Falling brake pedal

mjmanning · November 15, 2020

Could use some help and I will confess that I am not a mechanic! Bought a 2004 330 for my daughter and immediately noticed a falling brake pedal. Had the master cylinder replaced twice (!) and the problem still isn’t solved. Was assured the lines were bled. Mechanic guessed maybe it could done the abs pump? But I really can’t afford to keep spending money on fixes that aren’t working. Could it be the pump? Could it be the master cylinder booster which I did not replace? Has anyone had this ongoing problem? And lastly, I wonder if this is even worth fixing??
thanks in advance for any help. P

1990LS400 · November 15, 2020

Your mechanic "guessed"? Maybe you need a technician with diagnostic skills ... perhaps a Lexus dealership.

mjmanning · November 15, 2020

The dealership prices are out of my budget, including their $175 diagnostic fee. So I was hoping to get some ideas or advice here before proceeding. Or if anyone knows of any lexus specific mechanic in the dallas area, I’ll take that, too.

jmoe2012 · November 17, 2020

I wouldn't want to pay Lexus $175 to tell me that needs a master cylinder replacement again but this can be done at Toyota too. I don't know if you used the Original Lexus Toyota DOT3 fluid after the previous replacement. The failing of the original master cylinder seems like it has to do with the low or no polymer content in the aftermarket brake fluid after the brake pads replacement or serviced or flush at the 3rd party services. If you don't completely flushed out the offending brake fluid off your brake lines, chances are that the new replacement cylinder may start to wear out again pretty soon. I think it's Toyota / Lexus fault for not redesigning the master cylinder seal with a better one.

Where do you get the replacement master cylinder anyway? If it's not NEW OEM or you bought used one of ebay, chances are 50/50 that they are either failing or bad ones to begin with. I guess any technician could tell if the ABS pump is falling and it should trigger DTC codes since it's quite a danger to be on the road with the failing pump.

mjmanning · November 17, 2020

Thanks for offering this info. I actually had the master cylinder replaced twice since I thought the first one was faulty since the pedal was still falling a week later. The second one was purchased from Rockauto. The brand was Beck/Arnley. I read a bunch of reviews and some even said theirs came in a Toyota box/wrapping so it sounded reliable. Unfortunately, it did not fix the issue.
The brake fluid is a possibility as I’m sure the mechanic did not use a specific variety. Wonder if I can bring it to Toyota and ask that they just flush and fill?
Honestly not sure what to do at this point. There are no warning lights showing any issues. Would a wanting light come is if the ABS pump is to blame??
thanks again for the help

jmoe2012 · November 18, 2020

I think any good working master cylinder replacement part should have fixed the pedal falling upon braking issue. You would not have the same problem for months even if the fluid is not flushed correctly with a new master cylinder. It takes a few months for the master cylinder to fail again and would not happen again in just a week or two. I never trusted any rebuild stuff from the auto parts store. It's too much of a coin toss and only added more cost and misery in my experience. You probably can order a new master cylinder from online Toyota or Lexus dealer and have it installed by your mechanic.

I was looking to buy a used 06 RX330 many years ago and I found that car has the same problem upon test driving. I asked the owner lady politely if I can consider it overnight. Upon googling, I found it's a very expensive fix so I told the owner I can't buy it with the issues at hand.

Here is the recall from Toyota / Lexus for that issue. The proper fix would cost upward of $1000 but it should be all it's needed. A complete Toyota DOT3 Fluid flushed and a new master cylinder is all that is needed unless you have a leaking fluid line somewhere which would be obvious under the car.

I don't have RX330 but I think ABS pump would turn on very frequently when the car is parked and stepping on brakes with the engine running or even without stepping on the brake pedal in some cars. I think it's quite easy for a mechanic to tell if a ABS pump is falling. Techstream scanner can go even further to test the pump and all the other ABS functions on this. But I am 99% sure ABS and Check Engine Light would be triggered for the ABS issues.

https://www.carcomplaints.com/Lexus/RX_330/2006/recalls/brake-master-cylinder-10v499000.shtml