cwdtmmrs

I am interesed in feedback from anyone using the FJ60 oversized rear brake cylinders in conjunction with a 1" master cylinder and if it is worth the effort. Also, which MC is better, the V6 or the FJ. I did not get a lot of info from the vendors that sell them.

Thanks,
CWD

RustBucket

iTrader: (1)

I upgraded to the larger wheel cylinders. T100 application, 1" diameter. It helped a little. The 1" MC is also a worthy upgrade.

Inferno451

I run land cruiser wheel cylinders on my 87' 4runner with stock cylinder. Stops fine.

RJR

Ok, hydraulics 101. Increasing the size of the wheel cylinders increases stopping power at the expense of greater pedal travel. Increasing the size of the MC decreases required pedal travel but reduces stopping force. Increasing both the wheel cylinders and the MC by the same percentage does exactly nothing except move more brake fluid around and lighten your wallet. Take your choice.

RustBucket

iTrader: (1)

Wrong. If you have a larger slave piston then the total force it can apply is greater, assuming the hydraulic pressure is the same. (F = P*A)

But you're right about balancing pedal effort. You do want to keep the hydraulic leverage ratio about the same for pedal effort and travel to be reasonable.

RJR

Which is exactly what I said. If you increase the size of the slave cylinder, braking force goes up, because the hydraulic pressure stays the same and the piston area is greater. However, if you now increase the size of the master cylinder, hydraulic pressure goes down for the same pedal effort, and you're back where you started in terms of braking effectiveness. The only thing you've done is decreased hydraulic pressure in the lines and increased fluid flow.

For a given size vacuum booster, you can pick any two of the following three parameters; pedal travel, pedal force, and braking force. Once you pick two of them, the third one is mathematically set. Messing with hydraulic cylinder sizes is just one way to play with the parameters, but you don't get something for nothing.

The only way you can increase braking force while keeping pedal travel and effort the same is by increasing the amount of brake boost (a bigger vacuum booster, go to air brakes, etc.).

RustBucket

iTrader: (1)

I'll have to think about that more... time to draw a picture

RJR

Just for completeness, there is actually a 4th parameter, the travel of the brake shoe. However, I'm assuming that's fixed by geometry, at the minimum brake shoe travel required for the brake to go from full release to full lock.

RustBucket

iTrader: (1)

You know, you got me. If we assume that the force applied to the master cylinder is fixed (pedal effort, pedal leverage, brake booster added force) then you're completely right. If you put in a bigger MC, then your hydraulic pressure goes down and your hydraulic leverage also goes down. If you compensate with bigger calipers/WCs then your hydraulic pressure goes back to normal and so does your leverage (just a ratio of areas).

If you assume that hydraulic pressure is the fixed factor, then increasing MC and caliper size does help you. But that may not be a good assumption.

I guess the compelling reason to run large wheel cylinders would be to compensate if you've already "upgraded" your front calipers. This would keep your front to rear balance closer to factory.

RustBucket

iTrader: (1)

A stock 4Runner with 22RE has 13/16" MC, 43mm+34mm Calipers, and 7/8" WCs, which gives a 1:32.86 hydraulic leverage. Also they have the smaller booster.

An early 90's 4Runner with V6 has 1" MC, 43mm calipers, and 1" WCs, giving a 1:26.93 leverage. Plus the bigger booster.

I wonder what is the compelling reason for the larger hardware if our assumptions are correct? Why not a teeny tiny MC and teeny tiny calipers? Surely there is some benefit to the larger hardware.

cwdtmmrs

Thanks for the replies. I understand the math, and already did the calculations before I posted the question. On paper it is clear. The wild cards are pedal effort and fluid movement. I can live with a lot more pedal effort than I have now. My truck is a 1986 Turbo with the dual diaphragm booster, so I am getting some extra leverage there and my pedal is very light. I just wanted some real-world feedback from folks that had done both the MC and the larger WC swap. I might just have to try a set, except working on drum brakes is never fun.

CWD

RustBucket

iTrader: (1)

In my personal experience, since sometimes that is more relevant than math: I upgraded to the larger rear WCs, V6 front calipers (S12W type), and 1" MC + dual booster and have been really happy with the brake stopping power and pedal feel.

Daddyota

Sorry Im A little late here- but rustbucket, if you had to put a percentage on it, how much better do you realistically think your breaking has gotten with the bigger mc, calipers, dual booster and 1" wc's? I'm trying to see if it's worth the effort or if I should just be happy and shut my mouth.

RustBucket

iTrader: (1)

Errrm... 25%?

A couple notes: I think the bigger brakes also help with holding on really steep hills. Also, you may be surprised at the improvements to braking just by practicing good maintenance and adjusting the rear drums well.

wyoming9

iTrader: (1)

It would be nice to compare two vehicles one with the stock brake system and one with the upgraded system.

With all other things being the same.

So many factors enter into brake performance.

One could very well upgrade the hydraulics but go cheap on the pad and shoe material.

Myself it comes down to maintenance and driving style.

RustBucket

iTrader: (1)

Yes, good points. There is more to it than just bigger hardware.

In my case it is tough to tell because I have incrementally changed gears, suspension, tires, etc just like most everyone on this board. But I do know that each time I've made a change in the brake system it has been an improvement.