Author Topic: Stuck Caliper Piston and Hanger Pin Removal Tips ( ST1100\ST1300 ) **  (Read 7929 times)

Offline KoTAOW

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Problem(s) and solution(s) during a Caliper Rebuild:

1) Stuck hanger pin
2) Stuck caliper piston


Stuck Hanger Pin

Suggestions by Michael Martin:  

... try using an electric heat gun to heat the caliper body up to try to get the pin loose.  Apparently someone assembled it without using an anti-seize lubricant.  I'm afraid you will have to replace the piston if you used pliers on it.

There are some tips on the rebuild process here:


Comments from John Oosterhuis:

Here's some pictures:
Sorry, haven't gotten around to properly captioning them yet...

Here's some more:

Buy a new hanger pin, I replace mine every 35K or so.  Put a vice grip on the shank of the stuck one to 'assist' its unsticking.  Smiley

If the plier marks on the piston are on the last 1/8" or so, an area that probably won't have to slide by the outer dust seal (and certainly not the inner fluid seal) you may be OK.

Don't forget to get new copper washers for when you install the brake lines onto the replacement calipers.


Comments by Ted Norris:

If you look at the bottom of the Allen™ wrench you'll see that it's rounded, grind it flat, doing this really helps the wrench hold rather than tend to clime out of the bolt also don't be afraid to put some real heat on the alum. in that area, alum dissipates He so fast that there's little chance that you will damage anything, securely hold the caliper and when loosening the bolt give it a good snap and it will probe start to loosen.


Comments by WJ Bertrand:

I think a male hex key on a 3/8" drive would  be a lot more rigid and may allow you to get that pin turning.


Comments by Tony Pepenella:

Male hex socket on impact hammer.

Use manual impact hammer - you can control the 'collision' better.  

« Last Edit: January 22, 2013, 05:45:28 PM by Tom Melnik »

Offline KoTAOW

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Re: Stuck Caliper Piston and Hanger Pin Removal Tips ( ST1100\ST1300 )
« Reply #1 on: April 26, 2009, 05:35:02 PM »
Stuck Caliper Piston

Comments by Tom Melnik:

Using air pressure is the easiest way to get out the pistons.  Use different thickness wood blocks to keep the pistons from flying across the room, and inject air into the brake line hole and they should start moving in small steps.  You will need to insert the brake bleeder to plug up that hole. Work each piston out in steps.  Make sure BOTH pistons stay sealed or it won't work.  In other words, if you take one piston out, then air pressure won't work on the remaining one.

In leau of different thickness wood blocks, I use shims commonly bought for shimming doors and windows.

Be careful when injecting air, keep your fingers clear.  Sometimes when the pistons pop, they have a lot of force behind them.

Also, I would suggest investing in Speedbleeders™ at this point too and a MightVac™.

Be sure to lube up the piston seals and pistons with clean brake fluid before re-assembly.  And make sure to clean out all the gunk build up in the seal recesses.

Here's a link to a good article on bleeding motorcycle brakes:

Mike Martin's brake relining tips are also posted in the AOW:

Comments by Eric Russell:

Hydraulic pressure is more effective than air pressure (air being compressible). Either reconnect to the brake line or use a grease gun. The downside to using a grease gun is you'll need to get all the old grease out. The upside is a grease gun can apply tremendous force.

To connect a grease gun I've used plastic (nylon?) hose fittings screwed into the caliper. As long as the plastic fitting's threads are close it'll work OK. The plastic threads won't damage the threads in the caliper as long as you don't force it together.


Comments by Michael Martin:

If the air pressure doesn't work for you, then you were on the right track with using the brake master cylinder. That makes enough pressure to active the brakes, so logically it is enough to move the pistons.


Comments by Tom Melnik:

Sounds as if the grease gun method might be your last resort.

You'll need to replace the bleeder valve with a Zerk™ fitting ( grease fitting ) and plug the main port with a bolt.


.....leave the bleeder valve in and tight, get a metric bolt that fits the brake line port ( I'm guessing it's a 10mm ), cut the threads off, drilled a hole 7/32" all the way through the threaded section, and tap a 1/4"  28 UNF-2a thread and than add a standard grease zerk.

1/4"-28 UNF-2A Grease Fitting / Zerk Fitting =

THREAD/SCREW - Drill & Tap Chart

The grease gun can exert a lot of pressure, plus the grease won't compress like air.

If the pistons are REALLY stuck, and the gun can't hold onto the Zerk™ fitting enough, then you could try unscrewing the end of the grease gun off, and then make an adapter so that the grease gun hose would screw into the caliper brake line hole.  A standard grease gun hose has 1/8" pipe threads.
(National Pipe Threads)

NPT Size  Tap Drill Size (in.)  (Decimal) (in.)
1/16 - 27      "C"                    (0.242)
1/8 - 27       "Q"                   (0.332)
1/4 - 18        7/16                  (0.438)


Comments by Jed Gregory:

I did almost nearly exactly as described above.  I bought a 10mm bolt (I forget, but I think it's 1.25 pitch) and drilled it out with a 7/32" for about 1/2" deep, then drilled a smaller hole the rest of the way through.  I tapped the 7/32" hole with a 1/4" 28 thread and added a zerk fitting.  Total cost: $1.51.  I also purchased a brand new grease gun tip so I wasn't using a worn out tip to make sure it wouldn't pop off the zerk.

Let me tell you, it was AWESOME! The pistons came out nice and slowly and didn't hesitate to start coming out either. 
They came out almost like they weren't stuck at all. 

Here's a picture of the aforementioned tool: