Had my brakes inspected today during an oil change and was told the rear pistons aren’t compressing. Doesn’t look like any fluid is reaching either drum. The gentleman thinks a line could be blocked, but he was not equipped to do any further investigating or repairs.

Basically I’d like to at least rule out an issue that could be relatively easy to fix myself.

Any tips for how to troubleshoot this? I have found some write ups, but they weren’t specific to the 4th gen. Either way I’m gonna start checking hoses for issues in the meantime.

TIA for any helpful advice.


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You have disc brakes on the rear, not drum....right? If the caliper pistons were not moving, your rotor surface where the pads contact it would be all rusty, not shiny. Is that what you see on both wheels, both on the inside and outside surfaces? Unless you are ready to remove the calipers and replace the pads & rotors (and maybe the calipers and bleed the brakes) would recommend you take it to a mechanic and let them figure it out. If you are mechanically inclined and have tools, it is not a difficult job. If you want to try and confirm that fluid is not reaching the piston (which is not all the common), you could crack a bleeder and see if fluid comes out when you very slightly depress the brake pedal. If that's happening, you have fluid flowing to the piston. Make sure you tighten the bleeder before you release the pressure on the pedal to avoid introducing air.

"Pistons aren't compressing"? The only time they're compressed is to make room for new pads. Piston compression isn't done during an oil change brake inspection. If the guy had no useful diagnostic skills after making this pronouncement, I wouldn't take anything he said seriously. I would also doubt his qualifications to perform oil changes.

4th gen calipers "freeze" stick all the time. I have swapped rear calipers atleast 5 times over the years. you have two options.
1. Get lifetime calipers from an auto parts store and plan to change a couple times.
2. buy 5th gen calipers/rotors and pads, do the swap and be good to go.

It may be disc brakes on the rear, I used to have a Tacoma so I assumed they were probably the same. I definitely don’t mind to try to tackle this myself as I have enjoyed learning this stuff as I go along. I know there may be a point where I have to take it to a professional but at least willing to try first. I think I could handle replacing pads, rotors, and calipers.

Thanks for the advice and I will report back what I find.


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Interesting quirk I wasn’t aware of! I wonder if it’d be worth it to buy another caliper and test to see if that solves the problem?


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I may have misunderstood what he said. Basically I asked them to do a brake fluid flush, but they were not able to because there was no fluid coming to the rear calipers. Then he started checking the calipers. He had mentioned something about not being able to move the pads. I may need to clarify what exactly what he meant. It was a hectic day and I was trying to listen fast.


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If you have no fluid pressure at the back brakes, you either have a blockage in the brake lines or the master cylinder has an issue.

I would first check the rubber brake line coming down from the body to the rear axle, loosen it where it connects to the steel line up at the body and see if the fluid will flow then at that junction, sometime rubber brake lines deteriorate on the inside and can block fluid flow when bits of rubber breaks loose on the inside, if you get flow there then it's most likely the rubber brake line, if you get no flow there then I would look at the master cylinder.

The master cylinder has 2 sections one for the front and the other for the rear, there are 2 main brake lines on the side of the master cylinder, figure out which one goes to the rear and loosen it at the master cylinder and see if you have pressure/flow there, if not that's the problem, if it does have pressure then there a blockage somewhere between the master cylinder and the rear rubber brake line at the rear axle.

I don't know what year you have but my '03 LTD. if you want to bleed the rears : start the engine, have someone press the brake pedal and hold it and crack the bleeder screw and it should pump out a nice steady stream. If not you have a problem. Make sure your brake reservoir is filled.

I'm not entirely sure what you or this technician are talking about... but I'll take a stab.

I have run into this multiple times (actually just ran into it today on one Tundra rear caliper) where the bleeder screws get rusty and won't let you bleed them or flush fluid through them. Usually I just clamp off the brake line, remove the bleeder and take one or two of my assortment of tensioner pins and clean the bleeder screw out.

Another possibility (and one I see a lot, not just on 4Runners) is that one or more of the slide pins of the caliper have rusted/seized; sometimes you can get them loose to clean and lube, other times you just have to replace the caliper bracket and/or entire caliper assembly. It is also possible that the caliper piston is seized, but in the case of a seized caliper piston and/or caliper pin you'll see uneven brake wear and dull/rusty rotors.

I will also say that if you try to compress the pistons with the brake line kinked, it'll make you think their seized (I still do that every now and then when I'm not paying attention after I've removed a caliper for a brake job, particularly the rear ones as a lot of them are easy to kink when you flip them out of the way, lol).

Thank you! I knew there had to be at least some basic things to look for. I’ve learned a lot from DIY stuff but haven’t done much with brakes. There’s a good possibility that they are rusted as this one came out of the rust belt. Definitely will take a close look at the bleeders and calipers. I’ll get some pictures of the rotors as well.


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Thanks @AuSeeker you always have the best tips! I need to buy you a coffee! What tool do you use for loosening the connections? If it’s a blockage..any advice on how to track down a blockage or how to resolve it?



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Thanks, that’s what the tech did. He attempted to bleed the breaks for a flush, and nothing came out on either side. Then he started checking the calipers and noticed lack of any movement. He assumed a blockage but now I’m wondering if they have seized. I have an 07 SR5.


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Now that I've read more on how the Tech determined there's was a blockage, I now think it would be best to start at the caliper, it possible it's seized and why there's no movement of the pistons because of corrosion and the bleeder valve is blocked for the same reason, I would loosen the the brake line where it attaches to the caliper and see if you get any fluid to come out there before checking the other brake lines, I'm surprised the tech didn't do this to fully determine what the cause actually was, if you get fluid it most likely only the calipers are at fault, when working on brake or any hydraulic/fuel line fittings always use "hydraulic fitting/line wrenches" so you are less likely to round over the fitting, they are similar to a boxed end 6 point wrench but have a small slot cut out so it can slip over the brake/fuel line and then slide over the fitting, where a brake connects to a junction block or another brake line you may also need another wrench/pliers or vicegrips to hold the block and or other line to get the connection loosened.

Here's a link to a set that should have any sizes you would need for working on brake lines so you know what they are, you can find them most anywhere good tools are sold, even Home Depot, Lowe's, most auto parts stores or just order online, in this case you will need a metric set.

SATA 3-Piece Full-Polish Metric Flare Nut Line Wrench Set for Removing or Replacing Nuts on Fuel, Brake or Air Conditioning Lines - ST09033U - - Amazon.com

If you still don't get any fluid at the caliper, then just back track along the brakes line loosening fittings checking for fluid flow or not until you find the section that has the blockage, usually as I mentioned the rubber brake lines are the most common to deteriorate and cause a blockage, the only time I ever found a steel line to cause a blockage was because the line somehow got crushed or kinked which is very rare.

Excellent, thanks for the additional advice! Picked up some flare nut wrenches today from HF, as Lowes was out. I want to make sure the cap is off the fluid reservoir before opening the connections right?


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