Rear brake caliper piston will not fully retract any ideas? Or just rebuild &/or replace?

[SubjectX]

Greetings,

long time lurking, but I guess my time has now come and I need your help, fellow peeps.

On a RS, 2010, with 15,000 km, the rear brakes are working fine-ish, but the disc is glazed and there is a constant sound of grinding when turning the rear wheel.

So I decided to replace the pads and sand down the disc a bit to remove the glazing.

All is fine, but when it came to retracting the piston back into the flush position, since I couldn't install the caliper with new, thicker pads (but only for like 0.7mm thicker), it wont budge for the last 2mm. It compresses on the handle and on the parking brake, but always 2mm remains outside of the caliper.

The pads, still original, are not worn at all, maybe 0.7mm thinner than the new pads. Their surface has a similar roughness to the new ones.

I'm from Europe.

I guess the caliper with piston needs to be rebuilt, at least two separate AIs suggested that before getting a whole replacement. In Slovenia, I can no longer find any service places, that will work with this old model, thus I'm stuck in DIY mode.

I can take the caliper apart, but I would need to source spare parts in advance. Can anybody comment on my plan and/or point me to the correct rear caliper seal kit?

Also, while we are here, which engine oil, apart from that really expensive OEM labeled one, should be put into my Spyder?

 

[Snowbelt Spyder]

Apologies if you have already done all of this. Most common reason for this is that the internal parking brake mechanism still needs to be retracted further. You say it compresses on the handle and the parking brake, but not sure what you meant by that. In 2010, depending on when your bike was built, it had either a lever and spring or a cable pulley wheel that operates the parking brake. In either case, these components need to be completely removed from the splined shaft. Then turn the splined shaft fully counter clock-wise by hand until it stops. Don't worry, it won't fall out. The piston still may not retract perfectly flush after that, but it will be in far enough to get a new set of pads on.

To my knowledge, there were no spare parts or rebuild kits ever produced, but you could source a used caliper from various places such as eBay. Some have also mentioned that a Ural Gear Up model uses the same caliper. Good Luck.

 

[SubjectX]

Thank you very much, will give it a go in the evening.