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Left brake awol...

sj

sj

Staff member
Northwest Arkansas
Well, my left brake went out completely and instantly on the top cub. It has the boosters. There is no leak anywhere, but the pedal goes to the floor. We have bled and bled and searched and searched but something must be goofed up in the master cylinder or the booster cylinder. Anybody have a "best place to look" opinion? We took the brake apart and all is OK there. Of course, with a belly pod working on the brake is no great joy, looks like we MIGHT get it done without removing it....

Any thoughts would be appreciated!

sj
 
My guess is that the o-ring(s) in the master cylinder are worn out or degraded. This could prevent you from developing pressure on the back side of the piston, instead the fluid would just flow around the piston. Just a guess.
 
If the pedal goes to the floor, you had to lose fluid. Is there indication of a red fluid leak under the master or on the wheel?
 
Thanks, guys. No fluid loss at all anywhere, so I think there is a big hole in something (like a bad o-ring) also, this failure was catastrophic in the sense that it was working great one minute and not working at all the next.

Is there a drawing of the parts for this thing anywhere on the internet that anyone knows of?

I have been doing a lot of 270's during windy taxi and people are starting to talk...

sj
 
T.J. Hinkle said:
If the pedal goes to the floor, you had to lose fluid. Is there indication of a red fluid leak under the master or on the wheel?
Click to expand...

Not necessarily...there is a check valve inside the pedal cylinder that locks pressure when you push down, but once released allows the fluid above the piston to bleed back to the pressure side. I've had experimental pedal cylinders that this check valve jammed open due to things coming loose inside (or trash in the fluid).

Cheers,
Wayne
 
Wayne:
I don't think the Boosters have a release valve. I could be wrong but I think they only have the piston with 2 "O" rings, the main cylinder body and the actuation plug.
 
Steve, take all the screws that are in a circle out that hold the cylinder to the body which is bolted to the floor. This will give you access to the piston and o-rings. I figure you trashed an o'ring. I take it you alreadt disassembled the caliper since it is easier to get to.

PS It is easier if you slide the front seat out which requires removing the stick. Less head standing that way especially if you are on big tires.
 
I just sent you a PM. I had this problem on my Top Cub today. It is a mechanical problem with the piston pin, or more appropriately, actuator plug. It is coming out of the slot which is machined into the front of the rear pedal. I liked to of never found what the problem was and can't for the life of me see how this can happen. Has anyone had a problem with this before?
 
Thanks! Actually, that "actuator pin" is very loose and floppy in the slot, the first thing I noticed. Is this a "put it back in place" repair or one that needs parts?

THANKS!

sj

(P.S. If you sent ME the PM I did not get it.)
 
The put-it-back-in-place repair worked for me, but it may need parts. I'm going to contact Stan tomorrow and I'll post his answer.
 
I have seen the piston get sticky due to the two o-rings on it. The first is always in fresh fluid but the back one can start sticking not letting the spring return it properly. It would probably be prudent to replace the o-rings and clean the piston and bore to make sure it doesn't happen again soon.
 
While we are on the topic of o-rings, has anyone had any luck with standard Buna o-rings with aircraft hydraulic fluid? From a legal stand point it is probably a no-no, but it would be nice for us experimental guys. Standard Buna o-rings are a lot easier to come by than the MS o-rings.
 
MS o'rings are available at the local bearing supply here in a town of 5,000. A/C Spruce sells a kit with about every o'ring you will ever need. I have a cross reference book at the shop that gives material specs and compatability. I will get the info to order one and post it.
 
I talked with Stan at CC today and he said there's a service letter out on it. As usual with CC, when you call you'll always get an answer. The service is great!
 
You can call Cub Crafters for it. They're sending me the letter. If you don't get it before, I'll send you a copy of mine.
 
Steve, have you or anybody else accomplished the CC service bulletin on the master cylinder? I'm having a hell of a time getting the darn thing off. How about you?
 
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