Vanagon Repair: Cold Weather Vanagon Brake Fluid Leak and Fix

For the second consecutive winter, the cold and dry temps resulted in a steady dripping of brake fluid from the fluid reservoir/brake master cylinder vicinity behind the dash cluster.  Like clockwork, as soon as the weather reached a sustained freezing to sub-freezing cold, the leaking commenced (and I quickly contained the mess with a collection pan placed on the driver's side footwell).  I knew from my experience the previous year (and from corroborating posts about this very phenomenon on thesamba.com), that the leak would miraculously cease as soon as the warmer weather returned.

But this winter I wanted to determine  the source.  Had my relatively new brake master cylinder failed? Was the leak coming from around the brake sensors? Or from some less obvious failure point? It turns out that the leak was coming from the two grommets at the top of the master cylinder inside of which the nipples from the fluid reservoir are seated. The grommets are, at least in warmer months, soft and rubbery and intended to seal the connection between the reservoir and the cylinder. When I took a close look on an icy February day, I could see that the grommets were damp with brake/hydraulic fluid and when I wiggled the reservoir a bit I could see additional fluid oozing out. The conclusion? It appears these two rubber grommets must shrink a bit in the colder weather and take on a more brittle character, thus losing an effective seal.

I didn't attempt a fix over the winter. I never drive the van during those salty, corrosive winter months in the Boston area, and by the time I diagnosed the leak the reservoir had already drained enough that a brake bleed would be in order.  I left the project for warmer days and finally got to work over the weekend.

After removing the instrument panel I carefully pried the almost-empty reservoir from the master cylinder.  This is 25 year old plastic, so care should be taken to avoid snapping the nipples inside the cylinder.

I then used a small syringe (previously used for administering baby tylenol) to suck up any brake fluid that was sitting in the top of the master cylinder holes. After that, I popped out the grommets and thoroughly cleaned them with soap and warm water and set them aside to dry.  In the meantime, I also cleaned out the cylinder holes with a rag and a bit of alcohol. At that point I was ready to apply my experimental remedy.

The main ingredient of the fix is an anaerobic gasket maker. I used Permatex 51813. Others will tell you to use Loctite 518. They are exactly the same. Loctite owns Permatex (or maybe the other way around?). Permatex is widely available at your local auto shops, but  Loctite 518 is nowhere to be found. These anaerobic sealers are flexible, never fully harden, and won't degrade with oils or brake fluid. I also grabbed a spray can of the matching anaerobic gasket maker surface primer.

Spray the surfaces with the primer and let it dry for a few minutes per the instructions. Then apply a nice bead of the gasket maker. I sealed both sides of the grommet: the surfaces between the cylinder and the rubber, and the flat surfaces between the reservoir and the rubber.

After setting the reservoir back in place I refilled it with new DOT 3 fluid and bled the brakes.  And I finished off the afternoon with a fresh oil change. The application seems to have worked really well.  Definitely not a drop of fluid.

Ruby is ready for spring and running beautifully!

Permatex 51813 is the red substance you see on both side of the grommet.