Rear diff covers, worth it? Which one?

Jett · **Joined:** Fri Apr 17, 2020 12:07 am **Posts:** 250

Looking at doing a true trac rear diff later this fall and wondered if I should upgrade cover. Some look very strong and that’s appealing, however some cooling would be nice too. There is one from a company called PCE that is finned cast aluminum. The price is right, $85, but is it strong enough to hold up to mild wheeling? Or should I get an OX cast iron cover, or should I weld a bash bar that protects the area? Or should I run the stock cover and quit thinking about it? Decisions decisions.

WWDiesel · **Posted:** Mon Aug 24, 2020 4:03 pm

Installed this one when I installed a limited slip differential carrier.
Nice thick cast ribbed aluminum with nice O ring sealed type fill & drain plugs. Even has a dipstick oil level plug!
It comes in bare aluminum or also available in black for a little extra. I painted mine Red. :wink:

Be sure and order the LubeLocker Differential Cover Gaskets LLR-C825
Best (and reusable) differential cover gasket I have ever seen or used! No glue or sealant required with it! See picture below cover.

Sourced from Summit Racing:> https://www.summitracing.com/parts/gta-40-2029al
G2 Axle & Gear Hammer Differential Covers 40-2029AL

Jett · **Joined:** Fri Apr 17, 2020 12:07 am **Posts:** 250

Nice one! Yeah looks worth the extra cash maybe, although the pce one is pretty similar. Thanks for the gasket link though, I’ll definitely get that one, it’s 8x the cost of the cheap one!

Jett · **Joined:** Fri Apr 17, 2020 12:07 am **Posts:** 250

I guess the idea of a reinforced thick one is to add stiffness to the pumpkin and also for impacts on rocks if you reverse into a nasty one somehow. I’ve never had a problem with my stamped covers before so I’m a little unsure if they really make a difference

WWDiesel · **Posted:** Mon Aug 24, 2020 9:57 pm

Look up the "Heat Rate Transfer Coefficient of steel versus aluminum and it will help you understand why a cast aluminum cover is a much better cover than a steel one when it comes to dissipating/removing heat from of the thick oil in the differential....
Strength for the cover is derived from the thicker & ribbed casting. :wink:

Jett · **Joined:** Fri Apr 17, 2020 12:07 am **Posts:** 250

Lol, I don’t need to do that thanks tho. However you’re wrong, dissipating heat requires surface area. The covers don’t have a lot of surface area so I’m not sure the change to aluminum will result in that much heat rejection. Or if that is even necessary. Like, why? I’ve never seen a diff get so hot as to smoke the oil so what’s the gain in cooling?

casm · **Joined:** Sun Jan 29, 2006 5:05 pm **Posts:** 694

Jett wrote:

However you’re wrong, dissipating heat requires surface area.

Think of it this way: the diff cover (and, to some extent, diff housing, axle tubes, shafts, etc.) are all heatsinks. How much heat is transferred and dissipated is very much a function of the metal used in addition to surface area. This is why virtually all heatsinks found in electronics are made of aluminium; if cast iron were more effective, cast iron would be used. I realise that there are some constructive differences between a passive heatsink on a PCB and a diff cover on a Jeep, but the theory remains the same.

Quote:

The covers don’t have a lot of surface area so I’m not sure the change to aluminum will result in that much heat rejection. Or if that is even necessary. Like, why? I’ve never seen a diff get so hot as to smoke the oil so what’s the gain in cooling?

It's not necessarily a case of smoking the oil, but any heat you can move out of it will help to extend oil and seal life. I'm not going to pretend that I have direct-comparison numbers to hand between aluminium and cast iron in this regard, but one area I can see it helping with is limited-slip or locker engagement in scenarios where friction modifiers are necessary - in theory, the friction modifier should last longer with greater oil stability due to lowered temperatures.

Jett · **Joined:** Fri Apr 17, 2020 12:07 am **Posts:** 250

casm wrote:

Jett wrote:

However you’re wrong, dissipating heat requires surface area.

Think of it this way: the diff cover (and, to some extent, diff housing, axle tubes, shafts, etc.) are all heatsinks. How much heat is transferred and dissipated is very much a function of the metal used in addition to surface area. This is why virtually all heatsinks found in electronics are made of aluminium; if cast iron were more effective, cast iron would be used. I realise that there are some constructive differences between a passive heatsink on a PCB and a diff cover on a Jeep, but the theory remains the same.

Quote:

The covers don’t have a lot of surface area so I’m not sure the change to aluminum will result in that much heat rejection. Or if that is even necessary. Like, why? I’ve never seen a diff get so hot as to smoke the oil so what’s the gain in cooling?

It's not necessarily a case of smoking the oil, but any heat you can move out of it will help to extend oil and seal life. I'm not going to pretend that I have direct-comparison numbers to hand between aluminium and cast iron in this regard, but one area I can see it helping with is limited-slip or locker engagement in scenarios where friction modifiers are necessary - in theory, the friction modifier should last longer with greater oil stability due to lowered temperatures.

Okay maybe, but this is starting to feel like we are chasing our tails to find a reason to use aluminum. I’m not against it, I’m just saying, I’ve never heard of a heat related failure in a diff that could’ve been mitigated by an aluminum cover. In a street racing car, okay maybe, but a Jeep I’m not so sure. However I am into saving weight, and unsprung weight especially and those cast iron covers look heavy!

03black · **Posted:** Tue Aug 25, 2020 11:49 pm

We'll I don't know about heat transfer and all that, but I do have the SOLID diff cover and let me tell you, its heavy. But I will say it apparently saved my diff when I hit a rock. If the factory stamped steel was back there it probably would have punch a hole in it. Noticed this the other day when I went and changed out the C-clip and seen a good size knick in the bottom of the cover.

casm · **Joined:** Sun Jan 29, 2006 5:05 pm **Posts:** 694

Jett wrote:

Okay maybe, but this is starting to feel like we are chasing our tails to find a reason to use aluminum. I’m not against it, I’m just saying, I’ve never heard of a heat related failure in a diff that could’ve been mitigated by an aluminum cover. In a street racing car, okay maybe, but a Jeep I’m not so sure.

I tend to agree re: failures. Having said that:

Quote:

However I am into saving weight, and unsprung weight especially and those cast iron covers look heavy!

There's the tradeoff - less weight means using material that isn't cast iron. A given volume of cast iron is going to weigh more than the same volume of aluminium.

My recommendation would be to also consider these:

http://www.fourxdoctor.com/catalog/diff ... uards.html

I've run exactly those items on D44s, D35s, and C8.25s over the years, and they've held up extremely well.

WWDiesel · **Posted:** Wed Aug 26, 2020 2:38 pm

Jett wrote:

Okay maybe, but this is starting to feel like we are chasing our tails to find a reason to use aluminum. I’m not against it, I’m just saying, I’ve never heard of a heat related failure in a diff that could’ve been mitigated by an aluminum cover. In a street racing car, okay maybe, but a Jeep I’m not so sure. However I am into saving weight, and unsprung weight especially and those cast iron covers look heavy!

Even a thick ribbed aluminum differential cover will weigh no more than the stock steel cover, but it certainly will dissipate lots more heat from the rear end oil for the same given amount of surface contact area.
Not a big deal or need on a daily mall cruiser, but when you start dragging 4k or 5k trailer loads around for long distances or doing extreme 4x4 off roading in 4 Lo, it can become a concern or desire to achieve additional cooling. Rear ends (differentials) can and do fail from overheating due to bearing and / or seal failure, I have seen and rebuilt a few due to it.

A good comparison is aftermarket high performance automatic transmission pans; all the more expensive ones you see advertised are slightly finned or ribbed thick aluminum pans with all kinds of claims of better cooling, heat removal, etc. You never see aftermarket steel transmission pans advertised or claiming to remove heat unless it is a Derale type with lots of cooling tubes built into the bottom of the pan or a huge oversize pan that simply holds twice as much oil as a stock pan. Even then, I am not sure having additional oil volume helps lower operating temperatures once all the oil reaches working temperatures...something has to remove the heat out of the oil.
:5SHOTS:

Jett · **Joined:** Fri Apr 17, 2020 12:07 am **Posts:** 250

WWDiesel wrote:

Jett wrote:

Okay maybe, but this is starting to feel like we are chasing our tails to find a reason to use aluminum. I’m not against it, I’m just saying, I’ve never heard of a heat related failure in a diff that could’ve been mitigated by an aluminum cover. In a street racing car, okay maybe, but a Jeep I’m not so sure. However I am into saving weight, and unsprung weight especially and those cast iron covers look heavy!

Even a thick ribbed aluminum differential cover will weigh no more than the stock steel cover, but it certainly will dissipate lots more heat from the rear end oil for the same given amount of surface contact area.
Not a big deal or need on a daily mall cruiser, but when you start dragging 4k or 5k trailer loads around for long distances or doing extreme 4x4 off roading in 4 Lo, it can become a concern or desire to achieve additional cooling. Rear ends (differentials) can and do fail from overheating due to bearing and / or seal failure, I have seen and rebuilt a few due to it.

A good comparison is aftermarket high performance automatic transmission pans; all the more expensive ones you see advertised are slightly finned or ribbed thick aluminum pans with all kinds of claims of better cooling, heat removal, etc. You never see aftermarket steel transmission pans advertised or claiming to remove heat unless it is a Derale type with lots of cooling tubes built into the bottom of the pan or a huge oversize pan that simply holds twice as much oil as a stock pan. Even then, I am not sure having additional oil volume helps lower operating temperatures once all the oil reaches working temperatures...something has to remove the heat out of the oil.
:5SHOTS:

Well I guess the question is, why was the diff getting THAT hot in the first place? I agree towing heavy up the pass is going to make more heat than a mall crawler, which is exactly why I’m asking about these because I’m building my Jeep to be a little tow pig that I can use to tow max rating at max speed up max grades. That’s how doo doo gets hot, not off roading, imo. So, I’m into whatever heat rejection the alloy covers offer, but really I’m more interested in the impact protection and axle strength improvements, although I’m not an extreme wheeler anyway, but I’m not a mall crawler either.

Lancer · **Posted:** Sat Aug 29, 2020 10:41 am

I have the ARB on mine. No extra oil capacity, but good reinforcement for the axle, and very strong. Good fill plug with dipstick and magnet on the drain. Second the Lubelocker gasket!

Rear diff covers, worth it? Which one?

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