Jose Pena

Hey guys im rebuilding the rear drum brakes on a 89 v6 pickup. The rear wheel cylinders were both different sizes. Im guessing previous owner accidentally miss matched the rear cylinders. Now im not sure which bore size it originally had.
single rear tire and the vin says 1/2 ton.
it has F18Q front calipers and its an extra cab
Based on this info from rock auto im leaning on getting the bigger bore.
Would a slightly bigger rear bore cause any issue?
Would the rear grab more than the front?

Melrose 4r

I’m not sure but i would guess that if the cylinder is larger in volume and the master is pushing the same amount of fluid, there would be less movement at the wheel cyl.

Jimkola

I'd think it'd be easier to just get the size that Toyota matched with the existing system. That way you don't have to worry about the master cylinder being under-sized, or making any adjustments to the proportioning valve. The vast majority of the actual braking is the responsibility of the front brakes. The rear brakes just makes sure the back of your vehicle doesn't try to pass up the front when braking, especially in turns.

Jose Pena

Thanks for the reply. As of right now i have confirmed i have a double diaphragm power booster. I also have a 1inch master brake cylinder. It also has the bigger calipers up front the F18Q as well. I think the 15/16 wheel cylinders would be the better choice. I'll report how it feels after the install.