brake caliper pistons

[Burntboot]

Would you install a fr brake caliper that has different sized pistons?

The rebuilt calipers that I got for the truck, ls failed and they claimed to have no cores available.
They overhauled the blown caliper and when I get it back I find the lower piston is larger than the upper (you don't need a micrometer to see the difference) looks as though they have over-bored the hole and put in a bigger piston.
To my mind, this is not the way it should be, if your going to resize 1 piston, I would think you would need to do all 4 otherwise there will be dissimilar braking forces, no?

Everyone just keeps telling me to install it and it will be fine but I know that when the inner brake pad is smoked on an angle, 20K from now, no one is going to offer me free replacements.
Let alone all the other parts that will have been damaged in the process?

I would post a pic but don't know how, don't have a photo bucket account and am allergic to technology.
Just picture in your mind a 2 piston caliper where the upper piston is normal and the lower piston is a good 1/4" larger diameter (at least the part that sticks out of the seal)
Would you install it on your truck?

[timsrv]

Are you sure you're looking at the actual piston and not part of the rubber dust boot? I can't even imagine somebody boring one of these holes out a full 1/4" over stock...........let alone finding a piston that would work in an oversize hole like that.

To answer your question, NO, I would not run a morphodite part like that. Bore size and piston diameter are directly related to the amount of force that will be exerted on the pad (simple physics), so all pistons on both sides need to be the same in order to keep the forces equal. In addition to irregular wear you would most likely experience uneven & possibly unsafe braking during a panic stop.

I checked www.rockauto.com and see they have several of these to choose from. Price is around $27 each for most of the 4wd calipers. eBay usually has these too, but price is typically higher and in my mind some of the sellers are questionable. Good luck. Tim

[Burntboot]

Your right Tim, I was looking at the portion above the boot. I pulled apart one of my old ones and realized that the toyota piston has a very deep land.
I suspect, in reality, they couldn't source the correct piston and just found something that has the same bore diameter and overall height.
I still have fears that the larger diameter (contact area of the piston face to the pad) of the 1 piston is going to cause an imbalance in pressure on the pad, what do you think?

Unfortunately ordering more isn't going to be an option, my cash is already committed.
Not too mention the issue of shipping and customs fees....

[timsrv]

Surface area from piston to pad doesn't matter (at least not in terms of even braking). I might worry if it seemed inadequate in any way, but I wouldn't worry about more material here. Tim

[Burntboot]

So you don't there there are any issues to worry about here?

The Toyo pistons are thick and heavy I.D. = 25mm vs the oddball at 29mm, that seems like a lot less material.

It just doesn't look right and I hate the idea of possibly introducing new problems.

[timsrv]

I don't know. I can't see them so it's hard to get a grasp on what you're describing. If it worries you then make the $27 investment+ shipping for a rockauto caliper.

[djshimon]

I always get a new loaded caliper-it's much easier that way.

[Burntboot]

In the end I decided to swap out the offending piston, then I noticed their repair of the bleeder screw and lost all faith in the caliper in question.

I then ripped apart the original caliper, found it to be in good shape and as I now had a factory kit on hand, I overhauled it and am back in business.
I will return the offending rebuild.

While I was there, I repaired RS caliper saddle, heli-coils installed with red loctite.
(It is very satisfying being able to torque the mounting bolts to 61 ft-lbs without fear)

I then flushed the entire brake and clutch system hydraulics and was amazed at the amount of crude that came out, 1.5L of fluid before all ran clear.
I thought it odd that the manual states that the by-pass valve is the last to be bled.
I had clear fluid at the wheel cylinders, but what came out of the valve was shockingly filthy.

Brakes now feel 110% and stop on a dime with no trembling or noise.
Clutch feel is also hugely improved.