Gear issue in 8.8 with heavy duty rear cover

[N2FORD]

Sorry in advance for the long story. I have a 01 Sport Trac with a 8.8 4.10 trac loc. The pinion bearing had gone bad, lots of noise and movement. I decided to try and find a good used one. Found one at the pull a part near me and it seemed really good and tight with no leaks. I put it in about six months ago and added a heavy duty rear end cover. I added the proper fluid and filled to the fill plug on the rear cover. That plug is a little higher than the front plug. The rear end started to blow fluid out of the vent tube if driven on the interstate. I thought at first it was just a little over full and would settle. It did seem to get better. A couple of weeks ago it got warm enough to roll the back window down. Wow what I heard scared me, the rear end is howling pretty bad. Changes as I roll on and off the gas. Checked the fluid and it was still full by the front plug. Took the cover off and the gears seemed shiny and the fluid seemed frothy. So I have now gone to pull a part and picked up another rear end. My question is did the overfilling of the rear end cause my problem or the extra capacity with the larger cover cause the frothy fluid to cause the overflow issue? Just wanted advice before I decide if I want to use that cover again or not.

 

[swshawaii]

Factory fill plug level should always be used regardless of any aftermarket covers increased capacity. If you filled it to the "Solid" 8.8 covers fill plug, it was definitely overfilled. That was the reason for the vent tube overflow and likely the foaming. Surprised you didn't blow out axle seals.

leaky rear differential vent tube

 

[BKennedy]

I have a Solid cover on the front axle (Dana 44) and the first time I filled it, I filled it until fluid started coming out the fill hole. Fluid started seeping out the plug welds on the first trip. Realized it was nearly a quart overfilled and I just fill it with the recommended amount now. I use a zip tie as a dip stick to check the level. The Solid cover doesn't add any capacity, they just put the plug hole up higher.

With the 8.8, you could remove the OEM plug, then fill it from the cover as it would be easier and stop when it starts running out the OEM plug hole. Fluid capacity should be 3 quarts.

 

[CDW6212R]

Ditto, always use the stock fill hole as the proper level to fill it to. If an aftermarket cover is used, it's handy to be able to fill it with the larger or higher fill hole.

The fluid hand pumps are about the best way to fill through the stock hole. But if there's room at the back with a fill hole, that should be faster by squeezing the bottles above the diff. Amsoil just started to sell gear oil in quarts in flexible "bags" instead of bottles. I haven't tried any of those yet since I still have the stock covers on mine.

 

[N2FORD]

Thanks for the replies. I guess the excessive frothing of the excess fluid thinned the gear lube that caused the gear wear and noise? I plan on using BG fluid in the next one. We are a BG dealer at my work and seems like good stuff. It looks like the replacement rear ends is going to need spider gears, that should be fun.

 

[CDW6212R]

The spider gears are easy compared to the ring and pinion. Try to work with a good R/P already in place. Use the best gear oil you can, what is BG brand? I prefer Amsoil, which is now about $14 a quart plus taxes.

 

[N2FORD]

www.bgprod.com They are a automotive chemical supplier. Their BG44k is a well know fuel additive, they seem to make a quality product.

 

[Gary Crist]

I know this is an old thread but, SAVE YOUR MONEY!
Before you spend a cent on fancy diff covers, go and
find youtube vids by Gale Banks.

There are IIRC 3 videos that will explain the problems this
member experienced. Oh, and it would be cool if there
was a "Banks kit" for our EXs

 

[CDW6212R]

Good idea, but no 8.8 yet.

 

[Mbrooks420]

I know this is an old thread but, SAVE YOUR MONEY!
Before you spend a cent on fancy diff covers, go and
find youtube vids by Gale Banks.

There are IIRC 3 videos that will explain the problems this
member experienced. Oh, and it would be cool if there
was a "Banks kit" for our EXs

There’s nothing wrong with a more solid diff cover. You just need to keep the oil where it’s supposed to be on the gears, and it’d be fine.

 

[imp]

Factory fill plug level should always be used regardless of any aftermarket covers increased capacity. If you filled it to the "Solid" 8.8 covers fill plug, it was definitely overfilled. That was the reason for the vent tube overflow and likely the foaming. Surprised you didn't blow out axle seals.

leaky rear differential vent tube

How does excess fill "blow out" seals when normal fill does not? The vent tube relieves pressure either way, no?

 

[CDW6212R]

Good question, I didn't re-read the older posts, but maybe the vent hose was plugged? I've seen lots of cars with torn off vent hoses, which lets in dirt etc.

A friend at work had a hose hanging down in the front of his Jeep SUV, and I looked under the hood and found the other end open, and hanging too. Someone had run a new very large(5/8" ish) hose up around the master cylinder and hung it down from there. That front differential vent hose had come off and was almost to the ground. He had his mechanic guy look it over the next day, and decided it was no big deal, so he tied off the bottom end of the hose too. Some people shouldn't work on cars.

 

[CDW6212R]

I thought the aftermarket covers had the upper hole to make it easier to fill with, but not as a level mark. I thought the stock fill hole in the diff, was the right place to fill it to, no matter what cover is used.

 

[Gary Crist]

What I was attempting to do is show how the OP had diagnosed his own problem!
This is one of the videos I was referencing. It is about 9 minutes long. All the clues were there.
The pinion noise, fluid out the vent and all the way to a smoked rear-end!



Note the air whipped into the fluid!
The old Ford service spec back in the day for 8 and 9 inch diffs was about 5/8
below the fill plug. Maybe it changed as I have slept since then!

 

[CDW6212R]

I think I recall the 8.8 being around 1/4" below the fill plug. But I am almost always filling it with the back end up slightly, so the level ends up being some amount below the fill plug hole.