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914World.com _ 914World Garage _ Is this LSD ?

Posted by: drifter914 Nov 8 2019, 10:03 AM

So I have this '76 914-8 with an LS-1 conversion & one day while pulling out of a graveled area I kicked it a bit & noticed leaving 2 ruts behind instead of the one I was used to in a previous 914.
So the other day when I had it up on jack stands I started it up, put it in 1st gear & let it idle while I got out to look... left rear wheel was turning fwd at a constant rate, while the right was also turning fwd, but at a slower rate.
Could it be that I have some sort of limited slip arrangement here ? Transaxle is a modified 901 & has the numbers HA 22095 on the bottom of the case.
Thanks for any info on this... Terry

Attached Image

Posted by: mepstein Nov 8 2019, 10:13 AM

Jack up the rear. Turn one wheel forward. If they both turn, you have a lsd.

@http://www.914world.com/bbs2/index.php?showuser=15863

Posted by: GregAmy Nov 8 2019, 11:05 AM

The car that made these two equal-length tire marks had positraction. Can't make those marks without positraction.

And why not? What is positraction? It's a limited sIip differential, which distributes power equally to both the right and left tyres.

The 914 has a regular differential, which anyone who's been stuck in the mud knows you step on the gas, one tire spins, the other does nothin'.

Posted by: Retroracer Nov 8 2019, 01:54 PM

QUOTE(mepstein @ Nov 8 2019, 09:13 AM) *

Jack up the rear. Turn one wheel forward. If they both turn, you have a lsd.

@http://www.914world.com/bbs2/index.php?showuser=15863


agree.gif - as long as they both turn in the same direction.

- Tony

Posted by: burton73 Nov 8 2019, 02:50 PM

My Cousin Vinny (5/5) Movie CLIP - Automotive Expert (1992) HD

Positraction?



Bob B

https://www.youtube.com/watch?v=CFdJza0AbeA

Posted by: mepstein Nov 8 2019, 03:33 PM

Sorry, meant to say if both turn the same direction forward or backward, it’s got lsd. If they turn opposite, no lsd.

Posted by: drifter914 Nov 9 2019, 10:30 AM

QUOTE(mepstein @ Nov 8 2019, 02:33 PM) *

Sorry, meant to say if both turn the same direction forward or backward, it’s got lsd. If they turn opposite, no lsd.


O.K. ... this morning I jacked up the back end & spun the driver side rear wheel by hand... first in neutral ... then in 2nd gear same result... they turned in opposite directions... no LSD .
So the two ruts in the gravel must mean that with very little resistance, the wheels spin alternatively. I notice the right side rut is more pronounced.
I imagine on asphalt I would leave only a right tire burnout, but I just am not a burnout guy... so no LSD for me !
Terry

Posted by: settador Nov 9 2019, 11:19 AM

Last time I had LSD
I saw colors and
the road was like sea

Posted by: sixnotfour Nov 9 2019, 11:47 AM

Augustus Owsley Stanley III is rumored to have made the best

Posted by: Superhawk996 Nov 9 2019, 11:56 AM

QUOTE(drifter914 @ Nov 9 2019, 11:30 AM) *

QUOTE(mepstein @ Nov 8 2019, 02:33 PM) *

Sorry, meant to say if both turn the same direction forward or backward, it’s got lsd. If they turn opposite, no lsd.


O.K. ... this morning I jacked up the back end & spun the driver side rear wheel by hand... first in neutral ... then in 2nd gear same result... they turned in opposite directions... no LSD .
So the two ruts in the gravel must mean that with very little resistance, the wheels spin alternatively. I notice the right side rut is more pronounced.
I imagine on asphalt I would leave only a right tire burnout, but I just am not a burnout guy... so no LSD for me !
Terry


The reason you see two tracks is because the road friction is reasonably uniform at each contact patch at each tire. In the case of gravel it is a medium friction surface. Friction is referred to as Mu in reference to its Greek symbol that represents the coefficient of friction in physics equations.

A conventional open differential is able to drive both wheels with approximately the same force to each wheel on medium and high Mu surfaces. For typical passenger car applications It isn't until you get onto very low mu surfaces (mud, snow, ice, etc.) that the "one wheel peel" effect of spinning up one wheel becomes a problem.

Similarly, if you are cornering hard and unloading the inside tire, that wheel can spin due to the light load on it that limits the amount of torque it can transfer to to road. An open differential can only transfer torque equally between the wheels. If one wheel is lightly loaded or on low mu (like ice), that low torque transferred is effectively zero. One wheel spins and transfers very little torque and the other wheel therefor gets zero torque, and the car doesn't move. At that point you're giving up forward momentum. LSD's are used in performance applications to help overcome this limitation of an open differential but if you lift a wheel off the road even with a LSD, you'll quickly discover that even a high bias LSD can't transfer very much torque. Better than an open differential but still not very much. Modern electronic Limited Slip Differentials would be the sole exception but those really are a completely different animal vs. a clutch plate LSD or a Torsen.

In your case, with both wheels just going straight with no cornering, the load on each is about equal. The road surface is about equal mu from side to side. The open differential transfers approximately equal torque, therefore you get approximately equal spin out marks.

Posted by: rgalla9146 Nov 9 2019, 12:32 PM

QUOTE(drifter914 @ Nov 8 2019, 11:03 AM) *

So I have this '76 914-8 with an LS-1 conversion & one day while pulling out of a graveled area I kicked it a bit & noticed leaving 2 ruts behind instead of the one I was used to in a previous 914.
So the other day when I had it up on jack stands I started it up, put it in 1st gear & let it idle while I got out to look... left rear wheel was turning fwd at a constant rate, while the right was also turning fwd, but at a slower rate.
Could it be that I have some sort of limited slip arrangement here ? Transaxle is a modified 901 & has the numbers HA 22095 on the bottom of the case.
Thanks for any info on this... Terry

Attached Image


a 914 trans with OEM LSD would have HB as a prefix....but many types
are available for later install.
your two wheel burnout is due to reduced traction and a straight start.

Posted by: GregAmy Nov 9 2019, 04:21 PM

QUOTE(settador @ Nov 9 2019, 01:19 PM) *

Last time I had LSD
I saw colors and
the road was like sea

drunk.gif

If it's a torque-biasing diff, like a Quaife, it would roate different directions. The "jack up the rear and check for wheel rotation direction" only works for sprung-clutch-type or Detroit Lockers.

Two scratch marks? With a V-8? That's an LSD.

You really should watch your culturally-significant movies. Marisa got it right.

Posted by: djway Nov 10 2019, 01:28 AM

Back in the day my lil Baja Bug shot up two monster rooster tails and it was nuttin but a 67 swingaxle

Posted by: settador Nov 10 2019, 11:00 AM

QUOTE(sixnotfour @ Nov 9 2019, 09:47 AM) *

Augustus Owsley Stanley III is rumored to have made the best

So I have heard.

Posted by: 914bub Nov 10 2019, 11:33 AM

And if you do have a limited slip and you break em loose making a right turn at say an intersection brace yourself because as soon as you get traction again your going straight, and quickly into whatever you're pointed towards. I learned that one the hard way when I was 18 in a quick 68 Volvo 1800. In my case I was pointed towards a Santa Clara county bus stop bench. Wiped out the bench and the front end of my 1800. I also learned that Jack Daniels and limited slip + 18 years old = FAIL. Glad I lived through my stupid youth without hurting somebody.

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