The Cessna 120-140 Association Forum

Hello,

I have a 1946 C-140 with Cleveland brakes. The problem I am having is that if you apply slight pressure to the right brake (bottom of brake with toe), you actuate the brake slightly. This is making it a bit more challenging than I would like. I have been careful and have compared the position and pressure with both brakes. The left brake does not actuate under similar conditions.

I had my mechanic look at this and taxi the aircraft. He confirmed that it is not my poor technique but an issue with the brakes actuating when it should not. He was not aware of a fix.

If anyone has any input, I would really appreciate your assistance.

Thank you,

Brady Nelson

I think there is another thread on the same topic and it was determined there was a problem with the geometry of the system. When one of the rudders was pressed, the brake applied itself. If I recall the reason was that the rudder cables were not properly adjusted and the rudder was hitting its stop early in the pedal travel. Might want to check the rudder cable rigging.

If that doesn't help, perhaps you could post some photos showing what is happening.

[Edit] I think I have it backwards and the rudder was not hitting the stop, so the pedal traveled too far and hit something that applied the brake.

No thoughts as to why this is happening, but absolutely get it addressed. Using brakes on a tailwheel aircraft should be a deliberate, thoughtful, act. Not a byproduct of right rudder!

I had this issue when I bought mine last year. The rudder cables were incorrectly adjusted. I adjusted them as far as I could but my mechanic realized that one of the turnbuckles was the wrong one. He owns a 120 and a 170 so was very familiar. Search my posts and if that doesn’t help, PM me with your number and I can talk you through it.

Thank you for responses,

I really appreciate the insight.

Brady

I just updated my previous post...

If you have the cast pedals I think it is a design flaw. Take off your shoe and put it in the position it will sit in flight. My shoe, a 10 1/2 touched on the top of the round area and above the pivot point. so when you press the rudder pedal you get a little torque on the pedal in the direction of applying the brakes. The brake cylinder shaft on my plane had about 1/8 inch play before you would start feeling resistance.

I flew it for 150 hours this way, got used to just putting my big toe on the pedals on final, or actively pulling back on my toes.

I thought I had pretty good technique and was off the brakes, then I installed the stamped aluminum pedals so my son could start taking lessons and the ground handling changed entirely. Much less twitchy. The stamped pedals dont look as nice, but they have a bar about 1 inch below the pivot that your feet rest on, so until you pick your heels up you will be de-activating the brakes with rudder.

Bottom line for me is even with perfect technique you probably get a little bit of brake. Not enough to squeal the wheels, but some. Especially if your feet are bigger than 1946 feet. Your friend or CFI in the right seat wont have this problem cause there is a lot of slack in the linkage.

I agree with the assessment that these rudder pedals have poor geometry. The angle of the rudder pedal is such that I cannot pull my toes far enough back to avoid activating the brake, unless I slide my heels back and consciously actuate the rudders with my toes on the bottom of the pedals. This works, but imperfectly. It also means you don't have great braking authority available should you need it.

This was a poor rudder pedal design from Cessna. Later, they got it right. For example, on a 172, I can work the rudders with my heels and the brakes with my toes, and have sensitive independent control of each.

Granted, my shoes are only 7-1/2 (US), but I have never had an issue with the brakes applying accidentally. I push the rudders by extending my legs (without flexing my ankles) and apply the brakes by rocking my toes forward, bending at the ankle. The pivot for the pedals are somewhere near the balls of my feet.

I did once have a problem when I applied the brakes intentionally, but that's another story for another time...

BTW the PN for the stamped aluminum pedals shows on at least one Cessna parts list as superceding the early cast pedals so its an easy swap to make paperwork-wise. Those were used on most 1950s era Cessnas so not too hard to find.

Of course 75 years of experience says that original pedals are perfectly fine in the hands or feet of a competent pilot!!!