65GS.com - Buick Gran Sport Enthusiasts!
Drivetrain => Differentials, Axles & Brakes => Topic started by: elagache on June 12, 2018, 05:12:09 PM
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Dear mid-60s Buick owners who never have enough torque!
I'm finding myself between a rock and a hard place when it comes to selecting a rear end ratio for my trusty wagon. The latest numbers needed for towing that I'm coming up with would greatly increase the operating RPM on the freeway and therefore would greatly increase the noise. My Mom, who selected the car back in 1968, still occasionally gets driven in this car but doesn't like the noise as it is. So I'm pondering leaving the rear end ratio at the present 2.78:1 and leave the towing problem for some point in the future.
That leaves still one potential issue. The present differential is stock and not limited-slip. I was told if you have an engine that produces huge amounts of torque, that a limited-slip differential was an important safety upgrade. However, I have driven Biquette a fair amount without any problems. That doesn't mean it was prudent, basically that's the question. There is this Wikipedia article which is quite interesting:
https://en.wikipedia.org/wiki/Limited-slip_differential (https://en.wikipedia.org/wiki/Limited-slip_differential)
However, as best as I can tell, the real issue only occurs in situations were road conditions are slippery. So long as you avoid bad weather (which is easy in California) the limited slip differential doesn't seem as important. So is there some other safety issue involving high-torque engines that I'm overlooking?
A curious mind would like to know! :icon_scratch:
Cheers, Edouard :occasion14:
P.S. You never know what you'll find in a Wikipedia entry. For example, did you know that the Beach Boys song "409" refers to a limited-silp differential? Even more exciting is that in the 1992 movie My Cousin Vinny (https://en.wikipedia.org/wiki/My_Cousin_Vinny) two young men driving a 1964 Buick Skylark was shown to be innocent of murder based on evidence showing that the culprit instead had driven 1963 Pontiac Tempest, which did a limited-slip differential. (http://www.canebas.org/WeatherCat/Forum_support_documents/Custom_emoticons/wink.gif) I knew you couldn't trust d'em Pontiacs! . . . . :laughing7:
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Although not mentioned, you likely know that if the road is wet, loose gravel etc, or if one gets heavy footed turning out onto the roadway and breaks traction, the rear may swing pretty far and if no corrected, will get beyond sideways, and if the person unloads incorrectly, and gains traction, it can get ugly.
More power will exaggerate this.
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I think the 4-0-9 refers to the size of the engine.......but it does have a limited slip diff
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The safety factor is that you can wear out both rear tires evenly, instead of blowing just one down to the cords. :laughing7:
Mark
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.... if the road is wet, loose gravel etc, or if one gets heavy footed turning out onto the roadway and breaks traction, the rear may swing pretty far and if no corrected, will get beyond sideways, and if the person unloads incorrectly, and gains traction, it can get ugly.
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Yes, that is WITH limited slip! In those conditions (and ice and snow), an open end rear is almost safer....you spin one wheel but you won't go sideways.
A limited slip improves traction on dry roads with a heavy right foot, and is less likely to get stuck in mud or sand.
You're probably fine with the open rear. It depends on how and where you drive it.
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Edouard, and other safety buffs,
I'd like to throw my 2 cents in simply because you are speaking from a safety aspect.Without trying to sound contrary to what seems like common sense, in most instances a limited slip can be more of a safety hazard in a torque laden car. OK, let's establish that from a standstill on dry pavement the Posi wins all day long, but have you ever had a burnout start to slide sideways? Ok, With both wheels spinning especially in bad weather the back of the car is free to slide side to side at will. With an open rear the tire that is not spinning keeps the car from moving side to side thus much less susceptible to spinning out. With the posi if you break traction at speed the rear of the car can go wherever it wants. Conversely with an "open" rear the non drive tire will maintain some form of straight line traction even though the other tire is spinning like crazy.
Go down to the local cruise in and look at the burnout marks the one wheelie peelie's are pretty darn straight l The Posi burnouts tend to arc in a crescent so to speak ))
So before I get lambasted, yes a posi will pull you out of a corner faster although you increase the chance of spinning out. The posi will get you 0 to 60 faster. The posi is recommended for pulling a trailer. The posi will help get you out of mud and snow. The posi in theory will decrease gas mileage due to more rotating mass and inherent friction.
That all said, my GS and my tow vehicle have a posi rear ends. My daily driver with over 300 pound feet of torque does not.
Please don't drum me out of the cool kids club...I have a line Hurst lock and I'm not afraid to use it :rocker:
Jerry
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Yes, that is WITH limited slip! In those conditions (and ice and snow), an open end rear is almost safer....you spin one wheel but you won't go sideways.
A limited slip improves traction on dry roads with a heavy right foot, and is less likely to get stuck in mud or sand.
You're probably fine with the open rear. It depends on how and where you drive it.
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Amazing timing, I entered my post and saw yours! :hello2:
Jerry
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Dear Michael, Keith, Mark, Walt, Jerry, and mid-60s Buick owners who want the da' rubber on da' road!
Oops! I went back over my numbers and realized I had the torque value for Biquette's engine too low. So perhaps I can settle this rear end ratio once and for all!
http://65gs.com/board/index.php/topic,3925.msg28955/topicseen.html#msg28955 (http://65gs.com/board/index.php/topic,3925.msg28955/topicseen.html#msg28955)
Cheers, Edouard