M116A3 Master Cylinder Question

[ACO43]

Just starting to get into the surge brakes on my M116A3. I pulled the cap off the master cylinder, which unscrewed easily, and looked inside. The inside of the MC was just barely damp. However, it didn't look all rusty and corroded as the pictures of some that I've seen. (See for yourself)...



My question is, why would it be empty? I haven't pulled the drums off yet so I suppose it could be a leaking wheel cylinder but there's no residue that I can see on either wheel or drum to indicate that. There is, however, a bunch of silicone around the outlet and the beginning of the brake line...



...There was also a bunch of silicone around the cap of the master cylinder (did take a picture of that one). Could it have been leaking in these areas and the US Govt. agency that owned it prior just "sealed" it like this or is that silicone a common thing like that on these trailers? Given the lack of corrosion inside the MC does it appear to be in good order or is the lack of fluid an indication of a bad MC anyway? Would there be any reason that they would drain it and leave it empty on purpose? Thanks in advance.

 

[juanprado]

The cylinder looks good. I have seen them full of rust and corroded.

The master cyl can leak internally and the fluid would leak into the surge casting but...

My thought is that brake fluid eats paint and the fitting at the master cyl looks cruddy from leaking. There is usually a copper washer on either side of the brake line block with the banjo bolt to seal. I would disconnect it, clean all the surfaces and reassemble with 2 new washers ( NAPA, O'reilly etc should be able to match). Then fill with fluid and check it out. Line could also be bad but I would start with the obvious and cheapest in my opinion.
YMMV

 

[Tinstar]

It’s very common for any surplus item to have all the fluids drained.
It seems to be one of those.
You're lucky that it’s not all rusted like you mentioned.
I would fill it with DOT5, which is what was used, and call it good unless you see a wheel cylinder leaking.

Factory parts for the surge assembly are available from www.crofttrailer.com.
They will have new copper washers if you need them.
Looks like a waterproofing attempt.

They are also the least expensive on the surge shock.
That is another item usually needing replacement when the trailer is sold.
You’ll know right away if it’s bad and you hit the brakes. Trailer will buck back and forth.

 

[Tinstar]

The silicone around the cap isn’t normal.
Probably trying to keep water out is a guess.
Once tight they stay put. So it’s not to keep it from backing off.

NOS caps with new orings are available in the classifieds or eBay.