FORD 1999 Explorer - Manual (Page 209)

Brake fluid is toxic.
If you use a brake fluid that is not DOT 3, you will cause
permanent damage to your brakes.
Do not let the reservoir for the master cylinder run dry. This
may cause the brakes to fail.
CLUTCH FLUID (IF EQUIPPED)
Check the clutch fluid level. Refer to the Scheduled Maintenance Guide
for the service interval schedules.
During normal operation, the fluid level in the clutch reservoir should
remain constant. If the fluid level drops, maintain the fluid level at the
step in the reservoir.
Use only a DOT 3 brake fluid designed to meet Ford specifications. Refer
to Capacities and specifications.
1. Clean the reservoir cap before
removal to prevent dirt and water
from entering the reservoir.
2. Remove cap and rubber
diaphragm from reservoir.
3. Add fluid until the level reaches
the step in the reservoir.
4. Reinstall rubber diaphragm and
cap onto reservoir.
Maintenance and care
209