Foot to the floor, 10lb boost, accelerating towards 70-75 and then have your driveshaft twist in half. This is the end of the one piece driveshaft experiment and pretty much the end of what was once a very nice road car.
I'll get more photos later but the S2 is by all accounts toast. From 2 feet away nothing looks amiss but when you open the door and find the entire pass. side floorboards shoved up about 8" from the underside of the back seat (broke it from its mounts and it hit the roof) all the way past the trans crossbrace, of which broke. It was a very violent experience and I'm thankful nobody got hurt. The only thing that kept projectiles from entering the cabin was the carpet.
Damn, glad everyone is OK and it is only material (and financial) damage. Good that the rear section didn't jack the rear of the car into the air, saw that once at a drag strip, not pretty at all.
Holy crap! This was that heavy duty one-piece shaft you had built? I figured that thing was more than strong enough to put up with whatever you could throw at it.
I just about had to change my shorts when the guibo went out in my car, I can't imagine what this must have sounded and felt like.
It was rated for 700hp. I've had several words with the shop that built it and as expected they have done their best to absolve themselves of any wrongdoing. It's been on the car for over a year so there's not much that'll happen on that front. My insurance co. told me to pound sand so that's not an option either.
I'm pretty bummed about it but the ultimate blame is on me. After it's all said and done, it's just a toy. It was my idea to do the experiment so I really can't blame anyone else.
I would even consider legal action. Thier drive shaft failed under very mild conditions, and did incredible damage to your car. Thats very weak sauce.
You could try telling your insurance the damage was from debris in the road, but thats fraud. That really isnt right. If anybody else should be responsible for this it would be the shop that made that shaft.
Bill in MN wrote:I've had several words with the shop that built it and as expected they have done their best to absolve themselves of any wrongdoing.
How, exactly, did they attempt that? They rated it for 700 hp (hp being irrelevant in this case as torque is more important). No TCD car that I'm aware of has EVER made that much torque at any RPM (the record I think is ~520 tq at the crank), so I'm going to go out on a limb and say you were well below its rated limit.
Sucks however you look at it, but don't let those guys off the hook too easily.
Glad you're ok though! Flesh is so much more difficult to mend/replace than metal.
The shops stance is that they built the shaft to my specs and it was properly built and balanced. My car is highly modified and there are numerous other reasons the shaft could have fatigued over the year or so it had been in there. They had no control over how it was installed, the adaptor plates it was connected to, the structural integrity of the chassis.....you get the picture. Had the thing blown a week out of the box I would have a leg to stand on. It didn't. End of story on that one, unfortunately. I've also no desire to start a legal battle I probably wouldn't win.
I had pulled the boost back due to my wife driving it for work/DD duties so it wasn't getting whacked with big torque and hadn't for some time. I think this all boils down to chassis dynamics and the fact that I shouldn't have F'd with the thing in the first place.
This first one says a lot. The divot in the tar is the rear portion of the shaft doing the pogo. The car hopped a bit, wheels locked and the results are obvious.
This is the resulting damage. Now that the carpet is pulled aside, I'm beginning to think this is not repairable. I am, very, very, very bummed out right now, and as much as I hate to admit, to the point of tears.
I hope the frame guy knows what he's talking about. 'cause I don't know how the hell this can get put back.
Damn, that's some carnage! You are indeed lucky not to have pogoed and lost control. It's a shame that the car is toast.
I had the yoke (or u-joint, I can't recall) at the rear of the driveshaft break on my '57 Chevy and beat up the rear of the floorpan, smash the mufflers, and rip up the parking brake brackets in the tunnel. There was no back seat in at the time, and a couple of guys were sitting on the floorboard when it happened. Of course, I was showing off. The damage was pretty much repairable with bolt-on parts and a sledge & a block of wood.
Sorry too hear it man. Either the shop did some crappy work, your car puts out some serious ponies, or there are some the other dynamic factors that played a part in this course of events. Anyhow, take a few days to shake off the shell shock & don't beat yourself up.
I got rid of the eta early this spring so the floor option is a no-go.
It's still going to the frame shop but common sense tells me it's not worth putting money into if it'll require extensive work to make it safe again. It will be much more cost effective to find as perfect a donor chassis as I can find and transfer everything to it over the winter. I think it's one of those "suck it up and move on" deals
Bill this just sucks . If you want to save the car it may be time to look for a donor shell. In hindsight a driveshaft loop ( used by most drag racers ) may have helped save the car , maybe not. Its just a Damn shame either way.
I wonder if it's the fact that it was a single piece d/s. Perhaps the BMW really needs two halves to get some flex. That's a fairly long span for a single piece. Did you have stock motor/trans mounts and subframe bushings? Unless they were something stiff, maybe it was just too much flex. I'm just guessing though.
Huge bummer and I hope you can get things back together (or on a new car) in short order.
From the website linked to below:
"Critical speed is the speed at which a spinning shaft will become unstable. This is one of the single largest factors in driveshaft selection. When the whirling frequency and the natural frequency coincide, any vibrations will be multiplied. So much that the shaft may self destruct. Another way to think of this is that if a shaft naturally vibrates at 130 times a second, and one point on the shaft passes through 0 degrees 130 times a second (7800 RPM) then the shaft has hit a critical speed. There are several ways to raise the critical speed of a driveshaft. You can make it lighter, stiffer, or increase diameter without increasing weight. This is the reason carbon fiber makes a good driveshaft, it is stiff and light and can be made to any diameter or wall thickness. Aluminum, while it has a very good critical speed is not quite as strong as steel. Steel, with good strength characteristics will have a lower critical speed."
Could any of this apply here? Looking at the chart they provide, a long steel driveshaft could be getting into a dangerous RPM range at the speed of this incident. Shouldn't the driveshaft supplier know this?
It was 43", not overly long for a single length shaft. I'll have to look back in my records as to what the critical speed of the shaft was. It escapes me at the moment.
All mounts, (engine, trans, suspension, chassis etc.) are significantly beefed up. They were changed out within the last 5k miles and all are/were still in good shape. Interestingly enough, the trans crossmember is broken. It's very possible this broke first, leading to the rest of the damage. It's hard to tell which came first, though. The flailing yoke could easily have caused the crossmember to break as well.
Bill in MN wrote:It was 43", not overly long for a single length shaft. I'll have to look back in my records as to what the critical speed of the shaft was. It escapes me at the moment.
I measured a spare stock driveshaft(for a 5-speed G260/6 535i) I had laying around, it was around 59". How was yours so much shorter? Is that based on just the length of the main tubular section? I guess calculating the critical speed is standard practice for a custom driveshaft, then? Interesting stuff, anyway.
Daryl, that's the length of the tube. The rest of the length is taken up by the Ujoints and splined section.
Kyle, you're probalby right and a few candidates have already been brought to my attention. If this thing sees the pavement again at all it will likely be as a full cage track car, not as a driver.
Bill in MN wrote:Daryl, that's the length of the tube. The rest of the length is taken up by the Ujoints and splined section.
Kyle, you're probalby right and a few candidates have already been brought to my attention. If this thing sees the pavement again at all it will likely be as a full cage track car, not as a driver.
If you want a track car, save yourself the trouble and buy something smaller/lighter with readily available parts.
Bill in MN wrote:Daryl, that's the length of the tube. The rest of the length is taken up by the Ujoints and splined section.
Kyle, you're probalby right and a few candidates have already been brought to my attention. If this thing sees the pavement again at all it will likely be as a full cage track car, not as a driver.
If you want a track car, save yourself the trouble and buy something smaller/lighter with readily available parts.