Diff Rubber Mount

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Lancsbob
Joined: Fri 15 Aug, 2014 17:35
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Location: Ormskirk

Diff Rubber Mount

Post by Lancsbob » Sun 03 Jul, 2016 14:49

Been investigating the clunk noise when changing gear.
Does this diff mounting look collapsed or is it just the
weight of diff compressing it.
Difficult to get a decent picture lying on my back.

Image

Image

Also checked the wheel rotational play & found 1/2" turn without half shaft turning. Is this normal?
Looking like a rear end rebuild.... :(

Cheers Bob

Axelf
Joined: Wed 27 Apr, 2016 07:33
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Re: Diff Rubber Mount

Post by Axelf » Sun 03 Jul, 2016 16:59

Yes looks a bit like mine , I am changing mine to polyflex this week

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Brian H
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  Z3 roadster 3.0i

Re: Diff Rubber Mount

Post by Brian H » Sun 03 Jul, 2016 17:11

Your rear diff mount has seen better days, replacing would not go a miss however you will chase this clunk forever, have a search on here and you will see what I mean. Your car is getting on so refreshing the rear bushes etc will help matter but it will not cure it, call it a characteristic!

Axelf
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Re: Diff Rubber Mount

Post by Axelf » Sun 03 Jul, 2016 17:19

Yes another thing to check is the top mounts on the rear shockers as these make a hell of a clunk when the rubber is goosed .. I found out the hard way , buy expensive pay once buy cheap pay twice :)

Lancsbob
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Re: Diff Rubber Mount

Post by Lancsbob » Sun 03 Jul, 2016 18:10

Axelf wrote:Yes looks a bit like mine , I am changing mine to polyflex this week
I worry that polyflex may trasfere too much stress to the boot floor resulting
in the dreaded spot weld/mount failure. :?

Do you have to remove the diff to replace mounting?

Bob

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lightning
Joined: Tue 27 Nov, 2007 08:15
Posts: 814

  Z3 roadster 3.0i
Location: Stockport

Re: Diff Rubber Mount

Post by lightning » Sun 03 Jul, 2016 20:35

Take the tool tray out of the boot (one nut, can be removed with the spanner in the tool kit!)

Have a look at the line of spot welds running left to right under the tool tray, if any have pulled out or are cracked then you need a repair.

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BladeRunner919
Joined: Fri 17 Feb, 2012 20:18
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  Z3 roadster 1.9

Re: Diff Rubber Mount

Post by BladeRunner919 » Sun 03 Jul, 2016 21:35

The advice from the guru of rear subframes, Randy Forbes, is that the diffmount is the only one that should always have an oem replacement and that a polybush here contributes to the potential for subframe mount damage. You would be very foolish to ignore what Randy says!

Del
Joined: Sat 19 Nov, 2011 18:35
Posts: 2115

  Z3 roadster 1.9

Re: Diff Rubber Mount

Post by Del » Sun 03 Jul, 2016 21:41

I’m not generally in favour of boy racer modifications which have their origin in proper track-only cars but I must admit that I am a convert to the Powerflex (purple) polyurethane bushes. They are super quality and come with beautifully machined, heavy duty stainless steel fittings – they have a “lifetime” guarantee. I’ve examined them closely and manipulated them by hand and they are not that different from the OE Lemforder rubber bushes. I’ve fitted them on the front, the diff bush and the two main rear sub-frame bushes.

There are some cheaper, unbranded polyurethane bushes around which I would personally avoid. The super-hard, racetrack bushes made by Powerflex are (black not purple) and are unsuitable for normal road use.

They are relatively easy to fit in situ – no machine shop press is required. You need to cut out the old rubber bush and then carefully cut out the metal ring surrounding the bush and which kept it in place. Replacement of the poly bush is easy and lubrication is supplied. If you are doing the diff, it needs to be firmly supported whilst you do the job.

Thumbs up from me for Powerflex purple for the DIYer. :thumb:

Axelf
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Re: Diff Rubber Mount

Post by Axelf » Sun 03 Jul, 2016 22:17

Del that's great news... I am thinking like you if it's not the black track version I should be ok ... I lowered the car and the top mounts were goosed so replaced them with OEM .. They lasted 2 weeks and they were pushed out so replaced with polyflex and they are so much better

siwilson
Joined: Fri 19 Jun, 2009 10:54
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  M roadster S54
Location: Horley

Re: Diff Rubber Mount

Post by siwilson » Mon 04 Jul, 2016 08:53

The clunk you are referring to is also known as "driveline slack" and sadly a characteristic of these cars even when nothing is 'broken'. If you suspect that diff bush then have a really careful look at the mount to make sure its not cracked. A bad bush will allow the diff to twist and put extra stress on the mount and boot floor. Although it looks old I can't see any failure there form those pics. When and if you do replace I would absolutely go for OEM and NOT poly. Poly are great for most places, but the diff bust and trailing arms are places to keep stock.

Another place to check is the rubber flex coupling on the driveshaft and also the gearbox mounts. Both can contribute to the clunk and if original will be well past their best before date. The flex coupling especially.
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Antm72
Joined: Fri 01 May, 2015 14:53
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  Z3 roadster 2.8

Re: Diff Rubber Mount

Post by Antm72 » Mon 04 Jul, 2016 12:38

I replaced mine with the diff in place , the clunk is gone on mine you could clearly see the diff sagged in the mount a damaged oem bush is more likely to cause more issue to the mount than the poly bush.
The flex in the bush can cause issue to the mount as it jars the mount as the bush moves.
Remove the flex and its improved ..the difference in mind was night and day and worth every penny
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siwilson
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  M roadster S54
Location: Horley

Re: Diff Rubber Mount

Post by siwilson » Mon 04 Jul, 2016 13:06

Antm72 wrote:I replaced mine with the diff in place , the clunk is gone on mine you could clearly see the diff sagged in the mount a damaged oem bush is more likely to cause more issue to the mount than the poly bush.
The flex in the bush can cause issue to the mount as it jars the mount as the bush moves.
Remove the flex and its improved ..the difference in mind was night and day and worth every penny
Sorry, have to disagree. with most of this. For sure a bad bush that allows too much movement will put extra stress on the mount. However, a good standard bush will damp and absorb some of the movement. That is what it is designed to do. Replace this with a more solid Poly bush and much more of the energy will be transferred to the mount and boot floor where we don't want it. If the energy is transferred to the boot floor it will flex more and this is what contributes to failure. IMO don't do it.
2001 M roadster S54 Laguna Seca Blue

Antm72
Joined: Fri 01 May, 2015 14:53
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  Z3 roadster 2.8

Re: Diff Rubber Mount

Post by Antm72 » Mon 04 Jul, 2016 23:57

But then having done it and had no adverse effect except improvement i fail to see the argument? A knacked bush replaced with anything is an improvement its choice its has transformed my car and far cheaper and easier than replacing with oem.
The subframe damage is usually due to excess movement in a bush as the torque kicks causing excessive movement and damage.
The bushes are by design to tighten things up if you have fitted one and it hs damged the floor please show me .
As said i have fitted on as have many others with a similar view and my boot floor is fine and my drive train clunk has gone..
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bertiejaffa
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  M roadster S50
Location: Manchester

Re: Diff Rubber Mount

Post by bertiejaffa » Tue 05 Jul, 2016 02:05

2p worth - if the bush looks goosed (which that does) replace it - after all it can't do any harm. Knocks on these cars are normal, mine is 18 year old, been raced by Tiff Needell, fully fixed by BMW, fully invoiced b previous owners (not solely on the diff) in a folder till they come out of my ears, etc etc etc

However when I turn into my estate which is new so humps are standard, I have to knock it into neutral and let it coast over them to spare my bumper and my diff knocks in time with the speed of the rear wheels... 3 years ago when I bought the car I was beside myself with fear because of the knocking .... 3 years and 20000 (aggressive) miles further on I giggle knowing the car is mint. Change the gearbox and diff oil and if needed drop the box and refurbish the pins but I suggest you do this when you have a new clutch
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Lancsbob
Joined: Fri 15 Aug, 2014 17:35
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Location: Ormskirk

Re: Diff Rubber Mount

Post by Lancsbob » Tue 05 Jul, 2016 07:20

Thanks all for your input, have now ordered a OEM bush. Everone has their own
opinions on these matters same as the tramlining problem which i still have,
whatever works for you i suppose.

Cheers Bob

Del
Joined: Sat 19 Nov, 2011 18:35
Posts: 2115

  Z3 roadster 1.9

Re: Diff Rubber Mount

Post by Del » Tue 05 Jul, 2016 07:22

The Powerflex (purple) replacement bushes are not that rigid and stiff - I have examined them very closely. I would say very similar to a new OE bush. Obviously, the very old, sloppy and broken OE bushes on these old Z3s (some now 19 years old) will be causing all sorts of undesirable movement and vibration.

Whilst I've seen one member on this site say that he had a problem with the "boot welds" on his 1.9, the problem is overwhelmingly reported as an issue with the bigger engine cars - particularly the Z3ms. It is also a problem with the E46 M3s.

The only aftermarket part issue I have seen causing welds to weaken, reported here and in the US, is up-rated anti-roll-bars ripping their fixing points.

NZ00Z3
Joined: Thu 23 Jun, 2016 02:26
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  Z3 roadster 3.0i

Re: Diff Rubber Mount

Post by NZ00Z3 » Wed 06 Jul, 2016 01:15

Hi

Can I throw in another possible cause for your clunk when changing gears? It's your clutch slave cylinder flexible line.

I have had a similar clunk when changing gears in my 2.0 L manual Z3. Have bushings arriving this week for the diff, sub-frame and trailing arms plus a new Giubo. Currently running the original parts and had ordered the new ones to try and eliminate the suspension rattles and gear changing clunks.

Last weeks project was to replace the old rubber slave cylinder line with a new stainless steel braided one. The symptoms that I was having was stiff gear changes and a shuddering clutch. Diagnosis was that the clutch was not fully disengaging and was being caused by the old rubber slave cylinder line expanding at around the same pressure that it took to disengage the clutch. In other words, the fluid volume that was needed to fully disengage the clutch was being used to expand the rubber line.

New line installed and system bled. Resulted in smooth gear changes, shuddering all but gone (only for steep hill starts) and the gear change clunk in the diff has gone.

Hope this helps

Regards

Muzz

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