Brake fluid not coming out

[Sarcvicious]

I’m trying to get all the brake fluid out of the bike (there’s brown fluid in the rear m/c). Followed the steps that I would do on any other bike (hose on bleeder valve, connected to trash receptacle. Pump the brake, crack the bleeder value, close bleeder value, release brake).

No fluid is coming out of the bleeder value at all. Since the entire brake system needs to be redone, im
only concerned about getting the fluid out, rather than worrying about air getting in.

any suggestions on how to proceed?

1982 GS650 G

[grcamna2]

The front brake master cylinder or the rear master cyl:which one is not pumping-out the fluid ?
Do you have any close-up pics of the master cylinders ?

[Sarcvicious]

Well technically fluid hasn’t come out of either MC when I tried to bleed the brakes, but the front MC resevior is empty, so I just assumed that there was no brake fluid in there (probably a naive assumption). There was no pressure in the system in the front (no resistance when I pulled the brake lever in),

The issue is with the rear MC

https://postimg.cc/hQXDKmw8

[Rijko]

Why not take the brakes off as is, and just take them apart ?

[Rich82GS750TZ]

Agreed. Time to disassemble and clean/rebuild calipers and MCs, install new SS brake lines.

[Sarcvicious]

Why not take the brakes off as is, and just take them apart ?

Because we’re trying to establish a baseline, see if there was pressure on the line, parts moving in the caliper etc, before jumping to the most expensive solution.

Regardless, shouldn’t the fluid be removed before disassembling everything?

[rphillips]

If there's resistance (pressure) on the pedal, there's pressure somewhere. Start farthest away & work backwards. First open the bleeder, if nothing then loosen the banjo bolt on caliper, if nothing there loosen banjo on MC...Just say'in, you are keeping pressure on pedal while opening bleeder ain't you??

[Rijko]

I’m trying to get all the brake fluid out of the bike (there’s brown fluid in the rear m/c). Followed the steps that I would do on any other bike (hose on bleeder valve, connected to trash receptacle. Pump the brake, crack the bleeder value, close bleeder value, release brake).

No fluid is coming out of the bleeder value at all. Since the entire brake system needs to be redone, im
only concerned about getting the fluid out, rather than worrying about air getting in.

any suggestions on how to proceed?

1982 GS650 G

Because we’re trying to establish a baseline, see if there was pressure on the line, parts moving in the caliper etc, before jumping to the most expensive solution.

Regardless, shouldn’t the fluid be removed before disassembling everything?

Establishing a baseline is not what you asked.
And I think your original goal makes sense.
Redo the system.
You already have baseline :
an old non-functional system that needs complete overhaul.

And no, you cannot bleed the system completely by pumping the MC.
Take off the brake system as a whole : unscrew all components and let the brake fluid coming out bleed off in some container.
Now you are ready for that full redo you had planned.

[Nessism]

There is no baseline when the brake system is full of sludge.

As Rich stated: remove calipers, pop out the pistons, pull plunger out of mater cylinder, clean everything out and consider replacing seals (and the pistons and master if the bore is corroded,) and replace brake lines which are also full of sludge which can't be cleaned.

[Sarcvicious]

Thank y’all for the help!

Next question- I already sourced a front MC on eBay that was “pulled off a functional gs650”. Is my best bet to do the same thing for the rear mc? I know I need to replace all the brake lines & inspect the calipers, but do I need to replacing the master cylinders as well? If the OEMs are better than aftermarket, what do I need to ask the seller to make sure I’m getting an mc that’s in ok shape?

[Nessism]

The problem with used 40 year old master cylinders is there is often corrosion inside which causes pitting in the body rendering the master useless and not suitable for rebuilding.

For a 650 you need a master with a 5/8" or 16mm bore. You can find tons of options on ebay. A late model Kawasaki EX650 master is a good target, the version with a mirror threaded lug, because they are relatively new and not subject to as much corrosion. Or, get a generic master. The cheap chinese masters are okay since a master cylinder is a simple device. Needless to say you should inspect the bore of your existing master before assuming it's bad. Same thing for the calipers; you need to remove the pistons and look for pitting and corrosion. If you have damage and want to replace the seals get OEM Suzuki parts, not crappy aftermarket parts like K&L which basically suck. It pays to stay close to home when it comes to brake system parts. For brake lines, check out the Earls line thread here on this forum. Making your own lines is cheaper than most prebuilts and the parts are made in USA and high quality.

[grcamna2]

If there's resistance (pressure) on the pedal, there's pressure somewhere. Start farthest away & work backwards. First open the bleeder, if nothing then loosen the banjo bolt on caliper, if nothing there loosen banjo on MC...Just say'in, you are keeping pressure on pedal while opening bleeder ain't you??

Have you tried this yet ?
This is a good way to trace the problem.The master cylinder itself may not be pumping but that will be determined(at the end)by this procedure.

[Maddevill]

Just completely remove the bleed screw and see if it or the caliper are plugged. Often the bleeder screw itself is plugged.
Simple stuff first.

Mad

[Sarcvicious]

Edited to change question-

so when do I know when a caliper is reslly
beyond repair. This entire thing is gummed up. I can’t get the piston out and accidentally tore the dust cap. The braking system is in conplete disrepair ��

edit 2- got the piston out w the compressed air trick. But I’m still not sure how to tell if a good cleaning is all the caliper needs or whether I need a need a new one.

is changing the seals/gaskets enough?

[Nessism]

Inspect the piston for pitting in the chrome. If pitted, replace it. During reassembly replace the dust boot and caliper seals. Use OEM Suzuki parts, NOT K&L unless you absolutely have to.

https://www.partzilla.com/catalog/suzuki/motorcycle/1982/gs650g/front-calipers-model-z