So I definitely have one or the other judging by the greasy like substance that I see on the inside passenger back last of my 98 4 wheel drive 3.4 runner,auto none locker 190,000.any way I have not seen a thread on this about another way to distinguish the symptoms to diagnosis the correct problem....in my case it has been tricky...my rear brakes stick and are acting funny so I thought wheel cylinder for sure...no pressure to bring back the shoes..I smelled the fluid and I couldn't smell anything like gear oil....but here s the thing...I have a cold and realized I can't smell anything...I pulled off the drum and couldn't tell where the leak BC it was all over.....so my question is can I (not being able to smell), just pull off the abs sender and roll the wheels while off the ground and see if I can see gear oil??? Would I be able to...when u turn the whwels it could pick it up from the bottom of the shaft if it was indeed the axle seal leak...I also sprayed everything down with brake cleaner and topped my brake fluid off and will pull it off tom to check....let me know what u guys think...

you could clean it up, put the drum back on and pump the brakes for a little while and see if the fluid comes back.

I had the same problem a little while back, turns out both of them were leaking. just my axle seal was leaking worse.

Take a pic and post it. Then someone should be able to tell for sure.

My 2 cents would say leaking axle seal.

Will post pic tom after I pull the drum off for the second time.....do guys think that if it is my axle seal that it ruined my wheel bearing? Any way to see if wheel bearing bad???

X2 on the axle seal. This was the first thing I had to fix when I got my truck back in Feb. I remember taking the drum off and seeing the "grease" and thinking "what the hell how did so much grease get in here" What it is is the thick gear oil mixing with the brake dust and creating the "grease"
As far as your bearings, they are a sealed type and when the axle seal fails, it probably washes out the grease in the bearing, so even if the bearing hasn't failed (or maybe it has because a sloppy bearing can cause the axle seal to leak also) it's life expectancy has been diminished, and with your mileage, I would replace the bearings. Use OEM parts only. Good luck!

How much grease is it? Is your brake reservoir low on brake fluid? How does your brake pedal feel?

I had the wheel cylinder go on my old f150, and it was obvious that it was the brakes. The pedal got soft, and once it started going bad it just continued to get worse and worse until I replaced it. It is also obvious when you pull the tire and all off, you will see fluid coming from your wheel cylinder, won't be any guessing as to where its coming from.

Gear Oil= seal
Brake Fluid =cylinder
Should be fairly easy to tell the difference.

95% (not a real statistic) that it will be a seal caused by a bad bearing...this is far more common than a leaking cylinder.

When mine went bad I couldn't tell the difference in the two by just smell or feel of the fluid. It really didn't smell like gear oil, so I was thinking it was the wheel cylinder, it ended up being gear oil.

I would say axle seal. When rear cylinders fail enough to drop the fluid you will lose all brake pressure as if you had an open line. If its a small leak you usually wont see it at back drum.

Very surprising, gear oil has a very distinct smell and brake fluid it very watery. There was no mistake when we did a buddies rear seal.

No joke, one would think. I was pretty certain it was brake fluid just based on how the fluid looked and the lack of gear oil smell. I had to pull my abs sensor to confirm though.

If it is your axle seal you should look in to doing the breather mod for the rear axle. Mine was completely gunked up, there was no way air was getting in or out of it.

pull the drum, then use a pick or screw driver, and pry the boot back on the wheel cylinder. if fluid pours out, you know its leaking. that is only a dust seal, there shouldn't be any fluid under it.


as has been said above tho, likely its the axle seal that's leaking, as they are somewhat prone to it.

Quick run down.

Few reasons why I don't think it is the cylinder:
1. It is not common to get a leak. They fail, but leaks are not common.
2. If you have enough fluid out on the drum that you see it on backside then you would likely not have any brakes to work with as it would affect the whole system...that is a lot of fluid.
3. The leak flow would not allow it on the back side of the drum but rather flung outward on to the wheel from the outer portion of the drum. If there is fluid around the axle and outwards that is gear oil.

For a seal:
1. very common
2. leak pattern will put it all over the back of the drum
3. rear bakes will no longer work properly and will also create a burning smell. They do as a matter of fact soak up all that gear oil and then try to stop once the brakes are pressed.

There is also a likeliness that the seal has failed and you have a bad cylinder, but not necessary a leaking cylinder, which would account for the stickiness aspect you described. I pull all this from a recent diagnosis, remove, and replace project on my buddies 2000.

Good luck.

Yea I am sick and have a cold and thought that was why I couldn't smell....but the cold has cleared up an it is hard to distinguish...its snowed today so I am just waiting to get a decent day so I can pull the abs sensor and look straight into axle