AP Racing CP2623 Master Cylinder Repair Kits, Fits CP2623, CP4400, CP4623, CP5623 & CP6093

Price range: $22.95 through $28.65

Bore Size

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AP Racing CP2623 master cylinder repair kits

The CP2623 repair kit from AP Racing reseals one master cylinder, and is stocked here in all nine bore sizes from 14 mm through 25.4 mm (1.00 in). Select your bore size above. These are genuine AP Racing kits listed under AP Racing part numbers, so what arrives is what AP stamps on the box.

A master cylinder that is weeping past its seals takes pedal feel with it long before it fails outright. If the bore is still serviceable, resealing costs a fraction of a new cylinder and puts the pedal back where it belongs.

What is in the kit

Each kit contains one of each of the five wearing parts needed to reseal one cylinder:

Primary seal- #4 in below diagram
Piston washer- #5
Secondary seal- #7
Circlip- #10
Boot- #11

Not included, and reused from your cylinder: body, spring guide pin, return spring, piston, push rod and piston stop washer. If any of those are worn or damaged, the cylinder needs replacing rather than resealing.

CP2623 repair kit exploded diagram, AP Racing master cylinder seal, washer, circlip and boot

AP Racing CP2623 cross-section. Items 4, 5, 7, 10 and 11 are supplied in the repair kit.

Bore sizes and part numbers

The kit is specific to the bore. The bore size is marked on the cylinder body – check the marking before ordering rather than measuring a worn bore.

Bore	Imperial	AP Racing part number
14.0 mm	0.551 in	CP2623-88RK
15.0 mm	0.590 in	CP2623-89RK
15.9 mm	5/8 in	CP2623-90RK
17.8 mm	0.700 in	CP2623-91RK
19.1 mm	3/4 in	CP2623-92RK
20.6 mm	13/16 in	CP2623-930RK
22.2 mm	7/8 in	CP2623-94RK
23.8 mm	15/16 in	CP2623-95RK
25.4 mm	1.00 in	CP2623-96RK

Fitment

One kit reseals a single cylinder. These are universal repair kits and fit the following AP Racing cylinder families in the matching bore, in brake or clutch use alike:

CP2623 – vertical flange mount, forged alloy body
CP4400
CP4623
CP5623
CP6093

Shopping for the cylinder itself? See the AP Racing CP2623 vertical flange mount master cylinder, available in the same nine bores.

CP2623 repair kit specifications

Manufacturer	AP Racing
Bore sizes offered	Nine, 14.0 mm to 25.4 mm (1.00 in)
Kit contents	Primary seal, piston washer, secondary seal, circlip, boot
Fits cylinders	CP2623, CP4400, CP4623, CP5623, CP6093
Service	Brake or clutch
Sold as	One kit reseals a single master cylinder

Fitting the kit

AP Racing’s procedure, abbreviated. Work clean, and lubricate every seal with fresh brake fluid before it goes near the bore.

Remove the rubber boot and the circlip.
Carefully withdraw the internal components.
Replace the primary seal, piston washer and secondary seal, taking care not to damage the new seals as they are fitted.
Check the bore is clean and free from debris.
Lubricate the bore with brake fluid.
Reassemble the internal components into the body.
Secure with the new circlip and fit the new boot to keep debris out.

Good to know

Check the bore first.	A repair kit only works if the bore is in good serviceable condition. Light staining cleans up with a rotary clean and a flush, but a scored bore means the cylinder needs replacing.
13/16 in is a superseded design.	AP Racing’s original 13/16 in primary seal is discontinued and the replacement is not interchangeable. The kit listed here is CP2623-930RK, which suits the current piston. A cylinder still running the old piston needs seal kit CP2623-930PRK (piston included) once, and CP2623-930RK for every rebuild after that. If you are unsure which piston is in your cylinder, contact us before ordering.
Always fit the new circlip and boot.	They are in the kit for a reason. A reused circlip can relax and a reused boot lets grit into the bore, which is what wore the seals out in the first place.
Rebuild on a schedule.	Master cylinders should be resealed as maintenance, not after a problem. Front-running teams reseal annually or at a set hour count, whichever comes first.
Fluid compatibility.	These seals are for DOT-rated brake fluid. They are not suitable for hydraulic oil or silicone-based fluid.