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      04-01-2014, 10:18 PM   #1
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Rear diff fluid change?

I bought redline 75w-90 oil for my rear diff on my 2009 e90 lci 328i. I took my car to my mechanic to change a couple of fluids including the rear diff. I got a text from him today stating " diff has no drain plug so its not meant to be serviced." Is this true? I find it hard to believe that you can't change the rear diff fluid. I searched for a couple DIYs on servicing the rear diff but several of them stated "2007-2009 328i rear diff fluid change." Are lci cars rear diff different? Can you not service a 2009 e90 328i rear diff by draining and refilling it?
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      04-01-2014, 10:23 PM   #2
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I don't know about LCI, but my 2007 328i has a fill plug but no drain plug. To change the fluid you have to use a transfer pump to suck the fluid out and then refill it through the same hole.
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      04-01-2014, 10:33 PM   #3
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Quote:
Originally Posted by Squark View Post
I don't know about LCI, but my 2007 328i has a fill plug but no drain plug. To change the fluid you have to use a transfer pump to suck the fluid out and then refill it through the same hole.
Thanks! I'll mention this to my mechanic tomorrow.
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      04-02-2014, 05:02 AM   #4
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Quote:
Originally Posted by Squark View Post
I don't know about LCI, but my 2007 328i has a fill plug but no drain plug. To change the fluid you have to use a transfer pump to suck the fluid out and then refill it through the same hole.
+1

OP your mechanic is half right because (according to BMW) your diff fluid is 'lifetime fill' (ha ha) - hence no drain plug. As Squark says, suck out the old fluid through the fill plug.
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      04-02-2014, 06:04 AM   #5
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OP, if your mechanic doesn't understand how to change the rear diff fluid in your car, then take it to a different mechanic who does. Yup, BMWs used to have diff fluid drain plugs when the service interval was 30,000 miles, but fluid specs have changed. Regardless, any decent mechanics shop should have some type of fluid transfer apparatus to suck out the old fluid, and any decent mechanic would know that this is a situation where he needs to use such a device.
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      04-02-2014, 08:19 AM   #6
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Quote:
Originally Posted by Efthreeoh View Post
but fluid specs have changed.
Really? Not what I've heard. Same fluids, just a BMW decision to euphemistically call several items on the car 'lifetime fill' to reduce servicing costs. They're already going back on this decision in some cases (e.g. engine oil change intervals).
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      04-02-2014, 08:22 AM   #7
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Quote:
Originally Posted by Efthreeoh View Post
OP, if your mechanic doesn't understand how to change the rear diff fluid in your car, then take it to a different mechanic who does. Yup, BMWs used to have diff fluid drain plugs when the service interval was 30,000 miles, but fluid specs have changed. Regardless, any decent mechanics shop should have some type of fluid transfer apparatus to suck out the old fluid, and any decent mechanic would know that this is a situation where he needs to use such a device.
I agree lol... Time for a new shop
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      04-02-2014, 10:50 AM   #8
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Quote:
Originally Posted by Phil325i View Post
Really? Not what I've heard. Same fluids, just a BMW decision to euphemistically call several items on the car 'lifetime fill' to reduce servicing costs. They're already going back on this decision in some cases (e.g. engine oil change intervals).
Ever think that maybe the specs change in the material requirements and manufacturing processes of the diffs internals along with better chemistry of the gear oils, which allows longer fluid life intervals?

But really my point was the mechanic at the shop seems to be clueless.
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      04-02-2014, 11:27 AM   #9
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Quote:
Originally Posted by Efthreeoh View Post
Ever think that maybe the specs change in the material requirements and manufacturing processes of the diffs internals along with better chemistry of the gear oils, which allows longer fluid life intervals?
Sadly not only have lubricant specs not changed, but the internals of the diff have got worse. With the E9X 3 Series BMW changed to a very small pinion gear, no drain plug and an oil capacity under 0.5 U.S. quarts. Moreover, and most incredibly, BMW did away with the strong tapered roller bearing in favor of old-fashioned ball bearings. Worse, they are mounted in plastic bearing cages.

I rest my case...
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      04-02-2014, 12:55 PM   #10
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Quote:
Originally Posted by Phil325i View Post
Sadly not only have lubricant specs not changed, but the internals of the diff have got worse. With the E9X 3 Series BMW changed to a very small pinion gear, no drain plug and an oil capacity under 0.5 U.S. quarts. Moreover, and most incredibly, BMW did away with the strong tapered roller bearing in favor of old-fashioned ball bearings. Worse, they are mounted in plastic bearing cages.

I rest my case...
It wasn't my intent to get into BMW's lubrication requirements, but if you persist ...

The diff lube BMW specifies for my E30 and for my E90 are different, so something has changed regarding the specs. Secondly, the diff in my E30 (which I had since new) went 290,000 miles on the original diff (and if the car is still on the road somewhere maybe it's still on the original) and I followed BMW's "old school" maintenace schedule of fluid changes at 30K intervals. For my E90, I've followed BMW's new school maintenance schedule, which I believe calls for diff fluid changes at 100,000 mile intervals, and my current car has 245,000 miles on the original diff. I did change the diff oil early around 90K the first time, then at 185K, and I'm about to change it for the 3rd time (4th compliment of fluid). From what I can tell my diff is doing fine and is still quiet and noise-free (I just spun the rears and listened to it last weekend - the CVs are a bit noisey however).

I will postulate that BMW does not expect owners to service thier own cars these days, and eliminated the diff drain plug as a cost cutting measure with the understanding a professional shop will have the proper tools to extract the old fluid during a fluid swap (I do), which was my original point about the PO's choice in mechanics.

Peace.
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      04-02-2014, 06:23 PM   #11
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Quote:
Originally Posted by Efthreeoh
OP, if your mechanic doesn't understand how to change the rear diff fluid in your car, then take it to a different mechanic who does. Yup, BMWs used to have diff fluid drain plugs when the service interval was 30,000 miles, but fluid specs have changed. Regardless, any decent mechanics shop should have some type of fluid transfer apparatus to suck out the old fluid, and any decent mechanic would know that this is a situation where he needs to use such a device.
Wow. I would recommend finding another mechanic if he can't figure out how to replace your diff fluid.

On Bmw diff, you drain by suctioning it out of the fill hole then refill with fresh fluid.
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      04-02-2014, 07:09 PM   #12
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Thanks for the replys! I'm just going to do it myself. It seems like a pretty simple process.
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      04-02-2014, 10:00 PM   #13
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Quote:
Originally Posted by Phil325i View Post
Sadly not only have lubricant specs not changed, but the internals of the diff have got worse. With the E9X 3 Series BMW changed to a very small pinion gear, no drain plug and an oil capacity under 0.5 U.S. quarts. Moreover, and most incredibly, BMW did away with the strong tapered roller bearing in favor of old-fashioned ball bearings. Worse, they are mounted in plastic bearing cages.

I rest my case...
I was at work when I originally answered this so I didn't have much time.

So do you really know the engineering implications of not using a tapered roller bearing in this application? Ball bearings are not "old fashion", and tapered bearings have been around for, oh, about 110 years or so. The bearings inside the diff have low trust loading so tapered bearings are not necessarily the most cost efficient and low-friction solution, and perhaps a trained engineer, using the most recent material and lubrication technology available to him, knows better. And what is the issue with a "plastic" bearing cage? Do you know what that really means? What type of plastic is it? Delrin, Nylon, Teflon, Poly Ethylene, acetate, ABS? Depending on the design, the bearing cage has no structural significance to the operation of a ball bearing set. You don't know, but I'd bet the mechanical engineer at BMW does.

You read on the internet from Mike Miller that the diffs aren't built like the old ones (with plastic bearing cages! OMG!) and BMW just changed the lube specifications for no good reason; so it's gospel as spoken by Mike, the new diffs suck, and BMW doesn't care about diff longevity.

I know one person who has 245K on his.

Rant over.
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      04-02-2014, 10:04 PM   #14
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Quote:
Originally Posted by nick01234 View Post
Thanks for the replys! I'm just going to do it myself. It seems like a pretty simple process.
It is a simple process. Just make sure the car is level when you pull the fluid out and make sure you clean the diff and plug area really well before opening up the diff. And make sure you do not introduce any dirt into the diff when adding in the new oil. Dirt infiltration is the biggest issue here. It will destroy bearings; tapered, plastic caged, or not.
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      04-03-2014, 12:13 AM   #15
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its not bad to pump some out and refill at 70k miles right? already bought the fluid and pump also.
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      04-03-2014, 03:05 AM   #16
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Quote:
Originally Posted by Efthreeoh View Post
I was at work when I originally answered this so I didn't have much time.

So do you really know the engineering implications of not using a tapered roller bearing in this application? Ball bearings are not "old fashion", and tapered bearings have been around for, oh, about 110 years or so. The bearings inside the diff have low trust loading so tapered bearings are not necessarily the most cost efficient and low-friction solution, and perhaps a trained engineer, using the most recent material and lubrication technology available to him, knows better. And what is the issue with a "plastic" bearing cage? Do you know what that really means? What type of plastic is it? Delrin, Nylon, Teflon, Poly Ethylene, acetate, ABS? Depending on the design, the bearing cage has no structural significance to the operation of a ball bearing set. You don't know, but I'd bet the mechanical engineer at BMW does.

You read on the internet from Mike Miller that the diffs aren't built like the old ones (with plastic bearing cages! OMG!) and BMW just changed the lube specifications for no good reason; so it's gospel as spoken by Mike, the new diffs suck, and BMW doesn't care about diff longevity.

I know one person who has 245K on his.

Rant over.
Some 'peace' that was..!

My comments were probably influenced by the fact that my diff failed at 16,000 miles.
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Last edited by Phil325i; 04-03-2014 at 03:37 AM.
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      04-03-2014, 05:48 AM   #17
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Some 'peace' that was..!

My comments were probably influenced by the fact that my diff failed at 16,000 miles.
Which sounds more like a manufacturing defect or assembly error rather than a design flaw.
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      04-03-2014, 05:35 PM   #18
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Quote:
Originally Posted by Efthreeoh View Post
Which sounds more like a manufacturing defect or assembly error rather than a design flaw.
+1.

The "safety factors" (how much abuse something can take before it fails) built into these types of things have got to be quite high. Most failures of something like a diff would likely be due to defect in workmanship or material.
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