CP4527 - 'Seal In Bore' - 'Boot type Seal' - Replacement seal kit

Brake calipers are a safety-critical item and AP Racing recommends that calipers be reconditioned and piston seals inspected regularly to maintain optimum performance. Where calipers have been subjected to high temperatures or have been used in adverse conditions e.g. Off Road / Rallying, the calipers should be reconditioned and seals replaced more frequently to ensure that safety and performance levels are maintained. When cleaning calipers use warm soapy water or an alcohol based cleaning fluid e.g. Methylated Spirits.

DO NOT USE PETROL, GASOLINE OR MINERAL OIL CLEANER / LUBRICATE as this will damage the seals. Replacement seal kits are available for all AP Racing brake calipers. Depending on the seal type being replaced the following recommended procedures should be followed.

1. Use a reaction block selected to fill the full width of the caliper pathway as shown in Fig. 1. This block must span the length of the caliper opening and be well supported between the brake pad abutments at either end of the caliper.
2. Loosely insert a hydraulic fitting (M10x1.0) into the caliper feed port as shown in Fig. 2 (a spare Bleed Screw loosely fitted will suffice). Do not tighten to form a seal.
3. Press a hand held air gun against the fitting as shown in Fig. 3 and allow a short, high pressure burst of air to enter the caliper (a perfect seal between the air gun and fitting is neither necessary or advisable). Keep all body parts away from escaping air and caliper pistons.
4. A single burst of air should be sufficient to extend all pistons at once as shown in Fig. 4. If one or more pistons remain jammed in the caliper body after repeating this step then the caliper may need to be returned to AP Racing for assessment. 
5. Remove reaction block. It is possible that the dirt seals may become detached from the caliper body at this point. If so the pistons can be carefully pulled from the caliper body with dirt seals attached. It is also possible that the dirt seal may become detached from the piston in which case the piston should be pulled through the dirt seal to remove. Where dirt seal remains attached to both piston and caliper body a small blunt instrument (such as a rounded off screwdriver, see Fig. 10) should be used to carefully release the dirt seal from the piston, as shown in Fig. 5.
6. Fig.6 shows the pistons removed with dirt seals remaining attached to the caliper body.
7. The dirt seal can now be removed by carefully inserting a narrow, blunt blade (such as a medium sized screwdriver) through the seal opening and between the outer ring of the seal and the back wall of the dirt seal recess as shown in Fig.7. By gently turning the screwdriver the seal should work free. Only very light force is required to perform this operation. Never use excessive force as damage to caliper body may result.
8. Once dirt seal is removed the pressure seal will be exposed, located in the groove in the caliper body as shown in Fig. 8.
9. Using the small blunt instrument from step 5 (see Fig. 10), carefully remove the pressure seal from the caliper body as shown in Fig. 9.
10. All dirt and pressure seals should be removed from the caliper by following the above procedure. Before new seals are fitted all pistons and the caliper body should be inspected for damage. If damage of any kind is present on either the caliper bores or piston outer diameters the caliper should be considered unfit for use and either replaced of returned to AP Racing for assessment. 
    
    Refitting:
    
    
11. Before re-assembly ensure that all parts are perfectly clean and free from debris or moisture. Replacement pressure seals should be soaked in AP Racing brake fluid for 30 minutes prior to fitment. Do not remove excess brake fluid as the excess will aid fitment of pistons. Do not soak dirt seals.
12. Carefully fit pressure seal into groove in caliper body ensuring that it seats correctly in the groove. Seal should be free from damage and not be twisted or kinked. Pre-assemble dirt seal on piston (seal locates in groove on piston end). Carefully slide piston into caliper bore (pressure seal must already have been installed as shown in Fig. 11. Only light pressure applied by hand is required. If piston does not slide easily into place, remove and inspect parts. 
13. The dirt seals can now be pressed into caliper body. Carefully locate seal in caliper body using finger pressure only. Then select a suitable rigid, flat bar or similar as shown in Fig. 12, and position to cover dirt seal.
14. Apply slow and even pressure to dirt seal using bar as shown in Fig. 13, care must be taken to ensure that dirt seal is inserted square to the caliper body.
15. On correct installation the dirt seal should sit flush with the caliper body as shown in Fig. 14. Repeat steps 12 to 15 to fit all remaining pistons and seals. Once calipers are refitted to vehicle a pressure test should be carried out to check for leaks. With the engine running press the brake pedal and hold at a constant load for 60 seconds. No ‘sinking’ of the brake pedal should occur. If the pedal does ‘sink’ (travel further when under constant/steady load) it should be considered that a leak in the brake system is present. If a leak is suspected check all hydraulic joints and inspect re-conditioned calipers. The repair kit may also contain 2 off small ‘O’Rings for the replacement of Bleed Screw seals where fitted. There may also be replacement Bleed Screw dust caps included. Where included these parts should be fitted to the brake caliper. 

N.B. Excessive force should not be necessary. If the piston does not slide smoothly into bore remove & check seal has been fitted correctly.

Part Numbering

• Two letters after Kit indicates 4 seals - e.g. -JJ
• Bore Identification Letters:
• A - 25.40mm (1.00")
• B - 26.00mm
• C - 27.00mm (1.06")
• D - 28.60mm (1.125")
• E - 31.80mm (1.25")
• F - 34.00mm
• G - 34.90mm (1.375")
• H - 36.00mm
• J - 38.10mm (1.50")
• K - 41.30mm (1.625")
• L - 44.5mm (1.75")
• M - 47.60mm (1.875")
• N - 50.80mm (2.00")