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  Brake Master Cylinder Disassembly & O-Rings

Rebuilding Your Brake Master Cylinders

 

By: Arky Foulk

 

THE SYMPTOMS OF LEAKING BRAKE MASTER CYLINDERS ON BONANZAS AND BARONS ARE:

 

1. Parking brake will not hold.

 

2. Brake fluid on belly of the airplane or puddles fluid under floorboards.

 

3. Fluid puddles on top of Master Cylinders.

 

I have been able to rebuild almost all master cylinders without removing the master

cylinder from the airplane using the following procedure:

 

  • Open the engine cowling and find the brake fluid tank on the fire wall. Follow the brake line down to the top of the nose wheel tunnel. If the parking brake valve is mounted on the wheel tunnel, proceed as follows.

 

  • Without pumping the brakes, pull the parking brake handle to the ON position. This will prevent fluid from leaking out of the master cy1inder when the master cylinder is disassembled. 

 

  • If the airplane has the late-style parking brake valve mounted beneath the floorboards, it will be necessary to drain the brake fluid tank. Unsnap and remove the front carpet and carpet pad. (Do not remove the floorboards. Use a rag or shop towel and pack around the rudder pedal to prevent dropping tools or parts under the floorboards. This also will catch any excess brake fluid.

 

  • Behind the rudder pedal, remove the bolt, nut and washer where the brake master cylinder clevis is secured to the rudder pedal. Wipe off top of master cylinder. Using snap ring pliers, remove the snap ring from the top of the master cylinder.

 

  • Remove the moving parts Pull up on the shaft and remove it and all internal parts of the master cylinder as an assembly. Wrap the assembly in a clean cloth to prevent dripping fluid and take it to the bench. 

 

  • Clean the parts with solvent before removing them from the shaft. 

 

  • VERY IMPORTANT: count the threads or measure the shaft so the clevis can be re-installed later in the same position. Then remove the clevis and jam nut. 

 

  • Remove the top cap and all O-rings. You will probably want to replace the cap. It has a tendency to wear at the shaft hole because the shaft does not actuate straight up and down but at slight angles. 

 

  • Replace all O-rings. Near the bottom of the piston and shaft you will note a small cotter pin through the shaft. Remove this cotter pin and a small piston-type valve will drop out. This valve has a rubber seal molded on it, so you should replace the complete valve "piston" and cotter pin. 

 

  • Re-assemble master cylinder parts. Install all new O-rings and a new cap. 

 

  • Re-install the original washers, snap ring, jam nut and the clevis. 

 

  • Caution: Be sure to install the snap ring with the sharp side of the snap ring toward the top of the master cylinder to prevent it from coming out of the snap ring groove when the brakes are applied.

 


 

An experienced Beech Lister, John F., who also happens to be an A&P, offers the following additional thoughts:

 

"......recommends not replacing that molded "O" ring at the bottom. The valve piston as Arky calls it. I can't recall one ever going bad. If you must, you can also carefully unfold the brass around the "o" ring, and replace just the "O" ring, and fold the brass back, and not replace the whole mechanism. I have had good luck just using regular "O" rings from the local Nat'l Air Parts Association Store (aka NAPA....LOL)."

 


 

Here are some thoughts from Beech Lister and A33 owner John P., who had a pretty surprising experience with the "valve piston":

 

I did have one of these valves go bad about a year ago! The O-ring had popped out of the crimp when I set the parking brake during an engine run-up prior to take off. The result was it trapped all the pressure in the line and locked the brake up. Had to shut down, open the bleed valve at the brake to relieve the pressure to taxi back to the hanger.

 

When I got a rebuild kit from Johnston's Aircraft in Tulare, CA ($68ea, don't have the part number here at work) it came with a different style valve. There was "NO" O-ring...just a flat piece of gasket material glued to the valve. Sorry I didn't get a picture of it!! Anyway, to me it seems like a much better design that would prevent a failure like I experienced.

 

During my T-34 days with the Navy part of our landing checks were "Brakes Pumped Firm". If this o-ring fails airborne from pumping the brakes like this, or even after take-off to stop the mains prior to retracting the gear, one would sure be in for a surprise at touchdown!!!

 


 

Beech Lister, Stan S. offers the following comments from his experience:

 

"We are in the process of re doing three master cylinders. Thought we could do them in place but can't push the piston rod assembly down far enough to install the snap rings in place because there is not enough room to do it in place, so we removed the master cylinders. Avstat has overhaul kits for various master cylinders that cost us about $56 each, and consist of 100% RAPID documented parts, even the o-rings. The kit includes the o-rings as well as a wipe and another part that I can't remember the nomenclature.

 

Avstat's kits did not include new snap rings. Also recommend you get covers for the brake line coming down from the reservoir, the upper line going into the master cylinder, so the fluid doesn't all leak out while the master cylinder is removed. If you use new snap rings be certain to use genuine Truarc, we got new snap rings (not Truarc) that are plated and .37 thousands in thickness and the Truarc are .32 thousands. Truarc snap rings are steel, and not plated. After we finished up and started bleeding, a snap ring came off. Now we have to remove the three master cylinders and install the thinner Truarc snap rings. If you don't hear the snap rings snap into the grove nicely when installing it, the snap ring you are using may be too thick and can come off. This would not be a good thing when operating your airplane.

 

I recommend replacing everything in the master cylinder, which you get with Avstat's kit. Why go to the trouble of opening it up and not doing 100% of it?"

 

Avstat Aviation
7625 Hayvenhurst Avenue Suite 18
Van Nuys, CA 91406
     Phone: (818)780-6032

 


 

Here is a creative CSOB master cylinder plunger cover solution contributed by Beech Lister, Kevin O., host of the B2OSH Margarita & Pizza Party and Debonair owner and Beech parts maven extraordinaire.  Thanks Kevin!

 

Nasty 40+ Year Old Cover

 

Pretty Slick Huh?

 

Presto! A nice new cover for your master cylinder!

 


 

Kevin also reminds us that if you have a Bonanza with a VV-15-625 master cylinder, you're SOL, because it's no longer made or supplied by Beechcraft. BUT, you can buy the VV-15-625-1 and shorten the shaft and presto you are in business again. Reportedly, the master cylinder with the longer shaft is only $133.00! 

 

Here's the secret scoop:

 

 

the top one is a VV-15-625-1 which is available from beech for $133.00. They started using it on the P model and after----until the very latest airplanes (went to the Cleveland Master cylinder).

 

the one at the bottom of the picture is a VV-15-625 it was used on the straight 35 till the N model (maybe M model)

 

the VV-15 -625 is no longer available----but a Cleveland retrofit is available for around 8 or 9 hundred! (CSOB1 says: NO %$*$^$* WAY!!!)

 

NOW--the CSOB way to do this is to cut off about a inch--so its the same length--thread it to the same distance as the old one---and its a perfect match !!!---barrel and hook ups are the same --shaft is not hardened so it threads easy.

 

Special Note: If you use this master cylinder info find, you must come to OSH and personally thank Kevin O. for this info. You can find him every year at the B2OSH gathering in the North 40.

 


 

Here is a Baron Master Cylinder Extract #1 and Extract #2 to help you identify the O-rings required on some of the master cylinders. Remember, check YOUR illustrated parts catalog for the exact part numbers for your serial number airplane.

 


 

Thinking about adding Co-Pilot Brakes to Your Beechcraft?

 

 

This is what you'd be looking for from the Salvage Sources.

 

Rumor has it Beech made a kit back in the day to accomplish this with every piece required. The PN is rumored to be: 36-58000-3

 

 

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