Brake pressure differential piston/switch question

[Sean Roth]

So I rebuilt my master brake cylinder.

For those of you with knowledge about the inner workings, I am curious how the pressure differential piston works. I know it moves and releases pressure on the switch, but which way does it move?

When I put it back in I noticed that it seats without brake fluid pressure in the exact spot to line up with the pressure switch. Is that normal?

How can I test it to make sure it is working?

Thanks,

Sean

SF Roth

[HDRider]

It just looks for pressure differences between the front and rear portions of the master cylinder. Once it trips over the switch locks the piston in place causes the light to stay on. That is why you have to remove the switch when pressure bleeding the brake system.

There is a seperate pressure regulator just in front of the master cylinder to regulate pressure to the rear brakes to avoid rear wheel lock up.

Edward Hamer
Petaluma CA

[Sean Roth]

So I would think that if I am bleeding one set of brakes, front or rear, that the switch will turn the brake light on in the dash due to the piston sensing a pressure differential. Is that true?

SF Roth

[dursleyman]

Not sure if its that sophisticated, but it should react to a total failure in one of the circuits.

Russ

1980 TR7 Sprint DHC
Dursley
UK

http://tr7russ.blogspot.co.uk/