Air pressure in Differential?
Thread Starter
Pro
Joined: Dec 2011
Posts: 718
Likes: 69
From: North Reading MA
Air pressure in Differential?
I just changed out my diff fluid Thursday and noticed a loud rush of air when I cracked open the drain plug.
I just noticed that I have some gear lube in my driveway and it is dripping from the sway bar. I will pick it up on the lift tomorrow but wonder if the air pressure build up is normal, and if maybe this is related to the leak? It was dry as a bone before I drained it......
EDIT: Search results show that press is normal....I will have to have a good look at the vent...
I just noticed that I have some gear lube in my driveway and it is dripping from the sway bar. I will pick it up on the lift tomorrow but wonder if the air pressure build up is normal, and if maybe this is related to the leak? It was dry as a bone before I drained it......
EDIT: Search results show that press is normal....I will have to have a good look at the vent...
Last edited by Mastertvtech; May 20, 2012 at 12:22 PM.
Melting Slicks
Joined: Apr 2009
Posts: 2,479
Likes: 36
If diff fluid spews out of the vent, then it is usually an indication of an overfilled diff. You should bring the level down to about a quarter inch below the fill hole. I have also found recently that some gear lubes are more susceptible to blowing out of the vent after long hot drives than others. This may simply be related to their viscosity stability under extreme heat conditions and resistance to foaming.
Thread Starter
Pro
Joined: Dec 2011
Posts: 718
Likes: 69
From: North Reading MA
If diff fluid spews out of the vent, then it is usually an indication of an overfilled diff. You should bring the level down to about a quarter inch below the fill hole. I have also found recently that some gear lubes are more susceptible to blowing out of the vent after long hot drives than others. This may simply be related to their viscosity stability under extreme heat conditions and resistance to foaming.
Drifting
Joined: Oct 2011
Posts: 1,872
Likes: 333
From: Olmsted Falls Ohio
St. Jude Donor '12 thru '24
I changed my diff lube recently and did not experience a pressure release. Besides what has been said above, you might wish to check for a restricted or damaged vent valve assembly, as per the service manual (my manual is for the 2001 model year).
Team Owner
Joined: May 2005
Posts: 23,682
Likes: 9
From: Flagstaff Az.
Pressure build up in the case is due to a plugged up vent. Just over filling the diff will not cause it to retain pressure. This pressure will also force lube out around the seals.
Thread Starter
Pro
Joined: Dec 2011
Posts: 718
Likes: 69
From: North Reading MA
In my search here I found most threads regarding this state the pressure release heard when opening the plug is normal?
I just noticed a quarter sized drop of gear oil under the rear again...It is only happening once it cools down from a trip. I had no leak whatsoever before I replaced the fluid and filled just to the plug.
Le Mans Master
Joined: Jan 2001
Posts: 5,015
Likes: 508
From: Hilton NY
The differential operates with a vacuum so when you open the drain plug you are supposed to hear air entering the case when the fluid is cool.
Last edited by Fast one; May 21, 2012 at 09:23 AM.
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