Frozen Rear Brake Caliper?

My back brake had been sticking, the bike is a new purchase and had been sitting for 18 months.

I have the rear brake caliper off of the bike.

I removed the pads, pulled the two bolts and removed it from the arm that connects it to the axle.

I cannot get the piston to move. It wont budge. I rapped it with a wooden dowel and mallet through the aperture for the back brake disk, nothing.

Then I hooked up to the master cylinder again to use it to push the piston out. Would have been better with three hands. Still nothing.

I want to get this thing apart to see why it is sticking.

Suggestions?

You might want to hook up an air hose to the caliper's brake line inlet and use the compressed air to force it out. But for safety's sake use a c-clamp to prevent the cup from shooting out when you apply air pressure. Try soaking it in penetrating oil and let it soak for a few days before attempting this. If the cup still refuses to come out while under compressed air, rap the caliper gently with a hard plastic mallet to start the cup's removal.

Things to think about when you try this,

1. Safety Glasses,
2. Use c-clamp (this is a must!)
3. Start with low air pressure and step it up gradually as you work out the piston cup with the plactic mallet.
4. Use penetrating oil to lossen corrosion.


Finally, this is a must ... get a Sailor's Dictonary of cuss words. It may come in handy.

unomike wrote:

You might want to hook up an air hose to the caliper's brake line inlet and use the compressed air to force it out. But for safety's sake use a c-clamp to prevent the cup from shooting out when you apply air pressure. Try soaking it in penetrating oil and let it soak for a few days before attempting this. If the cup still refuses to come out while under compressed air, rap the caliper gently with a hard plastic mallet to start the cup's removal.

Things to think about when you try this,

1. Safety Glasses,
2. Use c-clamp (this is a must!)
3. Start with low air pressure and step it up gradually as you work out the piston cup with the plactic mallet.
4. Use penetrating oil to lossen corrosion.


Finally, this is a must ... get a Sailor's Dictonary of cuss words. It may come in handy.

Am not quite understanding about the c-clamp, in thinking the idea is to let the piston shoot out from application of air pressure. And not wanting a c-clamp to be holding the piston in position while attempting to remove the piston. :S

Have been using a rag or wood slat as exit cushion, keeping fingers clear, and air blasting away.

Anyhow, let us know if the air pressure method fails, and we'll get to the drastic more desperate methods. :woohoo:

Good Luck!

try compressing the piston back in to the caliper with a c clamp. or a caliper compressor.

or the compressed air through the line inlet method works great too, you'll need about 100psi id say just to be sure, with a piece of wood that the piston can hit and not get damaged when it shoots out.
watch your fingers though, it'll bust em!

Ive done that on stuck car pistons, it works every time.

Luke

Excellent! Thanks all.

The C-clamp is to keep the piston contained, not secured. just like the rag or piece of wood that was also suggested.

My only worry is that the piston is stuck in the 100% fully retracted position. If I hammer down when it is already down then I am both spinning my wheels and possibly damaging the part.

The piston is probably 3/16 of an inch up extended laterally past the rubber grommet that is past the plane of the caliper housing. The piston and grommet together are a half inch out past the caliper housing. I am going to take a peek at my other bike to see if this position is partially extended. Then I am going to whack it with a mallet. (I don't have an air compressor, Christmas is coming guys)

This appears to be out far enough that it should be ok to hammer on it.

I'll get a pic.

1) penetrating oil for a few days, replenish and move around, THEN............

2) try a temperature extreme -- freezer, then the air gun

3) or could try an oven then air gun, and since you're rebuilding it anyway -- non-metal parts damaged by the oven *may* (I did say *may* here), *may* not matter to you
(why I'd try #2 and the air gun first...)

It's probably oxidation of the metal that's making it stick. A combo of temp, oil and air pressure should
pop that sucker outta there like a BOO-SNAPPY!!!

I don't think it was meant that you hit the piston with the hammer, but rather tap the side of the caliper housing to help dislodge the piston. I have found that soaking a piston with a penatrating oil for just a few days will often work on it's own with just brake fluid pressure. Worse case scenerio you can always find another caliper.

Got it out with your help all, thank you. I used another brake master cylinder and mallet taps.

Crusty, mung covered dirty metal.

I soaked the rubber parts in gasoline (It was the 18 month old stuff that I drained out of the gas tank. I was trying to recycle.) and it seems to have "bloated" the inner O ring and louvered rubber protective outer gasket dust seal.

Read here i one of my manuals...

"Use only brake fluid, isopropyl or ethyl alcohol to clean brake parts.... gasoline, motor oil or any other petroleum distillate will cause deterioration of the rubber parts"

Well whoop-dee friggin doo, I guess I am buying me a rebuild kit tomorrow...