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Discussion Starter · #1 ·
Okay, I'm a still learning the terminology here. I was told that my rear end is a 3.08 open differential. What does open differential mean?

thanks
 

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Basicly it means that when you sit at the stop light with your foot on the brake(real hard) and you mash the gas and run it up, slipping the brake when the rear tire strats to move your only going to see one black stripe.

An open differential, or non-posi, means only one wheel is the drive wheel in either direction. When you go forward it's the passenger side wheel, when you go in reverse it's the drivers side.

Posi is not essential to having a "bitchin' ride", infact the only time posi does anything is when you decide to apply some racing stripes to your local "gas&rob"'s parking lot or your on a wet road.

Posi can be a problem if you live where it snows more than once a year... when you get both wheels on somehting slippery, all either one is going to do is spin and spin and spin. I can't wait to get my 14" studded super hard snow tires on with a 4.11posi....

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Francis Taracido
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Hey Fran, I would never run my posi ( '67 ) in snow anyway! In fact, we've got t-showers coming in today and I didn't even take the girl to work. Anyway, front wheel is the best way to go in snow.

Anyway 4DoorMalibu, you don't need a posi for general driving, only for hipo stuff. In fact I once had a posi rebuilt ( by a Chevy dealer) and it was so tight it chattered around corners. Kind of a PITA.
 

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Another way you can tell if you have open rear is take your car off road in the desert. When you get stuck in soft sand only one of the rear wheels will spin. Bummer when that happens. --- Carl
 

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If I am off on this somebody let me know but I think that I know what i'm talking about. Quadzilla said that only one wheel drives, this is not true. While both wheels have equal traction (neither are spinning) then both wheels spin. When you launch hard, your car twists to one side, pulling up on one of the rear tires which causes this tire to have less traction, so the tire with less traction will spin. With an open rear end the tire with the LEAST amount of traction will always spin. For a closing argument
, if only one wheel drives an open rear, then why is it that if you put an air bag in the passenger side suspension and get it set right that you can get both wheels to hook up on a launch? Hope this helps.

Chris
 

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Far as I know, with an open differential only one wheel is the drive wheel in either direction. As to which is which I'm kinda in the dark.

With a Limited Slip(posi traction) Differential the same holds true for some of the time. When you pound the gas on a posi from a standing idle the "drive wheel" takes all the power and starts to "slip", which is then "limited" by the positraction clutch pack; thus transfreing the excess rotating force to the opposite wheel to "limit" the "slip".Positracion only turns both wheels to avoid them from spinning and you from skidding. How many times have you "broken it loose" at a light in the rain.

If both wheels were to be be spinning all the time I would recomend that you remove the spool and save your tires some grief.

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Both wheels drive with equal thrust with a conventional differential. If they did not, the car would steer with the application of throttle because of the assymmetrical thrust. As was stated above, the wheel with the least traction will spin. At this point neither wheel is providing much thrust.
 

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Quad

No offence but the other guys are correct. An "open" rear end drives both rear tires but it will alow one tire to spin at a different speed than the other. If one tire has less traction then the other it will spin faster, this effectivly removes power to the other wheel. If the traction between the two wheels can be kept equal then both tires recieve the same amount of torque. Many racers have had respectable perfomance with an open rearend by tuning thier suspension to maintain equal resistance at both tires.

Clark
 

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A "posi" or "limited slip" rear has a clutch pack in it. A "non posi" or "open" rear has no clutch pack.
Raise the rear tires off the ground and put it in gear (manual) or park (auto). Turn a rear wheel. On the non posi rear the other rear wheel will turn in the opposit direction. On on posi rear the rear wheels will not turn.
 

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positraction is basically just GM's name for limited slip:
.. meaning the carrier will allow a limited amount of slip for normal cornering, etc but any more than that and the friction from the clutch pack will heat up the fluid and cause it to solidify, locking both wheels together. (I think the posi additive is silicone?)

theoretically and ideally you will be putting too much power to the ground for 1 tire to handle (as with an open diff) and the posi will kick in, giving you two tires with traction, helping you move forward instead of burning rubber so to speak. there is really no benefit in having posi in the snow or rain if anything its a disadvantage because driving surfaces are just plain slippery. there is no means for traction whatsoever, ie your car will slide sideways, etc... when the posi locks up in the snow or rain your entire rear end is basically floating and you cannot safely control the vehicle. On dry asphalt you should just let off the throttle and regain traction...

on the other hand, with a conventional open differential one tire should keep traction allowing you to steer, keeping you from fishtailing...

JWagner, Clark, and Gandalf pretty much said it all about open-diff drive wheels.. it is a common misconception that there is a "drive wheel".. on-road, its usually the twisting of the car and rear axle from rotating force/torque of the engine, and driveline...


anyways, malibu4door dont think your car is in any way bad because 99% of the cars on the road have the same type of differential as you..

hope this helps and if im wrong about the way the clutch-type posi works (silicone heating up and solidifying) please someone speak up, Id love to be proven wrong

Mike Reeh
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THANKS Malibu4door,
This is hilliarious, & I thought Gene's """""""""""""l-88"""""""""""""""were funny!!!
 

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Just to clarify:

Limited slip/posi units either have clutch packs as an Eaton posi does, or a cone style posi such as an Auburn.

Open diff's just have side & spider gears.

To clarify one other point mentioned above:
If you raise the rear of the vehicle, and spin one tire & observe the other rear tire:

If it spins in the opposite direction, you have either a worn out posi, or an open diff.

If it spins the same direction you have a posi. If you spin it, and it moves in the same direction, have an assistant try to hold the other tire still.

If he has difficulty holding it still, it's a good posi. If he can hold it still easily, you have a worn out posi.

If you have a worn out Auburn posi, you need to buy a new carrier.

If you have aworn out Eaton posi, you can rebuild it.

Hope this is clear enough.

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70 & 1/2 RS Camaro
SB406 & M20 4spd
9" Rear
70 Malibu
SB350 & TH400

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Discussion Starter · #15 ·
Wow, I didn't mean to start a discussion, but thanks to everyone who responded. I think my question was answered thoroughly, very thoroughly.

In north dakota, I think I'm glad to have an open differential. Lots of summer rain, and winter snow (my Malibu has never seen much snow in hibernation though).
 
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