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Pilot brakes stay engaged

C_Bailey

Registered User
Good evening,

Before I tear into a brake overhaul, curious what you think of this issue.

1950 -18, Cleveland 30-60A double pucks, Scott 4200 parking brakes, North River Boosters.

Co-pilot brakes work great. Piston pushes pedal aft when released.

Pilot brakes engage and will not release...really noticeable when slow taxiing and needing plenty of power for small movements. Like having parking brake engaged all the time. I have to hook my heels behind pedals and pull them back to disengage.

Is the linkage gummed up under the floorboards, or is that a sign of weak internals? No noticeable leaks.

Thanks,
Chris
 
I am scratching my head, the pedals in front should have a cable or rod connecting them to the brake master under the seat. Is this your setup?

There is some brackets holding the brake pedals to the floor boards, pull the panels from behind the boot cowl and you should be able to reach them and check things out.
 
New install??

Front pedals ARE NOT properly shimmed/free moving.

Give us more information


Sent from my iPhone using SuperCub.Org
 
I know, it is crazy. It has cables connecting front to rear brakes.

When pilot brakes engage, the cable obviously pulls the rear pedals forward, but the piston is unable to return any of the pedals.

When only rear brakes engaged, the piston snaps the rear brakes back just fine.

I also pulled the inspection panels under the front brakes and everything looks good, but maybe needs cleaning and fresh lubrication??
 
No, opposite of a new install. This setup has been in the cub for many many years, but i don't have any good information on them except the symptoms I've noted.

Everything in the brake system is fresh outside of the cabin. Everything in cabin is old. Fresh bleed job. Calipers move freely in torque plates prior to brake application. However, they remain tight and locked at first application of front brakes because they do not return aft.

For example, I start my taxi and do a brake check. I have to physically pull brakes back. But...if I had a co-pilot in rear do the braking, the whole shebang would work perfectly.
 
Let fluid out of brakes. Now go move front pedals. Are they free moving? I doubt it. Fix that. Then refill. Only thing that makes sense from you descriptions


Sent from my iPhone using SuperCub.Org
 
Let fluid out of brakes. Now go move front pedals. Are they free moving? I doubt it. Fix that. Then refill. Only thing that makes sense from you descriptions
Alternatively, disconnect the interconnect cable from the master cylinder pedal. This will isolate the front pedals. Now find what is binding the front pedals. Spring broken and binding? Clamps binding the pedal pivot under the floor? Those front pedals are supposed to have a spring which pulls them towards the release position. Pedal pivot tube worn and dragging under the floor?
What ever you find by your description the entire trouble is with the pilots pedals. Nothing wrong with the brakes.
 
Alternatively, disconnect the interconnect cable from the master cylinder pedal. This will isolate the front pedals. Now find what is binding the front pedals. Spring broken and binding? Clamps binding the pedal pivot under the floor? Those front pedals are supposed to have a spring which pulls them towards the release position. Pedal pivot tube worn and dragging under the floor?
What ever you find by your description the entire trouble is with the pilots pedals. Nothing wrong with the brakes.

Ditto what Pete posted.
 
Couple of things.

Just looking at the standard system, left and right brake are completely independent and there is no return spring on the front pedals, the rods/rear pedals/master cylinder internal coil springs pull them back.

If both pedals are sticking in the forward "brakes on" position then they individually have the same problem and it is either binding/bent shafts or weak/broken springs in the master units.........probably.

Kind regards

Stew
 
Couple of things.

Just looking at the standard system, left and right brake are completely independent and there is no return spring on the front pedals, the rods/rear pedals/master cylinder internal coil springs pull them back.

Stew
You're right, I was thinking of the rudder pedal spring.
This is what it looks like under the floor. There is something in that lower mechanism which is binding. Loosey goosey is best.
attachment.php


It's not a fault of the master's springs. If it were they wouldn't be functional from the back seat. Also those springs are not strong enough to overcome a defect in the front pedals.
 
Rereading this and ignoring your info.... see if brakes are free in calipers and if pistons are freely moving


Sent from my iPhone using SuperCub.Org
 
It is the front pedals. Either shoot some Tri-flow in there with cables released, or go in there and put shims between the U brackets and the frame brackets.

The parking brakes have nothing to do with this, but can be serious problems themselves. They get inadvertently applied, often at the wrong time.
 
Thank you everybody. Won't be able to dive into it until Friday morning. I hear all suggestions, but am very certain as Bob mentioned that working something like tri-flow into the pedals and/or shimming will end up being solution. Not certain how difficult it is to access the lube and/or shim job as I just moved from a cessna to this cub. The circular inspection panels under the pedals don't seem to fit much more than a flashlight..
 
For your first time working on Cub brakes why not find a A&P that will work with you on this and then you will know how things are set up. If the brakes lock up on landing a Cub will go on its nose costing a whole bunch more than an hour with a mechanic.Most guys will work with you thru this, also most don't even bite ( to hard) good luck with it.
 
Hope you get to the bottom of it on Friday, another pair of hands would really help as it is easier with someone on top with a spanner when you loosen the nuts on the pedal shaft saddle underneath, 1/4" drive socket set is good too.

Disconnecting the pedal interconnect is excellent advice but if the pedal interconnect is a rod, that is a bit of a struggle to disconnect unless you have to. Before you embark on that, get your helper to apply full brake on the back/main pedal and then move the front pedal with your hand bending the rod a little, you might confirm where the problem is without disconnecting.

Slightly concerned that the problem is both sides when the left and right brakes are completely independent. The only common part is the fitter who intalled them and they possibly did not shim them correctly and the shafts are tight in the saddle.

Here is a diagram of the system, pm me with an email and I will send you the original so you have a clearer copy.

Kind regards

Stew

13399_Brake Installation.jpg
 

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Or, simpler, just get a block of wood, and apply the rear brake with it wedged against something - the rear seat pan, maybe. Then work that front pedal until loose.

We kinda like the aftermarket rods, which approximate the original welding rods only with clevises and AN-3s holding the ends to the pedals. Makes adjustment trivial! Doesn't weigh much more than cables with swages.
 
I'm not a mechanic, but I slept in a Holiday Inn about 15 years ago when the Hampton Inn was full.

If Triflow or WD-40 don't fix the problem, then disassemble and reassemble the pedal assemblies. My basic approach to everything broken since I was a kid - first WD-40, then if still broken, take it apart. I'm still alive after all these years.
 
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