2012 Prius - New Calipers, Pads Still Dragging (hot brake discs)

Gotcha @ASRDogman!Actually, for the piston seal (official manual wording), in the manual (see p12 for eg in this excerpt) they call for "lithium soap base glycol grease" - I know people use brake fluid to lube. I suppose the grease is thicker and has a higher endurance, and temp rating?


A NOTE: Speaking of my disc measurements, page 30/41 of brake repair from manual - disc runout for rear .15mm. I had 0.08 mm so it's all good.

 

Thanks Chap - I actually edited the post because I think some of those guys are confused: they're talking about guide pins at some point. It's not even clear they're rebuilding the caliper. I'll go look for this paste.

EDIT: actually, @ChapmanF ,is that grease used on the pins also? That's what I read (edit: in the manual ). I wonder if I can replace it with the silicone paste that has been working well so far. Given that it's in contact with brake fluid makes me cautious, not sure how it will react.

 

The piston's rubber appears to be in great shape, any idea if I can replace the Toyota paste with silicone paste? Given that it did not affect the rubber on the slider pins?

Edit: Says on AGS Silglyde box: non-melting, good for o-rings, boots and other like pins. Gonna go ahead.

 

I had to cut off the parking brake support (the eyelet) off the old Tokico (seized by rust badly and I was dumb enough and didn't know any better) - anybody has an idea if bleeding can be done properly if that mechanism is not cocked?

Anbydoy has opened one of those calipers entirely? I wonder if I open those screws if I can re-assemble them given that there's a spring under tension inside.

 

EDIT: found this honda/acura rear caliper rebuild. Transplant complete - will post a couple of pics later.

Q: brake cleaner doesn't need to be neutralized, right? Once it dries off it's pretty much evaporated? It can't damage rubber if it's a residue film on the metal? (edit: I swept with isopropyl alcohol over it and used compressed air to blow inside there after - looks clean)

 

Pics from today.

I did some bench measurements of the pistons for Tokico and Raybestos (and got 0.16mm for both with the final method) - but first to explain what you're looking at. The neck which holds the parking brake on the Tokico - weirdly started to crumble as I was cleaning with a tiny stainless wire wheel+dremel. Then I cleaned the caliper well after I transplanted the Raybestos parking line bracket (the original was cut). The rubber looks new, no cracks, elastic, nothing dry; the install was easy with the manual's steps. I also took the 1st Raybestos RL caliper, pushed the piston back and got out the brake fluid - so I tested this with the original lubrication and a bit of brake fluid in it (not the smartest idea as I get a bit of if all over).

The "Proper-Final" Method: The comparative dial was screwed into wood (no magnet, some old thing). The wood was clamped onto the caliper - the whole thing ultra-solid. The clamp acted as a stop for the piston - simulating the brake pad. I put the dial's pin as far inside as I could, and the clamp a few mm after so the dial could travel. And like I said with this method I got about 0.16-17 mm for Tokico , and 0.15-165 mm for Raybestos. Usually it was 0.16 for both.

Now I agree with what Chap says: I should use the oem paste.

Stuff I learned - regarding bleeding and the parking brake lever. The lever acts like a one way car jack. It pushes the piston a few mm, without rotating it at all. So the piston could advance 1-3mm (depending on how much it's pulled) but then it retracts as much as the seal ring pulls back on it. The piston should advance under pressure (applied before opening the bleeder valve) but I guess Toyota wants to be extra sure the brakes are tight hence why asking for the parking brakes (the parking brakes are applying pressure for whatever nominal piston position is in there, and the piston advances as the pads wear down). I did a 100psi test with air (never thought it would be that violent) and shot the cylinder about 1m like a bullet - had a ring in my ears from the "pop" for a while, don't try: just laugh - I'm glad I didn't break anything; the car's brakes have much more pressure. When pressure goes through the caliper, there is no rotation. When the piston is screwed back, at the end it keeps on rotating without catching anything. Quite the engineering - still not sure why it works the way it does.

Now. I did several tests without stopping the cylinder - just some ranting here. I would blow air in (10 psi, regulated when open with a tiny paint gun regulator, 20-25 psi closed) I would control the pressure by letting some air escape, tilting the nozzle on the inlet. And I would watch that I'd move the dial 0.40-0.50 mm (say I'd stop and maintain constant pressure at 90 on the dial) and then I'd watch how many units it returned as I shut the air. The whole assembly was solid - no matter how much I yanked it, the dial would not move (the Bessy screw clamp is powerful). And I got any value from 0.10 to 0.30 ish - more on the Raybestos; the Tokico was more like 0.2-0.32. The bigger values were obtained when pushing the piston with the parking brake lever. Usually Tokico gave me 0.18-0.22. And Raybestos was all over the place. As the pistons went out further, there was less friction so it was hard to standardize it; so that's when I blocked the piston - I even forgot what Chap did in his experiment.

I consider the values from the "Proper-Final" method to be the most real word accurate.

@ChapmanF I was just reading your original caliper dial experiment (post #4 half way). I see that you mention 0.13mm (Cardone book) and 0.1-0.3 mm in Delphi Graphs. Now the manual says 0.05 disc runout (warping) in front and 0.15mm disc runout in the back. I got 0.08 for my bumpy burnished disc so I'm good. But this makes me think that the rear should have greater tolerances than the front, more space in between the pads - but I know that 0.3mm would suffice (not getting that so far).

Tomorrow I will take off the good RR caliper to measure it (dying at this point to know what is its travel). If it is 0.16mm I'm gonna be as that one is not heating and it would be a paradox. After that, I guess the course of action would be clearer.

 

The test was done with air and the piston landed on something soft (I was close to the ground too) - that caliper had no fluid in it. So it was all good. I thought too that since air compresses that it should be ok and I don't have a fitting - I loosely fitted the rubber tip against the hole so I thought a lot of the energy would be lost. Man was I wrong . You don't have to tell me not to do it again - for as long as I'll live I'll start my tests at 5 psi from now on . I grabbed the air regulator from the paint gun and started with 5 psi (valve shut) in increments - the sweet spot is about 10-11 psi when the air is running, 25 psi valve shut (the reg reads more when the valve is shut - spray gun basics). The Raybestos with a bit of fluid in it, kept letting out a bit of brake fluid all the time - we're renovating so nobody cares, the room is protected.

 

OK. I don't have conclusive numbers but I have conclusive results. Testing by eye, on the car I could tell RL (bad one) moves a tiny bit, a smidgen (1/10th mm is right in my books). Looking at RR (good one) it moves 1/3-1/2 mm. What is clear is that it moves A LOT, that it's so obvious by eye. Even after I got it off the car, when pushing it by parking lever or by air, I could see it retract a lot. I got numbers ranging from 0.3-0.5mm to 1mm sometimes. I couldn't clamp it solidly like yesterday, the numbers are not final. But the visual test is clear like night and day.

Now, @ChapmanF ,you mentioned a rebuild kit which comes with the grease - any number for that?

I'm thinking of rebuilding one of these. If the rebuild works badly, then I'm buying a pair of calipers (just the calipers, the brackets seem fine) from Amayama (I hope they sell Tokicos dammit - I don't need early Xmas presents now). Opinions?

 

Thanks. I'll do the rebuild kit first. There's life left in my Tokicos from the way they look.

 

Problem Solved: DONE - no more heating heels (unless I brake like a rally driver)

Today I was trying to get those dial numbers and I just couldn't get it to work. I noticed the dial jam too so I just relied on my eyes. Pumping the parking brake lever I found the Tokico is actually retracting well (the dial was on too registering 0.4mm of backing up) so I bolted it on RL side. I put back the working Raybestos on RR. RL is giving me about 5-6 spins (really spins freely, like really does, especially after I made those pads split like the Red Sea with those V clips) and Raybestos still does 3-4 spins (I noticed the disc is warped SO that's the issue now, but will change it: I got warranty replacements). Then I'm waiting for my rebuild kit and I'll rebuild the Tokicos, get in new disc and pads and that's it.

Did a test drive, all good. Got slightly more kick in acceleration. Fuel economy seems to have dropped - just recalling vaguely the figures for such short trips (9-12L to 6-8L).

A HUGE and warm thank you to everybody who took their time to help me out. I can't believe how long this dragged out. You guys are awesome !!! (This feel suddenly like a speech at the Oscars )