You probably just bent the dust shield behind the rotor. Take a peak, you can probably bend it back without much trouble.

 

The jack can put point loads on the cast housing, and the possibility exists that you could botch up the bearing areas and/or cause the cover to leak. Doesn't mean I don't lift by the diff! I'm just careful to get my "saddle" from the jack on a couple of points bearing over a large area. I realize it might do damage but I'm piloting an old '86 for a few more months and the diffy is in poor shape anyway. For an S197 I'd like to see an aftermarket cover w/a jacking point. Don't know why they don't make those.

 

Going back to one of the original statements. Both steel and aluminum have characteristic SN (fatigue curves) and they both have a differing stress level at which the materials exhibit infinite fatigue life. They also both have ultimate and yield tensile strengths, though differing by quite a bit. One would think (hope) that the designer of the aluminum drive shaft would be taking these differing material properties into consideration, as well as the anticipated torque, and to a desired / required design safety factor, rather than POA the wall thickness and running with it from there. I would suspect that for a given diameter, the aluminum shaft design is thicker wall (still lighter, less torsional stress) than its steel counterpart (assuming the aluminum tensile properties are less than the steel).

 

Well your owners manual suggests one don't. Apparently a lot of owners know better than Ford and jack on the center section. It is certainly convenient. I do not beleve its because of the sheet metal cover. Its just cast steel or iron, they did not make a nice pad to jack against (for reason?) and the bending moment on the center section is probably quadrupled when its jacked up in this manner. If it were to permanently distort due to that, then there goes your ring /pinion and carrier bearing adjustments.

 

Alright, here's the update. I took it to the dealer today ($98 just to look at it) and while they had it on the lift, they showed me what was wrong with it.
When the jack slipped off and the car fell on top of it, EVERY BAR in the rear end got in the way (a good thing too because jack hitting the top stabilizer bar stopped the rotor from hitting the ground in full force). So both the forward and rear (upper and lower) stabilizer bars as well as the anti-roll bar will need to be replaced. Aside from that, the diff cover obviously needs replacement and it's slowly leaking when the diff is warmed up (about 1 drop every 10 seconds). For the time being I put some grey RTV on it, which will hopefully slow it down till I can get a new diff cover on it. Interestingly enough, after the 30 miles of driving I was forced to do today, there's still plenty of gear oil left (so much so that I can't remove the drain plug without some more oozing out). That at least will give me a few days. I'm going to start another thread in the warranty and service issues thread about this and try to keep this thread about the original subject.

So back to the original subject, while I was at the dealer today, the tech enlightened me as to the purpose of the 2-piece driveshaft. The center joint is there for articulation purposes to reduce binding at both the tranny and diff ends of the shaft. Makes for smoother cruising and less energy used in rotating the drive shaft at the joints.

 

Well a 2 piece shaft may do some of that, but even a one piece for these cars has a slip joint to prevent the shaft from going into bind compression or tension as the rear axle moves relative to the transmission. But that's not the primary reason for the 2 piece shaft. The two shorter pieces have a higher natural harmonic frequency of vibration, so tend to be quiter than the long shafts which have lower natural frequencies.

 

Dude Paul, you know your stuff. I dont even have a reply.

 

Sorry for being a hog, you can have the next few ....

 

I'm impressed

Question on the Steeda aluminum driveshaft kit. I don't see any provisions for adjusting pinion angle, nor is it mentioned, unlike every other 1-piece driveshaft I've seen so far. What's the deal?

Oh yeah, the thread on the suspension repair from slipping of the jack is here.

 

Why wouldn't you put in on jackstands before you remove the tires?

 

While I was at a Mustang Rally, I had a chance to talk to one of the drivetrain engineers. That was pretty close to the explanation he gave me. I'm getting a degree in mechanical engineering so I know about vibration frequencys. You should have seen the look on his face when I mentioned the Hurricane motor. That's a different story though.

 

Oh come on, you can't tease us like that!! Did you get any info on it, or did he just give you the old "I can't talk about it" run around??