What finish on Toyota's Gen 1 (cast iron) calipers?

Discussion in 'Generation 1 Prius Discussion' started by ChapmanF, Mar 23, 2015.

  1. ChapmanF

    ChapmanF Senior Member

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    Last month I found one of my calipers had a torn boot, apparently for a while:
    tornboot.jpg

    This caliper doesn't look pretty after 14 years of Indiana road salt ... but strikingly, it shows very little rust ... just this overall tough gray surface, like it's hewn from a rock. The torn boot hadn't done the piston any good:
    piston.jpg

    My dealer couldn't get piston and seal kits right away, so I looked for a decent-looking reman caliper.


    reman_caliper.jpg


    It even claims to have an "exclusive rustproof coating." From the looks I was guessing yellow passivated zinc. Out of the box it looked a lot sharper than those 14-year-old originals, and it is based on an original core (I checked), not an imitation. I figured I could live with it. I even considered replacing the other side so they'd both look that sharp.

    So, umm, here's the reman "exclusive rustproof coating" after about five weeks:
    exclusiverustproof.jpg
    That's right, I said "weeks." Totally rust-covered even before the splodges of fluid could dry from hooking it up!

    I'm glad that's an exclusive rustproof coating. The only thing worse would be if lots of suppliers used it. Amazingly, it manages to make a 14-years-salted Toyota original look nice by comparison.
    oemfinish.jpg

    I am now glad that I passed up the small core refund and kept my core instead. I am likely to order the Toyota piston and seals and reassemble it myself, and let the exclusive proof-of-rust version be the spare. So this makes me wonder: what is the original finish on Toyota's $300 calipers, that holds up rust-free so long? Who's seen one right out of the box, and what do they look like?

    I ran into an interesting article on restoring classic Porsche calipers that seems to echo exactly what I just learned the hard way about big-box reman finishes:

    For restoring the surface appearance, I know there's powder coat and there's rattlecan paint, but that author strongly advises that zinc plate was original and zinc plate it should be. There is a plater near me and I have no idea what they charge, but if it's reasonable (e.g. with parts I still end up comfortably below the Toyota new caliper price) I might not mind restoring my originals for the next 15 years. (If the charge is mostly per batch, I guess I could have them toss the rustbucket reman in too.) :)

    But zinc plate finishes end up with different colors from different passivating formulas, so that's why I'm wondering if anybody's seen a new Toyota Gen 1 caliper close up. This article shows some caliper parts with transparent, blue, or black passivate. The "blue" looks grayish to me, I wonder if that's in the ballpark.

    More recently, zinc-nickel plating seems to be the trend on cast iron calipers, according to this article, with even better rust resistance than straight zinc. The article suggests it was simple zinc "in the 90's and early 2000's" so I'm guessing that was original for Gen 1 and zinc-nickel came later, but what do I know?

    -Chap
     
    #1 ChapmanF, Mar 23, 2015
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  2. ChapmanF

    ChapmanF Senior Member

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    I'd settle even for decent high-res photos from early brochures or reviews if they showed a glimpse of the caliper.

    Hmm, how about john1701a's old photos?

    [​IMG]
    [​IMG]

    Sure looks like zinc/transparent to me.

    -Chap
     
  3. ChapmanF

    ChapmanF Senior Member

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    I'm still not finding dates, but Toyota seems to have had a number of plating standards through the ages ... here's a list I've condensed from Marsh Plating Corp.'s literature.

    I'm guessing the date for when 6500G was obsoleted by 6524G would coincide with whenever hexavalent chrome was being phased out. I notice the zinc-nickel finishes (6530G) do blow everything else away on the salt spray test (how many hours in the test chamber before the first appearance of white or red corrosion) - by a factor of four, five, or more!

    platespecs.png
    -Chap
     
  4. ChapmanF

    ChapmanF Senior Member

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    Well, I haven't been back to this thread for a while, but there's interesting stuff to add.

    When last you heard from me, I had taken out a 14 year old Toyota caliper—because the seal was torn, and the brake dragged—and replaced it with a parts-store-special “exclusive rustproof” reman that looked swell in the box, and turned rust all over inside of five weeks. You can imagine how it looked a week ago when I finally pulled it back off.
    rustproof.jpg
    The dark part is just a brake fluid stain from when I pulled it ... dry, it's just that powdery, flaky, pitting red rust everywhere. "Exclusive rustproof" my eye. This is less than six months old.

    For comparison, here's the Toyota caliper on the side I didn't replace back in February, so it's been in service right up to this week. There are some scattered spots of red rust that have only just recently begun to appear. The car is fourteen years old.
    fourteen.jpg
    ... so that was one thing that made me (even more) a believer in Toyota's parts quality compared to the aftermarket, and made me wonder what finish their calipers use.

    But it's about more than the finish!

    So before I get back to the finish, something more important. After all, there was a reason I replaced that caliper in the first place. The brake was dragging! It was easy to see why, the boot was torn. So no matter how cheap the finish was on the parts-store reman, at least I completely expected my brake drag to go away.

    It didn't!

    Even right after putting on that cheapo reman caliper, there was never even one time when I could complete my 15-minute brake drag test without the rotor being hot. Of course I couldn't believe it was the fresh reman caliper, so I spent some unnecessary worry on whether I had some scary hydraulic actuator problem developing, or something like that. Yikes!

    Nope. It was the caliper. There's a side question that comes up right here: When a caliper works right, what makes it let go when you're not braking?

    On a drum brake it's no mystery, there are giant return springs to pull the shoes back. What pulls a caliper piston back?

    It's nonobvious enough that I found a thread in another forum (less friendly than PriusChat, naturally!) where in the first 16 posts, the right answer only came up three times—followed by other posts calling it ridiculous.

    So what's the answer those folks couldn't believe? Turns out the magic is in how the rubber piston seal deforms when the piston slides out. Not convinced?

    Toyota's convinced:

    brake04-8.png

    Cardone's convinced:

    brake2-2.png

    And Delphi has published finite-element modeling of the piston, seal, and groove the seal fits in. You can see even that machined groove the rubber seal lives in is part of the magic and, under magnification, nothing like a simple shape.

    Anwana-13.png

    So, can a caliper be tested for this? How far should a piston normally return?

    The Toyota picture shows the "amount of piston return" but doesn't give a number. The Cardone book suggests around 0.13 mm. From the Delphi graphs, a range something like 0.1 to 0.3 mm falls out.

    That ought to be perfectly testable. Here are a couple nylon blocks I had lying around with holes drilled through them. The blocks are stacked where the pads and rotor would go and the dial indicator stem goes through the holes to rest on the piston. Squirt compressed air in the caliper and the piston moves out to clamp on the blocks. Note where the dial indicator stops, then cut the compressed air and see how far it moves back.

    retracttest.jpg

    Here's that decade-plus old Toyota caliper, the one from the side I didn't change in February because the rubber boot looked ok. The thing looks old and beat up and dried out but there are no tears in the boot, the piston moves smoothly, and it has a very robust return, even slightly over 0.3 mm. It shows to the naked eye. You can watch the piston pull back.

    fourteenboot.jpg

    How does that compare to the cheapo reman, that I installed right out of the box off the store shelf just last February? That thing has a piston return of ... zero. Nothing. Zilch. The piston moves smoothly ... right out to the blocks ... and stays there. It's not binding or sticky. It doesn't leak. It just has no return at all. Whether it's because their seal is made wrong, or their cleanup/re-machining of the core casting messes up the shape of the groove ... one way or another, getting the piston to return properly depends on tricky details, and this reman supplier ain't got 'em.

    I think from now on I will do this test on any caliper I am about to install. It is too quick and easy to leave out, and it's too frustrating to go through the labor of installing a caliper only to notice later the brake is still dragging.

    Does anybody sell a decent reman caliper then?

    It turns out Toyota does! I didn't know that before, but you can just look up the normal part number, then look for the same number with -84 at the end. They sell some other things reman also, like A/C compressors, drive shafts, and so on, depending on the car model. (Now, a week after I post this about -84, they might change the magic suffix to -42 or something, but I can't help that.)

    There's a catch


    You have to be careful though. They play a game I don't think much of, where the part number with -84 doesn't include the same stuff as the same part number without it. If you order a new caliper, 47730-12490 or 47750-12490, you get everything shown in this box, but if you order 47730-12490-84 or 47750-12490-84, you only get the parts I sprayed green:

    remancaliper.png

    Oh, it also does come with the rubber bleeder cap, it's just not in the picture. If you'll be reusing those other parts, the reman caliper saves you a bundle (and it's only about twice the price of a craptastic parts-store version). If you need new slide pins or the mount bracket, you can order those as new parts a la carte, but if you want the whole works you only end up saving maybe $40 compared to the brand-new caliper, and you still need to put the pieces together.

    Naturally, the Toyota reman passes the piston-return test with flying colors.

    remanretract.jpg

    After installation, I repeated my 15-minute-drive drag test and that rotor was absolutely stone cold to the touch, and was still that way when I repeated the test a week later. Still too early to tell what that's worth in MPG, but it sure can't be bad.

    Ok, back to the finish question

    Remember from my first post that Porsche enthusiast advice that the best restoration for an original caliper is to re-plate the original zinc?

    Sure looks like Toyota's on board with that:

    [​IMG]

    I am guessing this reman will not turn to red powder in a month.

    To be honest, I guess I don't know for sure whether that's replated, or coated some other way with the same appearance. I hope it's not just silver rattlecan paint. Might find out next winter. According to the man with the tricorder, it's not an exact match for the mounting bracket bought as new:

    tricorder.jpg

    Ok ... technically ... "X-ray fluorescence" ... but can anybody here look at that thing and honestly say that ain't a tricorder? Here's what it got for the new bracket:

    bracketxrf.jpg

    And here's for the Toyota-reman caliper:

    caliperxrf.jpg

    I'm guessing the Fe isn't in the coating but being read through it, and there's a lot of Al showing up. Maybe this is something like Galvalume. We'll see how it holds up.

    -Chap
     
    #4 ChapmanF, Aug 15, 2015
    Last edited by a moderator: Jun 14, 2018
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