Rear Brake Piston Removal

Joined
Nov 25, 2013
Messages
7
Location
los angeles
Bike
ST-1100
After changing my brakes I'm experiencing some light seizing as others have on my 97 ABS ST1100. The rear wheel will usually spin freely while on the center stand, but now it will only spin about a quarter of a turn with a foot pressure spin. So I cleaned the pistons with brake fluid and a toothbrush until no more grime was coming back on the brush, then dried the pistons off with a rag, but still no luck (while pistons where sticking out and caliper on). The middle piston didn't seem to ever move out. Seemed like only the outer two would alternate if I pushed one in with fingers, the other would come out. Must I fully remove the pistons and clean inside? I've never had them out and cant find much information about how to remove the pistons themselves. I suspect its the pistons or SMC after research on the site here. Any help on how these pistons come out would be much appreciated, Id like to pull the rear wheel off and try to clean again with the pistons out.

Thank you,

Aidan
 
Joined
Mar 13, 2012
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5,045
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soCal
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'97 ST1100
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687
The middle piston didn't seem to ever move out. Seemed like only the outer two would alternate if I pushed one in with fingers, the other would come out.
Did you ever add brake fluid to the reservoir after the pads were partially worn? What you describe sounds like you have too much brake fluid in the reservoir so you're not able to retract the pistons sufficiently to provide enough clearance to work properly with the brand new pads. Remove a little brake fluid from the reservoir and try pushing the pistons back in again.
 

Firstpeke

NT1100D
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Okay, gven you have a '97 ST1100 and are talking a three piston caliper, it is an ABS2 bike.... the two outer pistons are operated by the SMC on the front left fork by the left front caliper moving when either the front or rear brake is applied.

The two centre pistons on the front calipers are operated by the rear pedal, but require a reasonable push on the pedal to make them work due to other components in the system.

The left front caliper, when the wheel is rotating, then moves upwards activating the Secondary Master Cylinder (SMC) which operates the two OUTER pistons on the rear caliper.

The rear brake pedal only operates the centre piston on the rear caliper AND the two front caliper centre pistons.

The front brake lever only operates the two outer pistons on both front calipers and when the front wheel is rotating, will operate the two outer pistons on the rear caliper....

No amount of front brake lever pulling will move the rear brake outer pistons if the bike is standing still and the front wheel is not rotating.

With the rear caliper removed from the mounting, to remove the pistons to clean them, the centre can be removed by pushing the rear brake pedal gently until the centre piston is far enough out to carefully pull it out of the cylinder... do this over a basin or deep tray with rags covering any paintwork to protect it from the brake fluid that is going to come out of the caliper.

To remove the outer pistons, have someone hold the caliper over the aforementioned tray/basin and then gently grasp the left front caliper an move it upwards to activate the SMC, have the person holding the caliper watch the pistons to tell you when to stop.... before they fall out.... same as before gently pull the pistons one at a time from the caliper.

Once cleaned, the caliper and pistons can be re-assembled with new seals if required positioned in the grooves in the caliper, use red rubber grease to coat the seals before refitting the pistons.... push the pistons carefully back in to the caliper.

When cleaning the caliper make sure the seal grooves are properly cleaned out.

You may want to leave the master cylinder top on to prevent all the fluid draining out, or you may wish to remove it and drain all the fluid and clean out the master cylinders.

If doing an ABS bike you need to do both front and rear ends and bleed both brakes properly as well as following the procedure for ABS brake bleeding....

This can be found in the technical section, I believe!

I have only detailed a small part of the whole process, make sure you read and understand the whole process before starting.....
 
Last edited:
Joined
Mar 13, 2012
Messages
5,045
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'97 ST1100
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687
I doesn't look like too much fluid, just under the full mark Dwalby.
Disregard my original comment, I'm not familiar with the ABSII brakes. I read the part about three rear pistons, but somehow forgot about that and replied anyway.

A couple more comments while I'm replying. If your brakes are binding, one cause could be corrosion on the pistons preventing them from retracting properly. Since you live in LA, is this a SoCal bike since new? We don't get much road grime to corrode brake pistons, and I've never personally noticed it being a problem on any of my bikes riding for 35 years in SoCal, but I guess its possible. Sounds like you've cleaned them up reasonably well already, with the possible exception of the middle piston. The other possibility would be as I mentioned before, excess pressure in the system preventing the pistons from retracting far enough to make room for the new thicker pads. Its easy on the non-ABS bikes, which is what I described. For ABSII you're going to have to read up a bit on how to remove pressure from all the various master cylinders that could be applying force to the pads, use FirstPeke's advice as a starting point.
 
OP
OP
Joined
Nov 25, 2013
Messages
7
Location
los angeles
Bike
ST-1100
A couple more comments while I'm replying.
As far as i know its been in SoCal for 90% of its life, I cleaned the middle piston today prior to reading all the comments, it now rotates almost 100% freely, but still 10-20% drag compared to when I release some fluid pressure from the bolts on the rear caliper and it spins 100%. I'll try taking all three completely out and get back to you. Thanks so much for the recommendations.



All the best,

Aidan
 

ST1100Y

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Once cleaned, the caliper and pistons can be re-assembled with new seals...
...
When cleaning the caliper make sure the seal grooves are properly cleaned out.
As our Scottish friend already wrote...
Cleaning the pistons alone is only like ~30% of the job... they most likely will seize again soon... if not right away...

Once those calliper pistons get stiff to push back (noticeable during preflight-checks, any time the wheels come out, the annual MOT, while washing the rig...), I always make a full overhaul: pistons (replace if they'd suffered scores or show pitting corrosion, noticeable due dark spots which won't wipe off), rings, cleaning the calliper bores/grooves, any while at it possible also install overhaul kits for the master cylinders...
After cleaning I assemble the rings and pistons with dedicated brake assembly paste (dunno if "red rubber lube" is certified for being in contact with brake fluid :confused:)
Depending on usage, riding distances and climate conditions is this job only required every couple of years, maybe once a decade...
While at it: remove the brake lever from the frame to clean and lube the pivot... its an exposed but unseen, thus neglected part...
And if a rig is like 15 or even 20 years old, new brake hoses are also well worth considering...
 
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