6 replies to this topic

[Davidmt]

Just removed the brake and clutch master cylinders.  I have bought a replacement clutch master and thinking about doing the same for the brake cylinder as not that much more than the refurb kit and the brakes are quite fundamental!. 

 

The new units do not come with a brake switch (unless you get one in the reservoir cap).  I have removed the existing switch from my original brake master cylinder - it was covered in crud but have cleaned it up.  No idea if it works or not so any ideas on how to test it before I buy the extra cap?

 

Thanks

 

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[nicklouse]

The brake switch (brake lights) was either hydraulic on the front right banjo connection or was mechanical on the pedal.

 

the master cylinder had the low fluid level warning switch that along with the illuminated switch on the dash was used to advise you if the fluid was low or if the warning bulb has gone.

[Davidmt]

Yes. It's the fluid switch. Removed from master cylinder but unsure how to test. It has continuity between both pins and the metal tip of the switch.

How does it switch?

[Designer]

Hi Davidmt

 

 

Try the following as you still have the old master  brake cylinder.

Refit the newly cleaned up switch.

Block all the exits of the cylinder fill the reservoir with brake fluid (old will do).

Rig up a circuit of battery switch and light bulb.

Slowly drain out some brake fluid through one of the blocked exits and hopefully bulb will light when the fluid level is too low.

Thus proving the switch is still working.

 

Paddy

Edited by Designer, 03 March 2024 - 04:17 PM.

[Quinlan minor]

Yes. It's the fluid switch. Removed from master cylinder but unsure how to test. It has continuity between both pins and the metal tip of the switch.

How does it switch?

It’s a float switch.
Unscrew it and hold it above the fluid.
The warning light should now illuminate, providing the ignition is on.
Assuming that you’ve already pushed the “switch” and the bulb has lit (test facility).

[Ethel]

Looks like  it's from a GMC167. It has a built in shuttle valve, that's accessed via the hex headed cap on the upper end.

 

If there's a pressure difference between the upper & lower circuits. The one at higher pressure pushes the shuttle to close off the lower pressure one. So fluid loss would be prevented if the cause was severe leak from a failed brake pipe etc. The switch sits in the middle of the shuttle and is operated  by ridges that will lift the plunger when the shuttle moves. You can just press on the end & test for continuity to test the switch, but that won't show if the shuttle is ok.

 

 

 

edit:

 

 

.... I think the switch circuit is a bit craftier than the float switch's, so pressing the rocker does more than just test the bulb.

 

edited edit:

 

Curiosity got the better of me...

 

There should be continuity across the electrical connections (pressing the rocker supplies the warning lamp via them).

 

If there's a failure, that operates the shuttle, the continuity is broken, but the shuttle switch earths the warning light via the cylinder.

[Spider]

These 'switches' aren't the same as was originally fitted to the Mini and in fact, are not a switch at all, but an electrical contact.

The 'White' switches were just that, a normally open single pole, 2 terminal switch, pretty straight forward.

These 'black' devices are just an electrical contact. The shuttle in the Master they work with is a different design to those used with the 'white' switch. These work by making contact with the shuttle when in a 'fail' mode and earthing through the shuttle.

I'd suggest blanking off the port in the master cylinder this fits in to (3/8" UNF) and fitting a float switch type cap, they are so much more reliable too.