brake pedal sinking

[high_lux]

we have a 98sh 3L diesel toyota hilux. the brake pedal slowly goes to the floor and is soft when the engine is running, when not running it seems normal. It has a new master cylinder as i thought that was the problem after checking the wheel cylinders and calipers,adjusting the shoes, bleeding the brakes LOTS...etc and there was no aparent leaks but it still does the same. If i pump the pedal about 5 times when the engine is running the brake light comes on, how ever after disconecting the sensor in the brake booster it no longer comes on. It looks like it has a very new altenator but it seems to be producing sufficent vacum for the booster. whats going on? is the booster faulty, if so i thought the pedal would just be harder to push down and not slowly travel to the floor? If i start the engine with my foot on the pedal you can feel the booster asist and pedal starts going down?

[matt dunn]

If you hold it down long enough does it make it to the floor?

[Lloyd]

As above, if it gets most of the way to the floor but never reaches it (ie, you don't run out of brakes) then its normal. A lot of the Prados and the like have pedals like that.

And that sensor is for low vacuum, should probably leave it hooked

[high_lux]

yeah i figured its for low vacum, but does this always happen? the pedal does not feel normal to me at all, I have left the sensor connected but i just disconected it to make sure it was the sensor making the light come on which it was...

[johndoe1025]

its obviously got a problem if your pumping the pedal and getting a warning light, should have the vaccum pump looked at maybe?

[Lloyd]

Most diesel will do that with a few pumps at idle

[johndoe1025]

hmm true, will havta try that tomorrow in the work van