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my drum brakes are building up pressure


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iv got a 1990 200tdi 90 defender iv been getting a build up of pressure in the rear drum breaks .on a long drive the break peddle bites at the bottom and ends up at the top and eventualy I can feel the breaks binding .iv had the car 2 years and its allways done this .iv now changed the whole system apart from the valve that's bolted to the bulkhead can anybody tell me what is its function and where can I get one or can it be stripped down .its only connected to the rear drum breaks if that helps .ps sorry for the pic I got it off the net

post-12254-0-44117800-1462296610_thumb.jpg

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That valve limits the brake pressure to rear so the brakes don't lock up before the front brakes have done the major braking effort & prevents the vehicle swapping ends too, don't think there's much working parts inside, a ball valve in a inclined gallery.

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Yes, as I understand it is a "G" valve. When you stop quickly, it closes off the rear brakes the harder you stop. I would take it apart and clean it out. These are the sort of things that die when people do not flush the brake fluid for a long time.

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the only thing I can think it may be is that the ball is getting stuck and stopping the fluid from returning back .every time I put my foot on the brake it build up the pressure until the brakes start to drag.if I put my foot on the pedal hard for a few seconds it seems to correct itself and its only on the back brakes . it may just be some carp in the valve it was an old farm vehicle and we all know how they get abused

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I had a similar problem when I adapted a RR master cylinder & servo to a Series pedal box - the master cylinder needs the pedal actuator to release fully (with a bit of slack) or it will gradually pump up and lock the brakes. In my case, I needed a spacer between the servo & pedal box to allow the shaft some slack. I don't know if there's adjustment in a standard truck but it sounded so similar to what I had I thought I'd mention it - possibly a previous owner has replaced the servo or master cylinder and not got it quite right?

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