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Two years ago I drained and filled the rear differential. Today I noticed that where the driveshaft meets the diff is covered in oil. I checked the vent tube and it is attached and seems unobstructed. I'm not sure how long it has been like this...
The bottom of the diff is oily to the touch, you can kind of see the oil buildup in this picture.
I checked the fluid level and it was very full. Oil started pouring out, and I actually lost about 1/4 cup of oil.
Is there anything that commonly causes this to leak? Given the level seems fine, is it worth fixing whatever is causing this?
pinion seal is leaking.
It is a DIY job but I suggest you watch a YT vid to understand how to preload the bearing correctly because if you do it wrong the bearing will be junk shortly afterwards.
Thanks pirate, doing some research it seems some people will just count threads and ensure it is in the same exact spot as before, while others say that method is incorrect and you need to set some drag (but not too much, or else you have to replace the crush sleeve). So, I'm thinking of getting it to where it was previously (counting threads), then seeing if there is any drag, and if not tighten a little more. Do you know if drag needs to be measured with the wheels removed? Or can I simply have the tires off the ground on stands?
Just use a 1/2" drive impact air gun when putting the nut back in as soon as it tightens you should be good, and don't use a torque wench as this will cause your diff to go capoot.
I don't know how much commonality there is between the diff in the Excursion and the one in an E-150, but I did the one in my van a number of years ago using the paint marker and counting method. Oddly enough, the world did not stop turning, the van did not immediately catch on fire, and there were no noises or other issues with the diff for the 30ish thousand miles that I put on it after that.
The seal goes because the pinion bearings are gone. I like the paint marker method but you still need to make sure the bearing preload is right. The mark just gives you something to creep up on. I prefer to do all the bearings since you need to drop the carrier to get at the inner pinion bearing. I also like to use a "crush sleeve eliminator" kit. "Mic" the crush sleeve and use that number as a starting point for your shim. If you do it correctly you'll get another 200k out of it instead of 20k or less from a seal only...
Clean it all up good and check tour diff vent. It could be plugged with mud and stuff. Then see if it leaks again. If it does push the pinion yoke up/down and in/out. If it has no play replace the seal. If it’s sloppy you may need new pinion bearings. Good luck.
No play, but the something in the rear has been clunking whenever I go into Reverse. It's been happening for a couple years though, and hasn't gotten any worse...
So is the best option to basically replace all bearings in the diff?
Your clunking going into reverse may be from a dry slip yoke, while you are dealing with the leaking pinion seal you should drop the shaft and grease that slip yoke.
Also I think you should drain the differential oil, you may have some water in the diff, that would explain why you had a level higher than the fill port. Something made that level higher than when you filled it. And I think having that level higher than designed would add to the chance of the pinion seal leaking.
I replaced the seeping pinion seal on my 4.88 differential before I installed it, I used the mark and count method and so far it has survived 45K miles with 35K of those towing heavy.
No play, but the something in the rear has been clunking whenever I go into Reverse. It's been happening for a couple years though, and hasn't gotten any worse...
So is the best option to basically replace all bearings in the diff?
no
find the source of the clunk and fix that. likely worn slip yoke splines.
Thanks pirate, doing some research it seems some people will just count threads and ensure it is in the same exact spot as before, while others say that method is incorrect and you need to set some drag
Thanks guys. I did grease the slip yoke about two years ago when I started noticing and it made no difference. I was told it could be excessive backlash which is why I brought it up here. I can live with it though, it hasn't really changed in two years, just don't know if it's a sign that the rear end is on it's way out.
As far as oil level, I'm actually on a slight incline with the nose down, so hopefully that is the reason that it appears overfilled. Although at 2yrs/25k miles probably time to change the oil anyways.
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