Morris Minor Owners Club

I have a servo fitted to my brakes, which work very well and the servo helps to counter the shoes being the modern, non-asbestos type. However, one weird "feature" seems to be that on the first press, the brake travels further than on the second or later presses. But after about 10-20 seconds, it'll "reset". Any idea what could be causing this? I wondered if it took a push to switch the servo from the bypass to boosting the pressure but that it then holds for a while.

I think this description of how it all works will answer your question.
On the first press, the Servo is starting from Nothing.
http://www.mgb-stuff.org.uk/servo.htm

Before you press the pedal there is no pressure in the brake system and the pistons will be as far in the cylinders as they can. Once you press the brake pedal, the pistons move out and push the shoes out.
Inside the master cylinder is a rubber washer which retains some pressure and keeps the pistons in contact with the shoe and the shoe in contact with the drum. The next time you press the pedal less fluid is requires moving to operate the brakes.

Is the rubber washer you speak of the same seal which is removed when converting to disc brakes? I recall seeing that and wondering why. What is the benefit with drum brakes plus servo?

nwxh wrote: ↑Thu Oct 21, 2021 6:14 pm Is the rubber washer you speak of the same seal which is removed when converting to disc brakes?

Yes, it looks like a top hat. You need to remove it when fitting disks or the retained pressure will keep the front brakes applied.

Fitting a servo reduces the effort required to press the pedal, so if you have dodgy knees you need less effort to apply the brakes. You should note that a servo will not increase braking efficiency.

Has the system been bled properly? To me, it sounds like air being compressed on the first stroke. Also ensure that all brakes are correctly adjusted.

The brakes were adjusted recently but it's possible that there is some residual air. Does the air kind of dissolve and then precipitate out after 10 seconds or is that more likely to be the effect of the top hat?

I would check to see if you have an air bubble on the brake light switch. This took me years to find literally. Creates thr symptoms you describe.

See this past topic and discussion:
viewtopic.php?f=4&t=73555&hilit=brake+servo#p667135
If your servo is mounted with the Air Valve topmost, it is an inbuilt air trap.
it will trap far more air than the brake switch.