Rear drum brake upgrade - Larger wheel cylinders?

Hopefully I didn't miscommunicate. Before any mods, I could only get my fronts to do anything like howl or lock up. Mind you I have 4runner calipers/rotors and Tundra master/booster on the truck. And I have 35x12.5 MT tires that are heavy. Never even on loose/dirt could I get the rears to activate ABS or lock up/howl. After the mods and with several trips worth of miles on the rear brakes, I can now tell it is improved from several observations, but due to other mods on the truck including more weight, different shocks, rear springs, different brake pads, etc that happened at the same time as the brake wheel cylinder mod, there is no way to do any sort of "measurement" of rear brake performance that is apples to apples.

If you were hoping for stopping figures in feet or something, forget it, not gonna come from me. If you can't follow the theory on this, why I did this mod and why it will or will not work better for your situation, you probably should not be doing the mod. I.E. if you need some sort of quantitative measurement of improvement to convince you of the benefit - you should not do it and look elsewhere.

I can however report that the rears will trigger ABS on dirt along with the front if I really try to make it happen. I can also tell you that the truck doesn't dive nearly as much in a hard braking situation, which to me tells the rears are doing more work, but also the fact I swapped shocks probably has something to do with it too. I can tell that the rear wheels get hotter than they did before, but that is only a touch test, not a scientific one. I can also tell you that after 6 hard stops from 60->10 MPH in rapid succession, I got the rear brakes hot enough to fade completely (ebrake pressed did nearly nothing). I didn't try to do that before, but I think they are generating way more heat now which is also a sign they are doing more useful brake work in relation to before. Granted, 6 stops like I did to get the pads hot enough to not have friction anymore is way more than any sort of braking you could do in real life. And the truck still stopped OK on the 6th, it was just much like it was before, where the fronts are doing all the stopping. After cooling, the brakes returned to normal and the ebrake will lock the tires up easily.

Hope that provides you with a picture for where I'm coming from with the work I did and the testing I did and observations I've gathered. It is far from a scientific comparison with variables isolated. But I think it works better than it did before.

 

Thread resurrection time.

It sounds like Racebug cloned my truck, even down to having to swap axles because he bent his first one (I assume like me: from too much weight combined with lots of wheeling action). So you, sir, have got my attention with this thread!

I've actually gone one step further than Racebug, however. I actually deleted my ABS pump completely ("completely" meaning hydraulically, still connected electrically), added an adjustable BPV, and made sure all my part IDs matched OEM (not an easy task, and required drilling out of several fittings). No improvement, also no problems introduced.

@racebug68 what is the final report? What are the part numbers I'm looking for? I'm assuming thread sizes all matched up. How much of the shoe horn did you have to trim? How well does the parking brake hold?

Oh, and if you're still looking for improved shoe compound, check out Porterfield R4S. They don't carry them in stock, but can make a set in a few hours.

 

Digging up an old thread that was linked from an older thread...Did the larger rear wheel cylinders improve or not improve rear braking?

 

Yes, It did improve for sure in my case. A few things to note.

• I did change many things at once, so any "testing" I did is not isolated to any one change, therefore I didn't bother.
• It is not easy to break in new shoes and new drums. Any testing done right away is also not apples to apples. It takes a long time of driving, and in my experience you can't accelerate it by driving with ebrake on or anything. Doing that will overheat the rear brakes to the point they don't work at all until they cool, ask me how I know. Actually, don't ask, just know.
• It would probably be a good idea to add residual pressure valves in the rear lines. I can tell a HUGE difference in the brake power when I push the first time, nose dive with less rear working (just like stock to be honest), and if I pump slightly, the truck does not nose dive as much and stops way better. I should try bleeding again, but I did it several times and fairly confident that the adjusters on the rear and the spring pressure pulls the shoes away from the drum a little too much, and it needs to engage sooner which is what it does if I pump slightly. Maybe I will try dialing up the adjusters again as well, but that only lasts until some brake lining wears away, then back to same.
• I get no lock up in the rear under normal braking no matter how hard I try to get it to. (Unless I use Ebrake, then it will lock up anywhere/anytime but besides the point). this is a good thing, rear lockup before front is not at all controllable in a panic stop. IMO, when these trucks are really really loaded up and heavy, like 7K plus, there is no such thing as too much rear brake. The more you carry with overland/camping gear, the more you need the rear to take up additional braking duty.

For me, the upgrade was very worth it. Some experimenting for sure. I didn't document it fully for a reason, if you cannot do this job on your own you shouldn't rely on me teaching you with pics. This after all is the braking system of your rig, and it is literally life and death criticality. So I'm not putting stuff out there for instructions of how much you need to cut off the shoes, what this or that, etc... Because I don't want some dumbass claiming I told them how to do it "wrong" and they killed themselves or others.

Would disc brake options work better? maybe? probably? I dunno. There are clear advantages, and disadvantages. For me, this was fun, and rewarding.

Anyone who says you can't improve rear braking on these trucks in certain scenarios, clearly doesn't have a grasp on hydraulics, common sense, or both. But it is good where we can have opportunities to do our own thing and suffer the consequences...

 

Thanks for the info. I'm going to do the Tundra booster/primary cyl upgrade soon and already have new rear shoes and drums. My buddy suggested smaller wheel cylinders, thinking less fluid needed to push the shoes farther. So I wanted to ask how the larger cylinders worked.

 

That person does not understand hydraulics in the same way I understand it. I'm not saying they are wrong or I'm right, but just not the same. To the best of my knowledge, it isn't about how far the wheel cylinder is capable of moving with some amount of fluid delivered, but rather what force it can exert with the same force applied to the fluid at the master cylinder. And in that scenario, the fluid working on a larger area, I.E. a larger wheel cylinder, will exert more force at the expense of some piston movement distance. And that is what you want, especially if you are adding the tundra/sequoia master, which does have a larger piston bore itself, so it does push more fluid. A smaller wheel cylinder will reduce force applied to the shoes for the same pressure applied to the pedal. And maybe I have it wrong and all my improvements are all in my head. To each their own...


For what it is worth, I did order a set of custom Porterfield RD-4 shoes. I will put those in for a test next time I have it all apart. But currently life is in the way, that project is way down the list.

 

Thanks for the update! I've got the larger Tundra master cylinder on my shelf.. This is still on my to-do list.
For now.. I'm actually manually adjusting the rears a bit tighter before each big trip. It makes a huge difference.. for a couple thousand miles, at least.

 

just wondering which wheel cyl(s) to look for, any chance you can post the part number or application? thanks