Persistent Rear Passenger Brake Dragging

[044Runna]

I am struggling with a persistent dragging/seizing issue on the rear passenger side brake of my 4th Gen 4Runner. Despite replacing almost every component in the system and performing extensive troubleshooting for many years, the corner continues to heat up and drag after a short period of driving but the issue seems to slowly build after I replace the calipers.

Vehicle Background/Recent Parts Replaced:

Rear Passenger Corner: New Powerstop caliper, rotor, and pads (less than 5,000km ago). I have never gotten through a pad replacement on this corner without having to replace the caliper. It's almost always been seized.
All calipers have been replaced multiple times on the truck from various manufactures (OEM, Powerstop, Generic Aftermarket). Fronts were replaced with 5th gen Powerstop and haven't been causing much trouble since.

Brake Lines: StopTech stainless steel soft lines installed recently.
Hard Lines: Some (not all) hard lines replaced within the last 5 years / 50k km.

Hydraulic Control Unit: Recently replaced with OEM part and installed by Toyota (note: the issue existed prior to this replacement).

Troubleshooting Steps Taken:

Pulled the caliper today. The piston moves very freely and is not seized. Slide pins are clean, rust-free, and freshly lubed. Contact points for the pads are cleaned and lubed.

Parking Brake Rule-Out: Disassembled and cleaned the parking brake assembly. The rotor spins freely by hand when the caliper is removed, confirming the parking brake shoes/bellcranks are not the source of the drag.

Bleeder Test: With the wheel dragging, I cracked the bleeder valve. Fluid did NOT squirt out under high pressure; instead, it exhibited a slow drip (approx. 1 drop every half a second).

Results of Bleeding: After cracking the bleeder, the wheel became slightly easier to turn, but still had more resistance than the driver’s side. Once the system was re-pressurized (ignition ON, accumulator pumped up), the dragging returned/intensified.

Driving Symptoms: The wheel does not seize immediately. It starts moving freely, but as I drive and apply the brakes, the passenger rear rotor begins to heat up significantly and the drag becomes noticeable. Rotor gets hot enough to smoke.

I'd like to avoid cracking lines at the Hydraulic Control Unit because I don't want to accidentally introduce air into the system and since that's an OEM part installed by Toyota recently I'm going to assume for the moment it's not the culprit.

Not sure where to go from here so thanks in advance for any guidance.

 

[ArthurKotb]

If I understand you correctly, there has always been a difficulty with this brake but only recently has it begun to seize. Is that right?

Have you considered letting a Toyota service department take a crack at it?
Is this a V8 or V6? (There are some differences in some of the brake components but that may be only for the front, not sure.)
Have you backed off the emergency brake adjustment for that wheel, just to make sure it's not the problem?
Have you recently replaced the brake shoes on the emergency brake?

 

[ArthurKotb]

Mine drag too much and so I removed some pad because I couldn't be bothered to adjust the drums. Now the brake doesn't touch the walls at all until I kick the pedal down quite a ways.

Besides the adjustment at the drum on the rotor there is an adjustment on the Emer cable at the back of the center console. You probably already knew that but...just in case you didn't

I replaced the shoes a while back but adjusted them so they just barely touched the drum and then backed it off again. It seems to be okay but there's a lot of play in the pedal. Next time I replace the pads I'll adjust it again.

 

[Cezar]

Nothing to add but I'm on my fourth caliper in like seven years on that same corner.

 

[ArthurKotb]

I have replaced the front and rear one time each per axle. In the early years the T4R sat in the driveway most of the time. I would drive it about every other week and take it on long drive fishing trips and the caliper pistons would seize. Once I retired and started driving it regularly I had fewer problems with the calipers.

 

[fnsquirrel]

I am struggling with a persistent dragging/seizing issue on the rear passenger side brake of my 4th Gen 4Runner. Despite replacing almost every component in the system and performing extensive troubleshooting for many years, the corner continues to heat up and drag after a short period of driving but the issue seems to slowly build after I replace the calipers.

Vehicle Background/Recent Parts Replaced:

Rear Passenger Corner: New Powerstop caliper, rotor, and pads (less than 5,000km ago). I have never gotten through a pad replacement on this corner without having to replace the caliper. It's almost always been seized.
All calipers have been replaced multiple times on the truck from various manufactures (OEM, Powerstop, Generic Aftermarket). Fronts were replaced with 5th gen Powerstop and haven't been causing much trouble since.

Brake Lines: StopTech stainless steel soft lines installed recently.
Hard Lines: Some (not all) hard lines replaced within the last 5 years / 50k km.

Hydraulic Control Unit: Recently replaced with OEM part and installed by Toyota (note: the issue existed prior to this replacement).

Troubleshooting Steps Taken:

Pulled the caliper today. The piston moves very freely and is not seized. Slide pins are clean, rust-free, and freshly lubed. Contact points for the pads are cleaned and lubed.

Parking Brake Rule-Out: Disassembled and cleaned the parking brake assembly. The rotor spins freely by hand when the caliper is removed, confirming the parking brake shoes/bellcranks are not the source of the drag.

Bleeder Test: With the wheel dragging, I cracked the bleeder valve. Fluid did NOT squirt out under high pressure; instead, it exhibited a slow drip (approx. 1 drop every half a second).

Results of Bleeding: After cracking the bleeder, the wheel became slightly easier to turn, but still had more resistance than the driver’s side. Once the system was re-pressurized (ignition ON, accumulator pumped up), the dragging returned/intensified.

Driving Symptoms: The wheel does not seize immediately. It starts moving freely, but as I drive and apply the brakes, the passenger rear rotor begins to heat up significantly and the drag becomes noticeable. Rotor gets hot enough to smoke.

I'd like to avoid cracking lines at the Hydraulic Control Unit because I don't want to accidentally introduce air into the system and since that's an OEM part installed by Toyota recently I'm going to assume for the moment it's not the culprit.

Not sure where to go from here so thanks in advance for any guidance.

I will tell you, in my experience, your symptom comes from having a bubble in your brake line. You probably have a bubble caught somewhere in your line. Look for a spot where the line curves and has a high spot (probably up where the hard lines are connecting in the engine bay). To get rid of it, gently tap the suspected are while someone uses pneumatic pump (not a handheld). It's the only way you'll get it out I think. :-(

 

[fnsquirrel]

I will tell you, in my experience, your symptom comes from having a bubble in your brake line. You probably have a bubble caught somewhere in your line. Look for a spot where the line curves and has a high spot (probably up where the hard lines are connecting in the engine bay). To get rid of it, gently tap the suspected are while someone uses pneumatic pump (not a handheld). It's the only way you'll get it out I think. :-(

*gently tap the suspected AREA...*

 

[ArthurKotb]

I will tell you, in my experience, your symptom comes from having a bubble in your brake line. You probably have a bubble caught somewhere in your line. Look for a spot where the line curves and has a high spot (probably up where the hard lines are connecting in the engine bay). To get rid of it, gently tap the suspected are while someone uses pneumatic pump (not a handheld). It's the only way you'll get it out I think. :-(

The rear brakes on a Gen4 4Runner can be easily bled by opening the bleed valve, turning the ignition to Run (not start) and pressing the brake pedal. The electric pump (accumulator) will continue to pump out fluid until you release the pedal. The OP says he has already done this and still no joy.

 

[88Center]

When you replaced the calipers, did you do a full brake fluid flush?

How long did you go between previous flushes?

Brake fluid is hygroscopic. Over time, it absorbs moisture which can cause internal corrosion. Perhaps somewhere further up that brake line is some internal corrosion causing the issue?

Toyota recommends changing the brake fluid every 2 years or 20,000 to 30,000 miles. Most people I know never change their brake fluid over the life of the vehicle and didn't even know they were supposed to. Lol

 

[Moist]

Nothing to add but I'm on my fourth caliper in like seven years on that same corner.

Also nothing to add, but I'm in the same boat. I think I'm on number 3 in 10 years on that corner. Last time mine seized in the shut position from overheat damage and I got stranded.