Debris in brake fluid from brake caliper

[Tomioka]

I used a clean water bottle to catch the brake fluid coming out of the bleeder as I compress the caliper pistons into it's bore. I've been seeing a lot of DIY videos where the mech or worker does not open the bleeder to let the old fluid out and instead pushes the fluid back into the reservoir but not without the debris going though the ABS pump and orifices.

This is on a 02 Silverado w/ dual piston rear disc brakes. Performing annual inspection and lube from brake sticking issues common in these trucks. This time I am trying out CRC De-Squeak to alleviate squealing from these Wagner ThermoQuiet brake pads along with grease behind the pads.

 

[Ducked]

Well, yeh. But as first-squirt expelled brake fluid goes, that's pretty shiny.

 

[andyd]

Any gunk in a brake system collects at the lowest point due to gravity. That is up against the bleeders. Why on earth push the gunk all the way back through the system when it is all collected at the bleeder? No fancy pressure tools involved. 2'of tubing and a little BF in an empty jar. Rig that and pump the pedal by hand. Or just let it drip into a can. When I open up a brake system, I have a qt of fresh fluid. Stuff is cheap. I pump about 6 oz out of each bleeder. The extra is for the air lock and eventualities. This method takes longer, than the 2 person pump and bleed, but I found it gives a better pedal. If a brake system was designed to be reverse flushed, why isn't there a bleeder on the master cylinder?

PS The incidental dirt may be from setting up the bleed. I agree with Ducked, BF looks pretty good. How old is it?

 

[Tomioka]

Originally Posted By: andyd
PS The incidental dirt may be from setting up the bleed. I agree with Ducked, BF looks pretty good. How old is it?

Didn't think of that also. The dust cap is gone so dirt might have collected in there too. The fluid is about a year old so while I'm at the rear brakes I'll bleed out the whole system and top it off.

 

[Ducked]

Originally Posted By: Kibitoshin
Originally Posted By: andyd
PS The incidental dirt may be from setting up the bleed. I agree with Ducked, BF looks pretty good. How old is it?

The dust cap is gone so dirt might have collected in there too.


Yeh, those do seem to get away, and I don't know where I'd get replacements here. I cover them with a few layers of aluminium foil and then press a tyre valve cap over it. Not as good but perhaps better than nothing.

 

[Ducked]

Originally Posted By: andyd
Any gunk in a brake system collects at the lowest point due to gravity. That is up against the bleeders. Why on earth push the gunk all the way back through the system when it is all collected at the bleeder?....If a brake system was designed to be reverse flushed, why isn't there a bleeder on the master cylinder?


I generally do reverse-flush lately, using a syringe. A possible answer to your "why no bleeder" question might be that there isn't a need for one, since the fluid reservoir has a free surface. This doesn't of course imply that the system is designed to be reverse flushed, but it can work.

For a partial "maintenance" bleed I remove the bottom 20 mls from the reservoir, then remove the first 10 mls via the bleeder then cycle another 10 mls in and out a few times, discard, and replace with 20 fresh.

If the system has been fully drained cycling seems to be a very efficient way of getting air out of it.

I've only used this method with my current car, which does not have ABS.

 

[Ducked]

Originally Posted By: andyd
Any gunk in a brake system collects at the lowest point due to gravity. That is up against the bleeders.


Unfortunately, that's not exactly true. The lowest point on calipers is generally the bottom of the caliper bore, and quite aggressive cycling of fluid via the bleeders does not flush it out. To thoroughly clean out calipers and wheel cylinders you need to strip them.