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Diff fluid issue

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chev4life

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Ok...I am having issues...many of them...but this one I think is easy...
I just did a fluid/diff cover swap on my FF 14. I filled it to the fill plug on the casing with semi-syn diff oil....well...I go out driving for 60 miles or so and get out and I smell fluid...its all over the bottom of the truck after blowing out the vent tube. So...my question is...did I overfill the case?...how much should be in there?...is there anything I should be worried about?
 
is it a positraction axle with clutches in it, or is it a locker or floater? conventional positraction works on the basis of friction between the clutch disks and generates a lot of heat.

what viscosity / weight oil did you put in it, and what kind? not ATF, right? I use 85 - 140 Valvoline in mine, with about 25% Lucas Oil Stabilizer (a 3:1 ratio, in other words), and that's with Eaton Tru-Trac's, not conventional positraction. You need a friction modifier if you've got positraction.

the worst case I can think of is that you put auto-trans fluid in a positraction differential, and when it got way too hot, it boiled out.
 
Its a detroit locker in the rear and I put 80-90 (i think...whatever autozone had listed for the truck) It is Valvoline semi-syn in it.
 
So...I put 3 quarts in to fill to the hole...is that what everyone usually puts in? Also...I have the rockcrusher 3/8 plate diff cover...which shouldnt matter.
 
I fill it until it overflows, wait a bit, add more until it overflows.....letting it BURP the air out and level off.
 
chev4life said:
Its a detroit locker in the rear and I put 80-90 (i think...whatever autozone had listed for the truck) It is Valvoline semi-syn in it.
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Its overfilled, i did the same exact thing and have the same combo with 5.38's, drove to palo alto and it was all over the bed, drove it back and again, fluid all over the bed. I just drained some and made sure it was on level ground when i checked the fluid level on the housing and its all good now. Steeper gears also spin the carrier more causing fluid to come out the vent tube especially when overfilled just a little and on the freeway.
 
If the diff is overfilled, the oil will come out of the breather hose. If the diff is getting REALLY hot, it will also come out of the breather hose.

There are some other cases (ARB's in dana 44's that need oil drains cut into the housing) that also have problems with puking fluid out of the breather hose (unless that drain is cut into the housing).

A 14 bolt should hold ~1 gallon of fluid. If you only put 3 quarts in, its not overfilled and you likely have bigger problems.
 
What kind of problems? All I did was swap the fluid and cover and then filled it up to the fill plug on the side of casing. Then I drove it around and had fluid everywhere. I have never had this problem before. What should I look for? 1-gal seems like a ton of fluid.
 
chev4life said:
What kind of problems? All I did was swap the fluid and cover and then filled it up to the fill plug on the side of casing. Then I drove it around and had fluid everywhere. I have never had this problem before. What should I look for? 1-gal seems like a ton of fluid.
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That's kind of a tough call. Bad pinion bearings can generate a TON of heat and would easily boil the fluid forcing it out wherever it can go (the breather tube is usually the easiest way out).

It seems wierd that it would suddenly do this.

My advice would be to fill it again up to the fill hole and drive it for a while (20 miles or so, highway is better) and then stop and put your hand on the pumpkin. If its too hot to hold your hand there you probably have bearing problems.
 
I'm wondering if it's not just getting too hot. I have a heavy duty cover that I am planning on using but was concerned that it may not cool sufficiently for highway use like it does with the thin factory cover.

Can anybody comment on that?

If you just changed the cover and fluid this time it could be the culprit. If you feel like experimenting you might try the old cover again.
 
You might check out this article from Four Wheeler magazine. It's about building an F-250 towing axle but there is a good section in it on heat, fluid, and the diff cover with temps for various scenarios at the end.
 
The temps can really change...but I wouldnt think the thicker plate would cause temps to jump like that and I am pretty sure my bearings didnt go out from great to that bad in cover/fluid swap. Think maybe I am going with the wrong fluid for my app?
 
chev4life said:
The temps can really change...but I wouldnt think the thicker plate would cause temps to jump like that and I am pretty sure my bearings didnt go out from great to that bad in cover/fluid swap. Think maybe I am going with the wrong fluid for my app?
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I've always used 80W-90, I believe that to be the right fluid for that application.

As I said before, if you can't hold your hand on the pumpkin its too hot. Maybe the diff was low on fluid before?

IIRC, diffs are supposed to run under 200F
 
I think I will drain to see how much I have left and then refill and try to get 4-quarts in. Maybe I didnt get enough in and it got hot...I will have to examine that.
 
chev4life said:
I think I will drain to see how much I have left and then refill and try to get 4-quarts in. Maybe I didnt get enough in and it got hot...I will have to examine that.
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Don't force 4 quarts into it. Fill it until it starts coming out of the fill hole, drive it around the block, let it sit for ~1 hour and see if its still full.

I'm pretty sure mine took 4 quarts, but I just filled it the way I just described.
 
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