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In one of the last steps of the "Highlanderfication" process of my RX350, I've set out to firm up the brakes as it's a major characteristic I miss when I switch between the 08 RX and my 02 Highlander. The HL has a 10" diameter power brake booster and a surprisingly firm master cylinder that provides good feedback without excess mushiness in the brake pedal. Along with a bunch of other things, this was toned down in 2004+ Highlander models as well with the introduction of the RX330. The booster was increased to a diameter of 10.5", and the MC was made less aggressive. It's not a deal-breaker of a difference, but it was easily enough to annoy me, so it's getting swapped out!
The stock 04-09 RX330/350 booster being a little larger at 10.5" required taking off the wiper cowl for removal. I also pulled out the alarm horn, a ground wire and some bolts holding in the wiring harness for some more wiggle room. It's a tight squeeze! Make sure to remove the 10mm brake lines with a line wrench so you don't strip them, get some towels and brake clean ready! Then, you'll need a 12mm socket to remove the master cylinder off the brake booster. Go inside the car under the driver's side dash and loosen the brake light switch with a 14mm stubby wrench and unscrew it (but don't fully remove it) so the stopper bracket on the brake pedal doesn't get bent (ask me how I know), crack the 14mm adjustment nut loose on the brake pedal adjustment, and finally remove the four 12mm bolts holding the booster to the firewall.
Got this thing out! What a fight!
At first, I tried an IS350 brake booster which was a total fail! It was 10" but it didn't have enough pedal adjustment and the pedal was very low, which made driving the car awkward and made the brakes even softer! The gasket for the booster (44785-0E020) is far superior though and is a direct fit!
That IS350 booster set me back a few months, I was about to go back to stock until I found a 2015 RAV4 brake booster at the junkyard and decided to try it as it had a lot of pedal adjustment unlike the IS.
More pedal adjustment than the RX, 10" size, nice gasket (44785-02060) and easy to find - I found an easy solution, right? I couldn't have been more wrong. This booster uses a different master cylinder vs stock, so I had to go even deeper into the rabbit hole.
With the discovery of the different master cylinder fitment, I gave up for a few months until I decided that if I was going to tear into this pain in the rear job again, I was going to do it right and finish it properly. I set out to find a master cylinder that would let me run this booster on the car. I spent countless hours on TIS (Toyota Information System) and at junkyards grabbing a bunch of master cylinders and whatnot until I found something that impressed me. The stiffest and most aggressive master cylinder I could find that would also fit the RX's stock M10 fluid lines happened to be from a 2011-2016 Scion TC. The 08-15 Scion XB one would be a good alternative for people who want a less firm pedal, but there's one thing I grabbed from that XB that ended up being used - the superior metal vacuum valve that is the subject of this post on dash rattles.
After the acquisition of the TC booster I was met with another unexpected hurdle. Despite appearing nearly identical, the RX's stock master cylinder reservoir WON'T FIT THE NEW MASTER CYLINDER! The spacing looks identical, but it is actually ever so slightly tighter on the newer MC so the reservoirs are not cross-compatible! I really wanted to give up now, but luckily, I did find a solution! I popped the engine bay of our 2014 RX350 and saw that it also used this modern style master cylinder that the TC has (It wouldn't fit though because the ports are in the wrong place and are M12 vs M10), but the little reservoir on top looked like my RX350's! I checked and that part comes on the 2008-2019 Highlander, 2010-2022 RX and 2011-2020 Sienna. There happened to be a 2017 Sienna at a junkyard, it was a far drive but I needed it!
IT FIT! (Of course it would)
The pin that retains the reservoir was back-ordered, so I just substituted it for an M5-50mm hex bolt and lock nut, it was a perfect fit!
Time to throw this stuff in, but first let's take a little weight measurement for fun!
RX booster
RAV4 booster
RX master cylinder
Scion TC master cylinder
Crappy pic, but it gives you a rough idea of why the two different reservoir variants are not compatible
Took about 0.81 lbs off the front end of the car, not bad considering these are heavy and any bit of weight lost would be nice!
Installed in the car, it fit nicely!
IT FITS!!! Bled all the air out of calipers, took it for a test drive and was very impressed. If you don't have at least the front 3rd gen RX dual piston calipers and rotors, you're missing out BIG TIME! Now the brakes come on nearly as soon as you rest your foot on it and it's very linear, just the way I like it! Lots of feedback too - no off/on switch shenanigans! It's even better than the Highlander now! That 10" brake booster gives you a harder pedal / less assist which was missed from the Highlander and was much appreciated on this older RX! These brakes are extremely satisfying now! The 11-16 Scion TC master cylinder is CRISP! Very BMW-esque feeling to me (reminds me of our E46 M3)! No remains of a squishy pedal AT ALL anymore! All of these MCs in this entire post as well as most of the passenger cars have the same 1.57" stroke and 7/8" bore like the stock 04-09 RX master cyl.
After all of this, I learned you probably want to skip the 13-18 RAV4 brake booster, in the feel department it is wonderful as is any Toyota 10" booster, but it has significantly shorter studs for where the booster is mounted to the firewall which made installation more tedious. I assume probably because the RAV4 and other New MC platform cars have a paper firewall compared to our beefier K-platform RXs or an equivalent Highlander or Camry. It is still possible to install, but these shorter studs make lining it up back-breaking! The 07-11 Camry / 08-12 Avalon one may be a better fit. It uses the updated MC like the RAV booster, has a similar amount of thread engagement like the RAV, AND has the longer studs like a Highlander or RX would.
Stud length sticking out before:
Stud length now with RAV booster: Lots of rotations still, so it's safe. But a little close for comfort
07-11 Camry USA-built / 08-12 Avalon booster (45mm of pedal adjustment) - 10" and uses modern MC plus has the right size studs. I'd use this knowing what I know now if I had to repeat the job
2006-2018 RAV4 booster (51mm of pedal adjustment) - you can see how the mounting studs are noticeably shorter
That concludes this post for now! This project isn't for the faint of heart, but I love the feeling of a 10" booster and the TC MC, now that's proper!
Replacement part list:
2013-2018 RAV4 10" brake booster (Reuse stock mounting nuts, clevis and 14mm jam nut)
2007-2011 US-made Camry / 2008-2012 Avalon 10" brake booster (Reuse stock mounting nuts, clevis and 14mm jam nut) - Use this instead!
47220-48200 (2008-2019 Highlander, 2010-2022 RX, 2011-2020 Sienna master cylinder sub-reservoir) - Get this at a yard, don't pay the stupidly insane dealer price for it!
44730-14050 or 44730-28010 (Bosch metal vacuum valve to prevent dash rattles) - Find from 08-15 Scion xB, 01-03 Highlander, etc
Maintenance part list:
44785-02060 or 44785-0E020 (Brake booster good quality gasket - grab it with the brake booster itself)
90480-24439 (Grommet for brake booster vacuum valve)
90029-15803 (Retaining pin for the master cylinder reservoir, I just used an M5-50mm hex bolt and nut instead)
90015-AH002 (Master cylinder to booster o-ring)
90029-48001 x2 (Master cylinder reservoir o-ring - (I didn't buy these as they were expensive and didn't seem to be needed)
Last edited by MattRX; 08-08-24 at 11:34 PM.
Reason: Confirmed USA Camry/Avalon booster has same 45mm pedal adjustment as stock RX
This answered ALL of my questions on this swap! The pictures were a perfect visual! I'm definitely doing this to my Highlander if the booster or MC goes! And a MUST on an RX350 down the line!
Saving this on my to-do list. Brilliant write-up!
Thanks for taking the time, as well as trial and erroring this for us Matt!
This really lets me enjoy the SS hoses and 3rd gen calipers! Even just swapping to an IS/GS master cylinder and adjusting the stock booster & brake light switch would make a massive difference I imagine.
UPDATE: This has been one of, if not the BEST thing I have done to my RX350! Night and day difference, working flawlessly! Driving enjoyment and braking confidence is a lot better now!
In other news, I found the 08-12 Avalon / 07-11 US Camry booster! This is the gold standard swap right here for the RX, just like I thought! A bit lighter than the RAV4 one I have, 10” diaphragm like the RAV, 45mm of adjustment (identical to 04-09 RX), the right amount of threads for the firewall and fits the modern 53mm booster used by the Scion TC! I’m not going to be taking my RAV4 one out as it probably feels the same, but if I ever have to replace the RAV4 booster (probably never), this one is going in!
11-20 Sienna, 08-19 HL, 10-22 RX master cylinder reservoir (top) VS. 2004-2009 RX330/350 master cylinder reservoir (bottom)
- This is why you need to swap the reservoir if you're using the Scion TC master cylinder, you can keep the stock one if you use the stock booster w/ the IS350 master cylinder
Also @Ambidexter777 I replied to you on RAV4World. This applies to the RAV4 4th gen as well. It will be a 100% direct fit on that car, no need to change the booster or brake lines.
01-02-24, 11:17 AM
Getting Rid of the Mushy Brake Pedal Forever (2004-2009 Non-Hybrid)
