VAC Differential Cover: My Review

[turugara]

Pros:

• Cools the LSD gear fluid much better than stock
• Adds port to monitor differential temperature
• Adds drain/fill plug for easy fluid change
• Shiny

Cons:

• $800
• Can be low to the ground (no issues surprisingly even in horrible Philly roads)

This is merely my opinion. Link to VAC's thread for more information:
http://bimmerboost.com/showthread.ph...erential-Cover


Why bother with this?
This is one of those items that seem like a true enthusiast product for the "hardcore track junkie."
I thought the same until I discovered that I might be in serious need of such a product.


Many of you have LSD's in your OEM diff unit with BMW's "lifetime" gear oil.
Unfortunately, I recently discovered that this gear oil doesn't last anywhere near the "lifetime" of the vehicle, especially when coupled with a Quaife LSD and a few (15+ ) very hot track days.


My old unit had begun to spurt gear oil after track events.
After track events I would go under my car and find the pumpkin to be covered with gear oil. I would then clean it off and begin to worry. At first I thought it was the seals so we replaced those. Then after replacing the seals, the diff was still getting fluids all over itself after track events.


After some researching, I suspected it was because the diff oil was boiling and coming out of the top vent. After opening my diff up and seeing that the gear oil had gone to an extremely nasty shade of black, it was confirmed that I had cooked my gear oil and cooked it pretty bad.


Old Differential Cover: no Cooling options, fins, or drain plug







Which begs the question...
If I, an intermediate level driver at best, is cooking diff fluid in the New Jersey weather, how the hell is your diff fluid holding up if you live in a warmer climate, producing more power (all tuned n54...), or have more experience tracking?????


New Differential Cover






Driving Impressions:


This was the most surprising part. My Quaife unit felt like it was slightly more progressive, almost smoother with the new fluid and not boiling the fluid at the track. I hadn't expected a change at all but it was noticeable today at the track in 100+ degree weather when compared to just two weeks ago. This could also be attributed to the fact that my previous fluid had been boiled multiple times and was probably in horrible condition. Nevertheless, it's looking like this new differential cover will prevent that from occurring again.


On the street I've had zero clearance issues. I don't baby this car around the mean streets of Philly and South Jersey. Our potholes and bumps are legendary. I've seen a Ford F150 get stuck in a huge pothole in West Philly before. So far my lowered 335i has confirmed the VAC note that the race length (long finned) differential on a lowered vehicle generally has no clearance issues. Obviously if you ran through a curb that would take off your front bumper and various other underbody parts, you would probably scratch this differential cover. Best part is that even if you do hit it, it's made out of one piece forged billet aluminum so it's strong as hell.


Because Racecar

[turugara]

A properly oiled LSD with proper cooling means you go faster and kill your tires more to the point where street tires give out suddenly. XD

[Sticky]

Nicely done review, thank you.

The track guys (we have a few) should definitely look into this and really everyone else as well. The fluid capacity gain alone is a major selling point.

[orange]

Excellent review.

[DavidV]

Great. Nice to hear from somebody who actually uses the car enough to notice the difference.
I do have a question for you.
How difficult is it to install?
What did you have to disassemble to install this?
I am considdering this as an upgrade.

[turugara]

Great. Nice to hear from somebody who actually uses the car enough to notice the difference.
I do have a question for you.
How difficult is it to install?
What did you have to disassemble to install this?
I am considdering this as an upgrade.

1. Installation isn't too difficult. It involves lowering the differential in order to remove the OEM cover. It can be done on stands but it would be infinitely easier on a lift. Expect 1-2 hours of work total on a lift because some of the screws are a little tough to reach.

2. My exhaust was being annoying so we had to unbolt section 3 and push them out of the way. Otherwise that's it. Unbolting and lowering the differential was the main thing.

[singletrack]

Your left hand placement in that video drives me nuts.

[onebadmofo]

Any point getting it for a street car?

[nitehawk]

The differential cover is all nice and dandy but I'm surprised no one has asked the obvious: why not just switch to a higher temp oil such as Motul Gear Competition 75w140? That is what Wavetrac recommended me for serious track use. It may have been adequate to solve your overheating woes without putting a dent in your wallet.

[Sticky]

It may have been adequate to solve your overheating woes without putting a dent in your wallet.

Your point has merit but the fluid volume still would not be as high.

[AR Design II]

nice write up and video!

[JamesM3M5]

The differential cover is all nice and dandy but I'm surprised no one has asked the obvious: why not just switch to a higher temp oil such as Motul Gear Competition 75w140? That is what Wavetrac recommended me for serious track use. It may have been adequate to solve your overheating woes without putting a dent in your wallet.

Your point has merit but the fluid volume still would not be as high.

Indeed. The fluid volume of the E9x diff is REALLY SMALL, and even a moderate HP 335i will cook diff oil in a hurry. Even Motul Gear Competition fluid was black (starts blue) after every event in our GA 328i, and that car had 100HP less than any tuned 335i.

[turugara]

Race diff holding up well. No problems in the years I've had it.

[idratherbesurfing]

Damn that's really low to the ground. I would honestly be scared to have that

[Sticky]

Damn that's really low to the ground. I would honestly be scared to have that

What is he planning on running over?

[135pats]

What is he planning on running over?

There are some outright holes in the ground that would happily eat that diff cover, i'd be scared as hell to run it in DC. It's a different ballgame in the mid-atlantic/northeast.

Beautiful product though.

[Jajou]

I had the rogue engineering mount on my Z and my butthole would pucker as if come to a dip or bump our pothole in the road.

Got rid of it after my first cruise. Mine was cast not billet. The one looks real nice.

[triggz]

too bad you can't use this cover with the defiv lockdown kit

[mjmarovi]

too bad you can't use this cover with the defiv lockdown kit

X2 this is the deal breaker for me. Great looking product, but I would like to see it improved for use with the defivfab lockdown kit and better clearance. Maybe defiv would be interested in making one? @rick@defiv

[Torgus]

Why not just tap the factory cover and run an exterior cooler? Should be less than the price of the VAC kit and you can still use the lockdown kit...or am I missing something?

[triggz]

Why not just tap the factory cover and run an exterior cooler? Should be less than the price of the VAC kit and you can still use the lockdown kit...or am I missing something?

It's not just the cooling factor that is the benefit here. It's the fact that you can run more fluid as well.

[Kommodore]

Has anyone run solid diff bushings without the lockdown kit as a compromise?

[Torgus]

It's not just the cooling factor that is the benefit here. It's the fact that you can run more fluid as well.

If you can keep the fluid cool enough you shouldn't need more of it right?

An exterior cooler + the lines to and from should hold as much or more than the VAC cover no? VAC says 50% more fluid.

That diff sits really low. In the NorthEast I would be scared to run it.

[mjmarovi]

If you can keep the fluid cool enough you shouldn't need more of it right?

An exterior cooler + the lines to and from should hold as much or more than the VAC cover no? VAC says 50% more fluid.

That diff sits really low. In the NorthEast I would be scared to run it.

Yeah, you're right, a cooler would work well, but where would you put the cooler? And unless I'm mistaken there's no pump on the diff to move the fluid, so you'd need that too, so current draw, a pump, and then the cooler. Sounds like a PITA to be honest, but I may be wrong, I'm open to suggestions, maybe I'll even do it.