I did my first tranny oil change at 130K with Redline 75W-90NS at the suggestion of a tech at Redline, who said that Porsche 911 LSD's tend to not chatter with it. The invoice on the previous owner's service said Redline 75W-90, but we thought the mechanic may have just left off the NS. I have never experienced chatter before, but this must be it: When I start out in first gear from any curve off of straight ahead, I feel a grinding sort of vibration that runs clear up the gas pedal to my right foot. When I start out straight ahead, no such sensation. I assume she be a-chatterin', so my questions are, do I need to order Redline friction reducer additive or can I get something at NAPA that will work? Anyone have experience with how much additive will take the chatter away? Am I damaging my car by driving it like this? Man, I bought a full case of NS with lots of shipping charge to Alaska. Oh well. Finally, she took about 3.5 quarts of tranny oil, is that about right?

 

Hi:

Sounds like the LSD is binding a bit.

You can find an EXCELLENT LSD additive made for this express purpose at your GM dealer. Its a small bottle of additive that you add to the tranny oil to prevent the "stick-slip" phenomenon of LSD plates that you are experiencing.

 

When my ZF chatters, you can feel it hopping around at the back slightly as the tires fight each other in a slow turn with the power on.
I use the GM additive, it works perfectly every time. With dino gear oil I would get chatter back in 10k miles, so I was on 10k gear oil change intervals. When you have a diff that's worth $$$$, spending $20 on gear oil every 10k is nothing.

 

Thanks, fellas, I'll get the GM additive and give it a "shot."

 

I put it in last night and it cured the problem. Seems to shift just great also. Just in time for a 720 mile round-trip to Anchorage this weekend. Thanks again.