RZ350 - Rear Caliper Overhaul
The rear calipers on my RZ350 are the single opposing caliper type. This means they have a single caliper and pad on each side of the disk rotor, and a static inside pad.
To remove the caliper from the frame, loosen the two retaining bolts. Also disconnect the hydraulic line while the caliper is still connected to the frame. Once the caliper is free of the frame, pry off the plastic cover at the top which exposes the brake pad system.
I left the hydraulic loine connected in these pictures but it is much easier to remove it beforehand. With the plastic cover off you can see the two pins that hold the brake pads in place. The parts manual also shows an anti-rattle spring under the cover but mine didn't have it. I'll update this section if it makes a huge difference installing one.
The retaining pins are held in place with small clips at one end. Remove the clips with needlenose pliers.
Then slide both pins out of the caliper casting.
The brake pads along with the small clip on shims can now be removed from the caliper.
I tried to uise compressed air to force the calipers out but found that only one or the other would come all the way out. The Yamaha and Haynes manual both say never to split the caliper halves but I couldn't figure out another way to dislodeg each caliper individualy... so I went ahead and split the halves by removing the two large bolts on either side of the caliper piston.
The caliper split easily and I found two rubber seals that connect the two halves and allow hydraulic fluid from one side to the other. I cut up an old inner tube and sandwiched it between the two halves to effectively block the hole. This way I could blast compressed air in the bleed hole to free one caliper, and the hydraulic line to free the other. It worked like a treat. Always cover the claiper piston with a rag to make sure it doesn't go flying when it pops out.
Once the calipers were out I could look out the outer dust seal (upper ring) and the hydraulic piston seal (lower ring) to determine if they should be replaced. Both seals looked rough and had turned over edges in some places so I ordered new parts and set about the replacement.
..and it finally came out but was not able to be reused. At this point the internal spring in the piston will push the pison parts out of the casting.
Remove them from the casting but keep good notes on the order in which they need to be reassembled. First is the spring, then a rubber cap, then the metal piston casting with a rubber seal around it.
The rebuild kit from Yamaha contains all new rubber parts, a new metal piston casting, a spring, and a new circlip.
The new seal needs to be installed over the metal piston casting in the direction shown. I found the easiest way to do this was to slide it over the small end (to the right above) and then stretch it over the first ridge.
Build the parts up in the same way that the old ones were removed. Use a little clean hydraulic fluid to lubricate the seals.
Insert the entire assembly into the master cylinder housing. I sanded down the casting with steel wool and refinished the metal with special casing paint. If you do the same, be sure to tape off all holes and openings to keep paint out of the working areas.
Push the piston assembly in and refit the new circlip. This is easy to do with circlip pliers because you can get access to the clip ends but these become partially hidden when installed. Finally fit the new dust seal and refit the single small lever spring.
Refit the lever with some grease around the pivot point and the point where the lever makes contact with the end of the master cylinder piston. Tighten the pinch bolt and refit the brake switch if it was removed during the rebuild.