Or the best kept secret in automobile maintenance? I'm referring to the dire warnings seen often here, similar to: "...if you drive the pedal to the floor while bleeding the brakes, you will badly screw up your master cylinder."

I've questioned this precaution since seeing it here on the BrickBoard, but nowhere else in my fairly extensive auto repair library. This includes the Volvo Green Books for 140 and 240—both of which use the dual-diagonal brake system with the double piston master cylinder, and permit pedal bleeding in lieu of the pressure method.

The 1971 140 manual says: "Check to make sure there is a full return on the pedal and that neither carpets nor suchlike prevent full travel (about 5 1/2") from being utilized during bleeding." And later: "Slowly press the brake pedal down to the bottom".

From the 1975 on 240 Manual: "Unscrew the bleed screws and gently pump the pedal 5 times. Keep the pedal depressed and re-tighten the screws."

The 700/900 Brake Manual does not mention pedal bleeding, but when replacing calipers, advises: "...the brake pedal must be depressed throughout the operation to ensure that the system is not drained of fluid." It also shows a drawing of a blocked-down pedal, saying: "Lock brake pedal in depressed position."
It implies full pedal depression and, like the 140/240 manuals, offers no warnings or precautions otherwise.

I'll admit the peril seems so plausible that I'm wary of going all the way myself. But why is the BB the only place it's mentioned, given the world of Master Cylinders out there that have been getting pedal-bled for decades?

My guess it that once upon a time, someone here on the 'Board found rust and pits in exceptionally bad MC and posted about it. Then after being repeated and embellished, it became BrickBoard lore to be applied to all Master Cylinders forever.

• So does anyone know of a reputable, documented source that warns against the heartbreak of "full pedal travel"? I have yet to find it described anywhere else — not it in some 45 years of DIY car repair.

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Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.