Brake Disk Distortion; Disk Deviation From Centre; Bleeding The Brake System Pipe - Derbi GP1 50 cc Workshop Manual

Brake disk distortion:

- Raise the motorcycle on the jack so that the tyre is clear of
the ground.
- To check the front disk, turn the handlebars completely to
one side.
- Place a dial calibrator against the disk (A) as shown, and
measure the disk's deviation from centre as the tyre is turned
by hand (B).
- If the deviation from centre exceeds the service limit, renew
the disk.

Disk deviation from centre:

Standard:
less than 0.15mm
Service limit:
0,3 mm

Bleeding the brake system pipe

The brake fluid has a very low compression coefficient, with
the result that almost all the movements of the brake lever are
transmitted directly to the calliper for braking. Air however
compresses easily. When air enters the brake system pipes,
the movement of the brake lever is partially used up in com-
pressing the air. This causes the lever to feel spongy and leads
to a loss of braking power.
WARNING
BE SURE TO BLEED AIR OUT OF THE BRAKE SYSTEM WHEN
THE BRAKE LEVER FEELS SPONGY AFTER CHANGING THE
BRAKE FLUID OR WHEN THE BRAKE SYSTEM PIPE HAS BEEN
LOOSENED FOR ANY REASON.
Extract:
- Bolts (1).
- Reservoir cap (2).
- Fill the reservoir with brake fluid up to the top reservoir
line.
- With the cap removed, pump the brake lever slowly several
times until no bubbles can be seen rising through the liquid.
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