So just what is the cause of those infamous frozen calipers anyway?

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I haven't had the problem yet but since no one has responded I'll kick in my two cents.

My understanding from reading is that it's something with the materials of the pistons that eventually corrodes and freezes up.
 
I believe Matt is correct. I've had two frozen calipers, and in both cases the pistons that were seized had some corrosion preventing them from moving freely. Here are some additional thoughts:

I believe piston corrosion is due to a combination of several factors, the first being use/environment. For those that like to wheel, water crossings result in submerged calipers and obviously water exposure will result in corrosion over time. And for those that live in areas with snow, road salt accelerates the corrosion of the pistons. And for those that like to do both, well....

The second factor is seal design. The seals around the pistons are supposed to keep water and salt out, but it seems like the OEM Toyota ones are not very effective. I recently replaced a caliper with a NAPA reman unit that has a snap ring around the seal (OEM units do not have this). I'm hoping this is an improvement over the OEM design and helps to keep water and road junk out, thereby extending the life span of the caliper. Time will tell.

The third factor is brake fluid. Brake fluid is hygroscopic, meaning it likes to absorb water. Over time, the water absorbed by the brake fluid can contribute to accelerated piston corrosion. Frequent brake fluid flushes probably help combat this a little bit.

And the fourth factor, which is basically a guess of mine, is that the internal design of the calipers contribute to pooling of fluid in the vicinity of one or more of the pistons. I'm thinking that the fluid within the caliper itself does not circulate well, so the fluid right around the piston(s) remains stagnant, absorbs water that may get past the seals, and causes corrosion. I believe that this is evidenced by the fact that so many people have the lower inboard piston freeze up on them--a piston that seems prone to poor circulation by nature of its location.

Anyways, just my thoughts.
 
From what I have seen and read on the forum it seems to be a combination of excessive moisture and/or salt corrosion that attacks the piston from inside and outside. A lot of members swear its not caused by road salt, but I've noticed a large trend of failures being in areas that either use road salt or are near coastal areas where salt corrosion is prevalent.

Unfortunately since I haven't seen or heard of a case in the Bay Area I can't actually look at the caliper to see. :(

MY best guess is its a combination of Salt/Moisture corrosion caused by ineffective dustboot/seals & improper brake fluid change intervals. The materials used in the calipers construction (steel body & aluminium pistons IIRC) are the same as most any other manufacturers, which makes me wonder how many other makes/models have a similar issue?

Edit- Sonerick is on the same track as me. :) Dunno why I can't like your post...
 
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Carfax shows where all 4 calipers on mine were replaced/repaired at 60,000 miles for sticking. The front two were replaced, the rear two were rebuilt by a Toyota dealership. This 4R was in New Hampshire for the first part of it's life, so it was subjected to snow and road salt and chemicals for certain.

There are no other notes about the brakes listed anywhere in the carfax, except that at 98,000 the previous owner had them inspected and the technician noted 80% good on front, 60% good on rear. I now own the vehicle with 105,000 on the clock and the brakes feel great to me and show no signs of pulling or grinding. So, the point is that they've been good now for 45,000 miles and hopefully the original problem was solved.

If not, my idea was the same as his ^^^^ which is that I will NOT buy Toyota brake parts. I will buy quality replacements from NAPA or AutoZone.
 
I think it's the cold weather and where salt is being used on the roads.

I have a few friends here in Southern California that have 4runners and no one has had a problem. I only read about frozen calipers on the forum never in real life.
 
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It's pretty amazing to me that brake fluid is not on the recommended maintenance schedule.... I would think it should be flushed at least every two years....:confused:
 
Bob J said:
It's pretty amazing to me that brake fluid is not on the recommended maintenance schedule.... I would think it should be flushed at least every two years....:confused:
Click to expand...

I guess they figure that with the junk calipers they put on these things, the fluid would naturally get changed bi-annually during the bleeding process. :love:
 
Is seems like a lot if the cases are on east coast runners where they use salt. My rig has been in more than enough snow over the past 6 years and I've never had any issues with my calipers. Seems to be a rare occurrence in Colorado, Utah and the west coast. I could be wrong thought, just my observation.
 
*Warning: my completely non-professional opinion*

I do believe environment plays a small part in making the calipers freeze. Cars in heavily road salted areas just have more problems with corrosion and rust in general.

However, there are tons of cars in these areas (in my personal experience VA and PA) that have no issues with brake calipers freezing. I think something about the design of the brakes is inferior.

Simply put I think the 4Runner brakes let in more "road gunk" than other manufacturers designs.
 
I think it is just a poor design from Toyota that they have stuck with for a long time. I had the same problem with my Tacoma in the 90s. You see tundras with the same issue. I don't know if anyone else uses a 4 piston caliper besides Toyota, but it could just be the nature of the 4 piston design. Great performance when it is new and working properly, but not designed to be long lasting.
 
I wonder if carefully painting the caliper body to prevent surface rust on the exterior would help to prevent the piston(s) from sticking. My thoughts are based on the fact that the surface of the caliper will rust, creating a porous surface for moisture to cling to... eventually the entire outside of the caliper becomes rusted, allowing the rust to continue and push under the edges of the piston seals, spelling impending doom.

Perhaps a coat of paint on the NAPA rebuild kit could help out.
 
Keros said:
I wonder if carefully painting the caliper body to prevent surface rust on the exterior would help to prevent the piston(s) from sticking. My thoughts are based on the fact that the surface of the caliper will rust, creating a porous surface for moisture to cling to... eventually the entire outside of the caliper becomes rusted, allowing the rust to continue and push under the edges of the piston seals, spelling impending doom.

Perhaps a coat of paint on the NAPA rebuild kit could help out.
Click to expand...

I've used 2 versions of the NAPA remanned calipers. The first, which lasted about a year, came with a nice coat of black paint but NO snap rings around the seals. Even though this coating lasted nicely, two of the four pistons still seized up.

The second version has been on the truck for a month or two now. It has the nice black paint AND snap rings around the seals. We'll see how long this version lasts.
 
Aliens. But really, I just had to replace one of mine a few weeks ago and it had a lot of corrosion. We do not get a ton of bad weather in East TN but they feel the need to salt everytime the sky turns gray so im guessing that over the years it may have worn it out or at the least aided in some of the problem.
 
So far with 65K on my Limited, I have yet to see any issues with the calipers. I live in Wisconsin where the DOT hasn't met a salt crystal that it doesn't like. I'm keeping my fingers crossed that I won't have the issue that I have been reading about. I do wash the 4R frequently during the winter to get the salt off of the truck, maybe that has been a factor.
 
Bob J said:
I replaced mine with the NAPA lifetime warranty remans.... Figured it made sense to plan on them failing again in the future.....
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I am leaning this way also. Is there a walkthrough on replacing calipers up anywhere? I also heard there are three different NAPA caliper models for our the 4th Gen. How do you know which one to choose?
 
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