Rear Brake Caliper - Stuck Again!

[rickt]

I finally summoned the courage to rebuild the rear brake caliper on my '78 GS750 restoration project. This bike was parked (in a garage) in 1981 and wasn't touched until I took ownership in the Fall of 2006. The caliper came apart easily enough, but that is where the fun began. I've had success in the past removing the pistons from the caliper body with compressed air. Indeed this method did work for the front caliper from the same bike. Not quite so fortunate with the rear. They appear to be really stuck - even with carefull application of adjustable pliers I could not get the piston to turn in the bore. I filled both reservoirs with PB Blaster and set them aside.

Any ideas on how to free these buggers?

rickt

[Road_Clam]

I finally summoned the courage to rebuild the rear brake caliper on my '78 GS750 restoration project. This bike was parked (in a garage) in 1981 and wasn't touched until I took ownership in the Fall of 2006. The caliper came apart easily enough, but that is where the fun began. I've had success in the past removing the pistons from the caliper body with compressed air. Indeed this method did work for the front caliper from the same bike. Not quite so fortunate with the rear. They appear to be really stuck - even with carefull application of adjustable pliers I could not get the piston to turn in the bore. I filled both reservoirs with PB Blaster and set them aside.

Any ideas on how to free these buggers?

rickt

How about hooking up the master cyl. and using hydraulic pressure to blow the piston out? Sounds like the caliper is badly corroded. You might end up trashing the whole caliper. A sticking caliper is a tell tale sign you have moisture in the system, and it has corroded the piston.

[bradleymaynar]

How about hooking up the master cyl. and using hydraulic pressure to blow the piston out?

That'd be my suggestion. The hydraulic force should be enough to force them out. Not to mention that the manual I have strongly advises NOT to do this when replacing the front pads for this very reason.

Brad bt

[rickt]

That will be the method I'll have to try if all else fails. My problem is that I have the entire rear brake assembly removed and I would like to apply paint to the frame before I put the brake components back into place. So I may try more soaking and air pressure. I don't believe the pistons are seriously rusted or corroded based on the appearance of the rear master cylinder. I suspect that the difficultly is being caused by the gummy residue that forms from brake fluid that has sat for 26 years in an unused brake system. The front caliper was "gummed" up in much the same way, but several good blasts of high-pressure air freed the pistons.

rickt

[Greg O.]

I have another idea that I have used to free stuck pistons in antique engines. Fabricate a grease fitting to fit the caliper, and then pump grease into it. Much safer than compressed air. A grease gun can produce about 2000 psi.

Greg O.

[anikmankar]

Try soaking the full caliper in break fluid for couple of hours and then try using the compressed air...

[rickt]

Wondering if anyone has used heat to free caliper pistons. It works pretty well for other frozen metal parts. Thinking about warming the caliper around the piston with a good heat gun or maybe even a plumber's torch and then trying to blow those miserable pistons out. I might even consider plopping some dry ice into the piston cavity after the caliper has been warmed. This should work the expansion with heat / contraction with cold for maximum benefit.

rickt

[t3rmin]

Just use the method being discussed in the appearance forum right now! Gas vapors ignited should provide the necessary pressure to break those puppies free!


Just kidding of course! ;-)

[KEITH KRAUSE]

How much PSI did you try? Maybe you just need more if your compressor can provide it.
Be sure to put a thick rag in there to stop the piston from being damaged.

[rickt]

Thanks to all for the suggestions. I reassembled the caliper and upped the pressure on my compressor. This worked for the inner piston. The outer piston remained "stuck." I took the caliper apart and screwed a standard grease fitting into the bleeder hole. I plugged the hole that transfers brake fluid between the caliper halfs with a rubber plug clamped with a C-clamp and pumped in grease with my trusty grease gun. Sure enough, the piston moved slowly, but surely out of the caliper. After cleaning everything up, I concluded that the pistons and the caliper were salvageable. A little work with the Dremel tool and a wire brush removed all the "junk" from the caliper. The pistons were smooth and clean.

Just a word of advice for those contamplating restoring a bike that has been sitting for many years (this GS750 sat for 26 years) - be prepared to deal with many parts that are frozen, corroded, or have otherwise been rendered unserviceable.

Thanks again for all the valuable suggestions.

rickt

[Zooks]

Beautiful

I have another idea that I have used to free stuck pistons in antique engines. Fabricate a grease fitting to fit the caliper, and then pump grease into it. Much safer than compressed air. A grease gun can produce about 2000 psi.

Greg O.

Been around workshops for more than twenty five years and I still learn something new every day. Thank you for this piece of brilliance.
I will remember this gem next time I need to free a stuck piston.

Grease - $10
Grease Gun - $25
Knowledge gained from the GSR - Priceless! \\/