I don't know why the seals are different. I do know that if the axle seal fails, the wheel bearing seal will not hold the gear lube. You get a nice starburst pattern on the wheel radiating from the hub .
Nice setup on your 4Runner, Brian. I'm curious if the 1 ton mini diff and the 80 reverse cut diff will swap?
Aren't the front axles a different diameter than the rear axles?
FWIW, the rear seals don't do any better at holding back the oil (thank goodness). At 105k miles my rear seals on both sides were leaking so bad there was no, repeat no, grease in the rear wheel bearings. There was 90wt gear oil in the hub and cleaning for repacking was a breeze. The rear wheel bearings looked great.
They must be the same diameter front and rear as the same wheel bearings are used. I remember that you had inner seal failure but did the 90 weight make it past the wheel bearing seals? If it didn't maybe that is the difference. :dunno:
Answer the dern question, did gear oil get past the wheel bearing seals or not?
I know that your axle shaft seal (s) failed and the bearings were washed. But, did the bearing seal hold the gear oil in the axle. If so, then that is probably the difference between the front and rear seals. :dunno:
The rear hubs, inner wheel bearing, and outer wheel bearing were being lubricated by 90wt. from the rear diff. No wheel bearing grease at all on one side; a tablespoon full on the other side. This was about 105k IIRC. There was a copious amount of 90wt in the hub.
DID THE WHEEL BEARING SEALS ALLOW GEAR OIL TO EXIT THE AXLE OR NOT?
My guess is...no. If I am correct then it is logical to assume that the main difference between the front and rear axle wheel bearing seals is the ability of the rear axle seals to keep gear oil in the housing as opposed to allowing it to leak out all over the brakes, ETC.... :dunno:
I don't think Beowulf understood your question. It gets too complicated when there is more than 1 seals involved.
My rear axle seals failed on both sides, all the bearings were nicely washed by the gear lube. However, the gear lube didn't get pass the bearing seal. All the brake parts were dry.
If the rear bearing seal is used to stop the lube from getting out, I would prefer to use the front wheel inner bearing seal on the rear wheel. That way, I know I need a new axle seal when I see a wet brake drum/disc.
I also guess that you MAY be able to use front seals on the rear axle. Aparently Toyota thinks that the seals need to be different. As I have been associated with Toyota for a bit past 24 years , I would defer to their wisdom in this regard.
They do not generally do something without good reason. Let me drift out a bit. I have a Dodge truck (1 ton 4wd) that has a Dana 71 rear axle.(huge). the wheel bearing setup is very similar to what the cruiser has. In the case of the Dana the gear oil from the housing lubricates the wheel bearings ON PURPOSE, they are not "greased". It is reasonable to assume that Toyota may have expected "cross contamination" from the axle housing to the wheel bearings and designed a seal to keep the oil in as opposed to letting it all come out when you are "way the hell out there" in the bush. It is also interesting to note that there is no published service interval for the rear bearings as there is for the front axle. It is possible that they expect inner seal failure to happen over time and they want gear oil to lubricate the bearings.........
SORRY BEO...opps :G Like I tell my kids "inside voices please" :G
Seriously, that could be the main difference between the front and rear seals. If gear oil is a good enough lubricant for wheel bearings in a 1 ton Dana, it would probably do ok in a FF cruiser axle.
I will also say that if any gear oil shows up around the rear wheels you should fix it right now.
Dan, I know this is a really really late answer to your question, but my inner oil seal has just failed (I'm sure because I'm splattering a small amount of gear oil on the rim). No gear oil leaked out of the hub from the back. Oil leaked past the dust gasket between the end of the hub and axle flange. I'm planning on tearing into it this weekend. I would say Dan's theory about the rear seal keeping the gear oil in is correct.
I rebuilt the axle about 10k miles ago, when I did, the lockout was cross threaded onto the spindle by the previous owner. I was able to clean up the threads, I'm hoping this isn't what caused this seal failure. Here's hoping that I just didn't install the inner seal properly.