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

[Mr Project]

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

[Mr Project]

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

[Mr Project]

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.

[repenttokyo]

it's a cool project - but if it breaks, while you are in the car, it could be very very dangerous - just keep that in mind.

[Jeff N.]

uh...why would it break?

[Mr Project]

I guess if I got t-boned by a train, having it break would be a concern...though not my primary one. It's not like I'm pre-loading it with thousands of pounds of force, so if the chassis really is moving enough to make it explode, I think I have other problems.

[repenttokyo]

uh...why would it break?

you've never seen a strut bar brake? in particular a home made strut bar?

[Mr Project]

I've never seen one break or brake. Though I have to admit, seeing someone brake with an STB would be cool. I admit my 2-piece unit would be more risky than a 1-piece, as a 1-piece should just bend...but either way, it's mild steel, not CF or something brittle.

[fin]

I'd be tempted to use some sort of mechanism similar to a chain load binder. As long as it is in compression, not tension.

If this is a initial piece that you are using to work out the bugs prior to the "show" piece, you may think about putting the nut/bolt on end of the bar and not the middle where you would want to minimize flex. And you could take it out by dropping only one seat out of the way.

I have taken out the screen roller thingy that sit in that same spot due to the amount of time that I was taking it in and out to haul things. I am curious how much it contributes to the rigidity of a touring? Did you think about building a brace that clips into and out of that position? Or is it too far from the struts to make a difference?

An Interested Touring Owner,

Fin

[Mr Project]

Fin, I'm curious about the 'chain load binder'. Can you describe that, or find a picture for me?

My screen roller thingy is attached to the back of the seats...is yours the same? I'm not sure how that would help rigidity any. At any rate, attaching anything to the fiberglass/carpet covers wouldn't gain you much, as you couldn't put much force on those.

This is just something I'm building for myself, not planning to market or 'show' it, really. I'm a form-follows-function guy myself. I do plan to improve on it, though, as I'm not really happy with the center 'tensioner' arrangement.

Initially, though, I'm really pleasantly surprised at how much of an improvement this makes. I was on some of the worst roads in town today, and out on the gravel roads to head to my parent's house. This made a world of difference..the car is much more solid feeling (and sounding) and more composed over the really nasty stuff that just felt unsettling before. Obviously all meaningless-butt-dyno stuff here, but I was skeptical this would make much of a difference, and I'm surprised at the extent to which it appears to help.

[leicesterboy15]

Sorry I can't add any technical knowledge but thats a great idea and very well executed for the initial attempt! How did you remove the rear carpet covers over the wheel arches? I have had the rear of the car apart and couldn't find any screws or clips for these sections at all.

[sneekens]

nice! did anyone try doing this on their e34 sedans??

[Mr Project]

It would be pretty redundant on a sedan, you guys have a nearly-solid steel panel between the strut towers anyway. :)

leicesterboy15 - The covers are a pain to remove, but they do come off. There are 2 screws behind the D-hooks, and 2 screws that go into the body at the top rear sections of each panel. Then you have to lift up the plastic top cover (couple screws to remove on that as well) just high enough to get clear of the side panel, and pull them off.

[BigKriss]

this must be the first e34 to ever have a rear strut bar - well the first one i'm aware of. it won't work in a sedan without cutting out the rear parcel shelf board.

Did you try a larger rear swaybar at the rear?

[sneekens]

It would be pretty redundant on a sedan, you guys have a nearly-solid steel panel between the strut towers anyway. :)


sir, is it as good or as rigid as a strut bar? im thinking if i should bother making one... if it won't make much of a difference then i guess ill leave it as it is... :D

[Mr Project]

IMO the sedan setup is WAY stronger than any little strut bar thing I could come up with.

Big Kriss, I have 25mm/19mm M5T bars already. These, combined with the Koni-Eibach combo and the 16" wheels, made the problem of structural rigidity much more evident...stiff suspension combined with an unstiff body.

[fin]

Mr. Project,

I am refering to the roll screen that sits behind the seats with the screen rolling back to the tailgate, not the ones that go up to the roof. I couldn't find it on realoem.com.

A load binder is the what is used with chains to lock down a load on truck beds. It overlocks after the chain is at it's tightest and in theory, shouldn't come undone without pulling the lever up.

http://www.cmindustrial.com/products/endproducts.asp?product_id=448

Also look at McMaster-Carr searching for Push-Pull toggle clamps. Ski boots/rollerblade latches work the same way. The pivot point of the lever goes past the hinge point so that the tension keeps the lever down.

If you get to the showpiece level, maybe ball joint attachments would work so you wouldn't have to worry about losing your attachment pins.

My Touring isn't anything special other than it has a 4.0 motor in it. Since it is red the kids and I go back and forth whether we should call it "Red Zepplin" or "The Killer Tomato". And being a farm boy that grew up with IH tractors, an IH sticker may appear on the back.

When I get my milling machine running in the garage, I need to fabricate roof rack pieces. I can't haul 4x8 sheets of plywood anymore.

My dad grew up south of Lincoln in Nuckolls County, Ruskin to be exact.

Cheers,

Ned

[bmwrp8]

sir, is it as good or as rigid as a strut bar? im thinking if i should bother making one... if it won't make much of a difference then i guess ill leave it as it is... :D

migs im working on a design right now with my uncle..i'll let you know asap.we're just trying to figure out how is the best way to fit it without damaging something. Its preety cramp in there. We've fitted a test strut at the rear already our only concern is our trunk space would be lessen.

[Mr Project]

Fin - Thanks, cool about your dad, it's a small world...not as small as Nuckolls county, population 5,057, though. :) I have to admit, I've lived here all my life and hadn't even heard of that county.

Interesting idea on the load binder. I'll have to look at TSC next time I'm out that way and see if they have something small I could adapt. I had thought about a snowboot-type binder as well, but couldn't find anything in metal locally and was in a hurry. I'll check out Mcmaster-carr.

Living here and in a 107-year-old project house, I have a 3/4 ton old farm truck for the 'real' hauling duties. Between the BMW, Corvairs, my wife's Saab, and my big old Ford F-250, my vehicles are a pretty eclectic mix for this part of the country. :)

[Ross]

No. I see no reason for concern.
Nice project. I'm curious to see if things are trying to flex around enough to cause wear at those hitch pins.