Supra master cylinder anyone?

[Steve240]

Hi all, been awhile since I have posted on hear.

Question, has anyone used a mk4 supra master cylinder on the 4runner to help with brake pedal travel?

I have been reading up on the master cylinder options, found links related to T100's and even a chevy blazer from 76. T100 I like due to the line size matching but getting a new booster is expensive. The blazer idea I do not like for having a bunch of adaptor fittings.

In researching master cylinders the supra one looks like it could be a good option. It is 2 post mounting, the turbo version is larger at 1 -1/16 bore. And line's would be the same Japanese standard.

Thanks in advance


Back ground is I took a dive into a rear disc conversation + already having the tundra brakes up front, and now I have 0 brakes. Pedal just travels to the floor. Bleed brakes a bunch / has a newer master cylinder so I am confident that is not the issue. I put pretty big calipers in the back from a ford GT 2008. They were basically free + my drums were f'd so that's why this happened. Now I'm trying to figure out the best way to get them working.

 

[Bad Luck]

Have you considered getting smaller rear calipers? It sounds like the rear calipers are requiring more brake fluid than the master cylinder can provide. 1/16" bore increase isn't that substantial over the 1" master cylinder bore size that we already have.

 

[Steve240]

I agree the 1/16 size doesn't seem like that big of a change. Even area wise it's only 12% larger. But, a Ford GT mustang has a 1 - 1/16 master with good size brakes. Also a supra had good decent size brakes. I am surprised the 1" master on the 4runner isn't moving enough volume.

 

[phattyduck]

I am surprised the 1" master on the 4runner isn't moving enough volume.

I agree with this. The 4Runner master cylinder (and probably the T100) has a little extra valve/whatever on the side to help with brake feel with rear drums. There is a special 'bench' bleeding procedure that must be followed to get good brake feel. Did you do this when you installed your brakes? See this from the FSM:

The other option is that there is still some air in the ABS actuator that is causing your issues. I don't know if there is a way to manually get the ABS system to cycle, but if you can get the ABS to actuate (on gravel, say) then re-bleed, that might help you out too.

Hope that helps,
Charlie

 

[RandyBobandy]

You should have at least some brakes even if your calipers are way too big for the master cylinder so you probably still have air in the lines somewhere. I have 199mm tundra brakes and rear disks with mustang calipers and my pedal feels as good as stock brakes, but I also have no abs

 

[Steve240]

Thanks for the responses.

For bench bleeding I just looped the lines back into the res and pumped the master in my vice until no air. Based on reading the FSM it's saying the same thing without having to take it out / make a line to do it. Not my first time so Iam pretty confident on the bench bleed.

You referred to a screw on the side of the master. Is that like a proportioning valve idea? I'll have to research that more.

The abs is also an interesting topic. I still have abs from a line standpoint, but I pulled the fuse years ago and have multiple broken sensors. Maybe it's time to delete the system. I'll have to look into that.

 

[phattyduck]

Thanks for the responses.

For bench bleeding I just looped the lines back into the res and pumped the master in my vice until no air. Based on reading the FSM it's saying the same thing without having to take it out / make a line to do it. Not my first time so Iam pretty confident on the bench bleed.

Nope. Re-read. It is NOT a normal bench-bleed procedure. You need to block the lines when the pedal is released, not just free-bleed into the reservoir. Without that, my pedal also went to the floor (Tundra 231 front / stock rear)

-Charlie

 

[DrewZ28]

You referred to a screw on the side of the master. Is that like a proportioning valve idea? I'll have to research that more.

From what I have read, that screw is just a piston stop. It prevents the pistons in the master cylinder from completely bottoming out. Someone can correct me if I'm wrong on that.

 

[DrewZ28]

Nope. Re-read. It is NOT a normal bench-bleed procedure. You need to block the lines when the pedal is released, not just free-bleed into the reservoir. Without that, my pedal also went to the floor (Tundra 231 front / stock rear)

-Charlie

Do you have any additional info on this? With the hoses in the reservoir, it should suck fluid back in when released. I bench bled mine the traditional way as well but I'm chasing a soft pedal issue with 13WL brakes. In theory, if the master is sucking fluid back in, it will still bleed properly. The FSM way just seems like it would be a lot faster. But if something is different on how Toyota built them, I'd like to learn about it.

 

[phattyduck]

Do you have any additional info on this? With the hoses in the reservoir, it should suck fluid back in when released. I bench bled mine the traditional way as well but I'm chasing a soft pedal issue with 13WL brakes. In theory, if the master is sucking fluid back in, it will still bleed properly. The FSM way just seems like it would be a lot faster. But if something is different on how Toyota built them, I'd like to learn about it.

The extra little cylinder thing on the side of the master is a front/rear balance thing (don't know what the real name is), but you can hear it 'click' into place when you bleed using the factory procedure. It needs the blocked ports and the 'sucking' pressure of releasing the main piston to set the correct position of that extra cylinder. If it is just free in fluid, it puts the piston in the wrong position and you get the ultra-soft pedal. Follow the factory procedure...

-Charlie

 

[Bad Luck]

The extra little cylinder thing on the side of the master is a front/rear balance thing (don't know what the real name is), but you can hear it 'click' into place when you bleed using the factory procedure. It needs the blocked ports and the 'sucking' pressure of releasing the main piston to set the correct position of that extra cylinder. If it is just free in fluid, it puts the piston in the wrong position and you get the ultra-soft pedal. Follow the factory procedure...

-Charlie

I've wondered that for the longest time. Thanks for solving that mystery for me!