Brake Cylinder Problem

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Brake Cylinder Problem

Postby VernH » Tue Mar 13, 2018 2:28 am

I have had problems with my right brake not holding during run up. I took the cylinder out and found the O ring split. I have replaced the O ring with what I believe is the correct one based on info from the forum. Now the brake holds...sometimes. I have to pump the brake, when it catches its firm and holds but after I release it the brake has to be pumped again. I bled the brakes from the bottom up, again, and have the same result.
Since there is only one O ring in the cylinder i am at a loss for what the problem could be so here I am. Is it possible that I still need to bleed the brakes? Any other thoughts?
Thanks in advance
Attachments
IMG_3157-Scaled.jpg
Can someone positively ID this cylinder?
IMG_3157-Scaled.jpg (25.21 KiB) Viewed 1813 times
IMG_3134-Scaled.jpg
cylinder piston
IMG_3134-Scaled.jpg (25.77 KiB) Viewed 1813 times
Fly safe!

Vern
1950 C-170A N5453C sn 19487
Based in Pensacola, FL. 82J
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Re: Brake Cylinder Problem

Postby johneeb » Tue Mar 13, 2018 2:41 am

Vern,
Is it possible your axle nut is loose or your rotor is warped? Either of these conditions would push the brake piston back into the caliper bore as the wheel rotated, causing you to have to push the piston back out with each brake application. This is similar to the way old shoe type brakes acted when the shoes whore down before you re-adjust them.
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Re: Brake Cylinder Problem

Postby VernH » Tue Mar 13, 2018 2:46 am

johneeb wrote:Vern,
Is it possible your axle nut is loose or your rotor is warped? Either of these conditions would push the brake piston back into the caliper bore as the wheel rotated, causing you to have to push the piston back out with each brake application. This is similar to the way old shoe type brakes acted when the shoes whore down before you re-adjust them.


I don't think so because the brake pedal is soft until I pump them then they are like they should be. This is while the plane is static. I then moved the plane forward under power and repeated the same thing in several spots. It sounds like air but I would think that it was out as much as I bleed them. Maybe not.
Fly safe!

Vern
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Re: Brake Cylinder Problem

Postby Bruce Fenstermacher » Tue Mar 13, 2018 11:16 am

It is the Parker Lock-O-Seal in the cylinder that needs replacing. No time to elaborate. Been there.
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Re: Brake Cylinder Problem

Postby Metal Master » Tue Mar 13, 2018 1:20 pm

I had the same issue with these older style of master cylinders.
Cessena Brake Plunger edited PRS.jpg

In the picture I have attached the black arrow points at the o-ring. When you actuate the brake the o-ring has to slide up the shaft and close the holes in the washer indicated by the green outlined white arrow. The gap shown has to be there if it is not, then when you release the brake the ports do not open. They need to open because if they do not then the piston moves back up the cylinder and draws the fluid with it. Pulling the wheel cylinder piston away from the pads. Then on the next application of the brake you have to push all of the fluid back through the system and you have no brake pedal.
Essentially the large part of the body is the reservoir and fluid supply. The fluid has to be able to get into the piston cavity. It does that by the o-ring being able to move up and down in the piston cavity on the shaft and the small amount of friction between the piston bore and piston opens and closes the fluid passes between the reservoir and piston bore.
Sometimes the ports will open when you pump it up and then you have brake pedal. This brake piston is not quite like the later ones that have the "loc-O-seal". I mucked around with these things in my airplane for weeks. I never could get the pedal to operate reliably. That is something I could not tolerate. For less money and time than I could have spent mucking around with these master cylinders. I purchased later style master cylinders that do use the "loc-o-seal off of e-bay and installed them. No more problems once adjusted to maintenance manual instructions. You will have difficulty trying to find maintenance instructions for these older style master cylinders as pictured.
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Re: Brake Cylinder Problem

Postby gahorn » Tue Mar 13, 2018 3:05 pm

Metal Master wrote:I had the same issue with these older style of master cylinders.... I purchased later style master cylinders that do use the "loc-o-seal off of e-bay and installed them. No more problems once adjusted to maintenance manual instructions. You will have difficulty trying to find maintenance instructions for these older style master cylinders as pictured.


+1 ...What MM said. (beware of e-bay regarding serviceability/traceablility...might get lucky...might get the brake "shaft". :wink:
Salvage yard such as ASOD or Texas Salvage might be better choice, IMO.)
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Re: Brake Cylinder Problem

Postby Bruce Fenstermacher » Tue Mar 13, 2018 3:47 pm

Now, with more time to study your cylinder, I realize it is the old style which does not have a Parker Lock-O-Seal. If you had the later style found in the B model or retro fit older 170s, the a bad Lock-O-Seal usually causes this. Go with the advice MM has given.
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Re: Brake Cylinder Problem

Postby VernH » Tue Mar 13, 2018 7:22 pm

From the 170B parts manual these cylinder are pn0541138-1 or 2 OR -6 or 7. There are many similar cylinders with the same pn but different dash numbers. Would you get the ones for the 170 as shown in the IPC? Would this be a 337 item since it is not listed in the A model IPC?
The ones Have found so far do have the "lock-o-seal" and small O ring on the piston end like mine.
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Re: Brake Cylinder Problem

Postby gahorn » Tue Mar 13, 2018 7:34 pm

Edit: Gary's answer below is much better than my opinion.
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Re: Brake Cylinder Problem

Postby n2582d » Wed Mar 14, 2018 12:50 pm

As you know, it's your A&P/I.A. that'll decide if converting to a later style brake master cylinder is a major or minor alteration. He might reference Cessna SNL 6-5-52 for documentation.
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Re: Brake Cylinder Problem

Postby VernH » Tue Mar 20, 2018 1:02 pm

I found a pair of cylinders on Ebay with new seals, lubed and complete with a logbook sticker saying what they are and what was done to them, signed by the A&P that did the work. They look great and arrived in three days. I'm pretty happy with the purchase. Now to get them installed and bled to see how they work.
Attachments
p.jpg
PN 0541138
p.jpg (3.07 KiB) Viewed 1494 times
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Re: Brake Cylinder Problem

Postby Metal Master » Tue Mar 20, 2018 1:28 pm

VernH wrote:I found a pair of cylinders on Ebay with new seals, lubed and complete with a logbook sticker saying what they are and what was done to them, signed by the A&P that did the work. They look great and arrived in three days. I'm pretty happy with the purchase. Now to get them installed and bled to see how they work.

If the picture you attached is of the brake cylinders you purchased you will most likely find that they are fitted with a pipe to Dash - 3 AN fitting. The late Cessna aircraft used 3/16ths brake lines not 1/4 inch such as 170's use.Your going to have to figure out how to convert them to 1 pipe or an O ringed fitting or go to 3/16th line all the way down to the wheel cylinder. You may need an AN819 reducer or a different or AN816 nipple. I can not remember if the fitting coming out of the master cylinder is O-ringed or not.
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Re: Brake Cylinder Problem

Postby VernH » Tue Mar 20, 2018 1:37 pm

I checked the IPC and found the cylinders I had were fitted with a -4 fitting. I specifically asked for that fitting on these cylinders and that is what they are supposed to be. Haven't tried them yet.
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