Ok, I've spent countless hours researching and reading old threads. I have the 13WL Tundra brakes on my 97 4Runner Limited. New master cylinder, all new rear brakes including wheel cylinders, and steel braided brake lines front and rear. Drums are adjusted correctly and the system has been bled correctly. I'm still troubleshooting a soft brake pedal. From what I have read it seems the master cylinder just can't push enough fluid for the larger calipers. The T100 1 ton master cylinder has a slightly larger diameter. I am seriously thinking about doing this but would like to hear from people who have done this and what difference it made. Does the ABS still work? Will it work with the 13WE calipers, or even the stock 4Runner brakes? Thanks for any input!

If I'm not mistaken the T100 used two different masters, the one with a larger bore needing a larger booster to pair with it. They also used 4 holes to mount to the brake booster as opposed to 2 like us.

You would need the one ton t100 master cylinder and booster, however I think you’d need to delete the abs to make it work, from a quick search it looks like they are all non abs master cylinders

That is correct. The one with the larger bore is on the 1 ton without ABS. The booster would have to be swapped out with it so it mounts up.

Well if you're going through all the trouble and work of doing a brake booster swap, why not just install one from the corresponding Tundra the brakes came off of?

I have not seen or read anything about this being possible. The booster/master out of the 1 ton T100 will bolt tight in. The Tundra booster is much larger and may not fit. The MC will not work with our booster. And the MC bore is actually smaller than ours. The T100 bore is slightly larger.

Yes, I know I need the 1 Ton MC and booster. But deleting the ABS or not is what I am wondering from anyone who has done it. I haven't found a definite answer searching through the forums.

EDIT: I have read on a Camry and Supra forum that the only difference is the ABS MC's just have a larger bore. If this is true, then in theory I can run the T100 MC and retain my ABS. I am really just hoping for people who have done this swap to post and say if it fixed the soft pedal issue and if they had any issues running it.

It's definitely possible, as is the T100 booster. Very few have done it because of how much is involved, but they're out there - swapping in a Tundra master was something I thought about previously and if I recall I think there were maybe two users on here that actually did the project. I believe Opt Offroad was who installed a T100 booster and it was pretty in depth - required refabricating the linkage* and whatnot. You should be able to ask him about the topic, Jason's been very communicative with me in the past
Edit: the T100 swap is on their instagram, must've been thinking of someone else that had the linkage issues, though he did have problems with the hard lines not matching up

Sounds like you need to do an ABS bleed with a scanner to cycle the pump and get the air out? Or how about holding the brake pedal down and cracking ABS lines to get the trapped air out?

Soft pedal = air. Regardless of any of the bore diameter nonsense, a closed hydraulic system will be rock solid as liquid won’t compress but air will. A smaller bore/larger bore system means less work or more work would be accomplished (harder or easier to stop, more fluid moving etc)

A soft pedal has zero to do with bore diameter of anything. There’s air somewhere or an internally leaking component.

Basically if the theory is the current MC can’t move enough fluid to create the work required to move the brake pads, the pedal would still be rock solid. But the truck wouldn’t stop as easily.

Mine is a 97. From what I understand it's the 01-02's that need the scan tool to bleed. I have tried locking up the ABS and re-bleeding. It doesn't act like air is in the system. It acts like there is not enough hydraulic pressure at the front calipers. Since the calipers take more fluid over stock, that can cause the issue I'm feeling. In theory the master just can't push enough fluid to fully engage the larger caliper pistons. At least this is what the main consensus seems to be by many. But here is a question that I have not been able to find an answer for. Is it possible for the ABS unit to be leaking internally?

I never heard of abs leaking internally but I guess it's possible. However, if all was perfectly fine and you changed your calipers then the issue started. I would expect the calipers.



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It won't fix the soft pedal issue. You have air in your ABS module, promise. I did the full swap 2 or 3 years ago. The brakes are absolutely stronger, but still had a soft pedal until I got the air out. I'm about to entirely delete the system. I have it disabled at the moment. It's a garbage system to begin with. The larger booster and MC are direct fit with a minor bend needed to meet the MC. See my build thread.

I had 0 issues bleeding my 01 brakes without a scan tool. I did an elocker swap and had the brake lines open overnight.

I firmly believe you still have air in the lines. Did you also do Stainless brake lines? Getting rid of the spongy OEM lines goes a long way to help pedal feel.

1st gen tundra's use a 15/16" master cylinder.

If a master cylinder can leak internally, a 25 year old ABS unit could certainly leak internally. Try key off/engine off, and rest your foot on the brake pedal. It shouldn’t slowly sink. If it slowly sinks or remains soft then there’s air and/or an internal leak.

While I fully understand the theory of under sized master pushing over sized calipers, a soft pedal as described in post number 1 is theoretically impossible with a fully bled hydraulic system. Liquid doesn’t compress. It acts as a solid rod.

Edit: @Bad Luck corrected me. Smaller input bore means less force required. Original paragraph to follow is wrong. Sorry internet.

I would argue if the undersized master was the only issue you’d have a rock hard pedal but the vehicle wouldn’t be as easy to stop. Principles of hydraulic fluid dynamics indicate a larger input bore in the master only reduces input force needed by your leg to do the work. (And vice versa for larger output bores in the calipers).

Based on this, a smaller bore’d master would require MORE force to do the job. Pedal would arguably be more difficult to press to accomplish the same job. (Also wrong)

That all being said, have you tried the “crack the fittings while pedal is continuously pressed” method? If air is stuck in the master this would help remove it.

1) Have a second person fully push pedal and hold pressure constantly

2) you go crack one of the hydraulic lines at the master until second person indicates the pedal sinks.

3) you re-tighten brake line

4) second person releases pedal and/or manually lifts to raise pressure

5) verify resovoir is still containing fluid

6) repeat at same fitting until confident zero air remains. (5-8 times is normal)

7) repeat for any other master fittings

8) repeat for any other fittings including ABS and/or caliper fittings as needed.

This is just to CRACK loose the fittings. Like 1/4-1/2 turn if that. Cover fittings with rags for fluid spray. Do it with key off so ABS doesn’t fire up.

Seen dozens of times where bleeding only at the bleeder ports on the wheels is insufficient.