Brake Fluid keeps coming out dirty

[DSA]

This is one I haven't encountered before...Just bled the front brakes, no issues. With the rear - I started by sucking out the cruddy old fluid, removing the base plate inside the reservoir (though I left the reservoir on the bike), then cleaned out the reservoir with new fluid and a paper towel. Then, re-filled with fresh fluid and started bleeding. I've now been through several (5? 10? reservoir-fulls of brake fluid, and the fluid coming out is still brown and gross.
Do I need to open up and clean up the master cylinder? The brake pedal is firm and the brakes appear to be working perfectly, but I can't imagine it's ok to have this fluid this dirty coming out.

[Fred Camper]

Have not seen that. I would start with the caliper as that seems like the biggest source of possible contamination since you already went after the reservoir. The rest of the Master and line cannot hold that much crud.

[Rat]

Unless the rubber portion of the brake line is rotted …

Gord

[pidjones]

Yep, sounds like the brake line is failing.

[joecoolsuncle]

is it a linked brake system? just sayin. but im on the bandwagon that says deteriated brake lines. first, bleed left front a few times, them bleed read some more, maybe the info you left out would have shown a linked system. ???

[Rat]

Yep … if it’s an 83 or 84 it is linked
Gord

[ritalz]

Helps to tell us what bike you are working on. Update your signature to include your bike(s).

[DSA]

My apologies, good point. This is a '76 GL1000, so no linked brakes. Oddly enough, both my other bikes (VFR and Blackbird) have linked brakes and while bleeding those is a pain in its own right, I've never encountered this particular issue with them.

[CYBORG]

I agree with pidjones. The rubber line is comong apart from the inside

[Sidecar Bob]

Have you rebuilt the master cylinder and caliper? If not you could be pumping out sludge from in one of them.

As for the brake line, manufacturers of rubber lines recommend replacing them at 5 year intervals. With the easy availability of stainless braided lines these days there is no excuse for not upgrading to lines that last practically forever.

[joecoolsuncle]

My apologies, good point. This is a '76 GL1000, so no linked brakes. Oddly enough, both my other bikes (VFR and Blackbird) have linked brakes and while bleeding those is a pain in its own right, I've never encountered this particular issue with them.

badabing! its 47 years old! get sum goodrich!