Vanagon Brake Pedal sinking to the floor

[Bikechunks]

My brake sinks to the floor, I’ve already tried bleeding, and with no luck I’ve come to The Samba for answers. I was thinking it was maybe the brake master cylinder???

Here’s the video of my situation…
https://youtube.com/shorts/qXq91V_oVyo?feature=share

[E1]

Every time that pedal is released, it’s sucking in volumes more air.

Also possible that every time it’s pressed, it’s spraying brake fluid somewhere.

I think your diagnosis is spot on, blown master cylinder it seems, but someone else will remember the sound from an actual experience rivaling the horrors of hell.
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‘84 Westy, 2.1L with Digijet, 5.43 R+P, GT Gears
"Adding power makes you faster on the straights.
Subtracting weight makes you faster everywhere."
— Colin Chapman

[Crankey]

Isn't the clutch slave part of the system ? Seems to me I lost brake pedal and it was the clutch slave leaking. Long time ago. Not really sure about it.

[?Waldo?]

Leakage in the clutch system will not cause the brake system to accumulate air as the line from the reservoir that feeds the clutch is higher than the ports that feed the brake system.

If the pedal is going to the floor AND the air is bled from the system AND the fluid is not leaking out of the system somewhere, then the issue is the master cylinder.

[sjbartnik]

[Bikechunks]

Update: I bought a new master cylinder and installed it. What is the best way to prime it? At the moment I’ve got everything set up but the pedal just goes to the floor and I know there’s fluid inside. Thanks!

[MarkWard]

Get a few rags under the master. Crack both hard lines and depress the brake pedal. Tighten lines and let pedal fully return. Repeat till you get brake fluid at the line fittings. You are now ready to bleed the brake system. Start RR then LR then RF and LF.
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[Bikechunks]

Thank you! That fixed the problem. I took the van on its first drive with new calipers, brake pads, new fluid, and new master cylinder and only a few brake pushed in I heard a loud pop and my brakes went dead. Lukily I was on a flat road but wow it scared me. My brand new Napa auto parts rotor blew a seal and sprayed brake fluid everywere. It’s all over my paint and the underside of the van. Brand new fluid too 😂

[MarkWard]

Rotor? Did you mean caliper? If so, the caliper may have been related to your pedal problem.
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[Bikechunks]

Woops my bad I did mean caliper. I think it just happened because after your advice, the problem went away. I just finished bleeding the whole system too

[MarkWard]

A caliper with a sticking piston or a poor fitting caliper seal could cause an unpredictable pedal. That it failed indicates there was an issue out of the box. Caliper seals failing even on 40 year old calipers is rare. It’s a very simple design. The dust boot may have been hiding the problem. I’m cheap and rebuild my calipers when needed. I did all 4 calipers recently on my barn find 911 without issues. Saved quite a bit of money over rebuilt ones and had control over the quality. I suppose you turned in your original calipers as cores? Generally I trust NAPA parts, but it’s likely they aren’t the ones actually rebuilding these parts. Water will wash the fluid off the paint and save it. Hope you already washed the paint. Sorry but at least no one was hurt.
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[Bikechunks]

Yeah I’m glad nobody was around. I actually only got the calipers a week ago so so I still have the old ones. I’m going to talk to Napa about the issue and meanwhile throw in my old caliper.

[MarkWard]

As long as the original caliper piston is not super rusted, yours are relatively easy to reseal. BD or VC likely has the seal kits. You’ll be surprised how simple it is. Get some brake assembly paste for the new seal.
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[Sodo]

I’m having a hard time believing a caliper seal could ever “blowout”.
Knowing how they’re built……
Brake design is highly refined, statistically reliable. All you have to do is “drive around” to see how reliable brakes are.
(Count all the other cars that are stopping reliably.)

Brake diagnostics by typing alone is a risky endeavor.
We can see that you’re a quick learner
….but we can’t see what you __don’t__ know.

Need pics of the caliper and pads and assembly.
A pic of where the “fluid came out from” is important here, not to be omitted.

If you’re going to do brake diagnostics by typing alone, and learn brake mechanics in parallel, then go drive 5,000 lbs at 60 mph, I recommend you slow down a little on the repair.
Post some pics of your progress, and give a little time for replies.

===== ……. OK onward ……. =====

[Bikechunks]

Here’s the video… I have yet to take things apart to figure out where it’s coming from, but once I find some time I’ll upgrade you guys.

https://youtube.com/shorts/AJ7Inc793cw?feature=share

[Sodo]

Link


Video is even better than pics.
OK I’ll agree now…… that’s conclusive its leaking at the caliper seals !
Good job communicating to your people!!

I suppose it was improper assembly of the caliper.
I can’t imagine what would “pop” though.
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'90 Westy EJ25, 2Peloquins, 3knobs, pressure-oiled GT mainshaft, filtered, cooled gearbox
'87 Tintop w 47k 53k, '12 SmallCar EJ25, cooled filtered gearbox
....KTMs, GasGas, SPOT mtb

[MarkWard]

A stuck piston could make a popping sound when it became unstuck. If the new dust boot had a good fit, it could have made a sound when it popped from brake fluid pressure. Both stretch diagnosis for a sound I didn’t hear.
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