Loss of Brake Pedal...your thoughts??

[Erock77]

On 2 separate occasions, we were traveling in our stock 84 Vanagon Westfalia on a trip, around 2+ hours I'd lose the brake pedal. Both times these were not downhill travels therefore I was not "riding" the brakes.

To describe the events, I would go to brake and the pedal would go to the floor but if I pumped it, they would return but felt stiff. It would stop me but it did not feel great. This would happen around the 2 hr mark of a trip. Most other trips we take are around that or shorter.

Brake fluid is full and not leaking anywhere. We just bled the brakes and clutch for the first time in years. We're about to head to Granny's and wanted any opinions on a Brake Booster possibly going bad? If so, where do you find them? I'd have to be certain that's it before purchasing. And if that all happened, I'd replace the master cylinder at the same time.

Any other thoughts on what may have caused this phenomenon?
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84 Westy = Bussey

"Seeking all that's still unsung" R. Hunter

[?Waldo?]

Brake booster going bad will not cause the pedal to go to the floor.

Causes of the pedal going to the floor are:

- bad master cylinder
- leaking slave cylinder/caliper
- mechanical issue that allows excessive movement of slave cylinder or caliper pistons or excessive movement at the pedal/master cylinder

Considering the issue appeared, disappeared, reappeared and if there aren't leaks or brake parts flopping around, then it is almost certain that the master cylinder is bad.

[Ahwahnee]

I don't think a failed booster would cause that.

In the absence of any leaks I strongly suspect the master cylinder.

They're easy enough to replace that were it mine I'd have at it. Otherwise, trying to diagnose a problem that is intermittent and possibly only occurs after hours of driving could be frustrating.

[hardway]

Another possibility for your loss of pedal is from boiling brake fluid. That it happens after extensive driving points in this direction. Anything that might cause a dragging brake might cause this. After driving for some distance check the hubs for heat. Driving with the parking brake not released will cause this. Fresh DOT 4 brake fluid will tolerate more heat.

[raygreenwood]

So....not going downhill and not riding the brakes. Ok....not overheating.

And anyway, typically brake fluid overheat turning to vapor will NOT cause total drop to the floor of the brake pedal....and when brake fluid overheating and vaporization happens, pumping it up will not help.

So, how old is your master cylinder.

What this sounds 100% like is one of either circuits....inner or outer....probably inner if it goes all the way to the floor......the inner u-cup seal on that circuit unit is failing and bypassing fluid toward the middle section of the piston.

The outer cup on each circuit prevents fluid from leaking out of that circuit. In the case of the inner piston, it's outermost seal prevents bypass of fluid into the outer piston area.

Likewise, the outermost seal on the outer circuit keeps fluid from bypassing and leaking all over your feet.

There are typically five seals inside of a dual circuit master cylinder. So far I have only mentioned four of them.
The fifth seal is the one that is usually mounted on the inner circuit piston (the inner piston generally has three seals)....and is facing rearward or outward. This seal keeps pressure generated by the outermost piston from bypassing into the inner circuit.

The two inner seals on each piston are the only seals that produced serious brake pressure.

What is happening is that with age, the EPDM rubber these seals are made from will typically increase its hardness (durometer) from about 45-50 Duro to about 55-60 duro. It makes the seals take on "compression set". They harden to the shape of the bore.
It makes them a little too stiff to properly inflated and seal the bore and generate pressure.

This is also the issue with about 90% of NOS master cylinders and is why they fail.

How old is your cylinder? I am not asking about miles. I mean years. It's a time issue.

Also, how often do you drive it and does it sit for long periods like months?

This is the failure point of NOS master cylinders as well. If they sit for long periods not being worked/flexed as the seals age....it makes this type of failure more probable. Ray

[dobryan]

Since you recently bled the brakes it is possible that during that process the master cylinder push rod traveled further than normal and the seal(s) were damaged on an unused corroded part of the bore.

Same conclusion as everyone else. Master cylinder failure.
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Dave O
'87 Westy w/ 2010 Subaru EJ25 (Vanaru) and Peloquin TBD

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[Erock77]

I think you all nailed it. I'm headed to Granny's this weekend in PA. Some of you might even be there. I'll be thankful to just swap the master cylinder. $$$

The Van is very original so I imagine this is the original from 84. I've owned it for 16 years and we're the 2nd owners. On it.

It does get garaged from Nov-April so it does sit for 6 months out of the year.

I suspect I should have used DOT 4 when I was suggested to use DOT 3...

Thanks for your alls input!
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84 Westy = Bussey

"Seeking all that's still unsung" R. Hunter

[Erock77]

[dobryan]

[1988M5]

[markswagen]

l just this morning replaced the master in my wife's '84.
she drove home the other night, l got in the following morning and the brake pedal went to the floor, it was an FTE part.
it got another new FTE part
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markswagen {mobile mechanic} san diego area all early VW's cared for.

619 201 0310

[harvgwen]

Mixing DOT 3&4 is not supposed to cause any issues. I don’t think you caused the problem by doing that.
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1986 Westfalia Vanagon, 2.2 Subaru
Okanagan Valley, British Columbia

[zerotofifty]

Rebuild the brakes, dont keep driving if you have loss of brakes.
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Sorry About That Chief.

Give Peace a Chance.

Words to live by.

[zerotofifty]