Repeated Brake Failure 07 Scion Tc [UPDATED]

This is the update to the original post, that I made 2 months ago. This is the original post, see bellow for updates. Thank you ahead of time for the input.

[quote=”Pav_Sul” post=200997]Hello everyone, first of all I want to thank you for any advice you might have as I am out of ideas.

I have a 2007 Scion Tc 2.4L automatic, 135k salvaged and rebuilt at 45k. About 2-3 years ago I started having problems with my brakes, first a squishy pedal and then a seized caliper. Over the last 3 years I have replaced 2 master cylinders, 3 front calipers, 3 rear calipers, 2 brake hoses. I get a seized caliper every 6 months almost on the dot.

Some of the work was done by a Toyota dealership when I got frustrated and desperate, and some work was done by a reputable local shop and some of the work was done by me. People that have worked on this car have more experience working on Toyotas than I’ve been alive and they haven’t seen a Toyota fail 2 master cylinders in 3 years.

I am writing this because my rear caliper seized up on my way home last night yet again.

I am going to try to list as much as I know:
Brake fluid is normal (yellowish, but not new)
Pedal feels squishy, like there is air in the system.
Rear passenger side caliper is seized
There is no fluid loss under the pedal or under the hood.

Master cylinder was replaced almost exactly 1 year ago with the driver side brake line, hose and caliper.
Front driver side caliper was replaced (seized) 6 months ago, system was thoroughly bled.

I am going to take a closer look this weekend, any ideas on what I am missing? I don’t want to sell the damn thing because I don’t know if it’s safe, the dealer isn’t going to give me shit for it because it’s a rebuilt title and fixing a seized caliper every 6 months is still cheaper than a car payment.

Thank you everyone,

Pav[/quote]

After a busy couple of months I finally had enough time to take apart the car and diagnose, it’s was also impossibly cold in the Midwest, I don’t have electricity in my garage.

Update:
Fluids: brake fluid is clear/yellowish, I found no leaks after pumping the brakes and checking all fittings. No fluid under the brake pedal.
Calipers: all caliper pins are free at all 4 tires, no rust and the original grease is still wet. Both rear calipers were seized, and I broke my C-Clamp pivot trying to compress one of them.
Master: No fluid leaks at the fittings. I pulled the master, the compression and decompression is not smooth, decompression specifically feels like the master gets a little stuck. I ordered a new master.
Booster: In the car test, holds vacuum, tested by pumping the brakes and the pedal getting harder and stays harder. Vacuum valve was tested when booster was pulled by trying to pull vacuum through it, works at it should.
Booster/Master push rod clearance: the clearance in the manual reads (0 mm), I measured a 1 mm clearance gap between the booster and the master.

This was measured using a vernier caliper. Basically following the instructions in this video:

I measured the depth of the booster rod from the booster face surface (datum).

I measured the distance from the master mount surface (datum) to the master hole entrance.

I measured the depth of the master hole from the hole entrance

I subtracted value in step 3 from value in step 2 to get the distance of the master rod from the mounting surface (datum)

The difference between value in step 1 and value in step 4 was 1mm

Yes I accounted for the thickness of the ruler I used to help measure the depths.

My question, could the 1 mm clearance (not interference) cause the master to fail and the rear caliper to seize?

What else am I missing? What else should I check?

Again, thanks for your help everyone.

-Pav