Z3 REAR DIFF MOUNT REPAIR !!

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Southernboy
Joined: Thu 07 Oct, 2010 12:39
Posts: 6436

  Z3 roadster 3.0i
Location: Johannesburg

Z3 REAR DIFF MOUNT REPAIR !!

Post by Southernboy »

Here's some very useful info for all Z3 owners.... (NON M CARS).
I have recently found 3 spotwelds in my boot have parted...so firstly read all the threads, researched the options, and 99% of the opinion was "Randy Forbes" repair Kit. ($. 460.00 +$. 460 shipping to S.A...+import duty and VAT = $. 1100.00 :shock: )
Fortunately some kind soul posted photo's of the RF kit, and the repair job...the main component being the Rogue Engineering dual ear rear diff cover.($.579.00 ex R. Eng no shipping incl).
The obvious benefit of dual mounting ears is that it anchors the diff both left and right to the sub-frame, and counters the twist of the motor on acceleration very very well.
The balance of the RF Kit are various metal strips,some angle iron to weld inside the boot to re-inforce the area above the subframe. Also new mountings for left and right under the car.
At that price...it's a NO GO for me...
I went up to my BMW mechanic, and chatted to him about it...eventually the issue of the dual ear diff cover seemed to be a "must have". He went into his BMW specs, and lo and behold...the e36 318,323,325 and 328 all have dual ear rear diff covers!!! Next he checked the par number for the paper gasket that fits between the cover and the diff housing...First he wrote down the e36 part number, then checked the Z3 gasket part number...Guess what...same part number!!! :D
That means, one can get a second hand e36 diff and use the rear cover..which fits perfectly to the Z3 diff..exactly the same bolt positions etc etc...and simply weld on a new mount on the opposite side of the diff to attach the "second ear"...
What a wonderfully cost effective solution....I have already aquired an e36 diff - dual ears..£100.00
The boot will still need welding / re-inforcing...but a huge saving !! :D :D
"Normal is overrated"
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pingu
Joined: Fri 30 Apr, 2004 16:01
Posts: 3412

  M roadster S50

Re: Z3 REAR DIFF MOUNT REPAIR !!

Post by pingu »

Failed boot welds

Check out the video to see another problem with the design (the ears are preloaded and pre-stress the crossmember).

I welded in a strengthening plate and added a washer between the bush and the rear lug to remove the pre-stress...

Repaired boot welds and strengthened diff "ear"

You can also use the patent pending :wink: special tool for fitting the diff bush...

Diff bush special tool
Pingu
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Southernboy
Joined: Thu 07 Oct, 2010 12:39
Posts: 6436

  Z3 roadster 3.0i
Location: Johannesburg

Re: Z3 REAR DIFF MOUNT REPAIR !!

Post by Southernboy »

Nice work mate...I did note the Randy Forbes Repair Kit did away completely with the OEM diff mount bracket. In fact they get cut off completely, and a 6mm thick single plate with a piece of angle iron welded to it to prevent the plate flexing, is then welde to the subframe / crossmember. In other words, whereas the OEM bracket has the diff ear fit between two plates, the RF only uses a single plate but substatially more robust.
The advantage of the dual ear rear cover is that one has a mounting point either side of the diff. The original one wants to pull downwades, but is now countered by it's opposite which restrains that movement because it's pushing upwards against the cross member, and the reverse on deceleration. It is undoubtedly a mod to prevent damage caused by the single ear on the OEM system, and the weakness of the spotwelds.
"Normal is overrated"
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Southernboy
Joined: Thu 07 Oct, 2010 12:39
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  Z3 roadster 3.0i
Location: Johannesburg

Re: Z3 REAR DIFF MOUNT REPAIR !!

Post by Southernboy »

I'll post some decent pics of the repair / upgrade to a dual ear cover as and when my mechanic can start. I've told him I want to photograph the procedure, so he's ready for the shoot too... :wink:
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Del
Joined: Sat 19 Nov, 2011 18:35
Posts: 2136

  Z3 roadster 1.9

Re: Z3 REAR DIFF MOUNT REPAIR !!

Post by Del »

Genuine query - is this mainly a Z3M problem (320 BHP powering through the back wheels) or are the smaller members of the range just as likely to develop the problem?
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Brian H
Joined: Tue 16 Dec, 2008 19:55
Posts: 2505

  Z3 roadster 3.0i

Re: Z3 REAR DIFF MOUNT REPAIR !!

Post by Brian H »

Del wrote:Genuine query - is this mainly a Z3M problem (320 BHP powering through the back wheels) or are the smaller members of the range just as likely to develop the problem?
Del,

This problem is throughout all the range of Zeds, the later Zeds have extra weld/s in the boot area but this did not stop the problem.

Ask me how I know :head:, 2 Zeds, 2 failures :head: :head:

Cheers

Brian
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Southernboy
Joined: Thu 07 Oct, 2010 12:39
Posts: 6436

  Z3 roadster 3.0i
Location: Johannesburg

Re: Z3 REAR DIFF MOUNT REPAIR !!

Post by Southernboy »

The issue is not with the Z's. The same applies to all the M3's and began in the 80's with the 5 series and 3 series...One would have thought BMW might have sorted it by now. :head:
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Sp1key
Joined: Wed 01 Feb, 2012 18:06
Posts: 124

  Z4 coupe 3.0si
Location: Bath

Re: Z3 REAR DIFF MOUNT REPAIR !!

Post by Sp1key »

Question - I have no access to ramps or getting the car up in the air to look under so the only time I get this view is at MOT time which has just been done

If you have this problem is it an MOT failure or will it pass with this being there.

How do you tell you have it from driving the car?
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Southernboy
Joined: Thu 07 Oct, 2010 12:39
Posts: 6436

  Z3 roadster 3.0i
Location: Johannesburg

Re: Z3 REAR DIFF MOUNT REPAIR !!

Post by Southernboy »

First place to look is in the boot. Lift out the boot floor carpet...look at the rear left, about 120 - 150mm from the back, you will see the spot welds. If they have come adrift, you will see rusty looking spots where they are. You can lift the left hand hand side trim, and look under there too. If they have come adrift, it's then a question of how far gone the damage is. To determine that, you would need to raise the car and get under to examine the same area as you did from the boot, and surrounding areas including the bracket that the diff ear fits between. Also examine the crossmember that the diff bracket is welded to. Look for cracks, loose welded joints etc. You wouldn't notice too much while driving until the diff mount becomes seriously loose, at which point you may find the propshaft moving out of center and causing vibrations etc. The sooner you examine it the better, and even if you don't see any damage, it's worth keeping your eye on it regularly.
Sometimes on looking at the spot welds in the boot, you will not see any damage...but it may be hidden under the paint. If the paint is cracked at those spot welds in the boot, it is likely the welds have yielded.
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Sp1key
Joined: Wed 01 Feb, 2012 18:06
Posts: 124

  Z4 coupe 3.0si
Location: Bath

Re: Z3 REAR DIFF MOUNT REPAIR !!

Post by Sp1key »

Thanks that's useful - I will need to have a good look :|
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Brian H
Joined: Tue 16 Dec, 2008 19:55
Posts: 2505

  Z3 roadster 3.0i

Re: Z3 REAR DIFF MOUNT REPAIR !!

Post by Brian H »

Sp1key wrote:Question - I have no access to ramps or getting the car up in the air to look under so the only time I get this view is at MOT time which has just been done

If you have this problem is it an MOT failure or will it pass with this being there.

How do you tell you have it from driving the car?
Sp1Key

A pic from Pingu's thread above for reference.

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Welds 6,7,8,9 & 10 are the obvious ones to look for.
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Southernboy
Joined: Thu 07 Oct, 2010 12:39
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  Z3 roadster 3.0i
Location: Johannesburg

Re: Z3 REAR DIFF MOUNT REPAIR !!

Post by Southernboy »

Some really good news today...The seller of the Dual eared e36 Diff I bought accepted £ 20.00 for the rear cover only...he'll sell the gears etc separately...£80 saving!!! now I'm seriously stoked!! :D :D
Pics of the repair coming up soon...
"Normal is overrated"
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Sp1key
Joined: Wed 01 Feb, 2012 18:06
Posts: 124

  Z4 coupe 3.0si
Location: Bath

Re: Z3 REAR DIFF MOUNT REPAIR !!

Post by Sp1key »

Brian

Thanks for the pic - it looks so innocent you wouldn't think it was hiding a problem

Anyway checked mine and they look sound :-)
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