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.