1. Get syringe and remove brake fluid from the reservoir.
2. Put some old rags/cloth whatever underneath and around the boost assembly.
3. Disconnect the ecu and power connectors from the unit and unscrew the throttle cable bracket.
4. Loosen the nuts for the brake lines - 2 at the front of the unit, 2 and the side (don't touch the red coloured one underneath as that's from the accumulator) - and pull those line out of the unit.
5. Get inside the car under the steering wheel and remove the parts of the fascia obscuring access to the brake pedal (iirc 3 part of fascia come off and you'll need to disconnect the petrol/boot switch unit).
6. Remove the brake pedal spring and r-clip etc. That connects the master cylinder with brake pedal and then unscrew the 4 nuts holding the booster unit in place on the chassis - the one on the top left side is very difficult to get to.
7. Lift/pull out the old unit - gently and carefully so as not to get brake fluid all over the place.
8. Put the new unit back in. In reverse order - the 4 nuts holding the master cylinder assembly to the chassis are tightened to 18nm iirc (but do check as my memory may be incorrect).
9. Fill the new unit with brake fluid and then with ignition still of pump the brake pedal more than 40 times.
10. Reset the abs ecu - this is a must as the unit doesn't work correctly if there are critical error codes still stored.
11. Bleed the brake system - this is where it is different from the procedures I've seen written about this but here goes as it is the proper method according to the lexus manual: - with ignition off pump pedal rapidly more than 40 times - the pedal should get heavier to pump during the process
- turn the ignition on and listen to the accumulator pump which should turn off within 30-40 seconds.
- now pump rapidly the brake pedal 20 or more times (warning buzzer will go off and should then go off after a little while)
- with the ignition remaining ON bleed the the brake system but start with the front right (i.E. Drivers side), then front left side. Going on to the rear, start with left side and then right side.
(as a note while bleeding the system it isn't necessary to pump the pedal several times before opening the bleed valve because the pump and accumulator maintain system pressure. This also can't be done if you're bleeding the system on your own). You will hear the pump switching on and off during this procedure which is entirely correct.
- make sure you have a lot of brake fluid I used nearly three liters in total due to some stubborn air pockets, so be patient and always put the lid back on the master cylinder reservoir.
- if you're doing the bleeding on your own an ideal tool is the europat vizibleed - it's about a fiver from Halfords. No need for expensive pressurised kits.
- with this kit you can press the pedal a few times then walk round the car to see if there are bubbles in the tube, top up the reservoir and then return for more pedal pumping - just don't open the bleed nipples too far as fliud may seep out there instead of the tube.
- finally, once bled, turn the ignition off and again pump the brake pedal more than 40 times and check fluid level, topping up as necessary. You're done.