How does a DIY check that brake caliper & pistons move freely.
>
> In a related thread on how to diagnose high speed braking induced wheel
> shimmy in a 98 Toyota 4Runner and in a variety of brake shimmy articles it
> was suggested I check that the 4 pistons move freely in each caliper. >
> ... (egformatting linkformatting linkformatting linkformatting linketc) ...>
> Unfortunately, neither the $20 Chilton nor the $200 Toyota Repair Manuals > I
> bought say ANYTHING about how to check the pistons & calipers for free > movement.
>
> Each caliper has 4 pistons (which the Toyota shop manual says to separate
> with a MONKEY WRENCH!).
>
> Do you know how to check that the caliper & 4 pistons move freely?
remove the brake pads and refit the caliper, it should now be possible to slide the caliper (if it is a sliding caliper) using hand pressure.
usually 4 piston calipers are not sliding type.
with the pistons pushed out a bit (by carefully pressing the brake pedal) it should be possible with strong hand pressure to push each and every piston back in to the caliper. A short lever may be used if you are weak or it is difficult to get a purchase. It is usually easy to tell if any piston is sticking, it will be obvious by the greater amount of pressure needed.
while the pistons are sticking out a bit you can check for rust or damage to the polished outside surface of the piston.
brake shudder is almost invariably caused by warped discs
mrcheerful