Overfilling rear diff

[Vspec]

On my Subaru, the rear diff holds approx 1 US quart of fluid. Is there any danger in over-filling the rear diff?

Not like by a extra quart, but like 1.3 quarts or what?

I understand the reverse of this in under filling, but what about over?

Thanks.

 

[aquariuscsm]

I don`t see how overfilling would be possible unless you could pump it in and screw in the fill plug faster than it flows out once full.

 

[Vspec]

It would be easy. You see I have to jack up the car to get underneath it to work, so I open the fill plug, then the drain plug and then lower the car so it drains all the fluid out.

Next I jack up the front of the car to tilt the diff to drain out as much as possible.

In the same respect I could jack the back end back up, and then fill the diff up with more then speced fluid.

I usually just leave the car level when I fill it up and when it starts to weep from the fill hole I call it day.

Obviously if the car was jacked up I could put more fluid in the rear diff.

Im not sure if this has an adverse\positive effects.

 

[Saturn_Fan]

I thought I was a worry wart. Just fill her up till she spills out and makes a big mess on the driveway, then replace filler bolt. Differential draining and filling is not an exact science really.

 

[SubLGT]

If overfilled, oil may be forced out through the breather, making a small mess on the rear of your car.

 

[gomes512]

Unless you plan to go rock crawling and always drive at speeds of < 5mph then I would not worry about i

 

[daman]

You'll be just fine...

 

[PT1]

My GMC has a very specific fill level 1/2" below the fill hole on both front & rear. I do believe the rear is vented but I don't think the front axle is vented so maybe there is an over pressure issue. They even spec using a bent pipecleaner to measure the oil level in the Service Manual. Better follow the directions.

 

[twentynine]

You are kidding? Right?

Jackin' up and down tilting back and forth.

My Dodge don't have no drain plug. I pull the cover, clean the magnet. Clean the surfaces, black RTV, button her up.

Put in the friction modifier, then the gear oil until it comes ou the fill hose.

Tilting your car back and forth, unless it's an acute angle can't be worth more than an ounce or two. If you are that worried about getting all the old stuff out, pull the cover.

 

[JTK]

If it was way overfull, like SubLGT said, the excess gear oil would puke out the top vent. Worst case, the vent is plugged with dirt (like they often are) and you will blow oil past the axle seals; The next path of least resistance in the system.

Joel

 

[unDummy]

Over/under filling is common. As long as you stick with 30k or less for intervals, don't worry about a few ounces either way.

I can add a pint by tilting the vehicle if I wanted to overfill for certain applications.

Gotta love GM. I guess it would be too hard to drill the fill plug in a better location. The engineer in charge of drain plug hole locations had a little too much to drink that day.

 

[PT1]

Originally Posted By: unDummy


Gotta love GM. I guess it would be too hard to drill the fill plug in a better location. The engineer in charge of drain plug hole locations had a little too much to drink that day.


Yeah and they really should offer an optional drain plug on a $56,000 truck. Both for the rear diff and trans pan. Of course that hole was probably located there in 1941 when they designed the diff case.

 

[widman]

Sorry to burst bubbles, but overfilling is BAD. maybe a couple of ounces is ok, but you need to keep the level low enough that you don't end up making whipped cream out of it. Beat air into it and you will have heat and cavitation of the contact surfaces.