Pilot side brake Cylinder flat, but copilot works

[asa]

Hello, came back to my airplane after a few months and the pilot side left brake pedal is totally "flat" - no resistance, goes to the stop, does not apply brake pressure to the line. I thought my fluid had leaked or something but I tried the copilot side and it works great, as normal.

I'm assuming the pilot left cylinder needs to be rebuilt? I looked up a drawing and there are 2 o-rings in there.

Has anyone had this happen? Was it an o-ring replacement? Figure I'll remove the master cylinder and tear it apart but thought I'd ask here first in case there's any insight.

Thanks!
-Asa

[Kirk]

Read through this thread: http://www.maulepilots.org/Hangartalk/v ... ing#p55638

The left side on my M5 has been prone to air in the line. Sometimes would act as you described. I would try bleeding it first.

I have a post on the above thread detailing the steps. Air can hide in the crossover lines between pilot and copilot side then reappear at the pedal.

Kirk

[asa]

Thanks! That would be very convenient if it just needed a bleed. I'll try that tomorrow. Still open to other suggestions if anyone has them in the mean time.

[asa]

Seems like it may have just been low on fluid on left side. Wonder where the leak is...

[VA Maule]

" where's the leak?" ...... It's the Angel's share. Over time some just seems to evaporate like whiskey from the sealed barrel

Mine have been soft on the left ( both of them) ( reservoir on top of the cylinder) ( right side solid as a rock) for quite some time as part of my pre-flight regime I pump the left petals by hand and they will eventually get firmer , never really solid ( but they stop the plain just fine and evenly I've rebuilt both reservoir cylinders twice, first time with kit from Maule, second time with kit from Aircraft Spruce with no improvement. Have bled the breaks from the bottom up too many times to remember with the assistance of several competent A&P/IA's , so absolutely not an air in the line issue ( have collected about a pint of fluid out of the top of the cylinder via an overflow tube screwed into the 1/8" pipe hold in the top of the reservoir with each bleeding, more than enough for a total exchange of fluid throughout the system. Once pumped up at pre-flight they'll stay up for days and days no issue then all of a sudden next pre-flight they'll be soft AGAIN . This condition affects right and left pedals seemingly equally on the left seat side, right seat co-pilot side as I said earlier solid as a rock.

I asked the same question you've asked several years ago and got some recommendations but no revelations came forward that lead to a fix. It's really not an issue that bothers me since I prefer to fly from the right since the " proper hand positions are right on the stick and left for the throttle and flaps".

I would however like to figure out how to fix the issue before it does become a problem. So hopefully someone has found the fix you ( ASA) and I can't be the only ones that have this issue, so I'll be watching this thread close.

[Kirk]

ASA glad it was simple. Mine sometimes gets low with no visible leaks too. Rare enough that I am not concerned.

Same experience as VA Maule rebuilt master cylinders etc. 99% of the time all is as it should be.

VA Maule, yours is acting like mine did with air in the crossover line. Bleed each side, pilot and copilot, as described. Might take many tries.

Kirk

[maules.com]

Pilot side brake fluid from reservoirs on pilot side feed through the co-pilot cylinders and then the brakes.
If oily residue is found anywhere on co-pilot cylinders or under the floor below then that's the leak.
If no residue of oil on calipers, oil line fittings or bottom bleed nipple then pilot side reservoir and/or cylinder is the culprit.
The pilot side reservoirs are not sealed, the top is merely held in place by a circlip(no seal).
The fill plug has or should have an air hole in it.
When pilot side pedals are pumped vigorously oil can come out the air hole especially if very full.
If the oneway seal is bad inside the co-pilot cylinder, oil can back up to pilot side.
Always apply brake pressure Twice during GUMPS, U for undercarriage(brakes). Should be spongy both times otherwise the brake lock has been inadvertently applied.

[Dkuber]

While not exactly the same, it still may help someone.
Went to go fly the other day and my right side brake (both pilot & copilot) was just mush. Not like it had air, just had no hard bottom. We tried bleeding with no change. Upon opening the master I found the clip had broken and the spring and bushing were in the bottom of the master cyl. Quick and easy fix. Luckily I was able to pull all pieces out with fingers and a magnet.


This was rebuilt about a year ago with new rings and clips.

[freedom]

when I installed mine I had this problem on both pilot brakes and seemed impossible to bleed the air bubbles between pilot and copilot brakes.
without removing the fluid lines I removed the pilot brakes cylinder and put them to the best of the possibilities vertical on top of the copilot cylinder so that the fluid lines would stay vertical rather than horizontal. this allowed the air bubbles to excape.

[drak130]

Okay, so replaced the tailwheel with Larry's solid tire. Both harder and easier than expected. Went to test the new kicks. Held the brakes on start...all normal. Started taxiing and left brake went soft. Was still working somewhat but by the time I got it pulled into the hanger it was going to the floor with little resistance and would not pump up.

Co-pilot brakes work and feel fine, which is where I have been flying lately giving my son with the broken left foot some flying time to keep him proficient since he got his PPL. Another story.

I pulled the plug and it seemed mostly full.

Gonna try bleeding the brakes first but cannot find any reference in the owners manual or otherwise about the brake fluid type. Any suggestions?

Any suggestions on a one-man bleeding process? Was trying to see if I could do it the automobile way by doing a single-handed arm stand but I'm old.

1998 M7-235C with the cleveland brakes master cylinder part no. 10-35

Thanks as always

Tim

[yanknbank]

I've never had luck getting the brakes bled the automotive way, even with help. I use a pressure bleeding, which can be done with one person, and takes about 5min, most of which is getting things hooked up and filled with fluid.

I don't know if much changed since my 74 m5, but the right brakes are slave cylinders, and the left are masters with the fluid reservoirs. I had an issue with one of my masters that's similar to yours. The co pilot brakes worked fine, but the pilot was a little spongy, and could not be bled. I solved the problem by replacing the o rings in the master cylinder. They get old, and can bypass fluid around the oring which feels like air, but it's not. They can be replaced with the cylinder still in the plane so as not to have to bleed the brakes again, but it's not easy, and youd need to know how they work and what you're looking at to be successful. I recommend taking them out to disassemble.

Fluid is mil-5606.

Before going down this route, make sure there is not air in the lines between the master and slave brakes by doing a pressure bleed.

[drak130]

Thanks yankandbank!

Set up to bleed brakes tomorrow.

AI on the field has the fluid and oil can. As part of the prep pulled up the floor panel under the pedals and wrapped the master cylinder with paper towels and shop rags. Also pulled the plug and threaded a 1/8 NPT barb onto to the top of the cylinder and have my old car tube and catch cylinder attached to hopefully keep the mess to a minimum.

As someone said earlier on this thread, the plug looks like a dog chewed it up. My guess is a piece of it fell into the cylinder and is mucking things up. Anyone have a source for those orange plugs?

Will still go with the easier option of the bleed first. I have a rebuild kit from Aircraft Spruce on the way. Someone said they rebuilt the master cylinder in the plane. They must be related to Houdini. No way am I gonna try that! On the bench for me!

Will keep you posted.

Cheers
Tim

[andy]

My previous A&P bled the brakes by connecting a squirt can full of brake fluid to the brake line at the caliper. His helper put paper towels around the master cylinder, took out the top plug and watched the level rise until he told the A&P to stop. This method got rid of all the air bubbles quickly since they floated up into the master cylinder and it was a lot less messy than feeding fluid in at the master cylinder. It does take two people.

[drak130]

So brakes are fixed (for now). Apparently, they just need to be bled. The A&P on the field had an oil can (goldenrod) filled with 5606 and rigged up with a clear tube sized to fit over the caliber bleed nipple. I threaded a 1/8 NPT barb onto the master cylinder and attached a tube and can setup (the automotive brake bleed kit) to catch the overflow. About 10 pumps and all the old fluid had been cycled through, closed the bleed valve and all was good. This setup allowed for solo operation.

Of course, as someone else mentioned "where did it go?" I pulled up the pedal floorboards and no leaks noted there. Will keep an eye out. The old fluid was kind of brown and could have been mistaken for oil on the belly. Now that it is new and red, if there is a leak it should be easier to see.

The master cylinder plug is a complete mess and I do worry about pieces of it falling into the reservoir. I ordered a plug kit from Amazon with various sizes. Will report if I have any luck finding one that fits.

I am seriously considering getting rid of the parking brake. I don't use it and do worry about the fore mentioned issues with it but as soon as I ditch it, I'll find myself parked on a hill somewhere trying to throw chocks under the wheels while I hold the brakes. If I do get rid of it, I have a 1/8 NPT brass plug that will plug the fill hole. Just can't get it on with the parking brake mechanism in the way.

Thanks again for all the help gang!

Tim

[andy]

Tim, I had a somewhat similar situation with my left brake a couple of years ago. It was suddenly soft while taxiing. My A&P added brake fluid but I asked where the old fluid had gone. I had visions of it pooling up under the floor boards and soaking into the insulation. He looked but said he didn't find any. There were no indications of a leak at the caliper. It's still a mystery to me.