Repeated caliper issues on 2013 Prius Two

is it at a dealer? perhaps they need to check the entire braking system, although it could be the aftermarket parts

 

I had an experience with an aftermarket reman caliper that I later removed again in favor of a Toyota caliper (from Toyota's reman program! nice to know about, but unpredictable what parts will be available through it), and the Toyota caliper was remanufactured to noticeably better quality, and passed a functional test that the aftermarket one failed.

I might not say never use aftermarket ... but since that experience, I would always test the caliper on the bench before spending any time putting it on the car.

 

Who’s doing the brakes and do they have access to the Toyota repair manual? It’s imperative that the rear caliper piston cross pattern be oriented like an “X”, when reassembling, and STAY seated thus, be well bedded against the back of inner pad thus. If it manages to rotate you’ll have steady drag and uneven/beveled pad wear.

 

As already stated, the pad must be fit correctly. Look at the work pads they should be even.
If one part of the pad is worn more than they other, they didn't put them in correctly.
If they did, you have either a sticking caliper, or bad flex hose.

 

+1. I had to repeatedly replace my rear brake bads due to uneven wear. It always happened after winter. I always replaced the brake hardware every time the pads are replaced.

1) My LR Toyota OEM pad died first after one winter. Outer pad grinded down all the way to steel pad backing plate on the top side of the pad. Replaced rotor with Wager ThermoQuiet Pads and Centric Premium Coated Rotors.
2) Rear RR pad wore unevenly again another winter. Replaced with another set of Wager ThermoQuiet Pads.
3) Next year, replaced brake guide pins and boots. Started using 3M lube to lube the guide pins instead of Prematex. I was hoping the lube didn't freeze or dry out in the winter.
4) Another winter happened and the LR caliper looked seized. The surface of the rotor started showing rust because pad was not making contact. Replaced with Raybestos Element3 Caliper + new rotor + new pads. Again, replaced with Wager ThermoQuiet Pads

I haven't had any problems brake problems within the last 2 years after swapping out to a Raybestos caliper. Although, I haven't been driving very much in the last year due to COVID-19. The Raybestos caliper doesn't have the "X" head as the OEM Toyota one does. It looks more like a flat clover which I hope would fix the uneven wear. I will be able to compare them more over time as my RR is an OEM caliper and my LR is an aftermarket Raybestos one.

Although, I have had no brake problems for a while, there was another Prius forum user who bought the same Raybestos caliper and has had hot burning rotors. I am not sure I can recommend them or not.

I thought it might have been the Wagner ThermoQuiet Pads I was using that was causing issues. They are aftermarket after all. I have been using them for my previous Corolla with no problems. Or maybe because I am using ceramic pads instead of the Toyota semi-metallic green ones. However, the inner pad always wore evenly. I mostly find the outer pad worn unevenly. The last pad I replaced, I filed off the top of the pad ear a little bit for the outer pad.

 

I’m thinking either or a combo of:

1. mis-oriented caliper piston
2. Dried out pins
3. Lube that swelled rubber (say the pin o-rings)

I’m using permatex anti-seize (silver) for contact points and Sil-Glyde Brake Lubricant for pins and boots.

 

Yes, it is a game of detective. I also use the silver Prematex anti-size for the pad ears. For me, I sort of ruled some of those out:

1. mis-oriented caliper piston //Not likely as piston contacts inner pad which wore evenly.
2. Dried out pins //Again, inner pad wore evenly. Unless both pins somehow pressed on the outer pad?
3. Rubber swelling lube //Yes the shorter rear pin has a rubber stopper boot at the bottom of the pin. I replaced that along with the dirt shield boots near the bolt head and changed my lube to the expensive 3M lube. Maybe this fixed things, but I would never know.

My theories are:
1) Bad aftermarket brake pad fittament (but why does the inner pad with squeal bar work fine? It means it fits) Inner/outer pads are both the same size.
2) Unclean brake hardware (which I replaced) or caliper requires more wire brush cleaning.
3) Bad brake pad shims. Wagner comes with a their own shims pre-installed.
4) Bad caliper design. The caliper arm that presses on the outer brake pad is just short by a few mm for uneven force. This is my leading theory. I should take a picture of my old pad, it wore at the top of the outer pad where the caliper arm pressed.

Replaced one caliper in the end. 2 years thus far. If it lasts, It doesn't matter anymore.

 

One issue that I measurably, reproducibly documented, including on an aftermarket reman caliper straight out of the box, was failure of the internal rubber piston seal to retract the piston when you are not braking. It is a subtle issue that is easy to check with a light puff of compressed air and a dial indicator, but otherwise difficult to notice. It doesn't present as anything being stuck or hard to move, the piston moves smoothly enough, but just doesn't pull back by that critical 0.3 mm or so when you are done braking.

Having encountered this, I know it does happen; I haven't done a large enough sample to say how common it is. It is, however, sneaky enough that it will drive you batty if it is happening and you don't check for it. I won't take a caliper out of a box and install it on a car anymore without testing this on the workbench first.

The causes can also be very subtle; in one case I suspect (no easy way to confirm) that it was down to the remanufacturer using a mirror-polished piston surface, where Toyota's pistons are more matte finished, enough to change the grip that the rubber seal has on the piston.