More rear braking problems w the GS 650

[Grimly]

Wrote a comprehensive answer and the auto save didn't save the info and deleted my answer before i replied when i was looking for some confirming info..................This site has some bad features.........Sorry i can't write it again.

Basically the piston looks to be still in there.

That's caught me out a couple of times - leaving the page to look something up on another tab, an on return, it's gone. Not even auto-saved as a draft.
Right now, the content I'm typing has been auto-saved, but has it really.

[steve murdoch]

As BigT mentioned, a grease gun is an effective method of forcing a stuck piston.

https://www.thegsresources.com/_forum/showthread.php?261026-GS1000G-Rear-Master-Cylinder-replacement&highlight=grease+and+piston

[Rich82GS750TZ]

If you want your pics to show up in the forum, on the IBB page, you have to go to the Embed codes (bottom Left) and copy the BBCode-full image, and paste it into your post.

[Cipher]

As BigT mentioned, a grease gun is an effective method of forcing a stuck piston.
https://www.thegsresources.com/_foru...ase+and+piston

I assume grease a mix of liquids and solids being virtually incompressible is the key

[Sarcvicious]

If you want your pics to show up in the forum, on the IBB page, you have to go to the Embed codes (bottom Left) and copy the BBCode-full image, and paste it into your post.

thank you! I knew there were instructions somewhere.

[Sarcvicious]

Wrote a comprehensive answer and the auto save didn't save the info and deleted my answer before i replied when i was looking for some confirming info..................This site has some bad features.........Sorry i can't write it again.

Basically the piston looks to be still in there.

yes this is an absolute nightmare. I’m considering looking for a new part on eBay. My man is saying we just need to drill it out, but he’s got to be careful since it’s a machined part. Damn braking system! Between the wiring gremlins and this stuck piston, this rebuild is really throwing us some curveballs

[Cipher]

yes this is an absolute nightmare. I’m considering looking for a new part on eBay. My man is saying we just need to drill it out, but he’s got to be careful since it’s a machined part. Damn braking system! Between the wiring gremlins and this stuck piston, this rebuild is really throwing us some curveballs

Id try the grease especially if your guy is not a machinist.
Theres a reason heavy equipment uses fluids instead of pneumatics
I saw one on ebay last night forget the price but getting it machined would likley cost more than a good used one

[Gorminrider]

I just use the brake itself to pump the pistons out...perhaps you take reverse that and take the caliper off and push the pistons in with a wedge of wood or clamps ..or, hook another Master cylinder up ...

but I see what looks like a piece of ring in there too.
Your photo shows all the parts including #2 from the part diagram so How could it be in the cylinder? Are these parts from somewhere else?

[Sarcvicious]

I just use the brake itself to pump the pistons out...perhaps you take reverse that and take the caliper off and push the pistons in with a wedge of wood or clamps ..or, hook another Master cylinder up ...

but I see what looks like a piece of ring in there too.
Your photo shows all the parts including #2 from the part diagram so How could it be in the cylinder? Are these parts from somewhere else?

Yes, it’s a rebuild kit w the OEM parts

He drilled out the piston already (he’s a tradesman)…. I’ll try the rebuild kit on this part and if the rear caliper still isn’t engaging w the rebuilt master cylinder, I’ll check out eBay and hope the replacement parts ordered aren’t also seal shut w decades old brake fluid

[Sarcvicious]

Alright I’m back to this post. So we rebuilt the yoke, but the rebuild kit didn’t come with instructions. I posted a picture above with the order I put the different components together. Used a c clamp and vice grip to get the c clip back in, however now the spring isn’t compressing/decompressing. I think the rubber cap on the bottom spring isn’t lined up correctly OR I have the order of the pegs out of order.

But there’s also a third hypothesis that maybe the spring doesn’t compress much until there’s pressure on the line?

any ideas?

[Big T]

Put the brake lever back on and clamp the MC back on the handlebar. It should move then

[Sarcvicious]

This is the rear master cylinder. Same concept? Hook it all back up and pump the break to see if the spring moves?