The International Cessna^® 170 Association

While cleaning the belly of my '48 170 I noticed a little red fluid around the drain holes of the panel under the main cabin area and the next one back. It wasn't dripping and was easily wiped off. Looks like automatic transmission fluid--could it be brake fluid? My level is ok and no obvious leaks. Maybe it is just a little residual cable lubricant from my annual. Any other ideas?

Did someone top off the brakes recently and/or back-bleed them
and spill a little bit? It can take awhile for the brake fluid to run
down to the drain holes.

Perhaps someone over-filled the master cylinder reservoirs....?

The 100 series manual says if it's not already there, drill a small
hole in the plastic vent caps located on the tops of the master
cylinders. On mine, the vent hole was in one cap but not the
other. The one without the drilled vent hole was pumping brake
fluid past the piston rod/hole out the top of the cylinder. After I
drilled the vent hole per the service manual, no more leaks....

Bela P. Havasreti
'54 C-170B N170BP

The master cylinders were serviced last annual in September. I've flown probably 20-25 hours since then (of course I might not have noticed for a while). I'll pull up the inspection plates to see if I can see spillage--you're right, it could take a while to work its way back to the drain holes. I'll check the caps too.

Bill,get a little on your fingertip and give it the old taste test.Then get a sample out of a can of #5606 brake fluid and taste it for comparison. That's the only way to know for sure!
If it don't taste-test to be 5606,it just might be Marvel Mystery Oil leaking from your gas tank. But I doubt it.
No charge for the advice.

Eric

Hey Eric, you haven't been sneakin' around other 170s doin' some sort of "hokey pokey" voodoo have you? I'll have to take a closer look at mine the next time

If the brake linings have been replaced then the master cylinders may have expelled excess fluid when the pistons were pressed back into the wheel cylinders/calipers. Filling the master cyls when the linings are partially worn may result in spillage for this reason. It's best not to completely fill the master cyls except immediately after new linings are installed.

I did a lot of work on my master cylinders but I still had the break fluid on the belly so I had to really hunt for a leak. One of the lines under the floor had been cross threaded so the fitting was leaking. It leaked for years before I finally found that! Just a note to say that if it is not leaking around the cylinders themselves then check all the connections under the floor. They make a couple turns and go thru some of the stringers.

Blue Skies, Dan

Thanks for all the advice--I've looked to see if I could find an obvious source, but nothing found--yet. There is a lot of debris and gunk down in the bays under the cockpit (including a 1947 penny!) and I am in the process of cleaning it out. Considering how little actually leaks and how much crap there is to absorb/retard any brake fluid flow, this could have easily been from quite a while ago and is finally making its way to the drain hole.