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While I have the front end torn apart to rebuilt the fork tubes I inspected the brakes. Theres lots of wear left in the pads but I noticed the exposed portions ofboth pistons appear to be badly corroded to the point of having a flakey surface. While riding the bike I noticed no problems with the braking action. Can the pistons be repaired (cleaned up)or should they be replaced? Is there a kit available to rebuild the calipers?
 

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I just ordered a rebuild kit and 4 new pistons. I also ordered 2 new pad sets for safe measure.
 

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I did a caliper rebuild on all three of my calipers on my 83 Interstate. It was SO easy, except for one piston that got bound up because I pushed it in without cleaning it first (crud got stuck behind the seal, made it hard to extract). I have good pics and experience here, so let me know if I can help.

Jack
 

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I rebuilt all 3 calipers on my bike this past Spring, the rear one had a good bit dirt inside the caliper. I only rebuilt the front master cylinder with new parts, all the rest I just disassembled and cleaned. I used a buffing wheel and polished the pistons before I reinstalled them.

If the GL1200 is anything like my '83 with the same type of brakes, beware that the front 2 calipers may have different size pistons in them. The front brake caliper had large pistons, the one linked with the back brake had smaller pistons than the other front.

Raymond
 

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Can anyone confirm the difference in the piston sizes left and right? The parts listings I have available to me only show the one part number for pistons.
 

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The first place I checked. They only show the one part number for pistons.
 

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mjpliv wrote:
Can anyone confirm the difference in the piston sizes left and right? The parts listings I have available to me only show the one part number for pistons.
The pistons are in fact different sizes on the 1100, but I'm unable to confirm the difference for 1200s.

Jack
 

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The pistons are only different on the '83 1100. Due to the new "unified" braking system.

Raymond
 

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mjpliv wrote:
Can anyone confirm the difference in the piston sizes left and right? The parts listings I have available to me only show the one part number for pistons.
On the 1200 series, the right front disc has different size piston/seals, I believe they are the smaller ones. ??? The left front, and the rear share the same size seals and pads. These are the two calipers in the integrated system. Manual is in the saddle-bag/pannier, so I can't give specific details for sizes. Good Luck
 

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I've got it....! Right front caliper piston: 25.310 mm (0.9965 in). Left front &rear caliper piston: 31.940 mm (1.2575 in)... Looks to me like the really are different.. Hope this helps... ;)
 

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Yeah, just like I said.

Hey Shooter the Guru, you got your left and right mixed up.

Raymond
 

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Silicon Sam wrote:
Yeah, just like I said.

Hey Shooter the Guru, you got your left and right mixed up.

Raymond

Now Ray, if you're gonn'a point fingers; I'll take my ball and go home.... :D
 

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The later GL110s with the linked brakes are similar. Smaller pistons in one front caliper (the linked one).
 

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Just like you stated, lots of crud and stuff. However, I posted a note in regard to not being able to bleed the front right side? Any ideas are appreciated since I just spent over 5 hours rebuilding both front calipers and puting on new pads, just to have the frustration of still not being able to ride as the whole right-side is not bled, nor fixed as far as spongy pedal.
 

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/forums/images/emoticons/tongue.gif If after a rebuild you STILL cannot bleed the brakes.. heavy sigh .. then you have air in the lines... or a bubble in the rebuilt caliber. In principal , regular bleeding should get rid of the bubble...but after several hours... (Been there,Done That !!!)  one can get discouraged..  Three tricks...  1) /forums/images/emoticons/confused.gif Tiny bubble ...sometimes the "bubble" is in the entrance to the line in the master.. and can be seen ...  take a tiny paperclip, and pop it out , under the fluid.... sometimes a tiny bubble can be made to "dissolve" in the lines by taking tape, applying the brake hard , taping it down,and leaving it overnight... brake lever applied....2) /forums/images/emoticons/shock.gif Medium Bubble.....Once I had to  borrow a friends "Mity Vac" to help me suck the bubble out of the  middle of the line... one hour of bleeding,and I still had not removed it ...its a nifty tool,and if you bleed a lot.. worth the investment..3) /forums/images/emoticons/mad.gif Its never happened to me.. but I have heard that after a rebuild , there can be a big , trapped bubble of air ,in the caliper itself..that got there after you re-assembled...  Others may correct me.. but I think the cure was to add some fluid on the bench, and do a partial bleed on the bench , rotating the caliber, as you do , trying to get the air out .... before you install it... You pays your money,you takes your choice,I guess Silverdave/forums/images/emoticons/emoticonsxtra/cooldj.gif
 

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All the linked brake models have different size pistons in the front calipers. The reason is to prevent front wheel lockup with pressure on the rear brake pedal. You can reuse cruddy brake pistons if the crud will polish off. It depends on whether they are pitted or not. If pitted, they will eat the seals and leak. If you can polish them smooth then they can be reused. I've cleaned up automotive caliper pistons using a brass wire wheel followed by 600 grit wet paper. I have a wood lathe handy, wish it were a metal lathe, and make up dowels for a snug fit into the piston so I can chuck it in a drill press. Real fine paper or crocus cloth or Never Dull leaves them smooth at the proverbial baby's butt.
 
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