I'm thinking it's the wheel cylinder. They're probably the original and it now has 239k miles. Around 31k miles ago, back in 2019, I replaced the wheel bearing and axle seals. It was quite an ordeal after a local garage failed three times to fix it. I bought the press fixtures, a press and fixed it myself. I watched it close afterwards and didn't see any axle leaks following my fix.

Today I decided to clean the layers of Fluid Film gunk out of my wheel wells to feel good after getting new tires and installing the Magnaflow Overland exhaust this week. I took the driver side drum off and was bummed to find fluid over everything. Judging by the pictures it I think (and hope!) its the wheel cylinder. It didn't smell as strong as gear oil, there was no oil dripping onto the wheel, no oil down the backing plate, and the bottom of the dust seal looks to be dry. The dust seal only had oily gunk build-up on top of it.

I monitor my fluids closely. Just about every fill up I look at the levels. My brake fluid is about halfway between full and low. I know I would have filled the brake fluid to the full mark the last time I worked on the brakes.

Would the brakes still feel pretty solid even with a wheel cylinder leaking? The pedal doesn't go the floor but maybe there's still enough pressure in the system even with a cylinder leaking?

Attached Images

         

If you have grease globs on things like picture 2 it’s the axle seal. The grease is being washed out by the gear oil.

But like you said grease has a distinct smell.


Sent from my iPhone using Tapatalk

There looks to be brake shoe fibers mixed in with the fluid making a type of gunk. I was thinking friction and wear was creating what looks grease globs. What gets me is, if it is gear oil, wouldn't it be leaking out the bottom of the dust seal, down the backing part and onto the drum? Only the top of the seal has build up of fibers and some oil so I was thinking whatever it is, is coming from the top down.

When my axle was leaking back in 2019 I could basically smell it before I even took the drum off. I had my nose right up to it and could barely smell it.

Sure looks like gear oil, but doesn't seem likely if you replaced bearing and seal. The wheel cylinder doesn't seem to have fluid running out of it. Pull the dust boots on the ends of the wheel cylinder back and see if brake fluid pour out.

I guess tomorrow I'll try to look behind the boots and try to pop the speed sensor out. I can't remember if I could get the sensor out or not. I think it was stubborn if did come out. Pulling the axle isn't hard but if rather not if I don't have to.

It's also weird that my brake fluid is low. My front brakes have about 34k miles on them and I don't know if that would be enough wear to have the level drop that far. The front pads are still pretty thick and I put new rotors on last October.

As your brake pads wear your brake fluid level in the reservoir drops.

I had to take a pair of slip joint pliers to rotate the wheel speed sensor while pulling until i got enough of a gap to get a flathead under the sensor mounting tab and pry with that while rotating the wheel speed sensor.

Yeah, I just figured my brakes didn't wear enough for the drop in level I see, but I don't think it's the wheel cylinder. When I got to work this morning I think I smelled gear oil. This is really inconvenient right now with my current living situation.

Definitely looks like an axle seal leak. I just started working on replacing my 3rd member and found both seals leaking when I pulled the shafts out. I also did not have any leaking from the drums onto the tires and no other signs of leaking externally. Rubber inner parts of the seals look fine so I think it’s the metal to metal connection on the outside of the seal. I’m gonna coat the outer edge of the seal with a lil FIPG, I’ve hear that can solve the leak from small imperfections or nicks in the axle housing.

It's definitely gear oil. The wheel cylinder isn't leaking on the driver's side but the axle seal is. The axle seal on the passenger side isn't leaking but the wheel cylinder has oil behind the seal. You win some you lose some. I think what is happening is the oil is weeping past the outer dust seal, wicking up and out the seal (that felt looking thing?) of the axle flange as I go down the road, which is why I don't see it dripping down and out of the dust seal.

I ordered some of that Toyota FIPG sealant. Do most people use it around the edge of the inner seal before installing it? Do they use it around the seam after they install the inner seal? Or do they do both? Thanks for the seal suggestion.

I put a light coat around the outside of the inner axle seal. Double check you are in the correct spot on the retainer with a sharpie test. With that much gear oil making it past the seal and through your axle bearing you will probably have to replace the axle bearing sooner than later. The gear oil leak washes out the axle bearing grease.

The last time I pressed the inner ring in about 4.5mm and that put the seal in the center of the ring. From what I remember, the sweet spot seemed to be 4.5-5mm for people.

I bought a Koyo bearing and ring set from napa which is what I used last time. I'll keep the bearing I pull out because I might be able to flush it and repack it for next time. I also bought Toyota snap rings, dust seal and inner seal. I'll seal it up good with the FIPG sealant. When I'm confident it's no longer leaking I'll replace the brakes. I bought Napa shoes and wheel cylinders but I don't want to do all of that until I have the gear oil leak fixed.

You might want to also put a little Toyota Red 1281 FIPG at the inner retainer connection to the axle. Once you've determined you have a good mating of the axle seal with the inner retainer by doing the sharpie test, I'd clean up the axle and retainer well with some brake cleaner. Then I'd smear some FIPG on the inside side of the retainer to axle connection and let it dry for a while. Gear oil can get past through 3 areas, between the inner retainer and axle seal connection, between the seal and axle housing connection, and between the retainer and axle shaft connection. If you have a good mating of the inner retainer and seal, and you've used FIPG at the two metal to metal connections (seal to axle housing and retainer to axle shaft), you've eliminated any potential for gear oil to get past and to infiltrate the bearing.

Now, why do some people have to use FIPG at these metal to metal connections and other don't. One reason is maybe there's some imperfections in the metal, like somebody used a hooked seal removal tool and they gouged the axle housing. Another reason is reusing retainers. I thought this was a good money saving idea at first, but then I realized some damage happens to the retainer when you press it off the axle. Metal is lost during the removal and there are noticeable grooves left on the inside of the retainer. This ends up being a pathway for gear oil to get past the retainer/seal connection. I now instruct people to use a new retainer at the inner position, but they can definitely reuse an old retainer for the outer position because that is just a place holder for the bearing.

Good luck with getting the leak to stop and you can put this repair to rest.

Like Tim said above me, if you are removing the retainer that the inner axle seal rides on then reinstall with a gear oil rated rtv/fipg. I had a reoccuring leak on my last 4Runner and ended up using rtv where the retaining ring/axle shaft and axle seal/axle housing mate.

Thanks guys. I'll definitely use the sealant as recommended. It was punch to the guy when I took drum off, and was surprised with oil. This sounds like it should do the trick. This repair can become stressful and expensive constantly trying to get a repair to stick.

I'll probably drive it a few weeks or a month after the repair, checking on it periodically, before installing the new brakes. I don't need to soak new shoes with gear oil.