BMW 1-Series Forum (F20) 135i - 1Addicts.com > Second Generation 1 Series Forum > 2012 BMW 1-Series Sporthatch (F20) Discussion > F21 OE underbody rear brace retrofit onto F20
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      10-05-2015, 02:56 AM   #1
Bee Pee
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F21 OE underbody rear brace retrofit onto F20

3 dr cars have a much better bracing between mid ships to fwd rear subframe connections. Installed the hardware below this week on my 5dr.

1 x 33326797099
6 x 33326764505 (or 07119907189 longer bolts if using m3/4 spacer, part no. 33312284647)
1 x 33326793651
1 x 33326793652
2 x 33306793892
2 x 33326796225
2 x 33306861221

I didn't get any photos - here's an extract from an F30post showing key extra F32 parts being swapped out on f30. Similar to what I did on my F20.

http://f30.bimmerpost.com/forums/sho...78&postcount=7

Components to be installed


F30 underside - f20 very similar and brace plate across transmission tunnel will be removed


As will these parts be removed


And replaced with these on both sides


How it will look when I'm done

Also I will re-use the f8x alloy cross bar de Item # 2 in the attached realoem page. Part no. 33312284647 and the longer bolts as a spacer / stiffener.

http://www.realoem.com/bmw/showparts...81&hg=51&fg=80

Best way to describe impact is its like having upgraded bushings in the rear subframe and rear suspension arms.

Much less flex when putting the power down on straight or out of a corner. Car feels more stable and less squirmy. Especially as I'm running Jb4 stg2 with ~ 400/460 crank power and torque c/w LSD.

On my regular commute this morning, there's a roundabout with my exit having a tight left immediately after the exit. Road was wet due to rain and 2 different road surfaces - grippy on the r'bout and shiny on the road with the tight left at the exit.

Normally, with a firm squeeze on the throttle, I get a tad of "hip wriggle" as the car's rear axle makes the transition from grippy to shiny surface. That's gone now with F21 underbrace and M3 x brace spacer.

BP
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      10-05-2015, 03:48 AM   #2
ovekvam
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So that probably means that BMW regards the 5 door body significantly stiffer than the 3 door body, since they only reinforce the latter?
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      10-05-2015, 04:21 AM   #3
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Not necessarily. I think it's more to do with weight reduction to help keep 5dr m135i in the same emissions bracket as 3dr m135i.

It's noticeable in terms of rear subframe location is more rigid than it was before fitting.
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      10-05-2015, 05:37 AM   #4
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Quote:
Originally Posted by Bee Pee View Post
Not necessarily. I think it's more to do with weight reduction to help keep 5dr m135i in the same emissions bracket as 3dr m135i.
Looking back at the E30, the 2 door version had less torsional rigidity than the 4 door version, but was also 20 kg lighter.

For the E36, BMW added reinforcements to the 2 door car, so the weight was the same. Now the torsional rigidity was also similar.
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      10-05-2015, 05:54 AM   #5
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Maybe so. I drove a 3 dr and 5dr F2x back to back and felt 3dr was a bit more focussed than the 5dr.

All I can say is that with M135i with ~400/460 crank power/torque going thru my QLSD, this relative cheap mod, easy DIY bolt off and replace bolt on has my rear s/frame is now tied down a lot better with this OE brace than without it.
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      02-08-2016, 03:39 AM   #6
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I'm planning on installing these including the F8x spacer.

Did you DIY it or get it installed?

If former, did you tighten the bolts to the specs that you can share?
I'm struggling finding the tightening torque specs...
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      02-08-2016, 08:11 AM   #7
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PCF,

An easy DIY job - all bolt off and bolt back on.

As for torque settings - Numbers relate to the diagram at the bottom of this post

No 5 - 108Nm
No 6 - 47Nm + 45 deg
No 17 - 24Nm
No 18 - 100Nm + 90 deg



BP
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      02-08-2016, 03:26 PM   #8
pcfanta
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Quote:
Originally Posted by Bee Pee View Post
PCF,

An easy DIY job - all bolt off and bolt back on.

As for torque settings - Numbers relate to the diagram at the bottom of this post

No 5 - 108Nm
No 6 - 47Nm + 45 deg
No 17 - 24Nm
No 18 - 100Nm + 90 deg



BP
Thanks Bee Pee

By the way, how did you get the numbers? Is there any service manual available for download in the forums?
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      02-08-2016, 04:24 PM   #9
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I just got a quote from a local dealer and the numbers are as ridiculously inflated as they usually are in Australia.

Bee Pee, do you mind if I ask how much all the parts set you back?
Can you give me the contact details of the dealer/seller?
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      02-09-2016, 02:13 AM   #10
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How much was it from your dealer pcfanta?
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      02-09-2016, 02:35 AM   #11
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Quote:
Originally Posted by WAY View Post
How much was it from your dealer pcfanta?
AUD631 in total.
Also they don't have them in stock.

Honestly not 100% sure if this is a rip-off, but I heard OE parts are pretty cheap in EU and US even for beemers.
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      02-09-2016, 04:26 AM   #12
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Quote:
Originally Posted by pcfanta View Post
AUD631 in total.
Also they don't have them in stock.

Honestly not 100% sure if this is a rip-off, but I heard OE parts are pretty cheap in EU and US even for beemers.
Give Southern BM a call. They may be cheaper!
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      02-09-2016, 05:42 AM   #13
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Quote:
Originally Posted by pcfanta View Post
I just got a quote from a local dealer and the numbers are as ridiculously inflated as they usually are in Australia.

Bee Pee, do you mind if I ask how much all the parts set you back?
Can you give me the contact details of the dealer/seller?
PCF,

Total parts cost was about 160 GBP here in the UK.

Bought mine from Cotswold BMW - parts dept contact is Phil Ennis. Have used this guys a lot and Phil is a top bloke so he might be able to give your a good price shipped to Oz.

Contact CotswoldBMWMini user as they are a forum sponsor, check here:-

http://f80.bimmerpost.com/forums/member.php?u=294804

Also a sponsor on BabyBMW.net forum too

http://www.babybmw.net/forum/viewforum.php?f=49

BP
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      02-11-2016, 09:40 AM   #14
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Quote:
Originally Posted by pcfanta View Post
By the way, how did you get the numbers? Is there any service manual available for download in the forums?
From another forum, which were provided originally by CotswoldBMW

As far as workshop/service manual - see below from Bentley's website but its not FoC

http://www.bentleypublishers.com/bmw...ir-manual.html
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      05-18-2016, 11:15 PM   #15
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Quote:
Originally Posted by pcfanta View Post
AUD631 in total.
Also they don't have them in stock.

Honestly not 100% sure if this is a rip-off, but I heard OE parts are pretty cheap in EU and US even for beemers.
Hi pcfanta

Did you proceed with this mod? If so, from where did you source the parts and how much?

Regards

Hoss
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      05-19-2016, 02:58 AM   #16
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Hoss,

If not spotted already across on BB forum there's a good thread about the brace on M135i with lots of info and photos

http://www.babybmw.net/forum/viewtop...93&hilit=brace

You should also consider the OEM M4 front lower control arm upgrade....

http://www.babybmw.net/forum/viewtop...8&hilit=camber

BP
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      05-19-2016, 05:46 AM   #17
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Quote:
Originally Posted by Bee Pee View Post
Hoss,

If not spotted already across on BB forum there's a good thread about the brace on M135i with lots of info and photos

http://www.babybmw.net/forum/viewtop...93&hilit=brace

You should also consider the OEM M4 front lower control arm upgrade....

http://www.babybmw.net/forum/viewtop...8&hilit=camber

BP
Hi BP

Thanks for the links. Most helpful as I haven't done much investigation about the braces or the M4 front lower arm upgrade.

Ian
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      05-19-2016, 06:10 AM   #18
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Theres now folk that have added M4 tension struts to compliment their M4 LCAs....



More details in the thread below:-

http://www.2addicts.com/forums/showthread.php?t=1250352

It can be a cash pit !!!
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      05-19-2016, 06:19 PM   #19
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Thanks for the pics of the M tension rods. Very nicely machined spacers.

You're absolutely correct about modding cars being a cash pit, BP.
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      10-30-2016, 04:57 AM   #20
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Took the plunge and fitted the subframe braces. Works sweetness with the b8/eibach combo and ch-r 18ers . Good value for money this one. 184 euro in Greece VAT inclusive. Cheers!
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      10-30-2016, 12:51 PM   #21
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Price includes installation?
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      10-30-2016, 12:54 PM   #22
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Quote:
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Price includes installation?
150/200 and about hour labour
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