cobalt

No I don't care if you took any in College.

I am confused by how to tell if mine is working properly or not. Tried to PM GT gears but his box is full.

I was under the impression an LSD should make the wheels spin in the same direction so both forward or both reverse. Another way to say it is if one is turned clockwise the other should turn counter clockwise.

An open diff I was always told should be opposite if one is turned forward the other turns in reverse. so both clockwise or both counterclockwise.

What I am confused by is happening in two cars. My C2 and track car. My turbo always turns the same direction but for the last few times I checked my C2 both turned opposite directions one forward one reverse. I assumed the plates had worn. Today I had the car on the lift and both were spinning in the same direction both forward and reverse. So why would it do it one way a few months back and differently today.

I am also seeing both turn in opposite direction on my track car previously they were both spinning in the same direction. Is this normal? Are my plates wearing out does it have anything to do with temps or any other factors?

Any input would be helpful.

Spyerx

Clearly matt is the expert here... on my gt3 how I was able to tell the plates were trashed: tight 180 corner mat the gas and the car will spin a tire or spin period. With a diff, controlled grip and acceleration out the corner.

That said, I believe the way to test while the diff is in the car is by having 1 rear wheel up in the air, one on the ground, trans in neutral, put a torque wrench on the axle nut on the side in the air, and measure the break away torque or when the wheel starts spin. I don't recall what OEM spec is but the spec of my GTPro diff in my RS is 88lbs.

cobalt

That is helpful thanks.

I will try the break away torque method and see what happens.

hockenheimr

I think it depends if the car is in neutral or in-gear......also I've hear that method doens't actually tell you if the car has a LSD or not! Plus, I think both tires need to be under stress for the LSD to work....hence the second method mentioned might be a better indicator.

We def need an expert to clear this up.

alexjc4

Assuming it is a plate diff not a gear (torsen etc) one, an Lsd will be setup with the friction clutch plates under a certain amount of "pre-load" pressure. This means if both wheels and the input pinion gear are free to spin then both wheels will turn in the same direction (fwd/rev) when you turn one of them.

The friction plates wear and get thinner and the preload can reduce, this will allow the diff to act as an open diff when you turn one wheel. It may still have enough life left to act as an lsd when driven from the pinion, just not as effective or predictable.

You can replace the worn plates or change the shim thickness in the clutch plate stack to restore the desired preload - up to a certain degree, obviously once the plates are past their wear limit they need replacing.

A fresh thick diff oil or oil without friction modifier may restore enough drag to the clutch pack to allow both wheels to turn the same direction again - at least temporarily.

cobalt

I tried the one wheel down with a torque wrench on the other in neutral I get the wheel to turn without any resistance with the car in 1st it seemed to begin to slip at around 88 pounds.

Both wheels spin in the same direction on one and opposite on the other. I know both have LSD's installed but was under the impression the one on my C2 was worn. Until recently I observed the C2 spinning in opposite directions now they are spinning in the same direction.

Winter is almost here might be time to open it up and take a closer look.

heliolps2

Hey air-cooled friends,

Reviving this thread, As said before, the way to test while the diff is in the car is by having one rear wheel up in the air, one on the ground, trans in neutral, put a torque wrench on the axle nut on the side in the air, and measure the breakaway torque or when the wheel starts to spin. I recall OEM spec to be 15 to 37 pounds on the 964 G50 LSD's

There has long been speculation that the sloughed off friction material from our LSD, as well as pretty much any LSD, factory included, could accelerate the wear on other components inside of the gearbox.

1. After the initial break-in of 500-1000 miles or so change your gearbox oil after installing our LSD or getting yours rebuilt. When you buy a new car, you do an initial engine oil change at an abbreviated service interval. You should do the same with our, or any new LSD you put into your gearbox.

2. Change your gear oil at a maximum of once a year. These are high-performance cars that get beat on. Guys change their engine oil at 2000-2500 miles against published factory service intervals of 3000-5000 miles, but they never seem to think that they should change their gearbox oil more frequently when they drive their cars sportingly. I change my gear oil every year.

3. Change your gear oil after every single race. If you "just" go to track days and run hot laps you can probably push it out to 2-3 track days/test-n-tunes. But if you drive the car in a racing environment at its mechanical limits for an hour or more, it's cheap insurance to spend $50-100 on gear oil.

This was advised by GT Gears.

Helio

cobalt

I trust Matt but think he was being a bit over the top with that advice. I have learned a lot in the past 5 years. I have discussed this with some engineers and mechanics and see no need to change the oil every year if not track driven and then it is dependent on miles not time. Sporty driving is far from track driving and I do mine once a track season unless I drive a lot of events or every 5 years for my street cars. There is very little friction material in our LSD's unlike Matt's LSD's which are far more robust. I have someone who tracked his 964 without ever changing his gear oil. No doubt it looked like the Northern lights in the oil and smelled like skunk butt. He was surprise he had shifting issues. He did end up screwing up his synchros from not changing his oil but it took 2 drivers and over 10k hard track miles to do so. I think for a street car flushing all fluids brake, trans oil etc every 2 years at min depending on miles driven will be more than adequate unless you drive 10k a year and if you track the car every 10 days on track or so will be more than adequate. Track weekends already run me around $3k an event so unless it is needed I will be fine with every 10 track days. I recently rebuilt my LSD on my C2 and inspected my trans. Everything was fine with no signs of wear other than the worn friction plates I was lazy and didn't change my fluid as often as I should have maybe 3 times in 10 years and about 20k miles so no worries of damaging the trans from what I observed. Interestingly other than the loss of friction material the trans and remaining LSD parts were all still in good condition although I replaced all the wearable parts while in there. This is 62 k miles of wear both track and street driven. As far as cost of you don't do the work yourself and pay someone you are looking at closer to $350 to change your fluid.