Rear brakes still binding after overhaul

Did you use new hardware with your pads and it doesn't hurt to change the old brake hoses at high mileage.

I have never worked on rear Prius disc brakes but have on other cars.

 

Did you rotate the rear piston(s) in order to seat correctly?


iPhone ?

 

Two problems I had on doing the back brakes on my (now my wife's) 2010:
The channels in the caliper that the sliders fit in got quite rusty and gripped the ears of the caliper pads too tightly - had to clean the channels out with a file down to bare metal.
The caliper pins even after cleaning were very stiff and didn't slide in and out very well. I'd (foolishly) used anti-seize to lube the pins rather than silicon brake grease (you'll see folks refer to Sil-glide), and the rubbery bits on the ends of the pins swelled. May need new ones of those.
Barring those things, maybe you've got some crud stuck in the dustbellows of the piston and it's not fully retracting.
As a wild thought, the parking brake cable is rusty and not releasing the piston - though you'd have problems putting the caliper on if that were the case.

 

You've very likely got misaligned caliper piston. It's imperative, that the rear piston face spoke pattern be oriented like an "X", so that the pin on the back of the inner pad falls in between the spokes. Further, you need to ensure, through multiple pushes of the brake pedal, that the pads and piston are well seated, that pin is solidly locked between the spokes.

The pin being locked between the spokes is Toyota's method to prevent the piston rotating when you apply the parking brake. If this happens, the piston will then be bearing only on the pin, the pressure will be skewed, and there will be a constant drag.

I'll attach an excerpt from the Repair Manual on brakes. This picture in particular shows the correct orientation:



Again, it has to be reassembled thus, and well seated, or the piston will rotate, and everything will be messed up.

 

Get it aligned properly (so pin falls between the spokes), assemble, press brake pedal multiple times. Do not use parking brake. Go for test drive, apply brakes gently. When you get back apply and release parking brake several times. Then raise rear and test spin the wheels. They should spin semi-freely. Being disc brakes there will be slight drag, but it should be very slight, the wheels should easily free-spin a revolution or two after you give them a good push.

I care about this, because it got me, the first time I looked at our rear brakes. Put everything back together, and seemed like an odd amount of drag. Oh well. Six months later, noticed scoring on the outer disc face:



Opened them up, and the inner pad in particular, the one in contact with the piston, had beveled/uneven wear. The rusty zone is basically unused:


(It looks like this because the piston is bearing just on that pin, terrifically skewed.)

And the inside face of the rotor, looks like this:



I ended up binning the pads and putting in fresh. The brakes sounded like shite for the first hour, noisy for a day, and within a week or two were completely healed.

I'd call this a design fail by Toyota, that you need to be cognisant of something so subtle/tricky, and the consequences of overlooking are a real mess.

 

While you'll see folks refer to Sil-glyde and various other goops, it's worth dropping a reminder now and then that Toyota specifies a grease for that purpose.



The 08887-01206 stuff is called "rubber grease", it's a kind of translucent red, and it's a lithium soap based glycol grease, not a silicone. If you don't want a whole tube, you get a little packet of it in any Toyota replacement rubber kit. That's the stuff that they know will not swell the particular rubber formulation they use.

I'm sure it's possible to get decent results with other generic brake greases (and especially if you have installed aftermarket rebuilt calipers or rubber parts, they might not be the same formulation as Toyota's rubber anyway, so any OEM compatibility specs might be moot). But if you do still have the OE calipers and/or if you do use OE rubber kits when overhauling them, it's worth remembering there is an OE grease spec.

The other greases shown in the photo above are the gray ones Toyota uses for the metal-to-metal locations, as between the shims.

-Chap

 

Yeah, I think the key is to position and seat the piston in that "X" orientation. After reassemble, push the brake pedal a bunch of times, test drive, and delay use of parking brake to after all of that. And then check, raise car again and verify it's turning semi-freely.

It's a pain, and it's a poor design by Toyota, to need to be so careful/vigilant. The Repair Manual just breezes by, mentions the orientation, but it takes care to ensure it doesn't jump back into misaligned case.

 

Thanks for the info on this. I am getting ready to do the brakes on our Prius v and this certainly will help...along with the nutzaboutbolts video...of course!

 

With the v a mini-drum is employed for parking brake, IIRC. So hopefully doesn't have that piston orientation issue. Someone should snag a pdf of it's Repair Manual, if such a thing still exists.

 

Hmm interesting. I was assuming it was the same as the liftback. Yes..a repair manual PDF would be ideal...but I'm not getting my hopes up.

 

@NutzAboutBolts video would be ideal too. But I gather he's busy, and he'd have to get his mitts on a v.

 

I prefer .pdf manuals, they are easy to search compared to a big old book.

 

The one I worked on had the mini drum and no alignment issue.

Will be working on a different one in couple of Friday’s.

 

Could you take a few pics when you do it? This will be my first brake job in a long time and all the info I can get beforehand will help tremendously.

So I'm assuming when you have a mini-drum the process is similar to the fronts then?

Edit : Sorry about the thread hijacking!

 

It’s the exact same as the @NutzAboutBolts video, you just don’t have to worry about the alignment pin.

I’ll do what I can on the 23rd.