Ok, I have a 98 F150 XLT, standard cab, 8 ft. bed, 2WD with limited slip - if any of that makes a difference.

The rear axle vent tube is literally blowing oil out the top, where it's loosely connected to the bed. It does this every few weeks. I pulled the hose and ran a rifle cleaning rod down it to make sure it wasn't plugged ... it wasn't.

It seems like it's building up pressure somewhere, then blowing all at once, but I have no idea why. Any ideas?

Thanks,
fitz

 

Take out the fill plug and make sure nobody overfilled it... if that isnt it, then I bet your axle is getting really hot. Go for a drive then touch the cover. It should be hot, but under normal driving it shouldnt be hot enough that you cant keep your hand on it.

Might try changing the oil in it? Maybe wrong weight and it is getting too hot?

 

Thanks, Bobby. I think it's safe to say that nobody overfilled it, since the "somebody" would have been me, and it was 2 years ago when I last checked it (and didn't add any). That's not to say I couldn't have made a mistake - I certainly could have - but it wouldn't make sense for the problem to start all of the sudden within the last two months.

Now, could it be the wrong weight? Possible. It was last changed at the Ford dealership when I had a leaking pinion shaft seal replaced. And that dealership is no longer in business, so ...

For my own curiosity, I'll try the "touch" test. Either way, I doubt changing the fluid would hurt, so I'll do that anyway.

fitz

 

It should have 75w140 Full Synthetic in it and it isnt cheap..

Definetly try the touch test. I tried it on my axle today to confirm. I drove about 8 miles to the parts store and then back at about 50mph. When I got home the axle was very warm, but not enough to were I couldnt keep my hand on it. If it is too hot too touch then you have a problem.

The axle doesnt "howl" or "growl" any right, any new noises? Also have you been in deep water lately?

 

Right, 75W-140 full synthetic should be in it ... although I have no idea for sure what's really in there. And yeah, it's not cheap, but I won't be changing it every month (at least I hope not ). I know I also need a bottle of the dreaded Ford friction modifier.

After a 20 mile trip, I did the touch test. Warm, but certainly not hot, and ambient temp was around 55 deg. F. Plenty comfortable to keep my hand on it.

No growls, grumbles, howls, squawks, squeaks or other noises, and the last time I was in any water (other than rain) was before the fluid was last changed.

In any event, changing the oil seems to be the first - and easiest - thing to try.

fitz

 

Any chance the "limited slip" clutches are slipping, heating up the oil?

 

True, but I think he would of noticed it when the felt the axle. Does it do it during certain styles of driving? City, highway, fast, slow.. etc?

I guess drive it around until it does it again, and then feel the axle temp. For the oil to be shooting out, it would have to be very hot.

Also after you cleaned out the vent tube has it done it again?

 

Well, the one touch test I did involved about 8 miles of city driving, followed by 8 miles of interstate (about 70 mph), followed by roughly 4 miles of 40 mph or so. I can try it again under different driving conditions. Now that I know it's a recurring issue, I have been watching for drips anytime I park the truck. Nothing yet ... but it only happens every few weeks.

If, in fact, the limited slip was slipping too much, would anything feel different? There are no new noises, and I do run with the windows open (weather permitting).

And, yes, it has blown oil since cleaning out the vent tube, unfortunately.

fitz

 

I don't think you would feel any difference unless you were to burn a circle. If the inside wheel really spins that would indicate that the clutches were slipping.

 

The rear end fluid has been changed: 75W-140 Mobil 1 full synthetic with one bottle of Ford friction modifier. I guess now I just wait and see.

The old oil didn't look or smell any different, nor was there any water in it (didn't expect any). No observable pieces of metal or anything else. I hope it just ends up being that the now-defunct dealership put the wrong oil in it. Otherwise, I think I'm in trouble.

(Side note: Before changing the fluid, I did a few more touch tests after various driving conditions. Never was it more than warm. Then again, I hadn't had the vomiting oil problem again, either.)

Thanks for everyone's help so far.

fitz

 

make sure the vent hose is clean. make sure the hole into the axlel housing thru the TEE is clean-- can you blow into it with a hose and your mouth? make sure the hose does not have a loop or p-trap type routing. any oil in the line should drain back down the hose into the TEE fitting, into the case.

 

Just an update ... almost four months after swapping fluid.

Problem has disappeared (knock on wood). No oil vomiting since the fluid swap ... none, zero, zilcho. Many thanks again for everyone's help.

fitz

 

I am having a similar problem. Recently the rear differential oil was changed in my 95 Ford Bronco and it has been gushing oil from the differential vent hose. It stopped for a while and I figured it was just overfilled. I had my Bronco parked in the garage for about a week, no oil leaking. I moved it to the driveway yesterday (10 feet) and today when I went outside there is a HUGE puddle that came from the vent hose. The driveway has a slight incline, but this should have made it less likely to leak as the vent was now slightly higher.

There is not much information on this problem, and there is no way 10 feet caused the differential to heat up and push the oil out.

I hate to do it, but I'm guessing the only thing that I can do is pull the cover and replace the oil with what I know is correct and hopefuly that will fix the problem. Any ideas?


Erik
95 Ford Bronco XL
Police Package

 

Erik -

Wow, it's been almost 4 years and I had completely forgotten about this post ... undoubtedly because my problem went away with the fluid swap.

A couple things come to mind - and I think all of these were suggested at one point or another earlier in this thread - but here it goes:

(1) The vent hose should go roughly straight up without any significant "drops". The best way I can think of describing this is a P-trap in your sink plumbing. You don't want a P-trap. It holds fluid, by design for your home plumbing - but bad for a vent tube because it holds pressure until there's enough to overcome the fluid. Then it's a pretty good blast ... and you already have fluid that far up the tube to discharge. When I had my problem, I had a possible P-trap scenario (sort of borderline). Although I don't think it was the root cause, undoubtedly it didn't help.

(2) When your fluid was changed, it could be that gunk, crud, whatever was knocked loose. If so, it's probably floating - and if you have an overfill condition, it may be finding it's way to the vent tube and clogging.

(3) I don't know this for certain, but I'm thinking that if you had the wrong oil in there ... and I mean "really wrong" (or contaminated) ... you could have a significant foaming issue (that may not be heat related). I'm guessing this would cause problems - although it really is a guess.

Again, my solution was to pull the cover and replace the oil with what I knew was supposed to be in there. While at it, I made sure the vent hose and tee were completely clean. I'll never know exactly what was wrong, but this worked for me. Hopefully it works for you.

fitz