How to tell if the diff is a LSD or not

geofd · #1 (**permalink**) 10-21-2006, 03:18 AM

Hi All
I have a 105 GTV 2000, wondering if there is any visual marking or way to tell if the diff is and LSD. It is an Australian delivered car ( I understand all US delivered cars have LSD units in the 2000 models)

Any help on this would be helpful so I ensure that I use te correct oil

Thanks

Geof

**Tifosi** · #2 (**permalink**) 10-21-2006, 10:50 AM

In theory, (based more on internal condition and clutch settings), if you put it up in the air so both hubs/wheels hang free and the driveshaft or input yoke cannot turn, (not by parking brake), then rotate one hub and the other hub turns in the opposite direction it 'should' be LSD.

If only the hub you are turning moves, then it's an open diff.

GTVdrifter · #3 (**permalink**) 10-21-2006, 03:56 PM

Both types of differentials have aluminum center pumpkin with cooling fins on them. An open diff has alternating long and short fins. A limited slip has the same size fins all around. This is the easy way of telling.

An Alfa limited slip uses a clutch disc between the spider gears but, there is no static load. It relies on force to load the clutch only when needed. If you try to determin if it is a LSD or not by jacking the car up, they act and feel exactly the same. Rear wheels off the ground, driveshaft locked (in gear) if you spin one wheel, the other wheel will spin the opposite direction. Both LSD and non will do the same thing.

It is possible to shim the clutch or double up on clutches to get a static load.

joecautela · #4 (**permalink**) 10-21-2006, 06:29 PM

The LSD diffs I've seen/used have a V shaped fin on the bottom of the cover. Another fun way is to get the car on a dirt road and do a hole shot at about 3k rpm. On a std axle one wheel will spin the other will follow, an LSD will spin both untril traction is gained. LSD's are fun and worthy for hard driving and racing. For the unknowing they can be tricky on ice and snow.

geofd · #5 (**permalink**) 10-21-2006, 06:56 PM

Thanks GTVdrifter, I thought that was the case with regard to jacking the wheels. The fins on the dif are equal so should be an LSD, but even some reading on that topic has rasied questions (mainly for non US delivered units)

Hi Joe not sure about the V shaped fin on the bottom cover, dont have that, but I guess I can try the dirt road trick, may be fun.

**papajam** · #6 (**permalink**) 10-21-2006, 07:10 PM

The 'V' ribbed housing and three extended cooling fins on the sump indentify an LSD rear. A non-LSD rear lacks these features.

geofd · #7 (**permalink**) 10-21-2006, 07:58 PM

Thanks for the picture, that makes it pretty easy to identify.
When I am home I will check. The car is locaed in Australia, its a holiday hobby.

**ddouglas77** · #8 (**permalink**) 10-21-2006, 08:12 PM

If it is spring loaded (I'm sorry, I'm a GM guy), if you put the rear end up in the air and turned one side one way a limited slip will make the other tire go the same way-not opposite-only if it is in gear would the other tire spin in the opposite, but would take some muscle to move. In GM, limited slip is always on, it takes the force of a car in a turn to slip on the clutch, which is why we always say never put a donut on the rear end of a posi-as the smaller tire would be rotating faster causing the clutch to slip and burn over time. Is Alfa different in this manner?

joecautela · #9 (**permalink**) 10-21-2006, 10:47 PM

ddouglas, good question as the old timey GM Postraction (limited-slip) units and the Ford Trction-Lok rears depending on the install would normally kick in and lock anywhere from 1800-2500 rpm. So I would think that running down the road at any more than 40mph in top gear may cause the clutches to try and engage. But it would most likely be on the larger size tire as the clutches would sense slower speed on the larger wheel. Remembering that a wheel broken loose of traction does not spin hence the engagement of the Posi unit. On my late model Buick there is a traction-lok disable switch. It is factory recommended to dis engage traction-lok in severe weather i.e. ice/snow to prevent the ABS from working itself to death trying to offset the spinning drivewheels and the natural transfer of power back and forth across the drive wheels when the traction-lok is working it's hardest. The ABS works as a traction-lok in reverse in severe weather.

**ddouglas77** · #10 (**permalink**) 10-21-2006, 11:12 PM

Hmmm, Gm and ford is not rpm sensitive, they're torque sensitive...Turning one wheel, will cause the other wheel to turn the same direction, if you apply 100ft/lbs of torque to the wheel you are turning and hold the the other one with the same amount of force, the clutches slip, not engage. Clutches in LSD are always engaged until the torque overcomes the holding power...Moroso sells aftermarket LSDs for GM and Ford and both use extreme spring pressure to keep clutches together, limiting slip, except when you turn, think about the torque required to make a tire spin-same is true with LSD, except you are keeping the tire from spinning while turning. A wheel broken loose from traction will spin-that is the whole point of LSD.