hey Guys, My wife's LS 430 brake pedal started stopping when pedal is almost on the floor. the mechanic that works on it when I'm not able said it was the master cylinder, I ordered one from partsgeek.com, put it on bleed system and the same thing. So I was told it could be a bad master cylinder so I ordered another one from Rockauto.com and installed it, and the exact same thing as the original. could there be another issue or am I to believe both new master cylinders are bad? Please help. All advise is appreciated.

 

Is it sinking and you can pump it up or is it just engaging close to the floor but otherwise feels normal?

 

Being on this forum since 2006, I don't remember hearing of a member replacing a master cylinder. With your replacing 2 masters, I'm fairly certain that isn't your issue. Wish I could give you a suggestion of where else to look but I'm sure someone on CL will chime in. Good luck and let us know how you make out.

 

I had that issue last year, the master cylinder had failed and leaked fluid into the brake booster. Both needed replacement, the brake booster (44610-50360) is a pricey part.

 

 

Sounds like air in the lines to me.

 

Hopefully air, don't ignore it....you don't want to unexpectedly not have the brakes work when you really need them....my .02. Ask someone to bleed all 4 calipers, I don't think the Lexus dealer does that with a normal brake fluid flush (I was charged $69 by a dealer, and in a matter of a day the color changed). Maybe if you ask they will, and charge more, not sure.

 

+1 on air in the brake fluid system... Also assume that you have confirmed that there's no leaks.

Replacing the master cylinder introduces air into the brake lines including the ABS. Attached is the complete bleeding procedure for post master cylinder replacement. The most important part of the procedure is to use new and correct type of brake fluid. The wrong or contaminated fluid with different viscosity will allow bleed-thru within the master cylinder and can damage the seals.

Other less common causes include:
1) Defective booster, or loose/cracked vacuum line to the booster.
2) Flexible rubber brake line balloons under pressure.
3) Bad (out of round) rotor that pushes the brake pads back excessively. This requires the pads to move a greater distance when you step on the brake.

 

Your LS430 may have a trapped air in the ABS & TRACTION actuator. You need to drive solenoids and the motor there using a special tool to bleed it. Without the tool, it is almost impossible to bleed fully.

 

 

I would go to a shop that has a good quality bleeding machine and try that brother, sounds like air, sir!

 

The following worked for me after numerous bleeding of the brake lines. To help get air out of the ABS system. Find a grass, dirt or gravel 'runway' or space to activate the ABS multiple times. Personally, I avoided dry pavement for this procedure as its just too hard on the car, suspension, tires, etc. Drive moderately and safely around 20mph and lock up the brakes on the lose ground, causing the ABS to pulse the brake system. Do this multiple times, 6+. You may even feel the brake peddle will get firmer from just this procedure. Best to follow this procedure with another manual bleeding routine.

I use and prefer pressure bleeding first as shown in the bottom image with a fabricated cap that I made from a visit to the hardware store attached to my home-made pressure bleeding tool. Also typically finish off with a 2 man bleed process to get the best results. Have plenty of quality brake fluid on hand and don't let the brake fluid reservoir run out or you are back to square one with air in the system and have to start over ;-).

BTW, I too thought it may be the master cylinder. To confirm, I sealed off the master cylinder from the rest of the system, using some crimped off brake line adapters pickup from the auto parts store shown in this picture below and tested the peddle, it was as hard as a rock. Moved on to change all brake lines (14 yrs is long enough on the originals) while typical bleeding and fresh pads helped, peddle was still to low for me. The forced ABS procedure above was my solution.

Hope this helps others.