The Cessna 120-140 Association Forum

Left caliper was dripping oil for the first time on the hangar floor. Bleed nipple was snug, so I tried the nuts on the caliper. They were rather alarmingly non-tight. Snugged them up and expect leak will be resolved, but would like to torque to proper spec. Is this on the cleveland website? Thanks.

Was the dripping oil hydraulic fluid? If so, there is a piston with a large O ring in the piston assembly. The piston or its housing may be corroded allowing fluid to leak past the O ring. I would get it checked.

Unfortunately, there are no bolts holding fluid in. There's an o-ring that you can replace, but the brake housing itself is magnesium and often there's corrosion in the bore that needs to be attended to.

I suspect the nuts you are referring to hold the anchor pins in place. Use the torque from AC43-13

Ah. Well, on to the O-rings then. Is there a caliper rebuild kit?

https://www.dropbox.com/scl/fi/5gs9a5pj ... zrebo&dl=0

https://www.dropbox.com/scl/fi/ezrlshwc ... h5zzl&dl=0

atypicalguy wrote: ↑Wed Dec 20, 2023 12:28 pm Is there a caliper rebuild kit?

Sorry, had to chuckle!

There's just the o-ring. You need the brake part number to look up the o-ring, or, you can probably match it up if your maintenance shop has a well stocked o-ring drawer.

(My memory says it might be MS28775-224).

If it isn't MS28775-224 it's a -222

usually.........the disc is worn (minimum is around .205 as I recall....memories can be faulty....) or the linings are worn, or both.
This leads the piston to extend out farther into the "pitted zone" of the caliper, causing your leaks.

New linnings, discs and some sandpaper (to clean up caliper bore) and then a new O ring and your drips should dis-appear.

This situation happened to me on both brakes (not at the same time) and I did exactly what was recommended in earlier posts. I had to replace the housing and piston on one side. The other side was not as corroded and I was able to clean up and polish the housing and replace the O ring.

Magnesium does not play well with a lot of potential abrasives. I would stick with aluminum oxide paper. Especially avoid emery paper, steel wool, Scotch Brite "S" and the like.

Thanks all. Happy to be a source of amusement; we all begin somewhere.

Interestingly, I tightened the four bolts (well 2 nuts and 2 bolt heads). Did not remove caliper.

I also gave the nipple in the bottom about an 8th of a turn; it was not loose but I had to snug it a bit to see how tight it was. It seemed pretty tight before I turned it.

There is no more brake fluid coming out. The leak has stopped.

I put some pressure on the pedal to see if anything came out. It did not. The pedal is firm.

So unless it starts leaking again, I have to assume either the bolts do more than we think (I know, they just keep the caliper floating in the proper range) or the nipple was leaking (also not likely). No corrosion, no o ring, no sandpaper, no pads, no rotors.

Kind or weird. Maybe tightening the bolts put the caliper piston in a new position within the bore? I know overtightening things can induce cracks in the casting; maybe it is cracked and tightening it a bit more sealed it past the end of the crack.

I never really use the brakes anyway. Occasionally to make the first ramp.

I will test it out tomorrow morning if the marine layer is not too thick.

Merry Christmas
Karl