Removing a stuck master cylinder piston

Question:

Does anyone have a method for extracting a master cylinder piston that’s now stuck from long dormancy? It will move forward into the bore, but the spring lacks the sufficient pressure to overcome the resistance in the cylinder to allow it to be removed.

I have thought about epoxying a slightly-smaller-than-the-inner-diameter bolt into the hole and seeing if that method would allow its removal.

However, I’m open to any other (better?) approaches.

Answer:

If you may need to reuse the old piston then you need to get it out without damaging it. In that case, securing a bolt to the piston with epoxy and then pulling the bolt and piston out together is a good idea. If you don’t need to preserve the old piston then just drill a hole through the middle and use an old-fashioned slide hammer-type dent puller to yank it out.

In the alternative, drill a hole, thread a coarse screw in, and pull and twist the piston out with a pair of pliers.

Another possible solution is to pour a liberal dose of penetrating oil into the bore and after letting it soak for a while apply high pressure air into the orifice in the master cylinder reservoir. This approach may apply enough pressure on the piston to force it out.

Answer:

I have been a subscriber for a couple of years and have always been impressed with the quality of your publication. For the past five years I have been restoring a 1960 BMW 700 coupe and found that one of the project difficulties is the lack of available parts.

There are a few interchangeable parts with other cars, but for the most part replacing anything on this car is challenging and often frustrating. Right now I am trying to upgrade the original rear suspension. Since this car’s engine is in the rear, I would like to replace the shock absorbers as well as the coil springs. Getting NOS shock absorbers is not a problem but the coil springs are another story. The rear coil spring measurements are as follows: the outside diameter is 3.75 inches, the inside diameter, 2.75 inches and the length is 12 inches.

I have searched every possible Web site for a matching coil spring, with no luck. I am sure that there is another vehicle out there that used this type of spring, but I need some help finding it.

Answer:

Just finding other coil springs that have physical dimensions that are similar to your old springs may not help you because all coil springs are not created equally. Subtle differences in dimensions as well as materials can profoundly affect a spring’s performance and longevity.

Call the nice folks at Eaton Detroit Spring, Inc. eatonsprings.com). This company has been in business since 1937 and is a prolific manufacturer of both leaf and coil springs for the restoration market. If they don’t already have the specifications for your BMW 700 springs among their 24,000 or so blueprints, they can likely make what you need using your old springs and information in their archive.