Corrosion on the vacuum brake booster near the master cylinder - Toyota 4Runner Forum

cl4Rk · 01-17-2022, 08:55 PM

Previous owner had the brakes done about two years ago. Fluid exchanged during frame swap a few months ago. No symptoms, no leaks, brakes feel great.

Today I noticed this corrosion on the vacuum brake booster near the master cylinder. Nothing is wet. It looks old. I just never noticed it before for some reason.

Thoughts? Maybe from a previous leak that has been repaired?

EDIT: clarified the location of the corrosion

Devbot · 01-17-2022, 09:00 PM

I'm thinking they spilled some brake fluid and didn't bother to clean it up. Brake fluid will eat through paint like nobody's business, and it appears to have left a trail where it ran down and dripped off. A leak would be possible in this regard I suppose. Just my opinion
If nothing is wrong I'd just try and brush it up, spray some rust reformer on it and call it good

alumarine · 01-17-2022, 09:04 PM

Take a wire brush to it to see if it's just a paint issue as Devbot said.
That's the vacuum brake booster btw.

brillo_76 · 01-17-2022, 09:38 PM

Verify your grommets are not seeping. I have one that had the grommets between the master cylinder and the brake fluid reserve tank. This leaks back to the vacuum booster then eats the paint off as it leaks down to the ground.

If it's grommets are seeping you see pooling under the tank on the master cylinder. May not be what is going on but worth taking a peak.

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cahilc · 01-18-2022, 07:14 AM

Everything mentioned above... Plus...

Clean it real good before painting. Chemical neutralizes or physically neutralize (sandpaper). Brake fluid cuts down to the metal and gets into the metal surface. That's why it's such a bane especially on an exterior surface. Once bubbled needs to be aggressively removed or will rebubble with the new paint.

It'll clean up real nice and look great. Just know you have to be real aggressive or it will pop back up again.

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