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Brake Regulator??

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Is there any kind of regulator in the brake system of a drum braked Defender?

The brakes are very spongy on the 1st press of the pedal, but the next press is what I would say was normal. During regular braking, ie around town, it is fine but any on longer runs (ie around 5 mins between presses) it seems to lose pressure and needs "primed".

Also the brake warning light came on yesterday but there is plenty of fluid in the reservoir, there didnt seem to be any problems and the brakes were working as usual.

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Sounds like theres play in a wheel bearing or similar.

The movement knocks the caliper pistons back, so the first press is need to push them back against the disk.

Afaik the light is connected to a Pressure Differential Valve, ie it detects a difference in pressure front to rear, rather than loss of fluid.

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I'd suspect you have a slight leak somewhere if the light is coming on. It is probably detecting braking that is not of normal proportion (cant remember what the split normally is) and is thus setting off the light. I havd it on my 110 and found a very slight weep under the rubber boots on the rear cylinders on both drums. I changed them and bled the system and the light has never come on since. The light only started to come on under heavy braking, my leak was not enough to cause it under gentle/slight braking.

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Did it come on under braking or just while driving along? Perhaps on an incline?

On my 200Tdi the light just measured fluid level. It flashes and flickers if the reservoir level isn't at pretty much max.

Some models (don't know which I'm afraid) there is a pressure differential valve that warns you of a pressure difference between front and rear lines (ie. a leak).

Mine has a 'contraption' of sorts on the chassis rail below the master cylinder, but there is no wiring coming from it that I can see. I think it may be a device designed to close off a circuit if a leak develops.

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yours is a G valve, to prevent the rear brakes locking prematurly under braking. some 110's [such as my '89] have a PDWA fitted to the vertical face of the drivers footwell on the engine bay side, this shuts off whichever brakeline front or rear if a leak is present on braking & gives a dual line front/rear split brake system, later vehicle this PDWA was dleted & replaced with the brake fluid switch cap to detect a low fluid level either through lack of top ups or leaking lines.

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