Moss Motors, Ltd

I was going to take my 76 Midget to work this AM but the break warning light stayed on when I started her up. I took the Sprite instead.

Here's the question, what exactly turns that light on? I don't have any schematics or manuals in-front of me, and its eating me up inside!

You know how it is when your baby's sick!

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On their death bed, nobody ever said, "Gee I wish I'd spent more time at work!"

'68 Sprite 1275
'76 Midget 1500

d,

There are two things which will illuminate one of these lights, assuming the warning system is functioning correctly:

 1: The handbrake is on. (Maybe just slightly), the handle will sometimes sort of "rebound" after being let go.

 2: There is, for one of several possible reasons, uneven pressure in the brake system, front to rear. The master cylinder is divided into two separate but aligned segments. When one produces less pressure than the other, a shuttle or bobbin in the brake pressure warning valve is displaced to one side (the "bad" side), tripping a switch as it moves, to warn that there is potentially a problem with that half of the system. Most often, it indicates that the master cylinder has bought it.

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Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon

mb66, 

That slide bobbin is the same set-up on my '68 Sprite (albeit on the opposite front fender wall).

When I came home today, I started the Midget and the light was off. The breaks have been on the week side so I have to look at the system anyway.

Can worn pads turn on that light?

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On their death bed, nobody ever said, "Gee I wish I'd spent more time at work!"

'68 Sprite 1275
'76 Midget 1500

Hey davey. From what Bill described it sounds like you have a Pressure Differential Warning Assembly (PDWA) similar to the one on my TR6. About a year ago, the warning light just came on, no leaks and no brake bleeding to cause the shuttle to shift position. 

 When the PDWA shuttle shifts position, it pushes a plunger up to bridge the contacts in the "plug" and complete the circuit so that the warning light comes on.

 In my case it was corrosion or some kind of conductive crud built up between the contacts that completed the circuit. It took some cleaning, but that was all. Another cause is that the wire in the plug in the PDWA switch can come loose and ground itself on metal and light the warning lamp.

It's not supposed to be an indicator of wear, just a loss of pressure in one side (front or rear) or the other in the braking system.

 At least that's the way the Triumph works. 

Ya pooly,

Unfortunately I'm not learning anything that I didn't already know. I guess it was wishful thinking!

If, after inspection, the light comes on again, I guess I'll be disassembling and servicing that PDWA..oh well.

Thanks anyway!

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On their death bed, nobody ever said, "Gee I wish I'd spent more time at work!"

'68 Sprite 1275
'76 Midget 1500

Guys,

We've had cases where the spool was displaced even though it seemed as though the systems were both doing their job. We have also had a spool go off center during a bleeding situation. In both these cases, we try centering the spool with a pick and screwing the switch back on to see how it behaves. Often, that's the end of it. Who knows?

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Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon