Hey everyone,
Yesterday I decided it was a good time to replace my rear brake pads. When I did that I had a lot of trouble getting the pistons back into the caliper. I used the "old brake pads + screwdriver method" I was able to get one piston more into the caliper but not far enough to fit the new brake pads and the other piston had no movement.
Today I tried to pump out the pistons a little bit in order to clean the pistons.
Here comes the problem
In the photo you can see that the rubber is loose, in the pic its not very visible but there is rust and other gunk around the piston. I also only have brake cleaner and as far as I know that stuff damages rubber.
I am pretty sure I will have take out the caliper and open it up, might as well get a rebuild kit. My question however is if anyone had this or a similar problem, they could give me some advice/tips of.
Thanks
Doeplidoep
The rubber bit is the dust seal rather than the main caliper seal so not utterly critical - I recently rebuilt two front calipers where some previous owner had completely omitted the dust seal for quite some time. Its not great having it loose as the piston will be that much more exposed but the dust seal isn't doing the main job of the caliper seal.
If its seized up a bit on one side you might be able to get it moving by jamming the opposite side in place, couple of bits of wooden or something against the stuck-sides far edges, this way all the master cylinder effort is focussed on the stuck piston and might unstick it. You can then work the pistons out a bit, the wind them back in a few times to see if they'll free off on their own. If you can get a few wooden shims in the recess of the piston (the exposed hole bit) A g-clamp works well as a rewind tool.
(https://wd46dg.dm.files.1drv.com/y4m3PW5N5IB4f5oq-WHF7QVFw1usZdOd1tgBQZn6IzwI-jpICMzs2yUmBpoHukniIAd6Cgjjv4ODoBq595LYxhXMI6MJk6eHMSsA9AxXIxZYgVjyKjRGB1iumaBn0zuFmUQ5Ibrhkx1NMcnQZ9v-hSomKhyN7Kejo-mdCpO73Z4aGfpGKc7GUZK-ng2cH-G0UMVgQRNUhaOxe-eZF9RA8o0GA?width=1003&height=973&cropmode=none)
Ideally you'll be able to pump out the pistons, getting them to 70% out, jamming one side and popping the another clean out then gently pulling the other out by hand. Replacing the seals is easy but use something like red-rubber grease and clean up the recesses where the seals live. you can clean up minor rust and pock marks on the piston with fine wire wool but if its all pitted and scored and wrecked you'll probably need a replacement.
You'll almost certainly need to get the pistons out to replace the dust seal though - but might get away with not having to split the caliper.
I've done this job three times on the front caliper and one in the back caliper, cause I like to soak parts in diesel to clean them. Diesel destroys brake rubber parts.
Howto:
- 1: disassemble the caliper from the bike.
- 2: remove the pads.
- 3: The hardest part: Get the pistons removed. I use to apply pressure to the pump (lever or pedal, front or back) and refill the reservoir if required. Using a wood piece and a clamp you can lock one of the pistons to get the other one moving. You can use WD40 (that will not damage rubber parts) to unstuck the pistons.
NEVER use PLIERS that could scratch the surface of the pistons. If a piston is scratched, discard the piston and get a new one.
- 4: Once the pistons are removed, clean the mess before it is too late, your wife will regret your motorcycle hobby, and you will regret the stains on the rim.
- 5: Use a wooden pincho skewer to remove rubber dustseal and piston seal.
- 6: If you split the caliper, consider replacing the rubber seal between the two halves. Use OEM parts or quality replacement. Tourmax work well, OEM work better.
- 7: Use the wooden pincho skewer to clean the seal and dustseal seating area. Some use a dremel and a plastic brush. Never use a stainless steel brush or you will ruin the seats. A rag of cloth will complete the required cleaning. Since caliper is made of aluminium, a caliper that has had a lot of water, will have aluminium rust (white crystals) that are a pain to remove or smooth, and usuallly are located in the dustseal seats.
- 8: Clean the pistons. Use WD40 to clean them. Check surface for any imperfections. Use a blue scotch bite to clean. Any rust or scratch will cause the piston to stick, and ruin rubber seal. Discard if any doubt.
- 9: eBay red brake grease to lube and improve sealing in: rubber seal seating, rubber dustseal seating, rubber seal lips and piston surface. A tiny amount will do. This grease will prevent caliper body rust inside dustseal seats, and will smoothen piston movement.
- 10: insert the seals and dustseals. Very easy.
- 11: insert pistons, that if properly lubed, will extremely easy get in. Push to bottom.
- 12: reasemble caliper halves if you had to split, remember to replace seal.
- 13: reattach the brake hose
- 14: replace pads
- 15: reassemble caliper to bike
- 16: do a bleed operation.