Seized ST1100 rear brake

Zider drinker · 2025-12-30T07:16:15-0600

Pan has been out on drive for sometime and,though covered,the rear brake has seized.I obviously need to unseize it but don't want to damage it in the process.Any ideas beyond WD40?

Sunday Rider · 2025-12-30T07:30:38-0600

Can you move the back wheel at all?

SMSW · 2025-12-30T07:36:43-0600

I'm not familiar with the 1100 but I believe you do not have the Secondary Master Cylinder. It would help if you post the year and if it is ABS or not. Not knowing, I'd open the rear caliper bleed nipples to relieve pressure. If the wheel unlocks, then you have a return port blocked in the brake system. If it is still locked, then the caliper is frozen on its pins (it should slide side to side as the pads wear). In this case you will need to remove the rear caliper, clean and lube the pins and probably clean the pistons as well. Corrosion does not heal by itself.

It is a good idea to keep WD40 away from the brake caliper!

ST1100Y · 2025-12-30T08:09:02-0600

Zider drinker said:
Pan has been out on drive for sometime and,though covered,the rear brake has seized.I obviously need to unseize it but don't want to damage it in the process.

Definitely leave that WD40 can in the house...

I'd gentle pry the pads apart/pistons back just enough the caliper can be lifted off the rotor, preferable with a tool like this:

drain the brake fluid with an appropriate bleeding tool and familiarize myself with removal of the caliper bracket and the methodical process of rebuilding the caliper (replace rings, possible pistons as well...)

Normally it should by possible to push the pistons in by hand force only (grab rotor with fingers, apply firm pressure on caliper with your thumbs); anything beyond that indicates that a rebuild is due...

John OoSTerhuis · 2025-12-30T13:35:11-0600

ST1100Y said:
I'd gentle pry the pads apart/pistons back just enough the caliper can be lifted off the rotor, preferable with a tool like this:

Nice looking tool, Martin. Hadn’t seen one like that before. Looks like Mac Tools really likes theirs ($159 USD) and Walmart not so much ($39).

John

wizel · 2025-12-30T15:58:10-0600

https://www.louis-moto.co.uk/en/rothewald-disc-brake-piston-spreader-10003009?filter_article_number=10003009

holm from germany

Zider drinker · 2025-12-30T18:18:37-0600

Thanks to all,its a v early Pan 1100 1990.

Zider drinker · 2025-12-30T18:19:43-0600

SMSW said:
I'm not familiar with the 1100 but I believe you do not have the Secondary Master Cylinder. It would help if you post the year and if it is ABS or not. Not knowing, I'd open the rear caliper bleed nipples to relieve pressure. If the wheel unlocks, then you have a return port blocked in the brake system. If it is still locked, then the caliper is frozen on its pins (it should slide side to side as the pads wear). In this case you will need to remove the rear caliper, clean and lube the pins and probably clean the pistons as well. Corrosion does not heal by itself.

It is a good idea to keep WD40 away from the brake caliper!

Thanks this helps

Zider drinker · 2025-12-30T18:22:27-0600

Thanks for the link

ST1100Y · 2025-12-31T05:24:38-0600

John OoSTerhuis said:
... Walmart not so much ($39).

Beats scratches and possible other damage whilst attempting to pry a screwdriver or tire iron between rotor and pad...
Often there isn't enough space for any lever (like the rear brake on my GF's NT700VA, sandwiched between the not removable panniers)