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Brake pistons wont push back? 0_0

  • Thread starter Thread starter gpans
  • Start date Start date
G

gpans

Guest
1978 GS550E

I just finished partially restoring the bike and getting it running relatively smoothly when I decided I should take a look at the brake pads. They were worn, so I removed them (they were very, very tight) and I accidentally pumped the brakes so the pistons almost closed on the disk.
I managed to push the pistons back a little more so I can put a screwdriver head between the space, but it refuses to push back any more. Reading other posts it seems like it should be easy to push back these pistons, am I doing something wrong? No amount of pressure seems to make it easier.

I have tried pushing on each piston with the corresponding bleed screw both loosened and tightened. Fluid comes out when it is loosened, but the piston refuses to budge backwards. Will I need to disassemble the caliper, if so, how would I start that process?

Thanks so much guys!
 
Open the bleeders when you squeeze. If necessary use a channel lock or other wrench with some decent effort - closing the bleeder so as not to let air in when you stop squeezing. Piece of cake normally. You must have some rust in there holding it up. Maybe time for the rebuild you suggested doing?

Make sure you put the wrench on the center of the brake pad for even forces.
 
Last edited:
I had the same problem with the brake installed on my 79 GS550. Open the bleeder and use a C-clamp.

The source of the problem was in the master cylinder and resivoir. Moisture had gotten into the resivoir and rusted the hell out of the screw on the bottom that holds the resivoir to the master cylinder. The rust gets into the cylinder and jambs up the reliefe passages that lets the pressure off of the brake when you quit squeezing the handle.

Take the resivoir off of the cylinder and clean them both thoroughly. Reinstall the resivoir with an new screw and flush a few oz of fluid through the master cylinder. Then reinstall it on the bike and flush and bleed the line to to and through the caliper.
 
I keep trying that and it doesn't seem to be working unfortunately. They simply refuse to budge. However, if I tighten the bleeders I can feel the pistons start to compress toward the disk more, does this mean it can't be rust?

I know it shouldn't be a complicated procedure (especially after the several weeks of work I just did), but I might still be having trouble/doing it wrong...
Here is a cookbook list of steps I am doing:
1 opening both bleeder valves
2 wedging an object between disk and piston
3 wedging a flathead screwdriver between the other piston and the disk
4 pushing the pedal down slowly
5 trying to separate the piston and disk further using the screwdriver
 
I didn't get a chance to read czav's responce before I made my own...so ignore my last message. I'll try that out, thanks.
 
If you put pressure on one side of the pistons they tend to jam. Try to get even pressure on two opposite sides and it should slowly move in. They prefer being pushed in squarely.
 
I decided I would rather not mess with the master cylinder unless absolutely necessary, it's pretty ancient and the hose to the caliper seems to be stuck on anyways.

I tried moving both pistons at the same time but still no luck. Can I just disassemble the rear caliper and free up the pistons manually? How would I start to do that? Whenever I push the pedal, only one of the pistons moves towards the disk. I can always get that piston to move back however much it moved, but not any more. Any new ideas?
 
gpans said:
I decided I would rather not mess with the master cylinder unless absolutely necessary, it's pretty ancient and the hose to the caliper seems to be stuck on anyways.

I tried moving both pistons at the same time but still no luck. Can I just disassemble the rear caliper and free up the pistons manually? How would I start to do that? Whenever I push the pedal, only one of the pistons moves towards the disk. I can always get that piston to move back however much it moved, but not any more. Any new ideas?
Click to expand...

The piston is frozen. You might disassemble and free it up (find your manual online if you don't have it, pretty simple procedure). When you do that you might find the pison is all pitted , or rubber fittings shot and needs rebuild.
 
I figured it out, thanks again for the help guys!

For anyone reviewing this thread for help:
The manual was a great help in disassembling the calipers, it basically gave a step by step instructions. I had strange chrome caps to some of my hex bolts that ended up needing a small hex L-key to turn and get off. That part wasn't mentioned in the manual and it took me a few minutes to realize the rusted spots on the chrome caps could fit hex to get them off. Maybe you were much smarter than me and realized it right away, but knowing that might have helped someone.

One of the pistons in a caliper half was frozen and the other in its caliper half wasn't set right. The frozen one just took some cleaning, but the other was my fault. From pushing in it with the screwdriver the piston angled to the side and didn't seat properly, getting itself lodged in and immobile. It didn't look like it was angled from in the caliper, but it was so stuck I had to use the vice to free it (I just squeezed the caliper and piston together until it set properly). The underside of the pistons themselves were covered in black muck so I am glad I ran into this problem, it probably saved me from another disassembly later and I learned quite a bit about brakes.
 
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