I’m with Ranger, 25 ftlbs is not enough. Buy the Condor subframe bushings…
Aluminum rear subframe bushing collapsed?
Som
#22
Yeah, I don’t really understand, either. He said that the factory torque values were specific to the rubber bushings. That the aluminum ones didn’t need nearly that much.
Thinking out loud here, but I’m trying to visualize the forces that are seen at those bushings. Also, I’m not an ME, so please don’t laugh if I say something stupid. 
The springs carry the weight of the car, so the up/down motions (z axis) of the wheel probably doesn’t really translate a whole lot to the bushings. That leaves the x-axis (side-to-side) and y-axis (accel/braking).
Looking at the acceleration (y-axis), that’s going induce a forward force on the control arm, which translates to the subframe, to the bushing, to the bolt. So… effectively… the wheels are pushing the car by pushing the 2 subframe bolts…?
Same deal with braking, but because the fronts are probably braking harder than the rear, probably less actual force applied to the bushing here.
Lateral (x-axis) forces would twist the control arms with one arm being the pivot point and either pushing down or up on the edge of the subframe (depends on the direction the wheel is going).
Don’t think I’ve really revealed anything, though. 
The only thing I can really think of is that the bushing is really only there to transmit lateral subframe forces to the bolt and back. There’s not really much vertical force to contend with. Maybe that changes with rubber – maybe the slight deflection induces more vertical force on the nut that could cause it to come loose?
One other thing to consider is that with 2 rubber bushings, you could have the whole subframe twist around one of the bolts – which could contribute to the bolt twisting and being undone. Maybe this concern doesn’t existing when you have solid bushings as there’s no twist?
I guess this would go back to why bolts are tightened to begin with. Can’t say I know all the physical/mechanical nuances to answer that question.
Som
Som
#23
Not saying a guy with 30+ years of experience is infallible, but I have to imagine the guy knows what he’s talking about with something like this, right?
The other thing I was thinking was – what’s the worst that could happen if the nut comes off? The subframe isn’t going to slide out because the bolt comes down from above. The question would be whether those little side supports can support the weight of the rear end (and all the forces applied to it). Assuming they can, it’s not really going to be catastrophic problem, right? But if they can’t, then having the nut loosen could cause the entire rear subframe to fall off the car…
Som
cwbaader
#24
I really like the idea of the tube on the inside to torque against. Of course, deletion of the tube cuts cost and angst…nothing to gaul against. I really don’t see a problem with 25# torque as long as you red loctite the nut. The stresses on that are taken up by the frame above and the plate below. There are minor vertical forces in the downward direction, usually only when the car is jacked up. Follow directions and see if everything works out ok.
FishMan
#25
Buy the condor bushings and torque them good and tight. I am a mechanical engineer and a subframe bushing that deforms with 25 ftlbs will never be in my race car…
Ranger
#26
[quote=“Som” post=79684]Not saying a guy with 30+ years of experience is infallible, but I have to imagine the guy knows what he’s talking about with something like this, right?
The other thing I was thinking was – what’s the worst that could happen if the nut comes off? The subframe isn’t going to slide out because the bolt comes down from above. The question would be whether those little side supports can support the weight of the rear end (and all the forces applied to it). Assuming they can, it’s not really going to be catastrophic problem, right? But if they can’t, then having the nut loosen could cause the entire rear subframe to fall off the car…
Som[/quote]
Lol, don’t underestimate how hard racing is on the car. Al K had those two little 8mm bolts loosen up and exit, and his subframe moved all over heck trying to get free. He had to have the whole mount point for that big 12mm bolt repaired.
Racing is so hard on these cars that every bolt that you don’t put locktite on will try to loosen up on you. As the years go by, on many occasions when you are doing something under the car you will find some critical bolt loose and exclaim “holy shit that could have been bad” which is racer-code for kids growing up w/o their father.
Develop a healthy mistrust…that’s not quite the right word. Be over-cautious. Routinely inspect every important part of your car. When you are poking around underneath it doing something, as a matter of course check every fastener you can reach. If something is loose, back it out and put in some blue locktite before putting it back in.
Don’t be too quick to use red locktite. It’s really strong stuff. Often it has to be burned out before the fastener will move. For most applications, blue locktite is sufficient.
If that subframe nut came free you’d prob be one hard lap before your rear end departed company. Then there’s be a shower of sparks for a couple inches Just long enough for your fuel tank to be scraped thru. You’d then be the subject of a thousand discussions each year where newbies were told to be serious about checking their fasteners. You’d be a legend.
cheapthrills
#27
+1 from another ME. I have the AKG poly bushings which are pretty much the same design as the Condor: two halves of an aluminum post in the middle surrounded by a solid UHMW polymer. This mimics and improves the stock design, which is to have a solid post firmly attached to the chassis at both ends, with some material doing the bushing between that and the subframe.
I get AKG’s argument that the clamping force isn’t critical: as long as the two halves are together, the bushing will be “solid” enough to keep the subframe and chassis in alignment. However, as Rich said, if this thing can deform in any direction that easily, I don’t trust it. These bushings (along with the differential bushing) transfer all of the forces from the rear wheels to the chassis. The amount of odd-axis forces and vibration they see during racing is high. Following AKG’s directions may make you feel better and put some amount of liability on them in the case of failure, but that isn’t worth a damn during the scene Ranger just described.
For the record, I use lots of AKG’s poly products, and I am very happy with them.
cwbaader
#29
Scott, we do. Stress on the bushing is not vertical. The stresses are parallel to the ground and are resisted by the three subframe mounts. (Which is why you always want all three to be of the same material!) All the nut on the bottom has to do is keep the pieces together and 25 pounds of torque is enough to do this. If you really want to check this out, call Andy and get customer names that are using the new bushings. Do your due diligence before condemning the produce.
Ranger
#30
The poke at mechanical engineers was just poking fun . All of us in this thread are ME’s. Well, except for SOM. I think he’s a computer geek. The primary target of my jape was myself.
The problem isn’t 25ftlbs keeping the 2 halves pressed together, the problem seems to be that the two halves don’t press together at all. They aren’t tall enough. As a result the openings of the subframe are encouraged to mushroom. Over time they’d open up a bit more and allow movement of the bushing halves. This would allow the whole structure of bushing halves, subframe opening, bolt head up above, and nut down below, to move around a bit. This would further damage all the pieces and they’d all get even more loose.
Even if the 2 halves were tall enough, I’m not comfortable with a torque spec that is 1/3rd of OEM. The way that vibrations can loosen fasteners is tricky business and I don’t understand it well. But the guidance from AKG was 20-25ftlbs. Heck, that’s 10mm bolt territory. To make matters worse, SOM didn’t get that guidance until he called them up. The normal thing to do would have been to treat it like any other 12mm 8.8 bolt and use >2x the ftlbs what AKG recommended.
cwbaader
#32
Anyone actually know what due diligence is? Has anyone talked with someone who uses these bushings? STFU till you do.
Ranger
#33
[quote=“cwbaader” post=79694]Anyone actually know what due diligence is? Has anyone talked with someone who uses these bushings? STFU till you do.[/quote] Lol
Som
#34
Spoke to Lisa at AKG this morning. Andy was out of the office and she left a note for him to call me back later, so I’ll have a chat with him more about it.
Lisa mentioned that they used to have 2 designs – one that had the “raise 12mm” option and the other that didn’t (I’m assuming that’s the one Scott had). She said that they weren’t selling a lot of the “non raised” versions, so they just stopped making it to consolidate.
She also mentioned that they’d been selling these exact versions for years to people (do-it-yourselfers and professional mechanics) around the world for racing applications for several years. That gives me some peace of mind.
I still plan on chatting with Andy about it.
I wouldn’t say I’m underestimating the harshness of racing. Having raced motorcycles, tracked cars for 10+ years, and been on NASA’s Nor Cal safety crew for about 15 (off and on), I’ve definitely seen a lot of “how the hell did THAT happen” situations that can only be explained by the stressful environment that comes with racing. I was more trying to play out the hypothetical “worst case” of the nut coming loose as it seemed like the part is sandwiched between the body and the plate below (that’s bolted to the body) and it has a bolt coming through it from the top.
It really seems dependent on the strength of that bottom plate that’s bolted to the frame and how much weight it can support. When the subframe nut is tight, I don’t think there’s really any vertical force on that plate – it sort of acts like a big washer in that case (as in, the plate isn’t holding the weight of the subframe or reacting to any of its vertical movement or anything like that). I believe the plate is there to protect against lateral movement at the bottom causing torsional forces pivoting around the body bolt hole at the top when the subframe moves forward/backward/side-to-side.
So, that said, if the nut loosens, the weight of the subframe then WILL sit on that plate. Can it support that weight? I don’t know. Plus, given the bumps that come with racing – there’s nothing to ensure that the subframe bolt itself doesn’t pop up into the chassis – which certainly would be catastrophic. Maybe that’s a good backup safety step – filling the subframe bolt hole the way it came from the factory so it can’t pop out on the off chance that the nut backs out. IF the plate on the bottom can handle the subframe weight, and if the bolt can’t back out up the hole – the only undesirable movement you would have would be whatever wiggle room is there between the bolt and the bushing and the plate’s bolt hole.
Som