Austin Healey Power Brake Servo Repair

No, this Texan has not been eating Loco weed. There is a connection between windmills and brake servo units.

The trail of events leading to the sources of key components missing in a brake servo repair kit is quite unique.

After suffering a servo unit failure, I assessed the damage. All that is needed is a repair kit. Wrong! The special coating had worn off the inside of the vacuum cylinder. The leather cup was damaged beyond repair and the air valves and seats needed some attention. The seals were also worn and leaking. This is where the unique trail began.

Because Kay and I planned to attend the Southeast Classic in Ashville, NC, I was reading a story in Healey Trails (North Texas AHC newsletter) about a past Classic. On the very next page was an article, “Restoring The Brake Servo Unit Vacuum Cylinder” By Richard Strunk. Richard provided the solution to the statement in the shop manual “No lubrication is needed for the piston seal as the seal and cylinder are specially treated during manufacture.”

The dry film coating that Sandstrom Products Company sells is 26A. This product works well for recoating the inside of the servo vacuum tank. A phone call and $15 brought a spray can to my door.

Now for the WINDMILLS. On a trip to Red River, New Mexico (in my BJ 8 of coarse), I recalled discussing with a friend, his unusual business. He sells windmills to many of the Indian tribes on the reservations in New Mexico to pump water. One of the major replacement parts is the leather cup used in the pumps. After many unsuccessful attempts to purchase a new leather seal from Healey parts sources, I called Beck Aitkinson and asked where they bought their’s. He said “one of the few sources is A-1 Gasket Company in Fort Worth, Texas.” This company will make an exact duplicate of the leather seal. This relates the unique trail in search of some missing components in repairing my servo unit.

The following are some special operations and repairs that will supplement the workshop manual repair procedures. After performing the special operations, I suggest you assemble the servo according to section MMM.15 of the workshop manual. The two plastic air valves showed some wear on their seating surface. I am told you can swap one for the other and reassemble them in opposite holes to compensate for wear if they aren’t worn to greatly. You can also use very fine emery paper and a flat surface to help true the sealing surface.

I did not use any of these methods. Instead, I used a lathe to chuck the valves in and turn a true seat on the face. I think that truing the valves on a lathe is the most precision method to ensure a good seat for proper operation of the servo. Your goal in retruing the valve seats is to obtain a non leaking air valve seat. The two seats in the valve body where the plastic air valves make contact should be true and free of pits. My unit had some pits caused by corrosion.

If the surface is not badly worn or corroded you can use a piloted counterbore to resurface them. To spot face the seats you need a piloted counterbore of the proper dimension. The operation in its simplest form is accomplished by holding the body square with the counterbore in a vertical mill or good drill press. Using a low RPM, to eliminate chatter marks on the seat, start the pilot on the counterbore into one of the holes. Lower counterbore until you cut a good true clean seating surface on the valve body seat. Remove as little material as possible. If this sounds like to much for you to do, or you don’t have the tools, take it to most any machine shop to have it done. If by chance your valve body seats can not be salvaged by this method, have a machine shop bore and rebush the seating area.

As mentioned, Richard Strunk has done the detective work on the dry film lubricant for coating the inside of the large vacuum cylinder bore. The Sandstrom 26 A product works very well. The cylinder bore should be super clean before spraying light coats of dry film lubricant on the bore diameter.

A word of caution, if your leather seal has been exposed to leaking brake fluid it must be replaced.

Tom Taff was rebuilding his servo unit and I let him use some 26A to coat his cylinder. Because the leather seal had absorbed some brake fluid, when he assembled the unit, the remaining fluid in the leather attacked the coating. The most important part is the leather seal in the vacuum cylinder. Most importantly, because I know of no Austin Healey parts supplier that sells them.

The A-1 Leather Gasket Company of Fort Worth, Texas can supply them for about $30. They are made of leather to the same dimensions and thickness as the original. I have talked to them about this application and they will know what you want when you contact them.

The leather seal on your piston can be removed by prying the retaining ring off toward the aside that has the valve stem rod attached. The new leather is assembled by pressing this ring on until it holds and seals the leather cup. The foam rubber material included in a servo repair kit is, and probably will remain in future kits, much too large. When this material is placed under the leather cup it will cause to much pressure on the lip of the cup. This increased pressure will not let the piston move freely for proper operation. Therefore a smaller diameter foam backing ring must be used. Tom Taff found some �” round material that works very well. This material was purchased at Home Depot.

I hope the information and sources will help in repairing your servo and keep your Healey healthy. Drive it !

Sources:
A-1 Leather Gasket Company 2103 Brennan Circle Ft Worth, TX 817-626-9664
Sandstrom Products Company 224 Main Street Port Byron, IL 61275 800-255-2255
Home Depot Retail Hardware Chain


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