There's some options out there for master cylinder upgrades, but it's been a couple years since I looked into it. I don't think I ever found a direct replacement for a larger master cylinder bore that would bolt up to the brake booster and have the correct brake line fittings and retain ABS. If you come across it please let me know. Here's a few threads I have saved on the subject:
Master Cylinder upgrade options
Tundra Caliper/pads/rotors upgrade but what about the master and booster?!?
Replace entire Brake system with Tundra's?

Thats about the point of research I had left off at. More pressing things to do then a nice to have.

I have never towed, but the TBU was the first mod I did when I got my 3rd gen. I have come down steep grades from driving in the mountains, and never once did my brakes overheated. I have been stuck driving in Sam Francisco, coming down one of those famous steep hills in the city, then bumper to bumper traffic getting on the bay bridge. Never have I ever had a problem. Now, the previous posts about the pedal traveling down longer is true, but it does firm up well before it even gets to be dangerous. You will definitely want to bleed the brakes when you upgrade the brakes, and make sure the rear drum brakes are adjusted properly.

I highly recommend the upgrade. There are no drawbacks from it.


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I can't wait to get my set on for the 199mm rotor. I cant stand warped rotors and been fighting this since 2015.

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Hmmmm, about to replace everything in my front end suspension and was going to do the TBU, but having difficulty finding the calipers (OEM) and was going to upgrade since it seemed plausible. I won’t ever tow and my truck is dedicated to camping / overlanding, so maybe not worth doing?

My stock brakes were already warped or warped immediately after I got the truck. I've never towed more than a utility trailer and I was at stock weight when they warped, too. No way I'd go without the TBU for a built rig, but my truck is also extremely heavy.

Unfortunately I've been dealing with the soft/extended travel on the first pump and then a firm pedal on the 2nd or 3rd issue for a while as well. It hasn't yet caused me any issues, but having to press the pedal 60-80% of the way to the floor, it's not exactly confidence inspiring, at least until the brakes do kick in.

I went with the 199mm setup over the 231mm as I figured it would result in a more balanced setup overall vs having huge in the front and drums in the rear. I remember reading ages ago that an unbalanced setup like this resulted in worse overall braking performance, aka longer stopping distances, in the context of track cars. If the stock balanced brake system results in the front tires accounting for 75% of the stopping effort, just due to weight transfer/physics, and you add big old brakes to the front that now cause the front tires to do 90% of the braking, you have a less effective brake system, since the rears are under utilized.

After reading this thread I'm now wondering if it isn't also the proportion of the new volume F/R vs stock.

This is obviously hypothetical (and conjecture, as I don't have experience tuning brake systems), but if the stock setup has an equal 1 volume unit [VU] required for the front calipers and 1 VU required for the rear drums, and the TBU results in something like 2 VU front / 1 VU rear, then I think this would be part of the problem. Without something else added to the system like a proportioning valve to send the new increased volume percentage to the front, the system sends an equal 1:1 to the front and rears, causing the rears to fill first and the fronts to be short the increased volume amount. Without increasing the volume of the MC I'm curious how adding/adjusting a proportioning valve would affect this issue.


I'm in the same boat. I read through the first thread a few weeks ago, and there was no real consensus. A page linked in that thread does have this chart, but there is no direct upgrade path, as far as I can tell. The booster seems to need replaced as well if you want to try one of the Land Cruiser flavors. The FJ45 does have a 1 1/8" bore according to the chart, but it came with drums front/rear. There does seem to be an option on the T100 to get a 1 1/16" bore, and it came with disk/drums from the factory like ours, but also requires a different booster. I find it extremely odd that the Tundra from '99-'14 came with a smaller bore MC than the 3rd gen 4R.

my 2001...if I keep for a long time , will get the TBU. I had it on my 2000 . I live in the hills. I have automatics.
my 2001 I have only owned since december and it was not until recently that I started to get the warp brake rotor feeling. I could down shift on the hills, but dont want to push this automatic ( 2001 and 2002 have weak automatics, a re-design in the palnatery gear that did not work)
For me the TBU worked ( on the 2000) it was a noticable difference, I also replaced all the brake hoses at the time with ss lines. My pedal was a little softer but I got used to it soon. Driving other 99's and 2000's, it was not that big of a differece. When I swapped to an elocker, it had 15/16 rear wheel cylinders, that I swapped to 1 inch. Did not feel a difference with that.

for me living in the hills and mountains...I would rather replace brakes....then work a automatic real hard ( down shifting) and replace that.

The 199mm brake caliper pistons are the same size as the 231mm brake caliper pistons. I believe you are correct that the increased change in piston volume is the culprit for soft/long brake pedal press. It's basic hydraulic theory. The master cylinder is still putting out the same volume, but the larger piston requires more fluid to move the same distance as the stock smaller piston. This causes a low pedal feeling. Another side effect of changing the caliper piston size is that it's easier to press the pedal down as well.

You wouldn't want to buy brand new OEM calipers, they are hundreds of dollars each. The vast majority of calipers are reman'd Toyota calipers where they replace the seals and pistons but keep the calipers. Powerstop, Callahan, etc. all use Toyota calipers.

I would do it just so I don't have to worry about warpage. It shouldn't be compelling to me because I have the 3rz (no real towing), no ABS, and a manual transmission to help down shift. If you tow you should do the TBU, the brakes as they come are barely adequate.

I ended up having the same issue but I've learned to live with it after having the dealer bleed the brakes and them still not getting much quicker on the actuation. I also have a 2002 with the newer electronic brake booster w/ black hole vacuum tech for what it's worth.

I still think the 231mm TBU is worth every penny though. Brakes don't seem like the area a wise man would skimp on.

As luck would have it, I FINALLY got a pair on EBay pulled off a Tundra. I could never find them in my area and EBay was slim pickings. Thanks for the info too!