliding joint pliers to extract it.
If you can't free all the pistons it's not too difficult to fit new
pistons where required and seals. It's a caliper off job to do this
comfortably. It's probably not a good idea to do just one caliper on any
Pedal is ok but can be spongy on first press, then firms up ok. The brakes
don't always pull but maybe 7/10 times so thinking sticking caliper. It is
used off-road most of the time so gets well caked in crud.
Mine does this every year, though not strongly. Invariably it's been
the rear brake pistons (either) getting crudded up and deciding not to
play ball anymore. Quick piston/caliper overhaul and it's OK for
another 10-12 months .. I really probably ought to get new calipers ....
Even new calipers are not a guaranteed long term cure. Unless you use
the vehicle in such a way as to make the rear brakes do some of the work
they will inevitably deteriorate with time through lack of use.
Check wheel bearings - if they are failing, this will allow the hub
and disc assembly to move laterally as well as rotating! If the
bearings are different on the two sides, this will show up as a pull.
Happened on my Disco years ago when I was in Zimbabwe. Front left
bearing had worm prematurely and was about to collapse.