possible to over fill diff and cause damage?

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Has anyone ever seen damage caused to a differential from using too much fluid?

yesterday I did the rear diff on my jeep wrangler (dana 35) and I was doing it all on jacks with the rear up. well when i was filling the diff i let it fill till oil slowly oozed from the fill hole. well this was done with the jeep slanting forward. I wanted to drop it from the jacks and let the fluid drain when sitting level but it would have been a pain. Now I am thinking about it and second guessing. with the angle of the jeep when I filled it my guess would be the level is somewhere along the fill hole instead of right below it. Does anyone of you think this will cause a problem?
 
Nope. Mine's like that too...easier to get the specified amount in there, or a bit more without making a mess. It's splash lubricated after all, so I would think it would take an awful extra lot to cause a problem. The diffs are even vented at the top, aren't they?
 
as long as the rear end isn't jacked up too too high I wouldn't be concerned. As KCJeep mentioned, the diffs are splash lubricated and unlike engine or transmissions, a little overfill wont harm your diff. You are better off having a little more then having less.
 
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no, overfilling a car differential gear case would almost never cause a problem not with the gears
the requirement is to have enough oil covering all the teeth at the bottom of the ring gear so that the ring and pinion gears get enough lubrication. Having too much oil would only cause parasitic loss. Where the fill plug is and the shape of the diff housing there's no way to overfill it even with a jack under one side of the vehicle. You'd have to be at a 30-40 degree angle before there's problems overfilling, and those things would only be leakage at the pinion seal and axle seals.
 
as was mentioned its not that sensitive
you might lose .02 mpg though
smile.gif


If you are worried about it next time instead of taking it off jack stands just jack the other end up level(as long as you arent under the vehicle)

ie fill then jack it up and let it run out.. then lower then put the fill plug in.
 
Thanks guys! I was thinking the same thing when I did it originally but after being bored on the computer I looked around just to see what others thought and I found some nasty theories and stories and let them get to my head.

Also I do believe the differential is vented. I know for sure the front one is and IIRC so is the rear.
 
There needs to be some sizeable air space for expansion.... that's the only issue.

Without the air space, the oil expands thereby blowing the seal(s) out causing the oil to rapidly drain out and thus, causing catastrophic failure if it isn't caught.

If there's a breather, it could make the issue moot, but I wouldn't bank on it. They're for breathing air, not 90 wt.
 
Originally Posted By: mechtech2
Trannys and rear ends are vented.
A breather will work with any fluid or gas.


I have an unvented 5 speed manual on my pickup, but generally most probably are vented.
 
Overly high oil level can cause foaming, and higher oil temps due to fluid friction. Has to be a lot, though. A little overfull isn't a biggie. Foaming increases the oxidation rate of the oil because it's being aerated. I don't know how fast this kills the oil but I know it's faster than if it wasn't being frothed up. I also know that the OE axle mfr. very carefully calculates the oil level.

I have demonstrated that higher fluid levels causes increased oil temps on my own trucks. Mag-Hytec ( I have Mag-Hytecs on both my trucks) advocates a higher oil level than the axle manufacturer recommends. I wasn't a big fan of the idea but ran it that way with no ill effects for a number of years. At a point, I had a pretty good database of oil temps and wondered if dropping the level would result in any drop in temp.

It did. Dropping to approximately the OE level (about the bottom of the Mag-Hytec dipstick mark) the oil consistently ran around 10 degrees cooler. None of this is a huge deal but it does provide some indicators. I now run my oil a little over the Mag-Hytec bottom mark. This puts a little more oil down the axle tubes and into the wheel bearings and I think this is a good compromise. At that level I see pretty much "normal" oil temps according to the OE level.
 
Originally Posted By: SteveSRT8
I would love to see that^^^^

I have never seen a manual trans or a diff that were not vented.


You'll never see that in a regular production vehicle unless it's broken.
 
If your worried that it may be a problem... put the vehicle on level ground and remove the fill plug and let the excess drain out.
 
Originally Posted By: yonyon
Originally Posted By: SteveSRT8
I would love to see that^^^^

I have never seen a manual trans or a diff that were not vented.


You'll never see that in a regular production vehicle unless it's broken.


This is on the Toyota pickup, I tried to find info on running a remote breather for the tranny as well as the rear diff, but the consensus seemed to be that there was none. I have seen pictures of people drilling and tapping a hole up top to make their own remote breather however.

Now I am wondering, and will have to double check this...
 
Well, since I can't just edit my post for some reason.

You are correct, my transmission breathes through the shifter apparently. Here is what some do to add an actual breather:
TrannyBreather_t.jpg
 
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