Sticky brakes and boosters mystery

[chromeowner]

As long as we're on the subject, there's an odd situation popping up where the brakes are sticking after rebuilding the booster. A couple guys have reported this recently. Problem is that it makes no sense mechanically; the rebuild is simply a replacement of o-rings and seals, and nothing fundamental changes. Even odder is that both guys reported what sounded like ABS activation before the brakes jammed.

Already considered and probably eliminated:

The brake pedal linkage adjustment; it has to be kept short enough that the booster piston fully retracts with the pedal up.

Activator rod reversed- The link rod between the two cylinders must have the end with the shorter tip and the beveled shoulders inserted into the booster. Backwards might (but just maybe) push the primary piston of the master cylinder in a couple mm at rest.

It's a head scratcher; ideas welcome.

[Mark in SBA]

Rod "shoulders" facing out:



and in real life:



I certainly wouldn't suggest either way works - it appears the rod is keyed into the brake master cylinder. Also, the shouldered end appears to have some hardening applied - the metal ball-end is definitely a different color/texture.

[Mark in SBA]

The brake booster actuating rod/clevis is misadjusted and opening the boost valve even at rest. The repair manual states the necessary clearance and I've found that while the booster is out of the car it's possible to inadvertently twirl the clevis around a bit and lengthen it. Once it goes back onto the firewall, it's too long.

[TxGR8White]

Had this on a BB a while back, turned out to be the rod was installed wrong side in. Truned it around and everything was fine.

[chromeowner]

make any difference which way the rod goes. The correct way is with the shinier end with the shorter nib and the beveled shoulder pointing into the booster. The small inner piston cap piece with the dinky o-ring is perfectly shaped to fit it that way. However, the receiving end of the primary master cylinder piston is basically amorphous, not shaped to receive anything more defined than a simple spherical end. The length of rod sticking out of the back of the MC piston is the same either way, and the rod will fully seat in both pistons regardless of orientation.

I'm beginning to think that there might be some difficulty in assembly as far as getting the inner piston to seat down in the bore fully while the springs are installed???