LEXUS / TOYOTA Brake Master Cylinder Diagnosis, Replacement & Brake Bleeding (GS300/400 shown)

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On this episode I will show you how to determine if your Hydraulic Brake Booster Assembly (aka "Brake Master Cylinder" or "BMC") is going out, how to replace it and how to bleed the brake system properly. BMC noise (screeching sound) and subsequent failure is a common issue on many TOYOTA and LEXUS vehicles equipped with this type of system. Basically the accumulator pump motor wears out and starts making noise. Generally it increases in frequency and the noise tends to be more prevalent in colder months. As the pump motor continues to wear out, the sound will increase in frequency and duration. Some people lose brakes altogether and others, like me, live with the noise with reduced braking performance until we cannot stand it anymore and don't want to chance complete failure.

Fixing the accumulator motor is far more costly than just swapping in a used BMC. Many other OEM units fit the GS/Aristo and vice versa. In my case, I chose to swap in a BMC from an 02 SC430 with 116K miles on it. If you can find a late model SC430 BMC, that is ideal. The design is improved and the piston size is slightly larger than the 2nd Gen GS.

Pricing at the time of this video for a NEW unit, installed at a dealer is $2500-$3000. Expect to pay between $150-$600 for a used unit and about $30 for other odds and ends such as fluid. I found my 2002 SC430 BMC for $185 USD.

R&R and bleeding should take about 4 hours for a decent wrench turner.

TOOLS
Mechanics tool set including ratchet, extensions, 3/8 swivel, deep 12mm socket
10mm box wrench for bleeding
30mm deep socket (used to swap over the pressure sensor if you get a different used BMC); this is the one I purchased: https://www.amazon.com/dp/B08DK2ZY35?...
Turkey baster or similar (to remove fluid from old BMC reservoir which is optional)
Brake bleeding clear tubes (so you can see the bubbles during bleeding)

SUPPLIES
BMC
Brake fluid
Towels/rags

BLEEDING
1) BMC after replacement (optional; just turn each hard line nut at the BMC 1/4 turn while an assistant pumps 2X and holds the brake pedal down halfway)
2) Pump pedal 40X with ignition OFF (block of wood under pedal!)
3) Turn ignition to ON, let pump run 30-40 seconds (be sure to keep the reservoir full!)
4) FRONTS: Pump 2-3X and hold halfway, bleed pass front, then driver's front. REARS: Have assistant lightly touch the brake pedal (activates pump motor) and let the pump motor do the work. Bleed pass side first until all bubbles are gone or the pressure sensor chime goes off, then the driver's side rear last. FRONT or REAR order does NOT matter! Side to side order is what matters.

0:00 Trailer
0:23 BMC intro
3:21 Reservoir prep
6:11 Old BMC removal
7:44 New BMC prep
9:28 Bleeding process
14:01 Finishing up


MUSIC
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Persuasion (Instrumental) by RYYZN   / ryyzn  
Creative Commons — Attribution 3.0 Unported — CC BY 3.0
Free Download / Stream: https://bit.ly/-persuasion
Music promoted by Audio Library    • Persuasion (Instrumental) – RYYZN (No...  
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