ctjw1982

Anyone else experience issues with the master cylinder part causing the brake to feel like it’s failing (no pressure when applying)? I tried a refurbished replacement part that was from a toyota 4runner but was compatible, and it has improved somewhat but the issue still exists. My mechanic is now recommending I could either try getting my original lexus part rebuilt, or I buy a brand new one and try again. Not sure what the smartest move is- a brand new lexus original part is over 2,000$, but if that’s a guaranteed fix then I don’t mind it.. i’m hesitant to try the rebuilt/refurbished route again, because it’s still pricey and it wasn’t 100% effective the first time, and I also don’t even know where to find someone that knows how to rebuild parts. any recommendations?

chiph9

The brake booster is indeed expensive. Since it's brakes, and thus really important, I wouldn't skimp on this. Go OEM. And get new fluid while you're at it.

Chip H.

ctjw1982

Appreciate the feedback.. dumb question: is the brake booster a separate part? When i look at lexus parts direct, i see two different items: one is the master cylinder, and the other is a brake booster. There’s no split on the price, just has one (big) number. Is that because they are sold as a unit? The refurbished part i got was a “abs master cylinder unit”, but it was already assembled so it doesnt really resemble either of the pictures on the lexus parts site... just trying to determine before i pull the trigger that im buying exactly what i need... like how would i know what the exact cause of my issue is, and if its the master cylinder or the booster thats failing? Thanks again for the insight..

chiph9

I have not yet had to replace this part, but my understanding is that what usually goes bad is the pump motor. The other thing that goes bad is the valve body (internal corrosion, age, etc)

Chip H.

Lexus4321

Can you list what parts exactly you already swapped out? The master cylinder is different than the brake booster w/ accumulator assembly.

ctjw1982

This was the part i replaced

Lexus4321

Probably need the booster/accumulator assembly.

chiph9

That's the master cylinder without pump assembly. The booster is part 12 on the second diagram:

https://www.mylparts.com/v-2004-lexu...ti-lock-brakes

Note that this is for a 2004. Your part might be different depending on year.

Chip H.

ctjw1982

Super helpful, thanks so much for sharing.. so if i were to play it safe, scrap the refurbished master cylinder i already got (thats missing the booster/accumulator piece), is it as simple as buying the #1 in the diagram, the master cyl including assy.? If im interpretting correctly, that appears to give me everything id need, but just wanted to confirm because it looks like you get a much better price as opposed to just buying all the individual components its comprised of separately... do i have that right? Looks like if i buy #1, its in the $2k range all in, but i could spend that same amount just on the pump parts alone...

chiph9

You'll get everything but the wiring sub-harnesses that way (which are no longer available) and you'll get a brand new part good for another 10 years.
But pricey - which is what throws most people off.

Chip H.

Billymartin

I just had Lexus shop replace for $2800. Needed entire new assembly and software update. My independent shop could not do it and sent it to Lexus. Toyota shop had estimated $2100 to replace but probably not accurate estimate.

CaliColin

Many years ago the master cylinder on my wife's 2006 GX began leaking internally, causing the brake pedal to slowly go to the floor when stepped on. After some research I decided it must be the rubber seal on the internal piston. Not wanting to spend $2K on a whole new assembly, I purchased a new seal rebuild kit made for the LX 470. I took a chance and pulled the master cylinder from the GX, pulled the piston out and found that all the seals were exactly the same. I replaced the rubber seals (which look like o-rings), bled the master cylinder on the bench, installed it back in the GX, then bled the brakes again and everything has been working perfectly for years. I do not recommend taking this on yourself if you're not experienced working on brake systems, but it's an option.