I have a CRG Ven brake system with weak pressure. I tried bleeding the caliper and no fluid was coming out the bleeders. So, I unhooked the brake line from the caliper, and squeezing the pedal there is still no fluid coming out (video). If I disconnect the brake line from the master cylinder, fluid does leak out.
Suspecting a clogged brake line, if I blow air into the hole, air does come out the other end. In the video, if I blow air into the brake line from the caliper side, bubbles come out from the master cylinder. Note that there was a lot of black gunk in there before I cleaned it.
My question: Why isn’t brake fluid flowing?
Note: I don’t normally mess with the brakes so it could be something stupid that I just don’t know.
I’d say the seals on the plunger are shot. You can dis assemble the plunger that pushes in and out of the master cylinder, it’s just a circlip. Put a new seal set on it and see.
Im my crg the oem Ceramic brakefluid was very dry. Changed couple times the ceramic with new ceramic fluid and situation didnt change. The pistons in the master cylinders had a lot of friction and didnt want to retract. Had black gunk in the reservoir too.
With another fluid the pistons retracted without friction. No more black gunk
Thanks, I will try buying a rebuild kit, kind of a pain to wait. FYI, the master cylinder is only about a year old. Though I bought this one new and just bolted it on. Am I supposed to grease the seals or anything like that?
I’m using Motul 5.1 fluid. The master cylinder says DOT 4 but I understand them to be cross-compatible. Hopefully that’s not causing the degradation.
I have used grease specially made for brake caliper seals during assembly
Your brake fluid should be fine. Does the master cylinder create pressure when the hose is removed? Check that first. Also is it possible the line became pinched or kinked at some point? If that checks out you may want to just disassemble, clean and reassemble. You can use the brake fluid as lube on reassembly.
Sometimes you need to put the cap on when bleeding. Give that a go if you haven’t already. just be sure to not let the reservoir drain, give it maybe 3-4 pumps, remove lid to check level, top off, replace lid and go again.
Oh, you need to move the pedal further. In the video it seems like the master cylinder piston hasn’t engaged in the bore yet… it’s in the self adjust/draw fluid position. Top off the reservoir, move the pedal slowly or it will spray back out the holes in the reservoir and get all over the powercoat
Welp, I put in a new rebuild kit (plunger/seals) and at least it bleeds normally with good pressure. When I took the plunger out, one of the two seals was still stuck inside, so it’s possible it came loose at some point and wasn’t doing anything. In any case, it was kind of a disaster inside so I’m happy to have cleaned it up. Thanks for the pointers!
Also, I’ve been overfilling the reservoir so maybe that caused problems.