Having Brake problems

How to keep the Cessna 170 flying and airworthy.

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Dr. Dave
Posts: 41
Joined: Sat Jul 27, 2002 3:51 am

Having Brake problems

Post by Dr. Dave »

Hi everyone,

Well, I began this project by rotating my tires on the wheels to even out the wear pattern. That worked out fine and I took advantage of having the wheels off to pack the bearings. So far so good... Then I noticed that Clevland disc brakes were sticking so I cleaned the main pins that the brake assembly floats on and cleaned off the brake pads. Everything seemed fine and I tested the brakes without actually taxing the airplane. Pressure seemed good on both sides. This morning I went out to go for a few circuits and discovered I had no thanks on the left side!! Curses curses! So I phoned up my friendly mechanic and he said "no big deal" when you have the break pads off the lower piston probably moved a little and created a small air lock... I'll come right over and flush a little brake fluid back up from the bottom and that should fix it... Well, he pushed a little brake fluid back up from the bottom and nothing happened... So he pushed a little more and there was a lot of brake fluid flowing out around the push rod on the master cylinder and still no brakes!... My mechanic figured that the O-rings must have gone... His explanation was that when I made those minor adjustments and allowed the plunger to move at the bottom of the system, it probably forced the O-rings to shift into a new position and they were just about ready to go so one of them went?? Sounds a little strange to me, but I'm no mechanic?? Anyway, we pulled both master cylinder's, (everything looked to normal to me) and it is going to put new O-rings in and reassembled everything on Thursday morning and give it a try... I'm wondering if anyone out there has any experience with brakes and would care to comment? I'm extremely puzzled about how the brakes were working fine after I reassembled them, especially, since I at no time had any fluid leakage or disconnected any fluid lines... Then after sitting for two days, I have no brakes!?
If anyone would care to comment, I would appreciate it..

Thanks

Dave
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GAHorn
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Joined: Fri Apr 12, 2002 8:45 pm

Post by GAHorn »

When you say you had "no thanks" on the left side,....Do you mean you had no pressure? Or you had pressure but no braking action?
Dr. Dave
Posts: 41
Joined: Sat Jul 27, 2002 3:51 am

Brakes

Post by Dr. Dave »

Sorry about that.. I often dictate my e-mails using a voice recognition program.. and it oftem makes some weird subsatutions....I guess I did not do a great job of proof reading that one... It should read no brakes on the left side.. pedel just goes down with no resistance..

Thanks


Dave
Dr. Dave
Posts: 41
Joined: Sat Jul 27, 2002 3:51 am

Brakes

Post by Dr. Dave »

thanks for the comments I received on my break problem. Just an update. I replaced all the O-rings and cleaned and reassembled both master cylinders and the breaks are now working just fine... It seems that the o-ring was the problem. My question is what made it fail at that particular moment?? I'm now fairly nervous about doing any brake adjustments at all for fear of repeating the problem. The system seems simple and straightforward and there's no obvious explanation for why the system failed with the rather simple manipulations I was performing...??
any guesses??

Dave
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GAHorn
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Post by GAHorn »

O-rings can get old and take a "set" that when disturbed, causes them to bypass fluid. It's not common unless they are old, or the cylinder is dirty. Remember that the wheel cylinder is open to a very dirty/sandy/wet environment. Contamination can collect betwixt the o-ring/piston and the cylinder wall. A grain of sand can cut the o-ring or mud/junk can dislodge it and cause it to lose pressure.
I always recommend testing brake holding power (not just pressure) following brake work.
GreggHorrell
Posts: 7
Joined: Tue Apr 23, 2002 1:37 am

Brakes

Post by GreggHorrell »

Dr. Dave,
A lot of things can cause brakes to go south...some are pretty subtle. You mentioned Cleveland discs and that brings a few things to mind. On disc brakes we often go annual after annual and replace pads as required. But, the system is filled with MIL-H-5606A hydraulic fluid which is vented at the top thru the filler plug or vent screw. Moisture enters the system and that water, being heavier than the hyd. fluid, will tend to settle to the brake wheel cylinders. It then allows for corrosion pitting in the cylinder where the o-ring rides. Allow these pits to get big enough and fluid will pass around the o-ring and you lose braking. To make matters worse, the pads aren't the only thing to wear out. How old are the discs? When were they measured last for thickness (.190 minimum thickness for most 170/172 applications)? If the discs are too thin the pucks have to travel further to push the pads tight. Thin discs also wear pads quicker. How old are the hoses up by the pedals? When I converted Matt's 170B to the Franklin engine I also replaced those hoses....they were dated 1951!!!!!
I agree with George....test the brakes for holding after maintenance. That is the only sure way to test the system. Get a micrometer and measure your discs and take a good look at the age of the other components. Cleaning the anchor pins is a great idea. But then, lube the pins with C5A hi-temp anti-seize (copper colored). The brake calipers won't hang up and it prevents rust :^)
Gregg
Dr. Dave
Posts: 41
Joined: Sat Jul 27, 2002 3:51 am

Brakes

Post by Dr. Dave »

Thanks gregg,

I am beginning to understand how this may have happened.. Your comments are very instructive..I did check the pads and the disc thickness... The one on the rt worries me a little because it is quite deeply scored but not yet too thin.. I plan on keeping my eye peeled for a replacement set.. The pins I cleaned work a lot better.. Several lubricants were suggested to me but I felt concerned that anything would tend to capture dust and grit material and make matters worse?? Your suggestion makes more sense as it is heavy enough to protect against water and probably would not allow dirt in...

Your comments on the age of these components ir well received.. I am now glad that I have serviced the master cylinders.. The brake lines are all rigid or flexible metal..probably not original??

Water from condensation never occurred to me but it is a good reason to keep the master cylinders topped up regularly so there is no air to form condensation.. also a yearly purge of the system seems in order??

Thanks again for all the help in understanding this important system.. We often bet our lives on our brakes when flying these planes.. makes sense to show them some respect..

Dave
GreggHorrell
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Joined: Tue Apr 23, 2002 1:37 am

Brake Hoses

Post by GreggHorrell »

They should be hoses up by the rudder pedals. Take another look under the flimsy pedal well cover on the left side and you should see the hoses connected to the master cylinders. Solid lines up there would NOT be a good idea...too much movement will lead to cracks/failures. Next annual you might peek at the complete system plumbing under the pilot's side floor and over to the right side to see if there is any weeping around the fittings....another neglected area. While you're at it....clean out those filthy wells under the pedals....hah!
Gregg
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Desertflyer
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Joined: Mon Dec 19, 2022 3:09 am

Re: Having Brake problems

Post by Desertflyer »

If you need to clean up your caliper bores and pistons Parker Hannifin's Cleveland Brake Division recommends using a scotch-brite pad to clean them and then alodining them to prevent further corrosion. I know because I called the factory in Cleveland, Ohio with repeated sticking of my pistons due to corrosion (airplane tied outside in rain) and several other unhappy comments about their brakes. They paid for my flight to Cleveland and a rental car and hotel so I could meet with their manager and engineers regarding all the issues. Regarding the sticking issue we agreed that I was servicing my calipers exactly per their maintenance manual and they were corroding and sticking. But they were surprised to discover that their specification that the bores and pistons be alodined before reassembly to prevent corrosion had been mistakenly omitted from the service manual. So since I was not alodining I had corrosion and sticking. They were going to correct the manual right away. I was very impressed with them. They are great people and very dedicated to making the best brakes possible.
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n2582d
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Joined: Mon Apr 29, 2002 4:58 am

Re: Having Brake problems

Post by n2582d »

It’s good to hear that Cleveland reps were so responsive to the issues you were having. The problem I see is that Alodine is intended for aluminum rather than magnesium. If you have 30-63A brake assemblies they are magnesium. Cleveland recommends Oxsilan as a conversion coating for magnesium. I found a cheaper alternative called Mag-Coat. See this thread. If you have a contact person with Cleveland I’d be interested in knowing if there is a place to buy Oxsilan in a smaller quantity than a five gallon bucket.
Gary
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mmcmillan2
Posts: 161
Joined: Sat Jul 04, 2020 9:30 pm

Re: Having Brake problems

Post by mmcmillan2 »

Are y’all referring to brushing on this product before reassembling?: Alodine 1201

https://www.aircraftspruce.com/catalog/ ... ne1201.php
170B owner, KCFD, CFI(I), ATP Multi
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