This is for my 2014 GX460, but I believe GX and 4Runner share same brake components so posting here for help.

I just found out the rear brake calipers (both sides, a little worse on left side) are wet and possibly leaking brake fluid. But I haven't yet had a low brake fluid and it still brakes fine.
First thought it might be from rain or carwash, but it hasn't rained here for last 5 days and I haven't taken it to carwash in the last week either.

It must be from brake caliper, right? Is it from the bleeder valve?
I looked at the piston but piston seal seems fine, it's dry there. But around the edge of rotor, splash shield, even the front of the caliper is wet.
Do I need a new caliper?

Thanks for your help!

Attached Images

   

Looks like either brake fluid or the axle seal is leaking gear oil. Does it have a strong smell? If so it’s gear oil.

Can you put a wrench on the bleeder valves and gently snug those up?

Easiest way to to tell will be to take the caliper off and inspect it more completely. While you have the caliper off, go ahead and pull the rear rotor off. My suspicion is that you're looking at an axle seal leak; usually the backing plate and the bearing housing (between the brake backing plate and axle flange) shows signs of seepage. But it does look more like an axle seal.

If it is an axle seal leak, I highly recommend replacing the bearing as well.The reason being the axle seal keeps fluid in the axle tube/axle assembly, when they leak it let's gear oil wash through the bearing on its way out to leaking over the parking brake assembly.

Checking both brake fluid level (at the reservoir under the hood) and the rear diff fluid level at the rear diff fill port should yield more info. Have car on level ground when checking. I agree that it looks like an axel seal issue; and diff gear lube fluid has a real distinct smell, so it should be easy to tell which is the culprit.

I had similar situation but not as bad. Turned out it was the outer rear axle seal. Replaced bearing, outer and inner seal. Mine was only on the driver side. If your not low on brake fluid, I’d check your rear axle.


Sent from my iPhone using Tapatalk

As I remember, rear axel seals / bearings are normally replaced in pairs.

Thank you everybody for pointing out the possibility of rear axle seal leak. I did not think of that. And as I do more research on that issue, it's a telltale sign of axle seal leak, and to confirm, I can smell it!

Now I kind of wish it was brake caliper - that's much easier issue.

Looks like I am looking at new axle seal, wheel bearing, parking brake shoes, and rear brake pads.

I've done front wheel bearing replacement but not the rear one.

Few more questions:
Do I need to drain rear differential fluid to replace rear axle seal? It's been only about a year since I changed that.

Has anybody had a good luck with bringing in the axle to independent shop (or a dealer) to press out the old bearing assembly and press in the new one? I can order and get all the required parts, but looks like special tool is required and at least a 20 ton press. Not sure if independent shop will have that special tool.

Thanks.

You didn't say how many miles are on the GX. Rare for both sides to be leaking at the same time ,your breather could be rusted shut. Never seen both sides go at the same time. Yes , diff fluid needs drained to change seals.

I never replaced a 5th gen bearing/seal but replaced several on high mileage 3rd gen 4Runners and 1st gen Tacomas .

The hard part of replacing the bearings is to find somebody who knows what they are doing as it takes a special tool to take the abs tone ring and seal land off as they are pressed on.Axle Bearing Puller Set for 95-20 Toyota 4Runner With Tone Ring Tool Installer | eBay

Friend of mine took his to a shop years ago and they cut them off. They screwed it up and beat the seal land on too far and it leaked again. When we took it apart to see what the deal is ,they had big cut marks in the axle from a cut off wheel.

The 4th and 5th gen axles are a bit easier than the 3rd gens, but you do want that SST as it makes life easy.

You might be able to get away with just washing off the parking brake shoes and inside of the rotor, followed by a bit of roughing up with coarse sandpaper. It all depends on how soaked in gear oil they are. Same with the brake pads, if they've been soaking in gear oil, probably best to replace them and cut the rotor. If they haven't really been that heavily contaminated you might be able to re-use them.

Some shops and/or dealers will press out and press in the new bearing for you. Always worth asking what they charge for that.

We have been through the leaking rear axle seal shenanigans on our '99SR5 twice .

Only a little over 90K miles on the GX. I was surprised to find out both sides of the seal fail like that. My 09 4Runner has more than 160K miles and never had problem with the seal.

Good point on the breather, I haven't checked that yet. Might explain the reason why the seals had premature failure. Will report back once I get a chance to take a look at it.

I'll have to call around to find a dealer or a shop who knows what they are doing. I placed orders for all the parts I think I will need yesterday, including bearing, bearing retainer, parking brake shoes, and rear brake pads. A lot of money, but hopefully I won't need to touch the rearend for a long time.