92-00 Lexus SC300/SC400 Brake Master Cylinder and Booster Replacement
Like I said in the last couple articles, if you don't flush and bleed your brake fluid system regularly, the brake fluid itself is designed to absorb moisture and in time dirt and grime start to build up within the system. In turn, the seals start to dry up and deteriorate which causes the brake fluid and pressure to leak.
Whenever you pump your brake pedal, your brake master cylinder's job is to push the brake fluid throughout the system to push the brake calipers pistons and cause the brake pads to squeeze the brake rotors and cause the car to slow down or stop. All the while the brake booster gets air from your engine's intake and use it as a pressure to help the brake pedal push the brake master cylinder with ease.
The common symptom of brake master cylinder failure is a mushy feel to the brake pedal, deeper brakes and loosing brake fluid from the reservoir. The brake booster on the other hand, will give you a very stiff feel and very hard to control braking. Although what I encountered was brake booster failure, it is customary to replace both, if it’s the booster that fails.
I used an old gear oil pump to drain the reservoir as much of its brake fluid content. Place rags under the brake master cylinder to prevent any brake fluid from ruining your engine bay paint.
Disconnect these two brake lines on the left side of the brake master cylinder with a 10mm open wrench. This shouldn't be so tight, just be careful to not damage the brake line flares or you'll add more work.
Unplug the level warning switch connector on the right side of the reservoir.
Take off these two 12mm nuts that hold the brake master cylinder on to the brake booster.
It's always a good idea to place old and new parts side by side to see if there’s any differences with them and if there are parts missing or needed. I already bought the gasket that goes between the brake master cylinder and booster, but wasn't prepared for the rubber grommet and just had to reuse the old one since it was still in pretty good shape. The refurbished brake master cylinder doesn't come with the brake fluid reservoir neither, which isn’t a problem reusing the old one.
With the brake master cylinder off, you can now work on taking the brake booster out.
Unplug the brake booster vacuum line.
This is one of those jobs that require you to find your inner contortionist to somehow make yourself fit under the driver side dash board and take off these four 12mm nuts that hold the brake booster on to the firewall. The two nuts at the bottom are easily accessible, while the upper left nut is a bit of a tight squeeze. Use an open wrench for the upper right nut after loosening a couple of bolts holding the black module in front of it.
Loosen these two bolts to free the module, to gain access to the upper right nut with an open wrench. One bolt is beside the brake pedal lever, and another right behind the steering shaft. The bolts are not too tight, once loose, you can remove it by hand.
You’ll need to disconnect the brake booster from the brake pedal. With a needle nose pliers, pull the spring(orange arrow) off the slide pin; be careful not to damage or loose it. Then pull the cotter pin(red arrow) off the slide pin. Lastly, remove the slide pin(purple arrow). And your brake booster is free to go.
NOTE: Once the brake pedal is free off the spring, it will make contact to the brake light switch atop. You can either secure the brake pedal lever by hooking the spring to the hole for the slide pin, or jam a tool between the pedal and the carpet.
Free this small black fuse/relay box from its clip to give space in getting the brake booster out.
Just pull the brake booster out slowly out of its holes and it's out.
The brake booster for the SC's only varied by the factory equipped TRAC control and the ones without. The ones with TRAC have three bolts for the brake master cylinder.
Installation is just the reverse of removal. The new brake master cylinder needs to be bench bled before install and should come with instructions of how to do it. Use the required DOT brake fluid.
Disclaimer: Use at your own risk. If you don't feel comfortable doing a procedure then don't do it. This information is to be used as a guide and is for illustration purposes only. By no means is my site a definitive source for the procedures listed; it is simply how I or the tutorial contributor did things. The tutorial contributor, and I are not responsible in any way for anything that happens as a result of following these guides.
Safety First: When working on your car put safety first. Use common sense and be careful. If you're doing electrical work disconnect the battery. If you need to jack up the car use jack stands and wheel blocks. Common sense is the key.