Bare "plug" near brake master cylinder

Technical MGB discussion
Vic Butler
Posts: 475
Joined: Wed Dec 21, 2016 6:07 pm
Forename: Vic
Surname: Butler
Location: North West Hampshire

Re: Bare "plug" near brake master cylinder

Post by Vic Butler » Mon Apr 27, 2020 3:28 pm

On my October 1977 manufactured MGB GT the switch for the brake failure circuit is screwed into the master cylinder underneath it.
1977 Stage 2 MGB GT
1975 SWB Series 3 Land Rover with a later 2.5 petrol engine

Vic Butler
Posts: 475
Joined: Wed Dec 21, 2016 6:07 pm
Forename: Vic
Surname: Butler
Location: North West Hampshire

Re: Bare "plug" near brake master cylinder

Post by Vic Butler » Tue Apr 28, 2020 10:09 am

Further to my previous posting the brake circuit failure switch broke off when I was trying to loosen it ages ago. Using a mirror and a torch and a pointed thing I managed to extract the broken bit and fit a replacement.
No fluid came out.
The manual states that when bleeding the brakes the failure switch should be slackened off
three and a half turns to release the switch plunger from the differential piston in the master cylinder. However, if pressure bleeding is carried out this is not necessary as the brake pedal isn't moved. Only if the brake pedal is pushed down will the differential piston be moved and detect any faults.
As the switch has been disconnected the warning light won't work in the event of a brake circuit failure.
I realise now my previous post is superfluous.
1977 Stage 2 MGB GT
1975 SWB Series 3 Land Rover with a later 2.5 petrol engine

Dave Wheatley
Posts: 96
Joined: Fri Sep 28, 2018 4:55 pm
Forename: Dave
Surname: Wheatley
Location: SW Scotland

Re: Bare "plug" near brake master cylinder

Post by Dave Wheatley » Tue Apr 28, 2020 11:43 am

Thanks Vic.

I realised looking at the diagram that no brake fluid came in contact with the pressure switch, and so lack of a switch would not compromise the braking system apart from lack of a brake failure warning light.

So the simplest answer was to just leave well alone.

However belt and braces meant that to seal up the broken off part of the switch would delay any corrosion of the mechanical parts of the piston operating the switch.
1978 MGB GT
1931 Austin 7 RM
1955 Standard 10
1972 Ford Cortina
No modern!

Post Reply