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Mon Mar 17, 2025 11:35 am

I had a nice puddle of brake fluid on the floor inside my van when I got it out of winter storage this year. I thought "hmm, guess its time to replace those brake fluid reservoir grommets again". But, when I pulled the instrument cluster I was surprised to see everything was nice and dry beneath the master cylinder. Crawling ever lower I found fluid on the bottom of the brake booster.

I haven't worked on that part of my van yet and don't really know how it functions. Is it likely that the booster is leaking fluid (is there even fluid in it?) or was that more likely some residual mess that dripped onto it from above?

Granted, I didn't really have great access or light while I was poking around so I might find out more when I get back to it. But in the mean time, is the booster a likely suspect?

Mon Mar 17, 2025 11:41 am

The master cylinder can leak fluid into the brake booster. This is a common failure. You'll want to address it asap, as the fluid will cause the brake booster to fail also. (I'm guessing it dissolves the coating on the inside the booster, which causes the diaphragm seal to fail.)

To verify, you can remove the instrument cluster and then the master cylinder.

You'll probably want to remove the booster and clean it when you replace the master cylinder. That's a bear of a job, unfortunately.

Mon Mar 17, 2025 11:49 am

zuhandenheit wrote: That's a bear of a job, unfortunately.

Ugh, I'll add that to the list...

- deal with Vanagon brakes.
- Replace Vanagon evap hoses above gas tank.
- Replace Suzuki brake proportioning valve.
- Adjust Suzuki valves and carb jets.
- Replace front deck.
- Replace carpet with hardwood on second floor of house.
- Decide to fix or ignore rotted fence post in backyard.
- Replace French doors onto back deck.
- Get a haircut.

Adulting is hard.

Mon Mar 17, 2025 11:50 am

If brake fluid is dripping from the booster that would be from the master cylinder.

Mon Mar 17, 2025 12:06 pm

As others have stated there should be no fluid in the booster, it operates with engine vacuum.

Mon Mar 17, 2025 12:27 pm

As an FYI new brake boosters are hard to come by.

You can have that one sent out and rebuilt. That is what I did, haven't installed it yet. It was cheaper than a new one.

Chris

Mon Mar 17, 2025 12:36 pm

While not a brake booster, I’ve had these guys make me custom brake lines and also rebuild some drum brakes for a tractor. They did an outstanding job for both, and I believe the testimonials on the website. If I have my booster rebuilt, I’ll be sending it to them.

https://www.brakematerialsandparts.com/products

Mon Mar 17, 2025 12:39 pm

A wireless endoscope that works with your smartphone can be bought cheaply these days. They are invaluable when trying to clean out a booster and check general condition, this can be done with the booster in place once the leaky master cylinder is removed.

Mon Mar 17, 2025 12:50 pm

Been a long time since I dealt with this but isn't there an O-ring between the master cylinder and the booster that can fail and result in a leak that will run down the booster and make it look like the booster is leaking?

Mon Mar 17, 2025 1:42 pm

Ahwahnee wrote: Been a long time since I dealt with this but isn't there an O-ring between the master cylinder and the booster that can fail and result in a leak that will run down the booster and make it look like the booster is leaking?
That would make a vacuum leak if that seal failed. The hydraulic system is independent of the booster.

Mon Mar 17, 2025 1:46 pm

FWIW, you're supposed to be able to remove the booster and pedal assembly with only the cluster removed and the dash still in place. I found it fairly difficult to do with the dash out. But even 30 minutes of wrestling it will still be less time than pulling the dash. It won't be easy.

Mon Mar 17, 2025 2:05 pm

4Gears4Tires wrote: FWIW, you're supposed to be able to remove the booster and pedal assembly with only the cluster removed and the dash still in place. I found it fairly difficult to do with the dash out. But even 30 minutes of wrestling it will still be less time than pulling the dash. It won't be easy.

Yeah, I've been watching some videos and it seems do-able with the dash in.

What I really need to do is get the van into the middle of my garage with some good lighting and do a better job of sussing out the leak. Hopefully I missed something that's easier to fix :lol:

I had already spent the afternoon working on another vehicle and when the "bonus" Vanagon job didn't go as expected I quickly switched to an attitude of "f- this, its beer time".

Mon Mar 17, 2025 2:12 pm

If you have never had the dash off it would be a good idea to get some penetrating liquid on the big Philips head screws that go along the base of the window. They can be a pain to remove if they have never been out.

Mon Mar 17, 2025 9:07 pm

I tried for awhile to remove my brake booster without pulling the dash, and I gave up. I can't really understand how anyone does it.

Tue Mar 18, 2025 5:53 am

It'll definitely be easier with an automatic. The clutch pedal splays out and makes it quite difficult to line up. With an automatic you only have the brake pedal and, honestly, it may just pull straight up and out.

Tue Mar 18, 2025 6:36 am

Has the brake booster been diagnosed as bad? I did not see that posted. While not ideal, I have had good results cleaning the booster in place with soap and water. Drying and reassembly with new master and O ring.

Tue Mar 18, 2025 8:11 am

MarkWard wrote: Has the brake booster been diagnosed as bad? I did not see that posted. While not ideal, I have had good results cleaning the booster in place with soap and water. Drying and reassembly with new master and O ring.

Not yet Mark. In fact, other than the puddle of fluid on the floor the brakes work great and motor runs like a top with no indication of vacuum leaks.

It's still winter in Montana so my garage is cold, dark, and the floor covered with puddles from my wife's car being parked in there after the daily commute. It'll be a little while until I dig back into the project. I'll post some photos when I do.

Each of the last few years I get a small puddle of brake fluid on the floor beneath the dashboard after our annual week of negative teens/twenties F. I replaced the reservoir o-rings some years back and that fixed it for a while. This year the puddle was considerably bigger so I ordered new o-rings and went to install them last weekend. When I removed the instrument cluster I found that the master cylinder and o-rings appeared dry. The 6-oclock position on the booster had a bunch of fluid on it though, either leaking from or accumulating on the crimped seam.

How does one bench test a master cylinder or brake booster to verify failure? Clean everything up then pump the brake pedal a few times and look for a leak?

Tue Mar 18, 2025 8:21 am

4Gears4Tires wrote: It'll definitely be easier with an automatic. The clutch pedal splays out and makes it quite difficult to line up. With an automatic you only have the brake pedal and, honestly, it may just pull straight up and out.

Yeah, this guy makes it look possible although I wonder if those metal support bars under the dash are bolted in or did he remove them with a hack saw and not show footage of the carnage?

Either way, thanks for the suggestions and information. I'll report back in a few days after I do my homework.

https://www.google.com/search?sca_esv=5f71ebaa1edf...vFK-8,st:0

Tue Mar 18, 2025 9:02 am

SCM wrote: 4Gears4Tires wrote: It'll definitely be easier with an automatic. The clutch pedal splays out and makes it quite difficult to line up. With an automatic you only have the brake pedal and, honestly, it may just pull straight up and out.

Yeah, this guy makes it look possible although I wonder if those metal support bars under the dash are bolted in or did he remove them with a hack saw and not show footage of the carnage?

Either way, thanks for the suggestions and information. I'll report back in a few days after I do my homework.

https://www.google.com/search?sca_esv=5f71ebaa1edf...vFK-8,st:0

If they are the ones that I am thinking about they are bolted in. I currently have everything apart updating all the clutch and brake parts and also trying to fix some obvious electrical issues before I install my TDI. I have the steering column unbolted and laying down along with those supports completely off. I also think they may be specific for drivers side and passenger side, but don't hold me to that.

I will try to get some pictures to post so you can see what it looks like.

Chris

Tue Mar 18, 2025 9:12 am

The master cylinder housing is sealed at the pushrod/booster end. Master cylinders can fail in a few ways. One way is the rear seal fails and brake fluid leaks out the rear. Because it’s bolted to the booster, the fluid typically runs into the boosters front section. With the cluster removed, you can unbolt the master and pull it forward enough with the lines connected to see if fluid is in the boosters front section.

There is a vacuum seal, square cut O ring that seals the master to the booster. I have seen brake fluid find its way down the face of the booster
at 6 o’clock. Either way, you need a replacement master cylinder if fluid is present and the reservoir grommets are dry. The booster should never have brake fluid in it. Only engine vacuum and atmosphere pressure.