Shimano HDB Pressure Test Process
Performing a pressure test on hydraulic disc brakes to locate fluid leaks
Performing a pressure test on hydraulic disc brakes to locate fluid leaks
Hydraulic Disc Brake Pressure Test
When a cursory visual inspection shows oil leaking from one component or another, a diagnosis is automatic. Sometimes,
however, we are faced with situations in which there may be a leak, but it is not so severe as to be obvious. In these situations, it
is often possible to rule a leak in or out by performing a pressure test. The following may be taken as possibly indicating a leak:
• Wet dirt caked onto the edges of pads, pistons, the outside of the caliper, or at the connecting bolts
• Repeated contamination of brake pads
• System requires frequent bleeding
• Mineral oil is severely discolored and/or contains particulates
This pressure test should be performed only after a thorough visual inspection of the entire braking system has been
completed and any obvious leaks corrected, and after all connecting bolts, bleed ports, and bleed nipples have been checked
for proper tightness.
Tools Required
1. Proper protective equipment, including gloves and safety glasses
2. SHIMANO bleed block for the caliper in question
3. Isopropyl alcohol
4. Cotton swabs
5. Piston reset tool or plastic tire lever
6. Lint-free paper towels
7. Toe strap or zip tie
Procedure
1. Remove the wheel from the bicycle and the pads from the caliper
2. Remove caliper from bicycle
3. Inspect the caliper for any signs of a leak, such as mineral oil residue or caked/wet dirt
4. Perform piston cleaning service as shown in the standalone guide “Hydraulic Disc Brake – Caliper Service” and reset
the pistons
5. Inspect the lever for any signs of a leak, such as mineral oil residue or caked/wet dirt, paying close attention to areas
under bracket or connecting bolt covers, the back side of the master cylinder piston, the edges of the reservoir, and
the connecting bolt
6. Clean the lever assembly with isopropyl alcohol, using a cotton swab to get into tight spaces
7. Wrap the bleed block with a clean paper towel and install into the caliper
8. Pull the brake lever to push the pistons into the wrapped bleed block, then use a toe strap or zip tie to simulate hard
braking on the lever for 2 hrs.
9. Undo the toe strap or zip tie and remove the wrapped bleed block from the caliper
10. Inspect the entire system for any evidence of leaking mineral oil once again – leaking components must be replaced
a. A leak coming from the hose-side of a connecting bolt may be remedied with a new olive and insert
b. A leak coming from the caliper side of a banjo fitting may be remedied with replacement O-rings
c. Small dots of moisture on the paper towel or around the seam indicate a leaking caliper that must be replaced
When a cursory visual inspection shows oil leaking from one component or another, a diagnosis is automatic. Sometimes,
however, we are faced with situations in which there may be a leak, but it is not so severe as to be obvious. In these situations, it
is often possible to rule a leak in or out by performing a pressure test. The following may be taken as possibly indicating a leak:
• Wet dirt caked onto the edges of pads, pistons, the outside of the caliper, or at the connecting bolts
• Repeated contamination of brake pads
• System requires frequent bleeding
• Mineral oil is severely discolored and/or contains particulates
This pressure test should be performed only after a thorough visual inspection of the entire braking system has been
completed and any obvious leaks corrected, and after all connecting bolts, bleed ports, and bleed nipples have been checked
for proper tightness.
Tools Required
1. Proper protective equipment, including gloves and safety glasses
2. SHIMANO bleed block for the caliper in question
3. Isopropyl alcohol
4. Cotton swabs
5. Piston reset tool or plastic tire lever
6. Lint-free paper towels
7. Toe strap or zip tie
Procedure
1. Remove the wheel from the bicycle and the pads from the caliper
2. Remove caliper from bicycle
3. Inspect the caliper for any signs of a leak, such as mineral oil residue or caked/wet dirt
4. Perform piston cleaning service as shown in the standalone guide “Hydraulic Disc Brake – Caliper Service” and reset
the pistons
5. Inspect the lever for any signs of a leak, such as mineral oil residue or caked/wet dirt, paying close attention to areas
under bracket or connecting bolt covers, the back side of the master cylinder piston, the edges of the reservoir, and
the connecting bolt
6. Clean the lever assembly with isopropyl alcohol, using a cotton swab to get into tight spaces
7. Wrap the bleed block with a clean paper towel and install into the caliper
8. Pull the brake lever to push the pistons into the wrapped bleed block, then use a toe strap or zip tie to simulate hard
braking on the lever for 2 hrs.
9. Undo the toe strap or zip tie and remove the wrapped bleed block from the caliper
10. Inspect the entire system for any evidence of leaking mineral oil once again – leaking components must be replaced
a. A leak coming from the hose-side of a connecting bolt may be remedied with a new olive and insert
b. A leak coming from the caliper side of a banjo fitting may be remedied with replacement O-rings
c. Small dots of moisture on the paper towel or around the seam indicate a leaking caliper that must be replaced
