Help with 170A Master Cylinder

[boydkl]

I would like to replace my left brake Master Cylinder (MC)
The left brake fails to actuate randomly.
The pads and caliper look OK. The pedal never gets soft; it just doesn't activate the caliper.
As long as I fill the cylinder up into the filler hole before each flight I'm OK for several TO & Landings (so far).
During the last year it has unexpectedly stopped working 4 times during taxi, usually leading to a brief off-roading event (until I can get the brake to work again -- after a full stop spinning to the right). It checked OK at annual and I could not duplicate the problem.
It only leaks slightly and takes about 1 spoonful to bring it into the filler.
(probably the spray due to being over filled)
Perhaps I can remove fluid a little at a time and finally get it to fail for the A&P while taxiing very slowly.
If we can't find a problem with the O ring and replace it, I will probably go to Air Salvage Dallas for a replacement.

The first time I had to replace a MC I went to Air Salvage in Dallas and they pieced together a working replacement that "looked" like the original. I have had no problem with that unit.

The MCs in the plane don't have any part numbers or markings.

Previous club postings listed Aircraft Spruce Cleveland repair/replacement parts and new master cyl. Model 10-35.
However, they (AS) indicate that they are like the model used on several production aircraft but that they are not FAA approved for Cessna 170 (or any other certified aircraft).

A call to Cleveland produced a nice product technical manual but still no "approved for use on Cessna 170" part number.
(We do have the approved Cleveland brake mod on our plane).

When I took the Cessna Illustrated Parts Book numbers and called the local Cessna supplier I didn't get very far (see below):

0441019-1 170 A Master Cylinder Assy-Right Brake sn 19200 on
# not recognized; no new #
0441019 170 A Master Cylinder Assy-Left Brake sn 19200 on
# not recognized; no new #

0541138-1 170 B Master Cylinder Assy-Right Brake pre sn 25000
superceeded, no # given
0541138-2 170 BMaster Cylinder Assy-Left BrakeBrake pre sn 25000
superceeded, no # given
0541138-6 170 B Master Cylinder Assy-Right Brake sn 25000 on
(haven't checked this one yet)
0541138-7 170 B Master Cylinder Assy-Left Brake sn 25000 on
(haven't checked this one yet)

0541138-18 Early 172 Master Cylinder Assy-Right Brake
good #, no stock $1000+
0541138-17 Early 172 Master Cylinder Assy-Left Brake
good #, no stock $1000+
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So, what have other club members done ?
Is there a cross reference from Cessna to Cleveland or other FAA recognized documentation which will identify an affordable and available replacement ?

[FredM]

I would do all that I could to confirm that is your problem before changing the master cylinder. Look at your brake lines while pumping your brake pedals. If the master cylinders are working the lines will flex slightly under pressure. If one side doesn't then you have a bad master cylinder. If both lines flex but only one brake is working then you have a stuck piston. You may also want to check your pistons for dragging while on jacks. If You can identify your master cylinders it would probably be easier to rebuild them if that is the problem.

[spiro]

The pedal never gets soft; it just doesn't activate the caliper.

sounds to me like the mstr cyl's working fine. I'll bet you've got some crud in the mstr cyl (or in the brake line) that's intermitently blocking the outlet port. I'd pull and clean out the mstr cyl (new o-ring while you're there) & flush the line. I suppose a piece of garbage at the caliper inlet could act similarly.

As long as I fill the cylinder up into the filler hole before each flight I'm OK for several TO & Landings (so far). .... It only leaks slightly and takes about 1 spoonful to bring it into the filler.

it *loses" fluid? as in an external leak? That should be fairly easy to identify and fix. Are you somehow introducing that "spoonful" from the top?

paul

[boydkl]

Great suggestions to try this weekend! It's just so sporadic...
The Cleveland MC model 10-34 (and 10-35) appears physically to be just like the MCs in our plane, anybody aware of any documents substantiating that?

[lowNslow]

Air Dog, I would diffenitly check out the caliper first. These are prone to corrosion and sediment, and if not to far gone can easily be cleaned up.

If this is not the problem, rebuild the master cylinder with new "Lock-O-Seal" (part no. 200AC-6) and O-ring (AN6227-8 ) and follow instructions in the "Cessna Pre-1960 Service Manual" for proper gapping of Lock-O-Seal. The service manual also has a trouble shooting section on the brake system.

[Metal Master]

Air Dog, I would diffenitly check out the caliper first. These are prone to corrosion and sediment, and if not to far gone can easily be cleaned up.

If this is not the problem, rebuild the master cylinder with new "Lock-O-Seal" (part no. 200AC-6) and O-ring (AN6227-8 ) and follow instructions in the "Cessna Pre-1960 Service Manual" for proper gapping of Lock-O-Seal. The service manual also has a trouble shooting section on the brake system.

I agree with this direction to go. I have seen these Lock-o-seals cause problems, if they are not set properly. If set too tight they pull the brake pads back off of the disc when the brake is released. If set to loose, it doesn’t close when you step on the brake and you get no brake action. It is possible that the seal is defective or that there is some debris in there that is causing it to stay open occasionally keeping the brake from operating.

[boydkl]

Whew! 15 long hours of sweat and grime, and all is well.
We took the left caliper off and checked it. There was a slight amount of rust and build up but nothing unusual. A bit of cleaning, sanding, polishing and it went back on the wheel. Next we pulled the top from the left master cylinder.
Good grief! What the H…
Why was the brake working at all? The shaft nut had backed up the threaded portion about an inch. So much for the .040 setting between the piston and loc-o-seal; I am 1 lucky pilot! We pulled the master cylinder out to check the bore; it had about ¾ inch of sludge in the bottom of the reservoir and broken washer pieces. I decided we would check the right caliper and pull the right master cylinder while we were at it.
We cleaned and polished the right caliper and rebuilt the 2 master cylinders (no damage to the bores) with new piston o rings, loc-o-seals and piston return springs (available from the local Cessna distributor –it turns out that I have the late 170B/early 172 master cylinders).
Pulling or installing the master cylinders seems to take about an hour each for a newbie (4 cramped, sweaty hours total).
The taxi test went well (9:30 PM Thursday) so Henry and I did our 3 take off and landings to a full stop to get night current (boy, was it dark!).
Special thanks to Ron (A&P) who studied the problem and patiently guided me through the entire repair and check out process.
I would also like to thank the club members who offered suggestions and advice. THANKS !!! What a great “family”!