Imo000

In both, the pic and the clip, the tires do the same thing, there is no difference as they are both one wheel burnouts. If there was someone on the other side of the road, all they would see was the S4 accelerating withouth any tire spin and a ton of white smoke pouring out the back. It would look like a 928 with a blown headgasket.

JKelly

Thanks for the verifications. I'm not questioning whether it has an lsd or not anymore. I am very pleased with the way the differential operates just the way it is. I previously assumed that it had lsd by the way it acted. Reading through many posts here on the forum, it is said multiple times by different people that an open diff will only burnout with one tire and an lsd will do it with two. This generalization is NOT TRUE. As others have said in this thread, they can burn two wheels and do not have lsd.

From what I've read in other places on the internet about the open differential and how it applies torque to the wheels it sounds like mine operates just as it should. Since LSD has been eliminated as a suspect for the noise, the next suspect is vibrating shift rods.

Dave, according to your photo, more than likely it is your tires that are crap. Mine are like new and at proper inflation. There is no binding when rotating the wheels either. Actually, even when I had crappy tires both of them would burn, so maybe there is something wrong with your differential or gears .

Thanks again for everyone's help. On another note, it would be cool to have a fiber optic snake camera to explore the transmission without having to take it out :

SharkSkin

Actually, when I did that burnout my tires were junkier than junk -- cracked sidewalls, corded, probably 10 years old. I was running what the car came with, waiting (and waiting, and waiting) for my 17's, so didn't see much point in buying 16's at the time.

So, your tires are fine -- what kind of surface were you doing this on? Looking back at previous posts, you say if you have one wheel on gravel and one on pavement sometimes the one on pavement will spin. This does not sound normal for an open diff -- not at all. Yet, if you say there is no binding in the spider, it's a big mystery.

My first impression from the pics you posted of the inside of the unit is that the ring gear appears to be very worn. Maybe it's just the light. I don't know if you still have it open or not, but if you do, can you get some detailed close-ups of the contact point? Also, if you can take good close-ups of the spider gears at various points that might be instructive.



Rotate the ring gear 90° from the orientation shown above, then put the car back in gear. Then take close-ups of the spider gears through the hole in the casting(hole in casting should be full-frame, if you can get sharp pics that close), rotate one wheel ~60°, take a pic, repeat 5 times.

If all looks good then we are back to

An open diff can leave two stripes, but only if all forces are balanced. An open diff leaving two stripes while turning -- and doing so consistently -- is almost unheard of. I think others here share my concern that if the spider gears are binding(one possible explanation for your observations), they may eventually grenade on you and cause collateral damage.

JKelly

Dave, I'll have to come back to this after the weekend. The gravel test was with very quick blips of the throttle and both wheels were in gravel.

I understand now that with an open differential the engine will deliver power to the wheel that has the least resistance (least traction). If both wheels have an equal loss of traction, then I guess both wheels would spin. If doing a sharp turn, the inside wheel spins and I guess the lighter line that the outside wheel makes could be caused by the friction from the lateral force (?). If one wheel is on ice and the other on pavement, then the engine delivers power to the wheel on ice because it has the least amount of traction. The other wheel has more traction and therefore doesn't receive power, but the car doesn't go anywhere because ice is slippery. It's clear as mud .

Here are some more photos that I had already taken (the diff cover is on now). The trans/diff has 78k on it:

T_MaX

As discovered, it is an open dif.! One thing I learned early on, just because your option sticker doesn't say you have an LSD, doesn't mean you don't

Vibrating shifter rod and "gear growl"?

How are your transmission mounts and wheel bearing?

SharkSkin

Sounds reasonable, and if that's the case then you're doing sharper turns than what I had imagined from your description. I had the impression that you were just nailing the throttle and swerving maybe 1/4 turn on the wheel one way, then 1/2 turn back, etc. -- just enough to unload the inside wheel.

Your description is accurate -- a diff will distribute power more or less equally until one wheel loses traction, then all of the power goes to that wheel; at that point the only force driving the wheel with traction is the cumulative drag of the various items in the spider gear assembly(not much).

The "one wheel in gravel, one on pavement(in a straight line)" test should never spin the wheel on pavement with an open diff -- try that, you will eliminate the variable of lateral forces on the other tire.

In your middle pic, it looks like one tooth of one gear has a small chip in it(10:30 position). Very minor, probably not worth worrying about. I only point it out because otherwise, they look perfect.

I'm still a bit concerned about the contact points on the ring gear. Again, maybe it's just a trick of the light/camera, but it looks rough. If it's really as rough as it looks that could be your growling noise.