Rebuilding calipers

rwthomas1

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Joined
Jun 6, 2020
Messages
1,162
Location
Rhode Island, USA
Bike
'01 ST1100 non-ABS
Hello,
Had a front brake dragging when cold so I disassembled and cleaned all three calipers while the wheels are off for new tires. The pistons had some corrosion. One at a time I pressed them out as far as I dared with brake pressure. Then used a long, thin strip of green scotchbrite dipped in brake fluid to clean them up. Gently used a razor blade to dislodge the stubborn chunks. Cleaned up nicely, but I assume the corrosion will return. Still have to flush the system but that will have to wait for the wheels.

I'm assuming this is a temporary fix, trying to get through the season. Planning on a full rebuild this winter. Looks like Honda stock type pistons are available or stainless steel aftermarket. Stainless seems like a no-brainer. Is there a preferred supplier? I see several different vendors....

Thanks, RT
 
I recommend Honda pistons and seals, and regular maintenance/fluid R&R. If you can’t press the individual pistons in by hand it’s time for a rebuild with new seal sets. Those pistons may clean up well with very fine polishing compound on a buffing wheel. BTDT

John
 
Piston corrosion is good to sort out, but you'll probably find that there is some alloy corrosion taking place in the seal grooves in the caliper which is making the seal a tighter fit than desirable.
 
BTDT! If they're still tight you'll need to take the pistion out, take out the seals, and then clean out the grooves behind the seals with a brush or a pick. (dremel tool and dental picks)
 
Well, thanks for the replies. The pistons move, but not really well by hand. I'm guessing there's corrosion in the seal grooves. Ugg. I was hoping to get to riding again soon. I'll probably reassemble since I shouldn't leave it torn down where it is for much longer. Get all the parts together and do all of them at once. RT
 
If you have corrosion in your caliper's bores (pistons, too) then you might double check the SMC. It's not advisable to try to rebuild this, a new SMC is still available and not exorbitantly priced.
 
SMSW said:
If you have corrosion in your caliper's bores (pistons, too) then you might double check the SMC. It's not advisable to try to rebuild this, a new SMC is still available and not exorbitantly priced.
Click to expand...
Non-ABS, didn't think it has, nor do I see a SMC?
RT
 
TerryS said:
You are pardoned, some of the 1100's use linked brakes like the 1300 and so do have SMCs.
Click to expand...
Ok, please educate me. What years did 1100's have an SMC? Or did they offer it as an option and mix SMC's with ABS or not? My apologies for hijacking this thread.
 
SMSW said:
Ok, please educate me. What years did 1100's have an SMC? Or did they offer it as an option and mix SMC's with ABS or not? My apologies for hijacking this thread.
Click to expand...
1996 and on ST110s had ABSII as on option, which had linked brakes with an SMC up front. More ST1100 info here.
 
Looks like I got lucky. The cleaning made a huge difference. No dragging anymore. New pads, flushed fluid, and brakes feel great. Hopefully I can get through the season and do a complete rebuild over the winter. Thanks all, I'm going riding!

RT
 
Don't use anything metal to clean the seal grooves - if the grooves are scratched, the seals may not seal properly. With the seals removed, the pistons should slide easily in the bores, BTW.

I like to liberally coat the seals & grooves with silicone dielectric grease to help prevent the corrosion build-up. Corrosion behind the seals is what makes the pistons tight and will cause brake drag.
 
Update:
Thought I dodged the bullet, but nope. Yesterday went to pushback the bike and the front calipers were grabbing. Got the seals, but the dealer only had two pistons in stock. Removed calipers, broke them down, scraped/cleaned out the crud, new seals and reassembled. There was corrosion in the seal grooves and the cylinder area between the seals. Once I cleaned it all up, the pistons fit nicely. Bolt it all back together, bleed and test ride.

For anyone that hasn't done this job, its pretty easy. The calipers come off in 15min or less. Put a putty knife across the piston "clamp" area, and blow the pistons out with compressed air. The putty knife is thin enough that the pistons are almost completely out, and can be removed by hand. Use picks, small screwdriver, etc. and CAREFULLY remove the seals. Don't scratch, scrape or dent anything. I used a tool I made a while ago, a flathead screwdriver with about a 1/4" of the tip bent over at a 90* angle, to GENTLY scrape the seal grooves. Remove the crap, don't scratch up the metal. Then a plastic brush, brakekleen spray and compressed air does the rest. Check piston fit when all is clean, should be nice and smooth. I had to scrape the area between the seals, again, gently, but it worked fine. My one mistake, I didn't have any "red rubber grease" on hand, so assembled with fresh brake fluid. The grease would help keep future corrosion at bay, so I will likely teardown again over the winter. Probably go to stainless pistons at that point as well. The calipers were a bit over an hour total for both, so its pretty quick. Another thing that makes the piston re-insertion easy is take a deep socket, whatever fits tightest in the piston cup ID, put a six inch extension on the deep socket and use it as a driver to push the piston back in. The extra reach and control afforded by the deep socket/extension handle, gently rocking in a slight circular motion, the pistons slide right in easily.

I'll probably look for a second set of calipers to rebuild and have on hand, and just swap them when the time comes. Pretty simple job.

RT
 
Good job !

Recommendation is for silicone (or red rubber) grease on the dust seal surfaces. Brake fluid in the fluid seal. When I clean the caliper pistons I pump them out a bit further than they need, shoelace them clean and shoelace red rubber grease on the exposed bits before pushing them in enough to fit the pads.

An old metal dental probe is an excellent spear for fishing out the seals. They aren't being reused, so I stick the sharp end at an angle into the rubber, and winkle them out.
 
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Just rebuilt my enitre ABSII bike, with new lines and ceramic pads. Its definitely worth the price of mind when taking a fast corner.

And all that stemmed from having a sticky piston on the rear caliper lol.

For anyone willing to get the most out of their brakes I highly recommend ceramic pads. The HH pads are too noisy and carbon/kevlar pads will stop your bike sometime in the bear future.
 
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