We all know that this is one of the weak links in the 700 series and I consider myself lucky that mine is still intact ... for now.

Matt and I have had several conversations around this part and affordable upgrade options. Over the COLD winter I would like to play with some unorthodox ideas, but to do this I need a good subframe as a template.

I know "PnP" but I am old and crawling around hurts and one can always hope

Here is my ghetto lazy solution:

Chop the middle out of one subframe. I did it with a big recip saw (sawzall?) and just made it so that the "walls" on each side were all that remained. Sand blast both. Weld the two sides of the one you chopped the middle out of to each side of your existing sub-frame. Paint or powder coat to finish it off. I also reinforced the parts at the back where it joins the chassis, as they bend where they join the subframe. That was sufficient for me to stop bending them.

Torque rods with stiffer poly bushings would be welcome. 740s feel really vague and squishy/squirmy to me when you really hammer them, and all that flex often helps distort the actual torque rods themselves. On the flip side, the OE torque rod bushings are extremely large and pliable, which is great for sound and vibration damping. I did find a poly 240 bushing that fit a couple of the bushings that go between the subframe and chassis. I'd be willing to make all that stiffer for the sake of better feel and strength, personally.

I have a sneaking suspicion that the adjustable torque rods that IPD sells for 240s would work from some preliminary research. I never got to try that theory.

Considerations:
On a stock 740, one of the exhaust hangers for the front muffler is attached to that thing. This may or may not be an issue for you. My 945T lacks a front muffler, so the slight encroachment inward on the front muffler cavity (you've just made the subframe "walls" double thick afterall) there was completely a non-issue, and the cavity is large (compared to a 240 especially). The hanger did have to be revised a bit, and I have absolutely no idea how the exhaust on your V8 car runs, so that may or may not be a problem.

I can say that my 3" mandrel bent over axle MVP exhaust still fits fine though.

Further, it isn't the most light weight or elegant solution. It works great, is very easy to make, and quite stong, but it is about as heavy as a field plow. I could justify the weight due to its location. It very low on the car, about as far back as possible whilst being within the wheelbase, toward the passenger side, and sprung.

Pulling them in the JY is no fun at all because the parking brake cable runs right through the middle of the subframe as I stare at Mom's 90 744ti on the rack (been a while since I pulled one). With very strong cutters, slicing the parking brake cable might be an option. I haven't had that option in the past, or haven't gotten smart enough to remove them quickly and cleanly.

I wish I had some picts of the "plow" as I call it, but once you pull one, you should see exactly what I mean.

Hope that helps.
-James

Sheesh James. Could you expound a little? You and your Readers Digest posts...

Thanks James, definitely one very good solution ... but I am considering a totally different approach. Not even keeping the stock configuration, just the stock (or somewhat stock) mounting points.

I am not concerned with weight (if this adds a pound or two not a big deal), it does not have to have the same look or configuration nor any mounting locations for muffler hangers, etc., it does not have to use the same torque rods (but if these are replaced, appropriate length and strength would be needed). James I love your idea of using the 240 torque rods ... more to add to the idea jar.

All I have to do is make sure the subframe allows for axle movement and clears existing components like the gas tank. Mufflers, exhaust pipe, brake cables, etc., can all be addressed later. One of my questions is why the subframe has to flair or has "bent" sides? Making the sides straight, either parallel or angled (converging) would reduce stress risers. I am sure the original design included measures for crumple protection in the case of a rear end collision, but did this compromise the strength???
If you can picture my train of thought the solution would be simple, strong, but definitely not a bolt in replacement in that modifications' would be required to the exhaust, etc (not a big deal in my case but would be for most who would prefer a simple bolt in solution.
Not sure at all if my idea is feasible or will work, but I do need a subframe as a rough template, so if anyone comes across one .... THANKS

p.s. keep your solutions coming, the more info

I'd love to assist, but I've got no idea what a 7XX series car subframe looks like. Send some photo's and I'll put it in the creative cue.

Here is a thread with some methods of strengthening
http://forums.turbobricks.com/showthrea ... t=subframe

or the EXPENSIVE fix
http://www.kaplhenke.com/index.php?opti ... &Itemid=34
which also needs these
http://www.kaplhenke.com/index.php?opti ... &Itemid=34

What's it look like mounted to the car or axle? Where do they break?

"click for additional pictures"
http://www.kaplhenke.com/images/700subframe/

Thanks...I missed that in all the triangle nonsense. Now it makes more sense. Now that I've seen it, I've got an idea (sure it isn't original). From a design perspective, you are wanting to keep the three factory mounting points and the mounts for the torque rods. Knowing nothing about the design, I'm guessing that aside from controlling the fore/aft movement of the rear axle, the sub frame seeks to isolate drive train noise from the cabin of the car.

Not that I'm suspicious of the triangle man, but there other ways of achieving the strength without needing to go water jet a bunch of plates then spend hours welding them all together. I would do this job with tube. It is inherently stronger than plate and has the added advantage of being less prone to rust over the long haul.

You would have to get some attachment plates plasma cut (or water jet) that would serve as bulkheads at the rear (where it looks like it bolts up to a rear cross beam...no doubt with rubber bushings). Then join the tubes to the flat parts by filleting the tubes. This is the sort of metal joinery that keeps planes in the air and is much simpler and stronger than sheet steel. Have a look here

http://books.google.com/books?id=cNpkIDQPPQ8C&pg=PA59&lpg=PA59&dq=airplane+repair+certification+cluster&source=web&ots=MjIw_wF7L4&sig=N-AdSjrkN34ADKVydOz_dVBarU8&hl=en&sa=X&oi=book_result&resnum=7&ct=result#PPA59,M1

If this link doesn't work google performance welding coupon or aircraft certification cluster. You'll note that the engine mounts shown on page 60 of this book shows what I'm thinking about.

No need to TIG this sort of thing (as only Andy has one, the one at school still hasn't been fired up), but any decent welder could fabricate up a rear subframe that could handle all the power the Volvord is going to throw at it. [/url]

I've got an IPD 240 torque rod right here, and a measuing tape to give you some rough measurements.

Full length is 17 5/8". That is full extended. You'll want atleast 3/4" more in the threaded nut minimum I would guess.

Shortest useable length is 15 7/8". Bolt hole to hole.

Width of bushing is 2" side to side.

Just thought I'd throw those in for you

Jordan

You are welcome to use my plasma cutter and tig if you'd like. I have to get a bottle for it but i'll worry about that when I return from my trip. We just picked up a new welder at work too, a millermatic 212 which has sexy written all over it too.

The subframe doesn't control fore-aft movement of the axle - that's the job of the trailing arms. The subframe's bushings are designed so that the whole subframe can slide fore-aft - in fact, that's necessary. The job of the subframe is to control axle torque, and that's it's only job.

Ben's plates are laser or water jet cut because they're designed to be jigsaw'd together. Tab A into slot B. That way he doesn't have to jig or measure or anything - they just press together and weld. That's why he does it that way. He designes them and then simulates loads using a finite element analysis program to ensure their strength. I believe they're chromoly as well, necessitating the TIG. Building a single one is probably much easier using tube mild steel, but for a mass produced piece I have to say I like his design.

The upper torque rod is much shorter than the lower one, and I'm pretty sure the IPD 240 torque rod doesn't have THAT much adjustment built in. You would have to cut and re-weld, I think. I'm pretty sure the 240 torque rod bushing is wider than the front bushing of the 740 torque rods, and I think the 740 uses a 14mm bolt on the rear bushings, larger than the 12mm of the 240 bushing. I could be wrong there.

Like Craig suggests, I'd build one out of tube steel and work around the obstacles. One major obstacle is the rear axle, which would come into contact with a straight piece of steel - this is why Ben's frame has a notch on the axle side portion.

Honestly, a properly reinforced stock piece is probably more than strong enough, and if you build adjustable rose-jointed torque rods, you'll probably be plenty happy.

Love all the input and ideas, keep them coming.
For clarification, by straight I am referring to "eyeballing" along each side of the original subframe where it fairs our at about the half way point, if the side were straight along this plane either parallel to each other or converging would this not be stronger and simpler? The same concept when using tubing (which by the way I really like that idea). Yes the design has to be notched, angled or something on the side elevation to provide clearance for the axle

I know I explain this poorly, but if you could watch my hands during this explanation you would see exactly what I mean

Good observations. The rear torque rod bolts are indeed M14. 240s are M12, good call. I of all people should know that, having bent two of the stupid subframe things.

The 7 series floor pan is pretty burly where the subframe joins it in front. I know the trailing arms are designed to crumple nicely in a rear end collision on both 2 and 7 series. I suspect that the factory subframe is made partly with that in mind, but given it is super quick to put together stamped steel and tack welds from what I can tell, I think banging them out quick and for cheap was also on the radar...like anything on large scale mass production really. I also think that the floor should be strong enough that I'm not that worried about my double wall one not absorbing energy decently still.

A friend of mine bent one of the Kaplan subframes. Kaplan makes really cool stuff, but he is such a weight nazi where he really doesn't need to be IMO. Having that thing be a little heavy and ugly doesn't hurt my feelings in the slightest. I mean, come on, look at where it is on the car. Good place for weight, and you are never going to see it. That is, unless Ian grows a tumor and strips his car of undercoating, polishes and powder coats everything, waxes the underside and starts becoming a show queen. But if that were the case, he wouldn't have time to actually drive his car, so subframe strength is moot anyway .

You have to be kidding, I will NEVER polish under my car
Although the outside looks OK, the underside of mine is just plain ugly and that is the way it will be staying, takes long enough to keep the shiny buts clean.

So I agree, the subframe does not have to look purdy, and it does not have to be light, functionality is the name of the game