LexusFan2

Hi,

My '07 ES350 started having this issue where the brake pedal has virtually no play when pressed down to start the car in the morning. After the car is started, I can feel the brake pedal move down as usual and everything brake related functions fine. Problem seems to occur only after the car sits overnight. Brake fluid level is fine and no service indicators in the dash.

I searched the forum and see that some people suggest the brake booster may be the problem. Also found some videos online on steps to take while in the driver seat to test the brake booster. Performed those and the results seems to indicate the brake booster is functioning normally.

If anyone had a similar problem that was fixed, please post what needed to be replaced.

jagtoes

There is a check valve in the brake booster vacuum line. It sounds like yours may have a slow leak and you lose vacuum overnight. Look for the valve and replace it. They are cheap. How many miles on the car.

LexusFan2

About 146k miles on the car. Schematics seem to the show the check valve located directly on the front face of the booster. I haven't looked under the hood yet but is it an easily accessible part to replace?

jagtoes

As I said it should be a cheap replacement . If this is not the issue then the booster may be leaking or the master cylinder may be starting to leak internally. The check valve is a one way valve where engine vacuum pulls on the brake booster diaphragm which assists in braking.

Lexmus

Mine is doing this too. I looked up the part and this is the diagram.
https://www.lexussouthatlantaparts.c...category=21744

The check valve part for 2007-2009 models according to Lexusparts now is 44730-28030.

Jagtoes, do you think the grommet should also be replaced?

jagtoes

I would think not unless you screw it up when you remove the valve. But saying that it is old and most likely hard so I would get a new one.

garrryy

Anyone have an update on this issue? I'm having the same problem on my GS and have replaced the valve and grommet to no avail. Would replacing the booster be the next step?

cl206

Sorry to bring this up, but Garrryy did you ever figure this out? Im starting to get that stiff brake pedal in the morning too. I have heard some people have success changing the valve and grommet and now this post says you didn't have success. Any one else have any insight/experience?

In addition my ABS has been activating sporadically/intermittently when slowing down to a stop. My searches suggest that the
wheel speed sensors may be acting up. so i might have to check that out too!

garrryy

I ended up replacing the brake booster and that fixed the issue for me.

cl206

Wow thanks for the fast reply! I just relubed the caliper pins and cleaned up a speed wheel sensor ONLY at the front driver side. This was an attempt to solve the intermittent ABS issue. Had no time so I will do the other wheels tmr and later. But that stiff pedal is intermittent and if it keeps coming back I might try the valve and grommet first before the booster.
-Charlie

AA2016

Do you recall the part you used?

I’m having the same issue and there aren’t a lot of aftermarket brake booster options. I see a new Cardone booster on rock auto for about $300, but not sure how reliable the brand is.

ESh

What about getting a used one?

AA2016

Not a fan of used parts, unless it's some non critical item.

TCoolest2

I wonder the same. Mine works fine but it has a small leak which causes my Fuel trims to go whack sometimes. I noticed there was a Bosch one on mine, which I don't think is OEM. I'd like to know as well in case I eventually replace it.