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Some of you might think of a vintage motorcycle
as having only drum brakes. On the contrary, since the disc brake
hit the market in the early 1970’s, it has been a great performance
upgrade to the older drum style brakes. Disc brakes are great until
the bike sits for a long time, when the metal housings start to rust
and the fluid turns into a jelly-like goo. Then the front brake
pistons no longer move in and out or in the worst case, the brakes
are frozen solid to the brake disc. Now you are faced with
repairing the brakes, replacing the seals and perhaps the rusted
pistons.
The main problem is getting the pistons out of
the calipers. Over the years I have seen many solutions to this
problem. Some are quite crude, such as drilling a hole through the
caliper, pushing the piston out and then plugging the hole with a
household pipe thread plug. This is not a good look for a
restoration; it’s really not even a good look for a daily driver.
Here is a great way to get those stuck pistons
out of the calipers. In this example, I used a dual piston caliper
found on the Yamaha RD’s, XS’s and TX’s. If you can master the dual
piston caliper, the single piston caliper will be a breeze.
Some special tools are required, but they are
available from any local tool and hardware store.
- Air compressor
- Air blow gun with a rubber tip
- Pick
- A heat source such as a heat gun or
propane torch
- Small piece of aluminum
- Two large hex nuts
- C-clamp
- Bench vise
- Basic hand tools
Begin by removing the brake caliper. Once the
brake caliper is out of the bike it will need to be taken apart.
Split the caliper in half by removing the two large bolts and the
two internal hex bolts.
Start with the side without the bleeder.
Carefully clamp the caliper half in the vise so the piston is not
obstructed by the jaws. Use the C-clamp and compress the piston so
it bottoms out against the caliper body. Be careful as the old
fluid will be ejected from the caliper. Remove the clamp to allow
for the dust seal removal.
Remove the dust seal (the slightly exposed
rubber seal) from the caliper with a pick. This will take some
patience and a little effort.
The main problem with the outer-side caliper is
being able to pressurize the caliper since there are two holes, one
where the line hooks up, and one where it crosses over to the other
half of the caliper. The crossover hole will need to be blocked
off. This can be accomplished with a small piece of aluminum, 0.020
inch minimum thickness will do. Drill two holes that line up with
the two bolt holes in the caliper. Hole placement can easily be
determined by using the bleeder-side caliper half as a template.
Using the old center caliper seal, place the
seal over the crossover hole in the caliper. Mount the block-off
plate on the caliper using the existing caliper internal hex bolts
and two large hex nuts. Because the internal hex bolts are too
long, the large hex nuts are necessary to tighten down the block-off
plate. Use a small amount of grease to keep the seal in place while
installing the plate.
After the dust seal is removed and the
block-off plate is installed, place the C-clamp back on the caliper
but do not tighten it. I use the clamp as a safety device for the
next step so the piston cannot fly across the shop. Place the
rubber tipped blow gun in the main hole where the brake line
attaches. Hold the air gun firmly in place to provide a tight
seal. Slowly apply pressure; the piston should slide out under the
air pressure. If the piston still will not budge, apply heat to the
caliper half until it starts to move. Remember the C-clamp is there
to make sure the piston does not become a missile. Adjust the
c-clamp as needed to allow complete removal of the piston. Also be
careful of the old brake fluid left in the caliper as it will also
be under pressure.
Once the piston is fully removed you can remove
the plate and the seal and move onto the caliper half with the
bleeder.
To remove the bleeder side piston, repeat the
steps above with the exception of the block-off plate. Leave the
bleeder tight and place the rubber tip of the blow gun into the
caliper crossover port. Do not forget the C-clamp!
After the pistons are out, you are all set to
continue your brake restoration. This technique can be used on
almost any brake caliper, single or dual piston.
Brad Obidowski
HVCcycle |
