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2007 w251 mercedes r350 3.5L 4matic
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Discussion Starter · #1 ·
So what i thought was the transmission thankfully wasn't it was just my front differential that blew clean in half at 85mph $1550 for oem rebuilt replacement (thats including labor) if anyone is wondering going threw the same thing my dif blew up around 130,200 miles on the clock
 

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Outstanding Contributor , SDS Guru
1998 MB E300TD, 1997 MB E36 AMG, 2001 MB E55 AMG. 2011 BMW 335d
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Front diffs are a known weak spot on those cars. The engine bay heat basically cooks them, the seals dry out and don't hold the diff fluid, it seeps out and kaboom.

Fluid needs to be changed at same schedule as transmission fluid... every 30k.
 
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Eeek!
 

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2007 w251 mercedes r350 3.5L 4matic
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Discussion Starter · #4 ·
Wow thanks for the explanation, i wasnt aware thats what the issue was with them. i figured it had has a stress fracture but i dont have any added weight in the front. My mechanics had never seen a diff come in this badly damaged before so they weren't even sure what could have caused it haha


Front diffs are a known weak spot on those cars. The engine bay heat basically cooks them, the seals dry out and don't hold the diff fluid, it seeps out and kaboom.

Fluid needs to be changed at same schedule as transmission fluid... every 30k.
 

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Front diffs are a known weak spot on those cars. The engine bay heat basically cooks them, the seals dry out and don't hold the diff fluid, it seeps out and kaboom.

Fluid needs to be changed at same schedule as transmission fluid... every 30k.
Thanks for the insight!
If you have no leaks from your diffs are you okay then?
The change interval for the w251's ATF is 70k (at least it is for the later model blue-fluid transmissions) and I believe they say to change the diff fluid at that time too.
Last time I changed my ATF I went ahead and changed the diff fluid with Mobil 1.
Im about to do the ATF again within the next few days and actually forgot all about changing the gear oil!
(Thanks for the reminder)

30k seems a bit excessive but your reasoning about the heat within the engine bay leads to to believe you.
 

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Outstanding Contributor , SDS Guru
1998 MB E300TD, 1997 MB E36 AMG, 2001 MB E55 AMG. 2011 BMW 335d
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Presence of leak or not doesn't mean much, it's the actual fluid inside that matters. Need to crack the fill plug and dip a finger to see.

If you primarily use the vehicle in stop and go traffic, meaning the vehicle spends most of the time in the city, or in stop and go traffic....then that is considered severe duty. All fluid change intervals must be shortened by a considerable amount to compensate. 70k OCI makes sense if the car does nothing but 100+ mile freeway commutes day in, day out, for years. Every other transmission manufacturer, notably Jatco (which may mean nothing, since they produce the trash CVT used in Nissans), and ZF, recommend 30k intervals.

Meaning if the vehicle is used for nothing but picking up kids, going to groceries and making various other trips like to the bank, etc....that is severe duty.

If the W164, X164, R251 had only a RWD system, then yes a 70-80k diff fluid interval makes sense. The rear diff is very far from a heat source, and it's surrounded by nice cold air.

In contrast with front diff, which is often right next to the oil pan, or under exhaust manifold, or any combination thereof, plus there's the engine undertray cover trapping heat, which means a very toasty environment. Combined with tens of thousands of heat cycles, is it any wonder that it grenades because no one pays attention to it?

4WD trucks like F150, Silverado and Ram don't suffer from this problem as much, since their front diff is really quite distinct and separate from the engine.

Fun fact: front diff and transfer case is also a problem in higher mileage BMW x-drive vehicles....particularly the ones with N63 engines. I wonder why.
 

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2007 w251 mercedes r350 3.5L 4matic
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Discussion Starter · #8 ·
Theoretically speaking, Would there be any benefits to wrapping the diff in a heat displacing material or make shift custom firewall around the diff to combat the heat cooking the diff? Im courious why mercedes didn't implement any sort of firewall as a solution to the heat build up from the engine.

In contrast with front diff, which is often right next to the oil pan, or under exhaust manifold, or any combination thereof, plus there's the engine undertray cover trapping heat, which means a very toasty environment. Combined with tens of thousands of heat cycles, is it any wonder that it grenades because no one pays attention to it?

4WD trucks like F150, Silverado and Ram don't suffer from this problem as much, since their front diff is really quite distinct and separate from the engine.

Fun fact: front diff and transfer case is also a problem in higher mileage BMW x-drive vehicles....particularly the ones with N63 engines. I wonder why.
 

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Outstanding Contributor , SDS Guru
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Should work, but just changing the fluid every 30k will significantly prolong the life of the front diff. That's all that's needed.

why mercedes didn't implement any sort of firewall as a solution to the heat build up from the engine
Your answer to these question is MB answer as to why.

1. Will the front diff fail within the warranty terms? (Y/N)
2. Will covering the front diff cost more per unit? (Y/N)
3. Will there be any significant difference in covering the front diff in terms of NVH? (Y/N)
 

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Agreed. It basically costs less than $10 per axle and requires no special tools to change the differential fluid which is easily accessible. Even with a more conservative interval change cycle of 30k miles, thats less than $100 per 100k miles for preventative maintenance and well less than it would cost to incorporate a heat shield design that would actually be MORE effective than simply changing the fluid at any given interval.

I went ahead and changed my diff fluids last night. I didnt see anything alarming in the color since it was charged 70k miles ago but Deplore's rationale for increasing the change intervals made sense. I have actually decided to change the front differential fluid every third item i change the motor oil )since im down there anyway) and the rear differential fluid when I flush the transmission fluid.
 
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