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6.9 “fun” in the rain

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p. rex:
Hello all,

Had a rather frightening experience in the Marschallin, my ‘79 6.9, in the rain yesterday and wanted to share.  I was on a rain-slicked access road, accelerating moderately (per the 6.9 definition of “moderate,” which was probably actually rather briskly, plenty of torque applied to the rear wheels in top gear at maybe 45-50 mph) toward a short on-ramp in anticipation of a difficult merge.  I was driving straight, more or less, rolling on a bit of torque as I crested a gentle rise, and the back end just stepped right out on me.  As in, I was going straight one moment and was hanging the tail out a good twenty degrees of rotation the next.  Took about two seconds of gentle countersteer and eased throttle to correct and straighten, but it felt like longer than two seconds.

So, I was just wondering, has anybody else had a hair-raising “surprise oversteer” moment in their 116?  It sure didn’t feel like I did enough to provoke that kind of response, so I’m thinking maybe I hit some sort of greasy spot and the LSD engaged and sent the back sliding. 

Hell, I’ll broaden the inquiry beyond that.  Those of you guys who have American muscle experience, is this something one generally has to look out for with posi-traction and big block torque?  I’d definitely heard stories about how this kind of car could put the hurt on you in inclement weather if you weren’t careful, but I was a little shook after this particular incident.

And before y’all ask, no damage except to my ego, thank goodness.

Cheers,

Rex

daantjie:
I had exactly the same thing happen to me on the 6.9  but I was not so lucky...I made "friends" with a concrete divider.  Tough day.
Road was damp and I was being dumb flooring it to force a kick down downshift as I was coming out of a slip way onto a banked turn.  Hilarity did not ensue...
I also read up on this a bit afterwards and apparently it has to do with the limited slip diff moving power to the outside wheel if the inside wheel starts to break traction.
Trouble is when the outside wheel also then breaks traction due to the slick road then it's game over with both rear wheels now without traction.  At least this is how I understood it.
Either way it sucked bad and for sure other 6.9 drivers must be aware of this phenomenon.
Cheers

p. rex:
My condolences about your 6.9.  I feel fairly lucky, it could have gone much worse. 

And I absolutely agree, this has to be because of the LSD.  I’ve overpowered the driven wheels in non-LSD cars before, and while you get some yaw action if you’re not going straight, they do not break loose in nearly as dramatic a fashion.  Never happened like this in my brother’s late-model Mustang 5.0, and never in my uncle’s ‘70s Corvette, those cars would just spin up one wheel and maintain a fairly steady direction.  I should have figured that losing traction at both rear wheels at the same time on wet pavement would be scary.  Very limited directional control, it was almost like hitting a patch of ice.

I suppose the one silver lining is that this confirms for sure that my LSD still works.

ptashek:
So many variables to consider. Tires, road surface etc.

I did try to throw the tail end on my 450SE a couple times for the sake of trying to figure out its limits, and the only time I've succeeded was exiting a roundabout quite briskly, dropping a gear manually and flooring it on a wet Irish road. No LSD on this car.

Step off throttle, slight counter steer and she righted herself without issues.

Maybe you've hit an oil slick or something?

p. rex:
Yes, I think it’s likely that oil or some other greasy substance was involved.  The back just let go without warning.  If it had been normal wet pavement, I can’t shake the sense that there would have been some warning that loss of traction was imminent.  I mean, typically you can tell when you’re getting near the limit, or such has been my experience in the past.

This seems especially likely given that there was no lateral cornering load involved.  To go from properly gripped to sliding as if on ice instantly, just due to application of a hair too much power?  Not typical behavior.  Although I do think that the LSD worsened the situation when I hit the oil.

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