Brakes, what to do?

[bajafgl]

Hi guys. I was going to to the 4 runner brake upgrade with the t100 master cylinder.
I could only get the master cylinder in, the calipers didnt fit over the disks, must have gotten the wrong ones, anyway. It feels like it takes a lot more effort on my part to stop the truck, the peddle is even squeeking becouse of the efort im puting on it to stop.

The back brakes are new and the settling in could be the reason why I have to press the peddle so hard, I dont remember having to press so hard before.

I wanted better brakes but feel It got worse.

Should I put the original master cylinder back on, or is it going to get better once the back settles.

Any of you running a bigger master cylinder only.

thanks for the help

 

[2mbb]

I'm not sure, but my guess is that you need both the "bigger" master cylinder plus the new disc calipers to get your good feel back. If the bigger master cylinder is a bigger diameter bore, then the same amount of force you apply at your foot (eg. 100 pounds force) gets distributed across a larger cylinder surface area (area is proportional to the square of the diameter), resulting in a lower brake fluid pressure (force divided by area--pounds per square inch). So you have to push harder on the brake pedal to get the same pressure applied to your old brake calipers using the new master cylinder. My recommendation would be to put the old master back in until you get the new calipers worked out.

 

[IH8Wood]

I Dunno. I have stock brakes and they stop fine.

 

[silicon_toad2000]

the master cylinder and slave cylinder volumes are like gearing in a block&tackle, they can be set up to move miles of chain and lift an engine an inch, it'll be easy work but a lot of it, or you can have them so you dont have to move as much chain for the inch lift, but it's going to be harder work.
You gotta think what volume of fluid you are displacing when you push the pedal down compare to how much volume it takes to move the pads.
By putting on a bigger master cylinder you don't have to push the pedal as far but you have to push down on it harder for the same effect.
Master cylinders and calipers should always be matched. I think you should either put the other master cylinder back or change the calipers.

 

[Marc311]

the master cylinder and slave cylinder volumes are like gearing in a block&tackle, they can be set up to move miles of chain and lift an engine an inch, it'll be easy work but a lot of it, or you can have them so you dont have to move as much chain for the inch lift, but it's going to be harder work.
You gotta think what volume of fluid you are displacing when you push the pedal down compare to how much volume it takes to move the pads.
By putting on a bigger master cylinder you don't have to push the pedal as far but you have to push down on it harder for the same effect.
Master cylinders and calipers should always be matched. I think you should either put the other master cylinder back or change the calipers.

x2

The toad and 2mmb hit it. The whole master cylinder thing had been debated here quite a bit - with many (myself included) not putting it on when they upgraded the calipers for the exact reasons they explained. My take is to leave it off entirely (unless you went to rear discs) and absolutely take it off if you have done no other upgrades.

 

[rchalmers3]

I wanted better brakes but feel It got worse.

Any of you running a bigger master cylinder only.

thanks for the help

No, 'cause it dosen't stop for sheite.

Dude, you have a unique opportunity to measure the operational diameters of your old and new components and KNOW what you will be doing to the effective brake force before the installation.

Compare the ratio of surface area of the old components (the areas of the master and front calipers expressed as a percentage) to the ratio of surface area your new components and divide the estimated operational pressure (say 1800psi) to find your estimated foot pressure required to achieve 1800psi operational pressure.

Use this method to determine if it is even necessary to install a master cylinder. By plugging in different master cylinder diameters (thus altering the area ratio) you can select a master that equals or improves the foot pressure required to produce the same operational pressure.

If you choose to perform this science, please post your findings so we can all have a chance to understand the science and make better informed decisions on mixing and matching brake components.

Rick