The car was munching miles over long trips and was performing well for a few months. Slowly, the brakes started feeling weird. The Montero's brakes are amazing and are pretty strong. The pedal started sinking on quick successive braking, I was not feeling confident to drive like this. This had to be fixed.
The Montero comes with the ASIN's Brake Booster unit similar to the one on the Toyota Land cruisers. This is an ABS Module + Brake Fluid tank + Brake Fluid Accumulator and the Accumulator's motor all combined into a single unit. The Brake Fluid accumulator is a pressurized metal canister that holds the brake fluid under pressure and a motor feeds the fluid into this canister. This keeps the brake fluid at constant pressure and boosts the brake. Every time the brake pedal is pressed, the fluid from the accumulator is passed on the brake lines, the pressure decreases in the accumulator and the motor is switched on immediately to pump the brake fluid from the tank into the accumulator.
Since the accumulator holds the fluid with high pressure, the brake pedal feel is consistent and pedal never feels hard even when the engine is switched off. Compared to normal brake booster setup where the pedal gets hard by pressing it 2 or 3 times when the engine is off, this system will need you to press the pedal 30 to 40 times for the it to feel hard. When the brake pedal is pressed 30-40 times, the brake fluid from the Accumulator will all get released into the brake fluid tank by then and only then the pedal will start feeling hard.
There are only 2 failure points in this unit.
1) The Accumulator - Overtime, the pressure drops and it starts making chirping noise. That's the time to replace this.
2) The motor that feeds the accumulator - This is a simple motor with carbon brushes and over time, the brushes dig into the contact surfaces and finally it stops working. When its about to fail, you can hear this motor struggling to build pressure and it will run longer than usual. Its important to catch this before it fails, because if this fail, there wont be any pressure in the system and the car will crash.
The accumulator was not making chirping noises yet and our problem was diagnosed to the motor. So I ordered an motor rebuild kit from
ebay.
The kit consists of 1 commutator, 2 copper-graphite brushes and 2 bearings
Let the pictures tell the story!
Don't loose the metal wedge connecting the motor and the accumulator
Inside the motor was too dirty and the commutator was worn thin. Glad I caught this on time.
Old vs New commutator.
All assembled and ready to go in. Notice the spring washer that goes between the small bearing and the motor casing.
All Assembled.
The brake was bled twice and the brake feel was back to normal.
Did a 700km trip to Coimbatore after this and the car performed very well.