New E34 Touring mod - Rear Strut Tower Brace

[Mr Project]

Ok, one thing has always really bothered me about my Touring. Compared to a sedan, the Touring body is REALLY flexible. Between the 4 foot opening in the roof, and the huge opening in the back, there's just not enough structural rigidity to do the E34 chassis justice. With a lowered stiffened suspension, this problem is just amplified, especially in the rear.

Long-term, I want to do some seam-welding underneath the car and maybe in the back end of the interior as well. For the moment, though, there was one thing I thought would be worth trying: A rear strut tower brace.

Since I'm going with the local BMWCCA chapter next week to SD to enjoy some challenging mountain roads, I thought this would be a good opportunity to slap something together that might help.

One of the biggest (and most complicating) requirements I had was that it must be easily removable, and cannot impinge on cargo space. Having a semi-permanent bar would make having a Touring pointless for me, since I am CONSTANTLY hauling around junk that requires me to fold down the seats. So I needed a bar that would be stiff enough to hopefully have some effect, but be easily removed in just a few seconds.

Here's what I did.

My temporary metal shop set up in the driveway today (garage is under construction...a whole different story :) )
http://img105.imageshack.us/img105/6850/picture001smallye8.jpg

Some 3/16" plate steel I used to make the tower plates:
http://img105.imageshack.us/img105/4010/picture003smallfh1.jpg

You can see that I welded 2 sections together, then cut out the holes for the towers and drilled the holes for the strut mount bolts. Please forgive the shaky hand on the cuts, I will say that plasma cutters are my new favorite tool, but I have a lot to learn about making good-looking cuts with them. :)
http://img105.imageshack.us/img105/4899/picture004mediumuu3.jpg

Now, I had some tube stock that I cut down to make a smaller diameter...you'll see why in a moment. First I cut:
http://img503.imageshack.us/img503/4216/picture008mediumpf6.jpg

Then I pinched it down to the smaller diameter, welded it shut, ground it smooth, and got it to fit nicely inside the diameter of the regular tube stock.
http://img503.imageshack.us/img503/9929/picture007mediumli2.jpg

These smaller diameter tubes were welded to the plates, which can then slide into the larger-diameter tube stock as shown here (this is just tacked together)
http://img503.imageshack.us/img503/506/picture010mediumhd1.jpg

Then I drilled holes for quick-release pins to go through both the small and large diameter tube on each side like so:
http://img503.imageshack.us/img503/9131/picture014mediumae0.jpg

Next I cut the center bar in half and welded a bolt and washer to either side so that I could create a tensioning mechanism in the center of the bar. This enables me to shrink the bar down to install/remove it from the stubs, and then expand it to tighten it between the strut towers and remove any slop in the pins:
http://img220.imageshack.us/img220/8468/picture015mediumxu9.jpg


Here you can see what the plates look like installed with just the small diameter 'stubs' protruding into the cargo area (one of these stubs was cut down about an inch after the picture, so it's even less intrusive):
http://img503.imageshack.us/img503/723/picture011mediumcp0.jpg

And here with the bar installed:
http://img503.imageshack.us/img503/6716/picture016mediumhn3.jpg

I know, I'm not a great welder. And no, the center tension mechanism doesn't work real great. I need to re-work that a little, though it's already much better than pictured, as I came up with a better nut-washer arrangement.

So, how does it work? Well, I just ran out to dinner with my wife, and the car isn't fully re-assembled yet (plus I haven't really thrashed the car yet) but so far I'm impressed. Less squeaks, creaks, and rattles from the back end, and generally a more 'connected' feeling back there, especially over uneven and broken pavement...which pretty much all of it is here.

[E34N]

Great 'quick fix'... Somehow, I see a removable X-brace in the future.

[sfgearhead]

great idea, and an interesting concept. test concepts don't need to be pretty, just effective! i was also wondering recently how much the big holes in the tourings affected rigidity, but i've got a stock suspension and big 60 series tires so it's hard to tell.

i think if you can get a tighter fit between the different size tubes you'll get slightly better results, and even better results if you could triangulate with the floor. but i can't think how to pull that off easily at 10:30 at night.

i'm looking forward to seeing the concept develop further!

[Mr Project]

I agree, triangulating to the floor would be REALLY preferable. But I couldn't come up with an easily-removable way to do that either. :) At least not without making this a really, really complicated project.

[5271990]

Hows this thing at drifting :D
http://www.mturck.com/e34Touring/MPD472.jpg

Is the red bit stage 2 and the yellow bit stage 3 :D
http://render1.snapfish.com/render2/is=Yup6aQQ%7C%3Dup6RKKt%3Axxr%3D0-qpDP-WtlfRt7Pf7mrPfrj7t%3DzrRfDUX%3AeQaQxg%3Dr%3F87KR6x qpxQQoexa0axPoexv8uOc5xQQQJeJ0eeJlPoqpfVtB%3F*KUp7 BHSHqqy7XH6gX0QQP0%7CRup6lQQ%7C/of=50,590,442

[brosher]

Well it's not as sexy as a 350Z, but looks to be effective. Nice work!

[Mr Project]

5271990 - if I could do stage 3 and keep all the cargo pass-through, I'd do it in a heartbeat. :)

[sfgearhead]

hey mr project, i had another thought. the single pin on each side will a little movement fore aft or up-down. can you add a second pin 90 degrees out from the first, to lock down the second direction?

another thought i had was to add a clampon the end, much like a bicycle seat tube, to better clamp the two tubes together and prevent movement.

cheers,
ian

[Mr Project]

sfgearhead - good thought, but I really wanted to keep the 'stubs' as short as possible, and I wanted to use big 3/8" pins for strength, so there wasn't room for 2 pins on each side unless I was willing to give up another 2+ inches of cargo area intrusion...and I wasn't.

The best part about the center adjuster is that it takes up all of the slop introduced by the pins, but I do like the clamp-on idea. I'll have to think about that.

[atl530i]

Nice work.

[5271990]

How about? Depending on what works best a mechanism in the middle for adjusting the bar once on. But if the loops were big enough and the bar was exactly the right length the adjusting mechanism probably wouldn't be needed.

http://render1.snapfish.com/render2/is=Yup6aQQ%7C%3Dup6RKKt%3Axxr%3D0-qpDP-Wt0fRt7Pf7mrPfrj7t%3DzrRfDUX%3AeQaQxg%3Dr%3F87KR6x qpxQQoexa0axPoexv8uOc5xQQQJeJJaJGGe0qpfVtB%3F*KUp7 BHSHqqy7XH6gX0QQQn%7CRup6lQQ%7C/of=50,590,442

OT. Is the space between the rear struts the same as the front? Would an adjustable ebay front strut fit back there? I can't tilt my seats forward anyway :help

[slocar]

Rear strut bars really do work on wagons. I got one on my Subaru; it really does improve structural rigidity and help turn in a lot.

[Mr Project]

5271990 - not a bad idea, I don't see why a loop arrangement of some kind couldn't work. I think it would need an adjuster just because I don't think you could make it fit tight enough to help and still be able to install/remove it by hand.

I don't know about the strut width, but I'll tell you the bolt pattern of the strut mounts is quite a bit smaller in the back, so you'd need to build your own plates anyway.

[Elekta]

If you left your roof racks on, would that add anything at all in terms of stiffness?

[attack eagle]

Mr project

If you remove those two plastic covers you will have a large bolt under each you could use to triangulate same side to same side (Think K on it's side), and the cover will already be notched out for them. You could reuse the existing center tensioner idea.


Those are the ones I use for the third row's seatbelts.

[Antrieb]

Nice work Mr. Project. You are an e34 touring pioneer.

[Itsnotme1988]

Subscribed!

[5271990]

5271990 - not a bad idea, I don't see why a loop arrangement of some kind couldn't work. I think it would need an adjuster just because I don't think you could make it fit tight enough to help and still be able to install/remove it by hand.



In theory if it was exactly the right length it would just drop down onto the bolts. Its only under tension once you're cornering so could be removed the same way.

In reality you wont be using space age alloys so it would probably stretch and get stuck :stickoutt


http://www.bslaustralia.com/qstage/qstage.jpg

1st off you need something to bolt the bar to, welding a bar vertically is out the question as it would need to be welded to the flexible pillar.

Parallel clamping a bar to what you've got in there would work but I dunno....

Eureka...... back in 5 min

[Dark Helmet]

bump... I rode in the car yesterday.... holy moly.... HUGE difference!!!

[h2oplaydamian]

yo , bump for this old ass thread , i have been looking on ebay and i see a cheep rear strut bar for the sedan e34 , wont that work on the touring ? any one know the difference between the struts tops ,, should be the same ?

[Travis R]

I don't want to start another debate about naming conventions, and what's a "strut" and what isn't, but the fact remains that there are no lateral forces transmitted to the rear top mount, only verticle. Just FYI.

[Mr Project]

I don't want to start another debate about naming conventions, and what's a "strut" and what isn't, but the fact remains that there are no lateral forces transmitted to the rear top mount, only verticle. Just FYI.

You're focusing on the forces exerted by the 'strut' and missing the overall picture. It's just a convenient place to brace against the bending/twisting forces the body is subjected to in the rear. If you don't recognize that, you clearly haven't ever driven or looked at a sunroof-equipped E34 Touring...there's really very little structure back there.

I think a sedan bar might fit between the towers, but the Touring has those covers for the strut towers, so if you have to install the bar before putting the covers back on, you'd have to cut big 'slots' or something in the cover to fit them around the brace to reinstall.

[ShapeShifter]

Nice work dude!

Did you ever fix the nut washer in the middle?

[Travis R]

I wasn't really trying to criticize your work. As a chassis brace I'm sure it makes a difference, especially with the tensioner design you used. But like some others have mentioned an X brace would be even better.

[89BMW535i]

I hate those turtle looking 350Z's.

[Mr Project]

Nice work dude!

Did you ever fix the nut washer in the middle?

No, actually I sold the car, and gave him the brace too. I need to update my sig sometime....

[h2oplaydamian]

I hate those turtle looking 350Z's. OH YES << HE SAID IT AND I AGREE WITH HIM :buttrock

[DTMkid90]

loving it, now find out how to make one for a E34 sedan n i'd buy one


OH YES << HE SAID IT AND I AGREE WITH HIM :buttrock
My mom drive's a G35 ha its the same base and is really tiny

[h2oplaydamian]

i am sure some this can be made to be removed http://cgi.ebay.com/ebaymotors/BMW-E34-5-Series-REAR-Strut-Bar-Brace-L-K_W0QQcmdZViewItemQQ_trkparmsZ72Q3a1205Q7c66Q3a2Q7 c65Q3a12Q7c39Q3a1Q7c240Q3a1318Q7c301Q3a1Q7c293Q3a1 Q7c294Q3a50QQ_trksidZp3286Q2ec0Q2em14QQhashZitem20 0283975229QQitemZ200283975229QQptZMotorsQ5fCarQ5fT ruckQ5fPartsQ5fAccessories

[ShapeShifter]

OH YES << HE SAID IT AND I AGREE WITH HIM :buttrock


http://www.youtube.com/watch?v=CMNry4PE93Y

[Eemueekmu]

Any improvements on a similar/newer design? I know its been 5 years but this seems like it could help out a lot.
anyone? :)