Inner or outer axle seal??

My brain hurts from reading so much trying to find a definitive answer..

My rear axle seal is leaking, the wheel and drum are soaked in oil. I had the inner replaced last week with what I believe was a National seal. Which upon further research I've found this may be a problem. Anyway, I drove about 20 miles and noticed the bottom of the brake drum had a drop of oil hanging from it.

I took the wheel and drum off and noticed the lip of the OUTER seal behind the brake shoes where the axle flange is, had a drop of oil around it as well.

Now my question is, does the inner seal prevent oil from getting past the bearing and outer seal and is that what's leaking? Or am I seeing both seals leaking?

It is my understanding the outer seal is basically a dirt, water, dust and to a lesser degree; oil seal.

I've checked the breather and replaced it a couple years back and I'm positive it's not a wheel cylinder leaking. It's going back in this week and I'm wondering if ordering the OEM seal will take care of the issue.

thanks for your help.

 

You’re correct in your understanding of both seals. The outer seal serves more as a dust shield, the inner seal serves to keep the oil in the housing and keeping it from running out.

I’ve been having the same issue with my truck. I replaced both seals with nationals, one side has yet to leak, the other side started leaking and I replaced with an OEM inner seal. It’s has since started leaking again even with the OEM seal. I’ve yet to replace it because it not my everyday truck, and it’s pretty slow at the moment.

The two most crucial things I’ve found about doing the seals. 1) the inner seal must be seated perfectly and not twisted or pushed in too far or deformed, and 2) if your truck is equipped with ABS or you have a locking rear without ABS, the ring that fits over the half shaft must be in the correct position to make sure it seats in the seal correctly. I have a feeling my issue is with the ring which seats in the seal. The shop I used did not press it on, but instead heated it up and then tapped it on leaving room for error. However, I did have more luck flipping the ring around so that the flat side of the ring is toward the inside of the axle, giving it more area for it to sit in the seal. It didn’t leak as quick as it did before, but has started to leak.

If you haven’t already, give this a watch. All of Timmy’s videos are well done and explains everything! https://youtu.be/AVhSDnw2ugo

 

The outer seal just keeps out the big stuff like dirt and debris out, I doubt it is oil or even completely waterproof. The inner oil seal is the the one that holds the differential oil in the housing and if the oil reaches the drum then it must have passed through the bearing which is then compromised.

I've had good luck using Timken inner oil seals on 2 separate housings (both ABS) without issue but I switched to the OEM outer seal due to the Timken starting to sequel on certain occasions. (I'd recommend using OEM for both of these in the future, just too big of a pain if an aftermarket one fails.)

Bottom line though, if there is visible oil seepage (should be easy to confirm if it is oil or brake fluid, both are cause for concern tho) you should take it back to the shop because they goofed something up. I would even demand new bearings because if oil has passed through them it may have removed/altered the factory grease within them and can compromise their longevity. It would also be good to check your brake shoes because if they get a coat of oil on them they will need to be replaced as well.

Some things I learned for anyone doing it themselves:

When you are installing the new inner seals make sure that the mating surface is pristine and not gouged, then make sure that the seal is installed evenly until it is bottomed out. Don't get too tough with them though, because they are easy to deform if you keep tapping and they are fully seated (learned this from experience). If you are unsure if they are evenly set you can use a set of calipers to measure the depth all the way around to confirm.

The orientation of the collar that rides along the inner oil seal shouldn't matter during normal operation as long as it is seated properly (square to the shaft) and is smooth without any nicks or other damage. Although if anything, the beveled edge of the collar should be facing inwards toward the differential so that the seal slides along this bevel during install/removal of the axle in order to reduce the risk of damage to the inner seal.

One final thing, I think I remember reading that the design of the OEM inner oil seal (and possibly aftermarkets seals if they copied) changed slightly from the original so simply measuring for the proper position of the pressed ring as given by service manuals could result in a poor ring position (possibly what happened to you, OP). The best way to confirm proper placement is to stop pressing the ring short of the expected location and to apply a thin coat of grease around the surface of the ring. Then instal the axle in the housing and give the axle a couple turns. The inner oil seal will leave a mark in the grease and give a visual if it is riding in the center of the ring as it should. From here it's just trial and error of pressing the ring into its final position.

 

ran into a leaky seal today OP. I decided to take it in and just have the toyota serv dept handle it. Have enough on the plate and am not one to mess with brakes - plus I've never done any type of brake work before. What I am wondering, are the seals normal routine maint items or...

Want to understand what caused this issue.

 

I just went through this and replaced inner seal. I caught it before it went through my bearing & outer seal into the brake drum. I'm hoping it doesn't start leaking again. I think the new seal seated well. I got the new seal at Napa auto and put new brake shoes on while I had it all disassembled.

 

did you replace the other side? keep wondering if doing one side the other side should be done as a proactive item