Sunday, December 16, 2012

All I know about cars I learned from the movies...

Posted: 16 Dec 2012 03:20 PM PST

My Cousin Vinny (1992) Court scene with Joe Pesci and Marisa Tomei

Vinny Gambini: Ms. Vito, it has been argued by me, the defense, that two sets of guys met up at the Sac-O-Suds, at the same time, driving identical metallic mint green 1964 Buick Skylark convertibles. Now, can you tell us by what you see in this picture, if the defense's case holds water? 
[Lisa examines the picture] 
Vinny Gambini: Ms. Vito, please answer the question: does the defense's case hold water? 
Mona Lisa Vito: No! The defense is wrong! 
Vinny Gambini: Are you sure? 
Mona Lisa Vito: I'm positive. 

Vinny Gambini: How could you be so sure? 
Mona Lisa Vito: Because there is no way that these tire marks were made by a 1964 Buick Skylark convertible. These marks were made by a 1963 Pontiac Tempest. 
D.A. Jim Trotter: Objection, Your Honor! Can we clarify to the court whether the witness is stating opinion or fact? 
Judge Chamberlain Haller: [to Lisa] This is your opinion, or is it a fact? 
Mona Lisa Vito: It's a fact! 
Vinny Gambini: I find it hard to believe that this kind of information could be ascertained simply by looking at a picture! 
Mona Lisa Vito: Would you like me to explain? 
Vinny Gambini: I would love to hear this! 
Judge Chamberlain Haller: So would I. 

Mona Lisa Vito: The car that made these two, equal-length tire marks had positraction. You can't make those marks without positraction, which was not available on the '64 Buick Skylark! 
Vinny Gambini: And why not? What is positraction? 
Mona Lisa Vito: It's a limited slip differential which distributes power equally to both the right and left tires. The '64 Skylark had a regular differential, which, anyone who's been stuck in the mud in Alabama knows, you step on the gas, one tire spins, the other tire does nothing. 
[the jury members nod, with murmurs of "yes," "that's right," etc] 
Vinny Gambini: Is that it? 
Mona Lisa Vito: No, there's more! You see? When the left tire mark goes up on the curb and the right tire mark stays flat and even? Well, the '64 Skylark had a solid rear axle, so when the left tire would go up on the curb, the right tire would tilt out and ride along its edge. But that didn't happen here. The tire mark stayed flat and even. This car had an independent rear suspension. Now, in the '60's, there were only two other cars made in America that had positraction, and independent rear suspension, and enough power to make these marks. One was the Corvette, which could never be confused with the Buick Skylark. The other had the same body length, height, width, weight, wheel base, and wheel track as the '64 Skylark, and that was the 1963 Pontiac Tempest. 
Vinny Gambini: And because both cars were made by GM, were both cars available in metallic mint green paint? 
Mona Lisa Vito: They were! 
Vinny Gambini: Thank you, Ms. Vito. No more questions. Thank you very, very much. 
[kissing her hands] 
Vinny Gambini: You've been a lovely, lovely witness.

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I've been trying to figure out if my car has "Twin Traction" in the rear axle, the Studebaker version of Non-slip differential, or Positraction. It was an option on the 58 Silver Hawk V8. It's a Dana unit and should have some marking on it.  I've been looking on Studebaker forums for discussion on this issue and as usual lots of interesting information on how to determine this.

One version is searching for emblems in different places, some on a tag on the case, some on the trunk lid, one even on the ignition switch. I managed to locate a single "T" and a number 4/1 on the rear axle housing cover.  (non conclusive)

 I also tried the recommended wheel spin "drive" test. Turning the lifted rear wheels forward and backward and observing the spin and direction of the opposite wheel. I discovered that the right wheel spun forward caused the left to spin reverse and spun backward caused the left to spin forward. However, the left wheel spun in any direction has no effect on the right wheel.  

I also read about some tests that required the engine running to jump the car off of blocks. I don't have enough room in my garage for that, plus that sounds like eminent damage to the front end or undercarriage. I could also rob a Sac-O-Suds and see what track marks I leave behind, just as risky.

The final check was to remove the plug bolt and peek inside to simply see if you can view the TT case assembly. Bingo.
I'm going to open it up anyway, because the seal is leaking, besides, I think I need a different lub oil if it is in fact TT.  TBD
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The following is from Wikipedia: 
In the 1950s and 1960s many manufacturers began to apply brand names to their LSD (limited Slip Differential) units. Packard pioneered the LSD under the brand name "Twin Traction" in 1956, becoming one of the first manufacturers. Other factory names for LSDs include:

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