There is a whining noise coming from underneath my car and I do not really know what causes it. I wont sit here and explain it since there are two types. Based on the research I have done, the differential (or a component of it) can be the culprit. The other day, I put my rear end on jackstands with the wheels up in the air to assess the problem. I then left the car in first gear while the motor was running. I went to see my back wheels and was confused with what I saw. The wheels were still spinning and then as they slowed down, they reduced speed, stopped moving (for a millisecond), moved forward, stopped moving (again, for an extremely brief amount of time) and continued this indefinitely. In other words, there seemed to be a hesitation or a restriction. I dont know if this is natural or if this is related to the noises I am hearing but I want to go ahead and inspect my differential since the car is an old AP1 and I am the second owner.

So here are my questions:
What do you guys think about the movement of the wheels when I put them up in the air?

AND

How much should I be charged for the differential to be inspected? What should be inspected?

 

The LSD (Limited Slip Differential) will cause that sort of wheel spin when the wheels have no resistance.
This maybe also caused if when, you did your wheel spin test in the air, you pressed in the clutch peddle and held it in. If the wheels spun freely while doing this and then slowed briefly then spun freely once again then, you may have a fractured pinion tooth. The only way to inspect the rear diff is to remove it and remove the rear cover. You would put it in a parts washer or a 5 gal. bucket with some cleaner to brake down the gear oil. This will allow you to see clearly everything and to check for broke or cracked gear teeth. If you find no damage you can check all the torque specs and wear pattern on the gears, you can check the back lash too. If all looks fine then it maybe the LSD if this is the bad part by process of elimination, it is not serviceable and would have to be replaced.

You can start out easy before you get this deep by draining the fluid and inspecting it and the drain plug for ad normal amounts of metal or debris.

Expect to pay for a removal and reinstall of your rear diff to set you back about $400 bucks Have a good diff sitting on standby just incase yours turns out to be bad. You can pick one up for about 500 to 600 used and in good shape.

This is a pic inside the rear diff showing the dye to check your back lash


This is a pic of a stock LSD


This is the cover that has to be removed

 

Oh my...

 

For starters you could try this: The Diff Test (as per service manual)

#1 - Put rear of car on jack stands, both rear wheels of the ground.
#2 - Make sure #1 is absolutely safe!
#3 - Put car in gear (any gear will do)
#4 - leave engine OFF!
#5 - turn one wheel clockwise, this should be possible without crunching noise or feel.
#6 - during #5 the other wheel should turn the opposite way.
#7 - perform turn test on both wheels.

S2KPUDDYDAD is right about the full tech inspection and the oil drain to see if that shows something.
This is something yo can do yourself.
And.. if you let the diff drain for a while you can see the ring gear through the drain hole.
You can inspect the ring gear for damage and or missing teeth.
You need a small flashlight for it.

Succes

 

What are the mileage intervals for changing the diff fluid? 15k or 30k miles?

 

Severe conditions 15k miles, regular 30k, from the manual.

 

Or like me at every oil change

 

Severe conditions = racing of any type?

 

Not just racing but, hi heat, excessive driving, dirty driving conditions like on un paved roads ect. Anything that can be categorized as