Leaking rear caliper

Recently bought our 2010 and we love it accept that recently after driving it I noticed that the rp caliper was leaking so I bought a new one from Napa and switched it out. Bled the line, all good…. So I thought. But then the new one started leaking….. I’m now on caliper number 6! And it’s leaking as well. I started with 2 Napa middle quality, then 2 Napa premium, one ac delco, and now I’m on a genuine Toyota brand new (not reman) with a new Toyota banjo bolt and crush washer.
I’ve changed out all the brake fluid and the soft rubber line. Have bled all four brakes in the proper order. I’ve even tested the brake pressure of both rear brakes through the bleeder screw and they are about 1000 psi at regular application and then max out at 2700 psi stomping on them.
Every caliper I’ve put in starts to leak at the caliper piston seal.
I’m at a complete loss?

 

You sure its 2700.

That is kinda high.

 

Yes I’m sure that’s the pressure that reads on the pressure gauge that I screwed into the bleed screw hole. It’s the same on both back wheels though, but only the passenger side is giving me grief.
It is a full stomp on the pedal though to get to that pressure.

 

I’ve heard that if you introduce air into a ABS system, it takes special equipment to properly bleed the system.

 

In a 'panic' brake application your pressure might get to around 1500. 2700 is off the charts! Better yet, how do you achieve 2700? Have you sought any local mechanics answers for your problem? Other than that, the complete at loss thing comes to mind. Best of luck with this.

 

I’ve talked with about 20 different career mechanics and nobody has any ideas. From what I’ve found online it’s possible to have even over 3000 psi in brake system. My thinking is that if the pressure is too high then why isn’t the other caliper leaking as well?
I’m curious though about needing special equipment to properly bleed the system and if my problem is somehow based on me not properly bleeding and somehow I’m leaving air in the system and that’s what’s popping my piston seal?

 

The rotor is not warped?

 

Maybe 3000 is certain crazy situations.

But sounds like you are replicating 2700 consistently and at the rear. I can see the 3K being the front once in a while.

There should be a proportioning valve built into the system I have no idea where it is on the 4Runner.

But the rear should not be as high as the front.

*edit
Some google posts I see says its attached at the bottom of the MC.

 

Air in the system is not the issue, hydraulic pressure will far exceed air pressure so air would only decrease the pressure which is why you have lousy brakes when there's air in the system, here's no way air can be the cause of seal failure.

What the problem is I can't say unless all of the calipers you have installed were re-mans and not new, if so then it's possible all 6 were bad re-mans and you just had bad luck 6 times!!

If they were all re-mans you may want to try a "new" caliper, unfortunately even "new" calipers can be bad if not a high quality part.

 

Welcome.

Have you checked for any contamination in the brake fluid? If you're unsure, do a brake flush.

Were you supplied the correct brake caliper for your car? It can happen, but unlikely if you supplied your vin to the dealer.

 

pressure is pressure, whether it’s hydraulic or air. The difference is that hydraulic fluid is non compressible. The air is compressible so will load up like a spring when you press on it which is what makes the pedal feel spongy.


I’m at a loss here like everybody else. Sounds like it could be some issue in the ABS unit or proportioning valve block sending too much to the rear but I’ve never had that issue before so wouldn’t know where to start diagnosing. Sucks but maybe a trip to dealer is in order….

 

Wondering if the rotor is an incorrect part. How far out is the piston traveling?

What brake fluid are you using? Toyota branded fluid? Prestone? Advics? DOT 3 or DOT 4?

 

New rotor, new dot3 brake fluid(flushed out all old stuff) new brake pads,
And current caliper is a brand new (not reman) Toyota part from dealership using my vin to purchase
From what I understand the proportioning valve is built into the abs module

 

good idea on the rotor. @badventures Is the rotor itself verified to be correct? Also, can you tell how the leak is being caused? I mean, can you look at a failed seal and notice any evidence of rubbing. Or is it pinched? Or did it just pop out? Looking at a failed seal very carefully might give you a clue? A

 

Also verify the leak isn't in fact coming from the hard line just upstream of the flex hose. The last few inches of line isn't coated and is a common rust failure point on 5th gens according to the Car Car Nut. Are you seeing brake fluid on the outer side of the brake rotor hat?