Lsd

3201 Views 14 Replies 8 Participants Last post by onefastx, Jun 30, 2005

rikramer

Discussion Starter · Mar 21, 2005

Not the drug. Limited Slip Differential.

Can someone provide me with the low-down on this option? I am buying the sky as a year-long driver (including Canadian snow storms). Would LSD help? Or is it purely for performance reasons?

Thanks.

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swatthefly

· #2 · Mar 21, 2005

doesnt it limit the amount of power flowing to each individual wheel based on traction? (or lack thereof)

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achieftain

· #3 · Mar 21, 2005

In an ordinary differential power is delivered to one wheel at a time, only. The wheel with the least traction gets the power. You can prove this to yourself by putting a car with normal diff (or a tractor) up on jackstands, manually rotate input shaft to diff, hold one wheel stopped and the other one rotates. Yes there are some times when traction resistance is exactly equal against both wheels but it cjanges rapidly and invisibly. A true locking differential will on demand rigidly lock the wheels together so that both wheels get equal traction. A limited slip differential has the ability to apply a portion of power to wheel that has traction, thus providing power where actually needed and therefore would be welcome in snow and ice. In cornering and acceleration it also helps put the power where needed. The advantage of limited slip over locking is in slow maneuvering such as parking the lsd will not be engaged and the vehicle will turn easier than one whose rear wheels are still locked together.

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swatthefly

· #4 · Mar 21, 2005

achieftain said:
You can prove this to yourself by putting a car with normal diff (or a tractor) up on jackstands, manually rotate input shaft to diff, hold one wheel stopped and the other one rotates.

kids, dont try this at home and make sure you have your parent's permission! we dont want any of you to grind your little fingers off!

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achieftain

· #5 · Mar 21, 2005 (Edited)

swatthefly said:
kids, dont try this at home and make sure you have your parent's permission! we dont want any of you to grind your little fingers off!

Notice I said manually. Never ever do this with key even in same room as ignition. I'm sure there is a web site somewhere with a video demonstration of the differential effect so that we don't have to use real cars.

http://www.4crawler.com/4x4/TrueTrac.shtml This one is very detailed on operation. Also good info here: http://www.trucktrend.com/features/tech/163_0206/index4.html

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Nocturn

· #6 · Mar 21, 2005

Howstuffworks.com has a great write up on differentials, and basically all the parts of a modern day car.

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NukePooch

· #7 · Apr 24, 2005

LSD's and winter...

You mentioned the winter driving...

One thing, LSD's can help if one wheel is on ice by providing power to the other wheel with more traction, but that same 'equalization' may cause the car to handle oddly in icy conditions. You may end up with the car understeering/pushing. (where the wheel is turned, but you're going straight) or oversteering/skidding (where the back slides out when you're trying to go straight ahead). Most limited-slips have little effect in icy conditions, but if the diff is tuned more for performance, then it might be interesting. I personally would buy the LSD and just be a bit more cautious until you learn the handling quirks.

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achieftain

· #8 · Apr 26, 2005

One interesting tidbit related not to this vehicle but to vehicles of the past. A rear wheel drive vehicle that has its parking brake on the transmission output shaft instead of the brake drums will - if conditions are right, when parked on an icy grade, can lose traction on one wheel and start to roll away all by itself.

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swatthefly

· #9 · Apr 26, 2005

achieftain said:
One interesting tidbit related not to this vehicle but to vehicles of the past. A rear wheel drive vehicle that has its parking brake on the transmission output shaft instead of the brake drums will - if conditions are right, when parked on an icy grade, can lose traction on one wheel and start to roll away all by itself.

i could see that happening, conditions permitting. but do you think they would have the parking brake hooked up to the transmission? i would assume that they would hook it up to the rear discs. why would they (or anyone else) opt for the tranny?

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achieftain

· #10 · Apr 27, 2005

swatthefly said:
i could see that happening, conditions permitting. but do you think they would have the parking brake hooked up to the transmission? i would assume that they would hook it up to the rear discs. why would they (or anyone else) opt for the tranny?

This is old - old technology I was relating, specifically a 1958 Dodge truck, but other vehicles of similar vintage were set up the same way, a small external drum (pad wraps around drum and tightened by hand lever engagement) directly mounted to tailshaft coming out of transmission, before driveshaft. My unproven theory is that because these trucks were available in multiple wheelbase configs and with and without bodies that this was just the way they did things. This was also the days of single master cylinder systems when if one brake line failed you lost all braking.

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dnjrboy

· #11 · May 12, 2005

2 lines instead of one

You could jack the car up, but the more fun way to figure out if you have an lsd is to step on it in first and count the black strips.

An LSD would be quite beneficial for getting moving in the winter. I don't know about how it would affect turning.

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achieftain

· #12 · May 14, 2005

dnjrboy said:
You could jack the car up, but the more fun way to figure out if you have an lsd is to step on it in first and count the black strips.

An LSD would be quite beneficial for getting moving in the winter. I don't know about how it would affect turning.

That's IF you can get the backe end to break loose. Being a 50/50 balanced car with such wide tires may be more difficult than just stepping on it. And the operation of this LSD is different from the Positraction live rear axles of the 60's and 70's. The L stands for Limited in this case.

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dnjrboy

· #13 · May 19, 2005

I'm pretty sure that if you rev it up to 4 - 5 k and pop the clutch you will be able to create a 'limited slip' situation tho.

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theirishgonzo

· #14 · May 31, 2005

i rember once they were fixing my tranny and had my car on the lift and was spinning the tires up to 40 so they could get it to shift right but it had a regular diff and i could do realey good 1 wheel peels.

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onefastx

· #15 · Jun 30, 2005

dnjrboy said:
I'm pretty sure that if you rev it up to 4 - 5 k and pop the clutch you will be able to create a 'limited slip' situation tho.

I,m pretty sure if you did that on the stock cluth you would be buying a new clutch it would be fun though does anyone know what type of lsd they will be using (wet or dry)

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