Reply to "Brakes locking up"

GhostRidr, The "serrated rubber" you refer to is a seal for the booster housing to master cylinder sleeve. The extended receiver tube from the master cylinder seals on the ID. of the seal and the booster housing seals on the OD. The pushrod moves through the center of the hole and will hang un-centered without the master cylinder receiver tube. That rubber seal maintains the vacuum in the booster, the adapter mounting plate should applied some pressure to the OD. of the seal against the booster housing. You will hear a hissing sound if this seal is not sealing properly.
I doubt it is related to your problem, I believe you have a master cylinder, booster or proportioning valve problem. Remove the master cylinder from the booster, then check the brakes. If the brakes are still holding that means the fluid cannot return to the MC reservoir, bad MC or proportioning valve. You can loosen the 2 fittings on the MC until fluid starts to leak out, then the brakes should be free.
If not brakes are NOT holding, then the pushrod/booster is not allowing the master cylinder spring to return completely. This can be a subtle problem, there must not be any mechanical force/binding on the master cylinder, the only mechanical energy to return the brake fluid is the return spring in the master cylinder.

Just because something is "new" doesn’t mean it’s operates perfectly or fits perfectly.