Remote Master Cylinder Modification

The master cylinder on my CJ3B is vented to atmosphere by means of a tiny hole in the cap. Because of this design the brake fluid eventually absorbs moisture from the atmosphere and contaminates the system. Fording through water does it too, just much quicker.

I suppose that if the fluid was changed and the brakes were bled annually, or after being submerged in water crossing, then this antiquated design would be (somewhat) acceptable, but changing the brake fluid seems to be a task that gets overlooked. So I set out to address this by installing a remote master cylinder reservoir, this has been done by many others so there is nothing new with the idea, this is just my version of it.

The location of the master cylinder requires one to remove the floor cover to gain access to it and, although getting a wrench or socket in there is doable, it is less than desirable. Then there is always the possibility of dirt falling into the reservoir, I usually bang on the floor panel and then blow compressed air around the area before removing the cap.

I started by removing and modifying the cap.
Here is the splash shield on the bottom of the cap, this was a friction fit and I removed it with a screwdriver.
Before


After


Here is the tiny vent hole


Welded shut


I drilled a hole, reamed it with a tapering reamer, threaded it with a pipe thread tap. Then installed a brass hose barb.


I had researched for what thread sealant would be resistant to brake fluid and although there are some rather expensive specific sealants available it turns out that loctite blue does the job too.
Tygon 2375 clear tubing is resistant to brake fluid so that was used to connect the hose barb to a remote reservoir, the tubing was the most expensive part.
The reservoir was an inexpensive item off Amazon intended for a motorcycle/ATV and the hose barb was a hardware store item.

So here is the completed setup.

View of the master cylinder through the floor


The remote reservoir has a diaphragm that separates the fluid from the air, here it is attached to the firewall



The total material cost was under $35.00 with the Tygon tubing being the most expensive part.
I should have done this long ago. It is so much easier to add brake fluid and now I can also easily see the fluid level too !