Brake booster pressure fade

[Drew Advanced Member Find all posts View Profile Close Drew]

Hi all,

I've noticed something strange with my Prado. When the vehicle is parked for a number of hours and I return to the car, the brake pedal is rock hard as if all the vacuum boost is lost from the emergency accumulator.

Every other car I've owned (apart from my 1958 Morris Minor which doesn't have a booster!) there is usually still pressure (vacuum) in the accumulator the next day, usually enough for a couple of pumps of the brake pedal.

Could others please check this in their Prados, just see if the brake pedal feels normal (ie it has power assist) after the vehicle has sat overnight. (Without the engine running of course!)

I remember from years ago that this was a sign of a slow leak from the booster emergency accumulator.

I'll put up a poll if people find it easier.

Cheers,

Drew.

[Drew Advanced Member Find all posts View Profile Close Drew]

Thanks for the reply Matt,

I was thinking about this a bit more today and thought that maybe it has something to do with Emergency Brake Assist. I've not owned a vehicle with that feature in the past.

ABS systems don't have anything all that different when it comes to the booster system, but I would assume that EBA systems have a different soft of boost circuit so that can apply max effort brake output once a certain input is reached.

I haven't tested the ABS/BA system in the Prado yet as I was waiting for the pads to bed in.

Cheers,
Drew.

[John Member Find all posts View Profile Close John]

I tried mine a couple of times over the weekend. The longest time between engine off to pumping the pedal was 14 hours. Each time I could pump 3 to 4 times before residual vacuum was lost. Same as all my previous cars.

Mine's an 05 TD auto.