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Old 08-23-2020, 12:09 AM #1
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How to make a brake job hard? - pop out the piston

I’m not too proud of this, but am posting in case it helps someone else. Plus I could use some advice. I had some pulsation during braking that I was pretty sure was coming from the rear (no steering wheel shake) so I decided to replace rear pads and rotors. Got the new OEM pads and rotors and was ready to tackle this relatively simple job (HA!).

Got the wheels, calipers, and brake pad brackets off, and was ready to pull the rotors, however the rotors wouldn’t come off. They weren’t seized, but after yanking a while it became clear the parking brakes were hanging the rotors up enough they wouldn’t pull free. This was on both sides. I decided to loosen the parking brake pad adjuster, which is done through a tiny hole in the rotor, however the hole has to be perfectly lined up with the adjuster, and I couldn’t rotate the rotor with the vehicle in park. (The mechanics smarter than me know exactly where this is headed).

No problem, I’ll just put it in neutral. I hopped in, turned the key, and pressed the brake pedal for a second to unlock the transmission while I shifted into neutral. Meanwhile I hear the power braking system whirring away and CLUNK. The #@!&$ piston popped out along with about a cup of brake fluid. I knew immediately I had taken a simple task and turned it into an all day affair. After some cursing, I used vice grips protected with cardboard to clamp down on the brake hose to stop the oozing fluid. Then I resumed the original task of getting the parking brake pads loosened. Unfortunately all the pulling I did caused one of the parking brake pad retention springs to come loose, so I had to disassemble and reassemble the parking brake on one side. If you haven’t experienced this, it is a real treat. Getting the retention springs back on is a major PITA. You need tiny, extremely strong fingers. I did figure out that you can stick a small, deep socket through the hole in the rotor to compress the spring and get the spring fastener back on.

Then I had to basically rebuild the caliper, which was not as bad as I thought. You can’t just stick the piston back in, but you can pull the boot out of the caliper, stick the piston through the boot, then pull the boot down so the outer lip of the boot is off the caliper. That allows you to seat the outer lip of the boot in the caliper, then push the piston in so the inner boot lip seats on the piston.

Finally got new pads and rotors installed. Just did a bleed of that one caliper and after a lot of air was purged, all seems to be well. At least the pulsing is gone! The braking seems to be smooth and strong during the 15 minute test ride. Will be going on a longer test ride tomorrow. Any helpful tips on how to know if I got all the air out of the line? This was the first time I’ve bleed an automobile brake system and I was wondering whether I need to bleed the other calipers or anything else.
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Old 08-23-2020, 01:08 AM #2
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Brake fluid is hygroscopic. I live in a very dry desert so I choose to bleed and flush brake fluid every 10 years or 100,000 miles whichever comes first. I can't recommend a change interval for your location as I'm not familiar with humidity and rainfall in your area. In older vehicles, flushing brake fluid restores anti corrosive additives and the vapor point. For modern vehicles, brake fluid boiling is seldom an issue and brake system internal corrosion protection is far better. If the brake pedal is as firm as it was before your mishap and mileage is low, then I'd say you're OK. Perhaps someone living in your area of Texas will offer a suggestion on mileage or time interval to replace the brake fluid. If you decide to flush the fluid, then the two biggest risks are (1) breaking off a bleeder screw, and/or (2) introducing air at the master cylinder because the fluid level dropped too low. I had no issues bleeding my 4Runner by following a process written up in the basic maintenance thread. Check for bleeder screw leaks one and two weeks after opening the system. It's hard to tell you how tight a bleeder screw should be to avoid a leak or not break it.

Last edited by DougR; 08-23-2020 at 01:19 AM.
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Old 11-10-2021, 05:10 PM #3
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Quote:
Originally Posted by dlstyley View Post
I’m not too proud of this, but am posting in case it helps someone else. Plus I could use some advice. I had some pulsation during braking that I was pretty sure was coming from the rear (no steering wheel shake) so I decided to replace rear pads and rotors. Got the new OEM pads and rotors and was ready to tackle this relatively simple job (HA!).

Got the wheels, calipers, and brake pad brackets off, and was ready to pull the rotors, however the rotors wouldn’t come off. They weren’t seized, but after yanking a while it became clear the parking brakes were hanging the rotors up enough they wouldn’t pull free. This was on both sides. I decided to loosen the parking brake pad adjuster, which is done through a tiny hole in the rotor, however the hole has to be perfectly lined up with the adjuster, and I couldn’t rotate the rotor with the vehicle in park. (The mechanics smarter than me know exactly where this is headed).

No problem, I’ll just put it in neutral. I hopped in, turned the key, and pressed the brake pedal for a second to unlock the transmission while I shifted into neutral. Meanwhile I hear the power braking system whirring away and CLUNK. The #@!&$ piston popped out along with about a cup of brake fluid. I knew immediately I had taken a simple task and turned it into an all day affair. After some cursing, I used vice grips protected with cardboard to clamp down on the brake hose to stop the oozing fluid. Then I resumed the original task of getting the parking brake pads loosened. Unfortunately all the pulling I did caused one of the parking brake pad retention springs to come loose, so I had to disassemble and reassemble the parking brake on one side. If you haven’t experienced this, it is a real treat. Getting the retention springs back on is a major PITA. You need tiny, extremely strong fingers. I did figure out that you can stick a small, deep socket through the hole in the rotor to compress the spring and get the spring fastener back on.

Then I had to basically rebuild the caliper, which was not as bad as I thought. You can’t just stick the piston back in, but you can pull the boot out of the caliper, stick the piston through the boot, then pull the boot down so the outer lip of the boot is off the caliper. That allows you to seat the outer lip of the boot in the caliper, then push the piston in so the inner boot lip seats on the piston.

Finally got new pads and rotors installed. Just did a bleed of that one caliper and after a lot of air was purged, all seems to be well. At least the pulsing is gone! The braking seems to be smooth and strong during the 15 minute test ride. Will be going on a longer test ride tomorrow. Any helpful tips on how to know if I got all the air out of the line? This was the first time I’ve bleed an automobile brake system and I was wondering whether I need to bleed the other calipers or anything else.
Hey, I just did the exact same thing. Looking for instructions on rebuilding the caliper and not coming up with anything specific to 5th gen 4runner rear brakes. is there a resource you used? (Sorry, in semi panic mode as I have. aroad trip starting tomorrow...) Thanks!
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Old 11-10-2021, 05:40 PM #4
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Originally Posted by slide531 View Post
Hey, I just did the exact same thing. Looking for instructions on rebuilding the caliper and not coming up with anything specific to 5th gen 4runner rear brakes. is there a resource you used? (Sorry, in semi panic mode as I have. aroad trip starting tomorrow...) Thanks!
I replied to your other thread. But the brake cylinder is just a tube with an o ring and a dust cover. It's probably a little crooked. center it push it in. It should go back in
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