Rear drum brake upgrade - Larger wheel cylinders?

Thanks for the tip on the brake pedal!

I agree on your other points completely. Fronts are doing all the work now and wearing really fast. Rear upgrade basics have been done and basic touch of the wheels for temp says they are hotter after doing some hard stops than before, and I can feel a big difference in overall braking. Front doesn’t dive as much since rears are doing more of their share I think. Getting it dialed in, trying with different adjustments and also I’m going to go ahead and try a different set of brake shoes so I have some comparison. I may also change out the wheel cylinders for a different size to compare that as well.

 

Thanks for the efforts! I am tuned in to hear how it goes. I'm optimistic!

 

I have a 2020 OR AT, so electronic ABS booster. I have the SOS front brake kit, it was a great improvement. Pedal feel was mostly the same, just a bit more surface area on the front rotors/pads, so definitely helped stopping.

So I just had the rear SOS kit installed. Now the pedal feel is trash. Nothing happens for the first second of pressing the brakes, they are very stiff. Then electronic booster kicks in and everything happens all at once. In a panic stop, this translates to shitting yourself because you're not stopping in the first second, to locking up the wheels in the following second.

Is there a way to dial in the pedal feel better? Or add a larger master cylinder for more fluid, etc?

 

Racebug, did you mention a part number for the cylinder you ended up with?

 

I did not post the wheel cylinder part numbers or the whole process I've gone through to this point. I had promised a full write up with pictures, descriptions, details, trials and tribulations, etc. I have all the pics, I've swapped all sorts of things several times with different trials, But I haven't gotten around to the write up and I'm not "done" with all the testing and trials I wanted to do (I don't think I will ever be "done" lol). The whole process of the write up sort of fell to the back burner with other higher priority things taking my time and the brakes working quite well for the time being.

I think instead of some huge master document with all the things documented perfectly and in order, i.e. "the book"... I should just write some basic stuff down and let you all go at it with the info I can more easily give. Will put some thought into that, but it likely will have to wait until after Thanksgiving.

 

Thanks.
I just ordered the parts for the Tundra dual diaphragm booster/cylinder. Hoping to finally be able to stop .

 

Hopefully you understand the parts and changes needed for the brake line attachment (I know some trucks have M10 brake lines and some have M12) as well as the pedal pushrod extension.

 

I think I've got it. I read the thread a couple times. It's not a daily driver, so if I have issues, not a problem.
I'll be posting if I have questions, or just to say thanks if it all works out. (But I might not start until after the winter.. Or whenever we get a few unusually warm days).

 

I'm curious if you've really slammed the brakes hard, since you've installed the larger cylinder.. I suppose there's a balance that needs to be maintained, so the rears don't lock up before the fronts, as I've read that can be bad.. (as in the rear end might start to slide around and you could spin).

 

The pedal feel improved quite a bit when the pads broke in after a few miles. Slow initial traction with the first touch on the pedal... into harder and harder stopping as you keep pushing.

 

I have really slammed the brakes hard several times... truck performed well. Fronts are still the ones that lock up first, so I can confirm I didn't overdo it in the rear, at least for my application and the weight I carry in the rear and the tires I have. Keep in mind I have a lot of weight when loaded up for a trip, 4000+ lbs on the rear axle. Even when I unload and not carrying consumables or some of the other gear, I still don't lock up the rear tires on flat ground with a panic stop. To me, this still confirms to me that the changes I made are in the right direction for me, given that the front upgrades changed the brake bias towards the front and the rears were doing less than their fare share of the work, even thought the rear has most of the trucks weight. Now it is more balanced, but not overboard on the rear.

 

Thanks for the reply.. I'm in the same situation..
This is empty:

 

Yep, I hear you on the weight, when all setup for camping and lengthy expeditions, they are heavy heavy...

 

Racebug...I'm late to the game and i know you didnt want to engage this guy but.....
@DG92071 until you can comprehend this link I'm posting you would do better to just not make the above comments that you made.
https://openstax.org/books/university-physics-volume-1/pages/14-3-pascals-principle-and-hydraulics

 

Ahh, pascal’s principle. In the AirForce, it is stated as “ pressure is equal and undiminished in all directions…at right angles. The last three words. Yep. True.

 

I could do better with a lot of things and you can too. I'll post what I want whenever I want to post it. Merry Christmas

 

OK fellas, let's just let it cool off and avoid escalation. No need to waste time on this piddly junk when we could be doing something productive.

Speaking of which, I've got lots of updates to do to hopefully benefit the community regarding the rear brake work I've done and the results I've seen. Hope to get to it between Xmas and New Years. But just found out that I likely have a broken front ring and pinion, so have some other work to get done too... boo...

 

I think DG is trying to say that although the force will be greater, the distance the piston moves will be less, because more fluid is required to act against the larger surface area. Thus not moving the brake shoe as far as the original wheel cyl

 

I totally get what he said and you are repeating. I guess it comes down to the distance the brake shoe, and thus the wheel cylinder piston has to move when applying the brakes. I know I have my opinion. Some research in the OEM world of all manufacturers that ever used drum brakes would indicate how they (OEMs) achieve more brake power for the same vehicles with different weight ratings or brake requirements. Toyota has done this in the past with 4 runner, Tundra, and Landcruisers, for example. They don't necessarily change the brake drum diameter or width.

 

What are you using to measure rear braking force before and after the wheel cylinder change? All you've said so far is you slammed on the brakes and the fronts locked up. How do you really know there's more work being done back there