bad brake fluid leak

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Mitch Covington
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bad brake fluid leak

#1 Post by Mitch Covington »

Brake fluid leak 1.JPG
I have a really bad brake fluid leak, car undriveable, big puddle under this access panel under the center of the car floor pan. What's the likely leak source? This boomerang-shaped access panel looks like it'll be hard to remove. Is this area accessible from within the car? There is no sign of fluid anywhere around the master cylinder that I can see/feel from accessing the reservoir/Master cylinder from inside the frunk access panel. TIA.
Mitch Covington
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'59 356 Cabriolet
'79 911 SC Targa

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Ken Tuvman
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Re: bad brake fluid leak

#2 Post by Ken Tuvman »

The boomerang shaped piece is what secures your brake / clutch pedal assembly to floor. Based on picture, it looks to me that leak is coming from brake master cylinder - possibly the metal tubing that feeds fluid to the brake calipers or slave cylinders (depending on drum or disc brakes). But you're saying no sign of fluid - you'll have to trace the brake line fittings to figure out where you're losing fluid. Maybe left front wheel brake hose? Seems closest to where leak is . . .

Interested to hear what others have to say . . .
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Martin Benade
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Re: bad brake fluid leak

#3 Post by Martin Benade »

It’s most likely that the piston seal is letting brake fluid leak onto the floor, and spreading from there. I had this happen a couple of years ago, it went undetected long enough to wick pretty far in the fairly young carpet too.
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Doug McDonnell
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Re: bad brake fluid leak

#4 Post by Doug McDonnell »

Remove your driver's side floorboard to access the most likely source mentioned by Martin. If confirmed you will need to remove your brake master cylinder which is done from under the car.
1965 356C 2000 BMW 740i Sport 1967 Honda CL77 There is never enough time to do it right, but always enough time to do it over.

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John Brooks
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Re: bad brake fluid leak

#5 Post by John Brooks »

Mitch

That’s typical of a master cylinder leak. Be sure to clean the lines and fittings with a small wire brush. Then a couple drops of penetrating oil on the lines and threads. The brake line tubing tend to rust inside the fittings, and fuse them. Then a use a flare nut wrench on the lines. Be careful the tubing does not twist with the nut when removing the nuts from the master cylinder. If it does, re brush the lines and re oil. It’s an east fix to rebuild the cylinder or replace it with a new one. Be sure the push rod has the 1mm clearance free space space after reinstalling the master cylinder. Not all that complicated just a pain to get to, and NOT twist the tubing when taking it apart.
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Mitch Covington
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Re: bad brake fluid leak

#6 Post by Mitch Covington »

Yep, it's a mess inside the cab... what's the best cleaning detergent for brake fluid? It's all down the tunnel too, will be a tedious chore to clean that out from under the cables.
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Mitch Covington
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'79 911 SC Targa

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Martin Benade
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Re: bad brake fluid leak

#7 Post by Martin Benade »

Jack up the rear so it runs forward. I’d soak up most of it with paper towels. Then most any solvent will work such as paint thinner or lacquer thinner.
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Mitch Covington
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Re: bad brake fluid leak

#8 Post by Mitch Covington »

This pile of insulation was in the tunnel... rat nest, or is there a reason to have insulation in there? I suspect a nest, as there were a couple of feathers in there too...
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Brake fluid leak 2.jpeg
Mitch Covington
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Re: bad brake fluid leak

#9 Post by Mitch Covington »

master brake cylinder.jpeg
The previous owner retrofitted disk brakes on the front, so I suspect that this is not the original master cylinder? This is a '59 Cabriolet.
Mitch Covington
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'79 911 SC Targa

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Doug McDonnell
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Re: bad brake fluid leak

#10 Post by Doug McDonnell »

Rat/mouse nest for sure. And dual Master Cylinder upgrade which works fine for disc or drum brakes and safety feature not found on a 356 when new.
1965 356C 2000 BMW 740i Sport 1967 Honda CL77 There is never enough time to do it right, but always enough time to do it over.

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Martin Benade
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Re: bad brake fluid leak

#11 Post by Martin Benade »

The replacement will ideally be dual and specifically for disc front drum rear, I think 1968 Karman Ghia is that. This gets the correct type of residual pressure valves. You’ll have to drill out the threaded mounting holes to 8 mm.
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Re: bad brake fluid leak

#12 Post by Mitch Covington »

Thanks, didn't realize this was a VW part, but sure enough, this seems to be the exact one here. I'll have to drill out the mounting holes? Darn.
vw master cylinder.JPG
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Martin Benade
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Re: bad brake fluid leak

#13 Post by Martin Benade »

Yes, just a cleanup to remove the threads. But look a bit further, you’ve found an all drum brake one. The Ghia one looks identical but is set up for front discs. Also if it specifies, 19mm bore is what you want. Bigger will not be better.
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Re: bad brake fluid leak

#14 Post by Doug McDonnell »

Try Klasse 356 for a Master cylinder.
1965 356C 2000 BMW 740i Sport 1967 Honda CL77 There is never enough time to do it right, but always enough time to do it over.

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Martin Benade
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Re: bad brake fluid leak

#15 Post by Martin Benade »

They only offer all disk or all drum. Chances are either would function, but not as correctly as the KG one.
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