Melted ABS Sensor

Terrell - My guess...Wisconsin winters>>>road salt>>>rust 'frozen-dragging' caliper>>>very hot rotor>>>melted-cooked ABS Sensor.

 

The amount of power it takes to get a rotor really, really hot under a constant drag is a pretty small fraction of the power needed in driving the car, so you might not notice much really.

I once did the brakes on my former vehicle and got tired of the bleeding process (looking back on it, I think the wheel cylinder seals were holding fluid just fine but admitting air on the return stroke, which apparently is a thing, and makes the usual pedal-pumping DIY bleeding method into an exercise in frustration, while a shop with a pressure bleed kit solves the problem completely in seconds), so I got it to Good Enough and then drove to a dealer and asked them to finish bleeding for me.

When they came back out they said "we bled your brakes and we also adjusted your master cylinder pushrod, they should feel a lot better now" which was rather strange as I had just done the pushrod adjustment exactly per the manual and knew it was right, but I thanked them and drove home (couple miles). When I got out I could see the air shimmer around all four wheels. They had backed out the pushrod to the point the master cylinder never completely released.

When I drove it back they had the temerity to tell me it was normal. "Yeah, the brakes on those trucks always get hot."

To ice the cake, there was still air in the lines. I let the indy shop across the street from the dealer fix that, which they did with a pressure bleeder, in seconds flat.

-Chap

 

ugh, another 2010 brake problem. o/p, i think it is a bad design, many more complaints on 2010's than newer. check out member 'mendel leisk' threads on rear brake lubrication. it does seem to have something to do with use, as fronts don't seem to fail. maybe the rear collects more snow and ice as well?

 

Have the brakes been opened up before, say by the dealership? The rear disc brakes have an incorporated parking brake. Every time you depress the parking brake pedal, a lever mounted on the rear caliper is rotated, activating a cam to slightly extend the piston, clamp onto the disc.

The axle of this lever goes right through the cylinder back, into the piston. There's a clever spring wrapped around it, that only allows rotation in unscrewing direction. This accommodates reduction in brake pad thickness, over time.

One issue though: whenever the parking brake lever rotates, the caliper piston might ALSO rotate. To prevent this, there's a cross pattern on the head of the piston, and a pin on the back of the pad, that's supposed to lock between the piston spokes. There's instruction in the Repair Manual, to ensure proper alignment of the pin between the piston spokes, during assembly.

What I suspect is that just ensuring alignment of pin with cross pattern is insufficient. You also need to ensure the pad and piston face are well seated right after reassembly, by multiple presses of the brake pedal, before the parking brake is applied, or the piston may still rotate, the pin riding partially up onto spoke of the cross. If this happens, you get a grossly skewed pad, and lots of drag.

 

yesyou may be able to save the other side with disassembly, cleaning and lubrication.

 

agree. i would try to find a local mechanic. there is a service procedure for lubing the brakes. unless they're too far gone, the dealer should be willing.

 

I don't think Toyota mechanics are averse to routine caliper maintenance, ie: pad removal/check/cleanup, caliper pin relube and rotor inspection. This is normal duties.

Caliper overhaul I'd think they don't do, it's more cost effective to use a refurb'ed.

 

DO keep in mind labour rates are now -over- $100 per hour. In some places -way- over. It's much less expensive to replace rather than repair. It's also much "nicer" for the mechanic. If you've ever worked on old brakes you'll understand what I'm saying.

Another possible cause for rear brake failure from corrosion is water in the brake fluid. It tends to accumulate at the calipers (heavier than the brake fluid so flows down to the bottom of the system). It does dissolve into the brake fluid, which is glycol based, but gravity rules, pulling it to the lowest point of the system.
How does water get in? Past seals when parts move, a very small amount at a time. This is why it is recommended brake fluid be changed every two years or so. Water in the fluid lowers the fluid boiling point, and can be the cause of braking loss at extreme braking events (such as mountain pass descents).
Not such a big issue with a Prius and regenerative braking, but the problem with a Prius is the brakes tend to be ignored, and that is a recipe for disaster.

 

Yeah, Toyota Canada's finally acknowledged brake fluid replacement is worthwhile. An excerpt from the 2014 Prius Scheduled Maintenance Guide:

If the above-and-beyond chore you're referring to is caliper pin lube, that's a fast, trivial chore, if you've already got the caliper pulled off the mount for pad check and disk inspection. Replacing a caliper rather than do something like that would not make sense. If there's a problem with the piston, I think what they commonly do is pull replace the caliper with a previously pulled one that a specialty shop previously refurbished.

 

There's something that puzzles me about rebuilding these calipers. If I look on, say, Village Toyota Parts, I can see a rebuild kit that includes the slide pin boots, piston boots and seals, just like the rebuild kit for any conventional caliper, but it doesn't say (or the illustration doesn't show) anything for the seals where the parking actuator goes through. I don't know how to buy those (if you can). Maybe it would be worth somebody asking at a dealer parts counter (and posting the answer, I'd be interested)?

I'm sure it would be interesting to the group to post some disassembled closeups of the failed caliper to try to get some idea how bad it is. I have a bad feeling that even if the original cause was something else, enough heat to melt the ABS sensor probably also melted the piston boot, allowing road spray in and now the piston and bore will be rusty to some extent.

-Chap

 

Overheating accelerated the bearing failure?

 

When the overheating was on the left side and bearing failure was on the right?

 

Details!