Brake system not holding pressure?

[keenasmustard]

I have reposted this in the 100 series section as I believe 100s run the same ABS accumulator / brake master cylinder as the 105.

I have recently purchased an automatic HZJ105 Landcruiser with ABS and I am finding that the brake system is not maintaining pressure. The brakes generally work OK and bring the vehicle to a stop, but after a few seconds the pedal softens and the car begins to creep forward, requiring you to push the pedal further to stop it moving. If I'm stopped for a while I need to release and reapply the pedal to get pressure back.

There are no visible leaks on the brake system and the the fluid level in the reservoir has not gone down. I understand these vehicles run a hydraulic booster / ABS accumulator which is prone to problems, but there are no warning lights coming up on the dash and the accumulator motor is not making any strange noises. I also believe the accumulator and master cylinder come as a complete assembly from Toyota for about $3500 AU, but the accumulator motor can be rebuilt for about $200.

I am thinking that the problem may be an internal leak in the master cylinder. Keen to hear thoughts or opinions from anyone who has experienced similar issues. Thanks in advance.

 

[uHu]

Not having a lot of experience with the issue myself, but that sounds like an internal leak in the master. There is a OE service kit with all the seals you need, and a good write-up on mud: Master Cylinder Rebuild - DIY - [Leaving Land Cruiser Club]
The piston is somewhat complicated with a double action, piston inside piston.