[heavyhaulerss]

I just noticed my rear, rear had a film of oil around what I would call the pressure relief screwed into top side of rear. what is strange to me is, I have never seen it do this before, I always change rear oil every 6 months or 45,000 miles. wich ever comes first. I always checked fluid level & never had to add any. the rear has always been dry for 10 years now, maybe just a lil oil residue, barley ,slightly, but not like this. I replaced valve. still puts out oil only around that area of valve. it does not leak a lot out, but this is a first. changed fluid today nothing on mag plug. so why, all of a sudden would oil come out thru valve? also when I changed the fluid is was after running 104 miles at interstate speeds, I parked truck & within 10 min oil was draining & it was not real hot at all, just warm, not sure if that means anything or not.

[Larry227]

Does it have a locker on it and if so have you been using it? If the answer is yes it could have a bad seal in the locker and when you engage the diff lock it is letting some air pressure into the diff and coming out the breather.
That's the only thing that will literally force oil out of the breather. If it's not that and it's not ever low it's just breathing and I wouldn't worry about it. At least if it's getting a film there you know it's not plugged which would be worse.

[heavyhaulerss]

thanks for the reply larry. my neighbor truck driver told me all the trucks at his co have the same thing. & most are new trucks. I have not used the p.d.l . I thought if a bearing was going out & heating up the oil to a high temp, that it would push some oil out, but as I said the oil is not hot when I checked just after shut down. I was just concerned, cause when I go over my truck & see something that I have not seen before. I think something's ready to give out on me. after 10 years & never being broke down on the road, I can't tell you how many times I saw something needing attn in my drivway, that if not taken care of would surley have left me on the side of the road. thats why I go over, around & under my truck every time I get back. sometimes that means every day if I do my dedicated daily runs.

[heavyhaulerss]

WAIT A MINUTE!! I just remembered something. this may or may not have something to do with leak... I had the in dash pdl replaced cause it was leaking air. now that I think of it it was only after that point the rear leak occurred. coincidence or no? I dont know. I have not used the pdl, but.. if the shop that installed it, crossed the 2 air lines would that be the problem ? I know there was only 2 wires & 2 air lines. one top line, one bottom line. so maybe he put the botton on the top & vise versa. does that sound like it could have caused the leak? & how can I check to see wich line should go where, to check this?

[Larry227]

To test just take the airline off at the axle and see if air is coming out when the switch is off.
If the seepage is on the #3 axle and the switch you replaced is for the power divider on the #2 axle it would not cause your issue. When you said rear rear end I'm assuming you meant the #3 axle. (I call #1 axle the steer). The switch being changed is probably a coincidence. I'm sure it's just On/Off anyways and makes no difference which line goes where.

I'll ask the guys at work today if the bearings could cause that. They know way more than I do.

[heavyhaulerss]

When you said rear rear end I'm assuming you meant the #3 axle


this is correct. the only reason I mention bearing is a person told me if the temp in the rear got to boiling temp & was too hot, that could cause the oil to come out of relief valve, & the only thing he could think of was if a bearing was going out that would raise oil temp. to be honest. when looking diff.. I dont know wich one gets locked. I assume one is always engaged & the other engages only when pdl switch is flipped.

[YerDaddy]

No axle temp gauge? They are easy to add. Just one hot wire to a sending unit and ground the axle to the frame with another wire.

[heavyhaulerss]

Originally Posted by YerDaddy

No axle temp gauge? They are easy to add. Just one hot wire to a sending unit and ground the axle to the frame with another wire.

it does not have a gauge. where would i put the sending unit?

[Kranky]

Originally Posted by heavyhaulerss

When you said rear rear end I'm assuming you meant the #3 axle


this is correct. the only reason I mention bearing is a person told me if the temp in the rear got to boiling temp & was too hot, that could cause the oil to come out of relief valve

It's not a relief valve, it's a vent.

As was stated, it's important that the vent is checked often and cleaned out if necessary, because a clogged vent will allow pressure to build up inside the diff housing, resulting in blown wheel seals or blown pinion seal.

Have you changed to a different brand or type of rear end lube recently?

From mineral to synthetic?

[heavyhaulerss]

vent is new. it leaked with the old one. it leaks with the new one. same type lube in rear for 10 years. changed every 6 months/ 45,000 miles.