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  Brake Master Cylinders & Parking Brake Valves Disassembly & O-Rings


Rebuilding Your Brake Master Cylinders


By: Arky Foulk




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.


Click HERE to read about a modern synthetic, flame resistant alternative to 5606 hydraulic fluid that is used by the military, MIL-H-83282.


Click HERE to view the Cleveland Master Cylinder parts catalog to identify o-rings and other components in the Master Cylinders.


Click HERE for the Parts Catalog extract for the Beech PN: 169-380100-3 Master Cylinder



Below is an IPC Extract for the VV15-625 Master Cylinder

Click HERE for a narrative on Rebuilding the VV15-625 Master Cylinder

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Goodyear Master Cylinder Fail and Deconstruction



After snap ring removal, the whole plunger/shaft body is extracted. Replace 2 O-rings, fill with 5606 or THIS flame resistant alternative, reverse bleed from caliper then test with A&P.




Mysterious Brake Pressure Failure After Multiple Bleeding


Below is a pirep from F33A Bonanza owner, Greg S., regarding a continuous mysterious brake pressure fail that would not resolve after numerous brake bleedings.


"I chased this problem for 11 years in my 1992 F33A with my left brake, and occasionally the right brake. The problem kept getting worse over time. Numerous well known mechanics chased this problem all those years and never found the problem, just kept bleeding the brakes. It got so bad at the end that re-bleeding the brakes was futile. Could get the brakes to firm up for maybe one flight.


Actually replaced all 4 master cylinders, that didn't solve the problem.


3 years ago based on the advice of Bob B, I ordered all 12 brake line hoses from PHT.


Upon replacing the hoses one at a time, we found the left brake problem main culprit was the upper hose going to the pilots side left brake master cylinder. It was completely saturated with brake fluid on the exterior. The reason we hadn't suspected any of the brake lines was that the clear tygon tubing sleeve that the brake line is in was catching the fluid, then apparently evaporating, so it never dripped onto the belly. It was real visually apparent after we actually removed it from the plane.


While we had all the brake fluid drained to replace the hoses, thought we might just as well rebuild the parking brake valve. Sure enough, the exterior of the parking brake valve was all sticky from brake fluid residue. Those o-rings are stone simple to replace.


So, 12 new brake lines and 7(?) new o-rings later, 3 years of totally trouble free brakes!!!"




In the '50s they started with the tygon. Not much chafing, but a reasonable idea. On the later ones the plumbing was changed rather dramatically when the dual brake option went to series rather than parallel; on those, the tygon is a must.

See the complete thread discussion HERE at

HERE is a part diagram of the Paramount PN: 96-380034-1 Master Cylinder showing the shaft O-ring (#12) as a -008.



Below is a pirep from Leo regarding his Gerdes Master Cylinder replacement experience:



"I just replaced the right side Gerdes on my Citabria. Could not find mechanical parts. Decided to R&R left side as well. It turned out to be a Cleveland 10-54. It was working fine when removed. PM me and I can supply more info and be willing to sell the removed cylinder. Also have the pieces from the Gerdes if that will help. Rod is not in good shape with pitts etc. I suspect that is why it failed, finally ate the O ring.


The Gerdes just started leaking. It was dated 1973, IIRC the Cleveland is 2006 vintage.


Bought new cylinders from American Champion, which are manufactured by Grove."



HERE is an OUTSTANDING narrative from Debonair owner, Fernando E. on his master cylinder o-ring replacements to knock out his leaks! Don't stop there, check out the rest of the page for more insight into this area of your Beechcraft.




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 was only $133.00 several years ago! 


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.



Parking Brake Valve (PBV) Info

Here is an image of the internals of the Scott 4200-A1 PBV showing o-ring part numbers. These ancient nitrile rubber o-rings can be the cause of inoperative parking brake function.


Click HERE to see the resource for converting the AN part numbers to MS28775

With the MS28775 numbers the flurosilicone numbers would seem to be

AN6227-5 = MS28775-010 = M25988/1-010 (flurosilicone)

AN6227-1 = MS28775-010 = M25988/1-006 (flurosilicone)

Be sure to secure A&P approval prior to any 0-ring substitution!


If you have a HOOF Model A53-T PBV (common in Bonanzas and Barons), in your airframe that is acting badly or leaking, you're in luck because McPeck Aviation has a $9 O-Ring repair kit available for it.


The plunger seal is in Fluorosilicone and has a very nice tight fit. The brass fitting seal is in Viton with an upgraded modern spec seal design replacing the originally supplied square ring. McPeck also includes a Fluorosilicone alternate for the brass fitting seal should anyone prefer it. Includes all seals to do one PBV. Price per complete kit is $9.


Click the PayPal button below to make a $9.00 payment to place your order with McPeck Aviation.






Contact Adam McPeck for additional details on the Hoof O-Ring kit or to place an order




Below is more info on the Hoof A53-T PBV


Gerdes O-Ring Interchange to MS Number

Gerdes A-850-8 or Cleveland 60-10 Parts Catalog Extract is HERE

B58 PBV Location

Photo Courtesy of Nick E.



Gerdes A-850-8 or Cleveland 60-10 Fluorosilicone O-Ring Replacement Parts

from McPeck Aviation

McPeck's Gerdes/Cleveland Fluorosilicone O-Ring replacement set is priced at $25.

McPeck also offers Parker O-Ring Lube for $21/tube.

Click the PayPal logo below to make a proper payment to McPeck Aviation for your

Gerdes/Cleveland Parking Brake O-Ring Kit.





Click below to email Adam McPeck for additional details or to place an order



Musketeer owner Bruce B., offers the following excellent insight and photo of the Hoof valve

If your parking brake is a Hoof A53-T7 which is on many Musketeers and some Bonanza's, the seal that is probably giving you the problem was originally a round Teflon O-Ring looking "thing" that is larger than a normal -008 and smaller than a -010 O-Ring.

That unfortunately does not mean it is a -009 but it might have been. The Hoof seal has a chamfer on the ball side so the ball sits a bit lower or tighter in the ID of the O-Ring.

A -010 Teflon will not fit at all and neither will a -009 Teflon either - well it can be forced down in there but Teflon is hard. As such, a -008 fits loose but probably seals OK.

I used a -009 Viton O-Ring as the least worst alternative to the non existent Hoof seal. This might be called up as a AS568-009 V75-MS FKN O-ring where V75 is a Duro 75 hardness.

Also when putting back together, after you drop the ball bearing in, push it hard against the seal with the eraser end of a lead pencil just to sort of set the O-Ring and the ball.

When you put all back together, blow into the pressure end of the unit (the brass hex fitting end) and operate the lever. It will surprise you. Also do this prior to disassembly; probably it would not hold even the pressure of blowing. After the rebuild, you can then pressure test it - say to 500 psig for further confirmation.

The seal around the shaft is an MS28775-010.

The seal between the aluminum body and the brass hex threaded fitting is either a Boss O-Ring MS28775-6 or the more common MS28775-113 / AN6227B-11 O-Ring. I believe that the -113 is the better choice.


Here is the PBV for the later model F33 Bonanzas



Here are the IPC extracts for the F33 parking brake valve Extract #1 and Extract #2

Photo Courtesy of Tom N.



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 SN.



Thinking about adding Co-Pilot Brakes (Dual Brakes) to Your Beechcraft?



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


HERE is a Google Photo Album of how Jason M. documented his dual brake conversion.

HERE is another Google Photo Album documenting another dual brake conversion in a B55

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