DID YOU KNOW....diff noise revelation!!!

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Southernboy
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DID YOU KNOW....diff noise revelation!!!

Post by Southernboy » Tue 17 Dec, 2013 05:51

Whilst visiting my local BMW dealer on an unrelated matter, I got chatting to one of the senior workshop guys on the subject of the "noisy diff" syndrome which seems to plague many BMW's. I was told that BMW often have this as a complaint, and that they had noticed the total lack of complaints on the subject by owners of certain models in spite of the fact that those were built using the same components / diff type etc.... with one exception.
In the diagram below, Item # 1 is essentially the diff carrier / axle carrier, on those BMW models where no complaints are ever received regarding diff noise, this item is filled with very fine metal "shot". The appearance of this is akin to minute balls of iron of aprox 1mm diameter. In those cars where this carrier has been filled, the purpose is to add weight to the rear of the car (aprox 30kg). All these axle / diff carriers have access holes and on those that have been filled they are then plugged using rubber bung s to keep the shot inside. A consequence of this filling is it cancels and "resonance / amplification" of the diff noise. Whta they do with cars coming in where complaints are logged about diff noise is to use a high density expanding foam which is pumped into the axle carrier effectively filling it and achieving the sane result as the shot, but without the excessive weight. Obviously, the holes don't need plugging as with the metal shot filling. According to BMW it has the desired effect, and effectively reduces / silences the resonating amplification. To apply this stuff, which comes in a pressurised canister and can be bought from your local builders supply, it is necessary to raise the car, and using a suitable jack etc, onbolt and lower the diff. On the inner side of the diff carrier area, there are 25mm D access holes into which the foam can be pumped until it begins to ooze out of various other apertures in the axle carrier as it expands. Once dry the excess can be trimmed away with a blade / sanded and painted over if preferred. Den Braven seems to be their product brand of choice, as it seems they supply a high density type expanding foam usually specitied for use in sealing metal tubing by filling it. It was demonstrated to me by the workshop man where he used a spanner to tap a filled and unfilled axle carrier.... the unfilled one undoubtedly ad a "ring" to it whereas the filled one was simply a dull "thud".
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Joycey
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Re: DID YOU KNOW....diff noise revelation!!!

Post by Joycey » Tue 17 Dec, 2013 07:37

Very intresting, My Zed has suffered this noise all the years i have owned it. I have a new Guibo to fit but still havent got round to fitting it.

I will bare this in mind.

Joycey
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Southernboy
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Re: DID YOU KNOW....diff noise revelation!!!

Post by Southernboy » Tue 17 Dec, 2013 08:57

I just popped past the Den Braven offices which are a few miles away from me...good excuse for some top down driving....they sell a can of the stuff for £10.00 here, so basiccally it would cost that to do the filling...I'm sure the cost there will be about the same or less... :wink:
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Boysie
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Re: DID YOU KNOW....diff noise revelation!!!

Post by Boysie » Tue 17 Dec, 2013 10:40

Joycey wrote:Very intresting, My Zed has suffered this noise all the years i have owned it. I have a new Guibo to fit but still havent got round to fitting it.
Showing my ignorance
I just goggled Guibo thinking whats that :dunce:
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Del
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Re: DID YOU KNOW....diff noise revelation!!!

Post by Del » Tue 17 Dec, 2013 10:41

I like to imagine I'm in a high performance track car with "straight cut" as opposed to helical gears. I find my mind wanders a lot these days :D

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Southernboy
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Re: DID YOU KNOW....diff noise revelation!!!

Post by Southernboy » Tue 17 Dec, 2013 10:47

....whatever "Guibo" blows your hair mate - straight cut or helical..... :roflmao:

(correct spelling - "GIUBO"..... :wink: )
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Boysie
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Re: DID YOU KNOW....diff noise revelation!!!

Post by Boysie » Tue 17 Dec, 2013 13:59

Taken from Wikipedia

A giubo (/ˈdʒuːboʊ/ JEW-boh; etymology: Giunti Boschi), also known as a flex disc,[1]
and sometimes misspelled as guibo
Ray

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Southernboy
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Re: DID YOU KNOW....diff noise revelation!!!

Post by Southernboy » Tue 17 Dec, 2013 14:54

It isn't PC to say Jew - Boh !! You'll have the Israeli SS after you.... :roflmao:
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DanHolman
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Re: DID YOU KNOW....diff noise revelation!!!

Post by DanHolman » Tue 12 Jul, 2016 17:16

very interesting, Ill look into this.
Last edited by DanHolman on Fri 15 Jul, 2016 17:41, edited 1 time in total.

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Southernboy
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Re: DID YOU KNOW....diff noise revelation!!!

Post by Southernboy » Tue 12 Jul, 2016 17:29

I would say you need to use a high density foam with properties which will not succumb to damp or absorb it in any way. The Den Braven products are excellent. If you google Den Braven, and have a look through the many options they market, you will find the right / best stuff. Oddly, it's recommended that the surface of the containing shape be wetted with water. Apparently it allows the foam to move quickly throughout the area before expanding and creating blocks. I would say a good jet of water sprayed inside the axle carrier will do the trick, and probably best with a lower vs high temperature day to ensure there is no evaporation whilst doing the job.
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Brian H
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Re: DID YOU KNOW....diff noise revelation!!!

Post by Brian H » Tue 12 Jul, 2016 18:17

Great info SB :thumb:

Vic-Z3
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Re: DID YOU KNOW....diff noise revelation!!!

Post by Vic-Z3 » Tue 12 Jul, 2016 19:02

----------------- BMW Z3 Das Beste Auto -----------------

Mein altes Auto riecht nach Nudeln, hat dieses Auto eine Wurst Geruch.

handsomejackuk
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Re: DID YOU KNOW....diff noise revelation!!!

Post by handsomejackuk » Wed 13 Jul, 2016 00:13

i notice a very slight noise on my diff but seems to quieten after a few miles... would this be needing attention.. maybe a change of oil ?

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Southernboy
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Re: DID YOU KNOW....diff noise revelation!!!

Post by Southernboy » Wed 13 Jul, 2016 06:58

If it's a "hum or whine" consider it common and perhaps even normal. The diff oil in these cars is classified as "lifetime". It begs the question if it's the lifetime of the oil, the diff or the driver... If it has never been changed since factory, I would say it would likely be beneficial to renew it - it certainly won't do any harm. :wink:
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EarlLeeBird
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Re: DID YOU KNOW....diff noise revelation!!!

Post by EarlLeeBird » Sat 25 Feb, 2017 19:57

Hey guys, it is an old topic but just to point your attention to one maybe important fact - BMW is not using just any foam there and its purpose is not sound isolation. Sound isolation from diff whine is just a positive side effect. They are using a very special structural foam that is actually a light weight epoxy resin/glue with a purpose of strengthening the sub frame in critical rear dif attachment areas.

Spraying some random foam in there that has maybe too extreme expanding characteristics could possibly result in a faster sub frame tearing issue and Z3 is known to be very vulnerable for this. Not to mention the risk of flammability when it is later needed to weld on some reinforcement plates.
Here is a sample video of a wrong foam used and what problems it could cause, it is not of a Z3 but most BMW's are affected from same problem anyway: https://www.youtube.com/watch?v=Mz-heUBPyxY

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Southernboy
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Re: DID YOU KNOW....diff noise revelation!!!

Post by Southernboy » Sun 26 Feb, 2017 06:47

I think you're confused..... The foam is filled into the tube like carrier which extends on each side of the diff. What you're seeing on the video is someone having put foam into the body structure above in an effort to support a weak structure.
The post above is referring to item 1 in the graphic below. The arms either side of the diff carrier housing are hollow. On M version cars, these are filled with a heavy metal "gravel" to add weight to the rear axle and provide better traction. That gravel has a side effect of reducing diff whine which would otherwise be able to resonate in those hollow arms. By using a suitable expanding foam in those arms on non M cars, it results in less diff noise. If you get under your car and have a look, you will easily determine that the axle carrier is bolted at the ends of the vehicle as you can see in the graphic. The diff itself and it's mountings to the underside of the boot / bodywork is where the weak link is. This is generally caused by there being only one diff mount from the rear diff cover to the body. Later diffs had a dual ear configuration - one each side which strengthened the structure, but in some cases did not exclude the destruction on the mountings to the body. What was / is actually required to prevent the problem is a strengthening of the weld to the body and the body itself. Filling the axle carrier with foam obviously needs a dense foam to provide the best sound dampening properties.
Finally, BMW do not use any foam in the axle carrier, but do it as in response to customer complaints about diff noise.

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EarlLeeBird
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Re: DID YOU KNOW....diff noise revelation!!!

Post by EarlLeeBird » Sun 26 Feb, 2017 12:23

OK, thanks, this is more clear now when I see the picture :)

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