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> OK I need some brake help.., Dammit
914werke
post Jul 11 2026, 05:31 PM
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So Ive done a lot of brakes, but this is the first time Ive experienced this one.

Had a OE MC fail, got my hands on one of the NEW 17mm units, Replaced F. calipers with rebuilt, + all the soft lines, the MC & the (Blue) res. line sections.
All went as expected. No drama just the typical PITA installing the MC.
Went about bleeding & got the pedal to near the point I thought I was done when testing a full pressure hold ...the pedal travel "breaks" & continues to the floor.
(IMG:style_emoticons/default/headbang.gif)
I think Ive got a leak but inspection shows its all still dry... (IMG:style_emoticons/default/blink.gif)
Can a MC fail internally?
Anyone witha BTDT?
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Ninja
post Jul 11 2026, 05:51 PM
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The aftermarket (usually Chinese) ones do all of the time.

Sometimes they wait 2 to 3 weeks and only fail when your customer really needs it...

Do the pressure/fails/drops to floorboard a few times.

See if master fluid level stays the same.

If so, they only thing can it can be doing is internal bypass in the master.

Bad master!

I LOATHE aftermarket stuff now...
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914Sixer
post Jul 11 2026, 06:05 PM
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Rich,
Did you bleed the MC before installing? I can send you one of my aftermarket German ones to try.
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914werke
post Jul 11 2026, 06:07 PM
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QUOTE(Ninja @ Jul 11 2026, 04:51 PM) *
pressure/fails/drops to floorboard a few times.
See if master fluid level stays the same.
If so, they only thing can it can be doing is internal bypass in the master.
Bad master!

Help me out the plunger circuit is a Aluminum piece with a pair of wiper seals, behind it is a pretty beefy spring? What fails, the spring?
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914werke
post Jul 11 2026, 06:08 PM
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QUOTE(914Sixer @ Jul 11 2026, 05:05 PM) *

Rich,
Did you bleed the MC before installing? I can send you one of my aftermarket German ones to try.

I did. (IMG:style_emoticons/default/wacko.gif)
Edit: pulled the wheel, pedal board & the cluster plunger rod .... now has .5 or more travel before it contacts the plunger
(IMG:style_emoticons/default/chair.gif) WTH! Depressing the pedal there is a definite *break* in the travel feels like a mechanical failure. (IMG:style_emoticons/default/headbang.gif) (IMG:style_emoticons/default/popcorn[1].gif)
Mark Ill take you up on that offer.
Now I gotta recall where this one came from.
(IMG:style_emoticons/default/dry.gif)
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914werke
post Jul 11 2026, 06:40 PM
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Superhawk996
post Jul 11 2026, 06:43 PM
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QUOTE(914werke @ Jul 11 2026, 08:07 PM) *

QUOTE(Ninja @ Jul 11 2026, 04:51 PM) *
pressure/fails/drops to floorboard a few times.
See if master fluid level stays the same.
If so, they only thing can it can be doing is internal bypass in the master.
Bad master!

Help me out the plunger circuit is a Aluminum piece with a pair of wiper seals, behind it is a pretty beefy spring? What fails, the spring?

It’s usually the seals that fail and allow an internal bypass
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SO.O.C914er
post Jul 11 2026, 07:30 PM
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QUOTE(914werke @ Jul 11 2026, 07:40 PM) *

Attached Image

Breathe Rich breathe help is on the way! I see Superhawk has zeroed in so good hands.
(IMG:style_emoticons/default/popcorn[1].gif) (IMG:style_emoticons/default/shades.gif)
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SO.O.C914er
post Jul 11 2026, 07:31 PM
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Oh and I’m saving this most interesting man.
That is outrageous!
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Superhawk996
post Jul 11 2026, 07:56 PM
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QUOTE(914werke @ Jul 11 2026, 07:40 PM) *

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The problem is that I was a brake engineer for 4 years and I can completely sympathize with the meme graphic I’m stealing that one. (IMG:style_emoticons/default/av-943.gif)

Based on Rich’s description it almost sounds like there may be a flaw in the casting that represent the point at which the pedal fails. If there is some sort of casting flaw or surface finish problem it will eventually chew up the seal. Could also explain why he was able to get it bled initially but then it failed when trying to finish up.

Said differently it sounds like it is OK initially and building pressure but at some portion of the pedal travel the seal encounters a casting flaw and then rapidly leaks down as a circuit failure.

The problem is to figure it out is a (IMG:style_emoticons/default/stromberg.gif) ton of work and I’m sure Rich just wants the job done and to get paid. Who has time for trying to root cause the failure of a new part that was just supposed to work.

This enshitification of everything is getting old real fast.
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Front yard mechanic
post Jul 11 2026, 08:35 PM
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Make sure the plunger is seated properly
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bkrantz
post Jul 11 2026, 08:56 PM
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QUOTE(Superhawk996 @ Jul 11 2026, 07:56 PM) *

QUOTE(914werke @ Jul 11 2026, 07:40 PM) *

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This enshitification of everything is getting old real fast.


Faster than my old man aging-grouchiness.
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mgp4591
post Jul 12 2026, 12:09 AM
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I've had a little experience with this sort of crap, so I sympathize 100%. The next thing I'd do is isolate the problem to verify what's actually wrong. Using the correct brake line clamps, clamp all 4 of the soft lines to isolate the m/c, then pump the pedal and see how it feels. If it sinks to the floor and you didn't bench bleed it, you can still remove the lines from the m/c, have someone pump the pedal while you hold a finger over each of the ports and let any air get released. Try it again after screwing in the lines and doing a quick pump to purge any air from the line connections, then see how the pedal feels. If it still sinks, that's a bad m/c...if it feels better, take the r.r. clamp off and bleed it again. Then remove the l.r. clamp and repeat, then the r.f., then the l.f. That should about cover it. Oh, and while you're bleeding the rears, pump the pedal while actuating the parking brake...that can jar loose any other air bubbles that may be hiding out.
Hope this helps.
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rjames
post Jul 12 2026, 01:30 AM
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Sorry, Rich! As if the fun of replacing the brake system wasn’t enough on its own.
I would like to know if the MC you have is the same brand that I bought somewhat recently. If so, I think several were sold. Mine was put on the shelf for a future install. I wonder if anyone has had problems.
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