I purchased a 3.90 Differential from LAPD and had their service Dept. install it on Friday. Up to now, Ive installed all my mods (LAPD 218 cam, upgraded valvetrain, x-pipe, Corsa mufflers, new brakes, LAPD Billet gas pedal, etc). The diff install looked like something best done on a lift, and after watching LAPDs skilled mechanic, Im glad they did it not me :yesnod: The new gearset gets really hot during the break-in, so they suggested ~20 miles of easy driving at various speeds, 1 hour cool down, then repeat one more time. I guess that the gears have to "lap in" because of the type of metallurgy, but stock gears don't seem to require a break-in. After the two break-in cycles, I made the 140 mile drive back home without any WOT driving about 8:30pm. Forum members Stan and Karen (Stano) came by my house around 9:00pm after leaving our local Theater, So I took Stano with me for my first couple blasts with the new gears. My impressions: The car is more pleasant to drive around town with the 3.90's and does feel great in 2nd thru 4th at WOT. 1st gear ratio feels a little steep at full throttle, even though it is only about 10.37:1 (2.66 trans x 3.90 rear). The Z06 has a different set of transmission gears, so my total ratio's are now very similar to the Z's. I'm glad that I didn't go with 4:10's because first gear is already pretty snappy with the 3.90's. Quite a few forum members have 4.10's, so I'm sure it comes down to personal preference. The 3.90's definitely compliment my other performance add-ons and I am very happy with the results :D

Had a great time hanging out at LAPD with Shawn, AL and the crew. A couple forum members came by (b_pappy, jbsblownc5) to discuss issues of great social importance:...more horsepower!

Thanks to LAPD for the great parts and service, as well as the entertainment. (throughout the day, Shawn was busy using his 600+ rwhp C5 to paint new parking stripes on his lot) :lol:

:cheers:
Stan


[Modified by BlueRag, 9:40 PM 5/2/2004]


[Modified by BlueRag, 5:26 PM 5/3/2004]

 

actually they do. Thats a reason (among other reaons) why GM wants you to keep your C5 below 50mph when brand new for the first 200 or 500 miles (or whatever the spec is ???)

I take it you're not running with EMT run-flat tires anymore ?

 

No, I ditched the EMT's last November for Goodyear GS-D3's.......They are really great tires! Quieter, much better traction :)

Stan

 

Congrats on your new gear settup :cheers: now we want track times! :yesnod: :thumbs: :seeya

 

I went to our local po-dunk track at Inyokern last month for the first time with my 2001 M6. The track is 2489ft elev and the temp was ~77F'. I was only allowed two runs in my convertible (no roll bar). I managed a 13.2@111.4mph. My 60ft was 2.3sec with street tires. I'm hoping my 60ft will be 2.0 or better with the new 3.90 gears and more practice....If they ever let me run again :cry

:cheers:
Stan

 

Not trying to rain on your parade, but I want to make you aware of a potential problem. I had 3.90s installed near the end of JAN and loved them. No noise and the acceleration was great, but as I put some miles on the car I began hearing noise and initially I thought it was a throw out bearing because it sounded like it was coming from the front. I later find out that because of the C5 set up rear end noise can be transferred to the front right to the shifter. Turns out that the gears had not been properly heat treated during manufacture in Germany and that several of them are failing with low miles. The supplier in CA did not know when to expect a new shipment and after a couple of weeks of waiting I am going for a 3.73 gear set.

 

Who was the supplier in CA? My diff had paperwork from West Coast Corvette. This unit has a 1 year warranty, so I hope it is a "good" one.
Thanks for the heads-up :seeya

Stan

 

Glad to hear you like your gears. I too, had 3.90's installed on Friday. WCC did the install and told me to drive it home and let it cool overnight. It's about a 30 mile drive from their shop to my house. The next day I took an easy trip thru the twisty's in the local mountains and stopped about 5 miles into the trip and noticed smoke coming from the back. It didn't alarm me too much as I thought it was grease on the exhaust from them working on the car. Drove it some more and the smoke went away. I'm wondering now if it was the gears cooking themselves in.?? If that makes sense. In any event, these gears rock. I thought there would be a major traction problem, but it's better than the 3.42's. 1st gear comes and goes fast, about 35 mph and 2nd just barks and goes. It's funny, I'm actually getting 4th gear chirps. But you're right, drivability around town is great now. If anyone's contemplating a gear change, DO IT!! Best mod you can do.

 

Stan,
Yeah, like I really need a reason to swing by and the see Shawn & Al! Good to see you and glad you're enjoying the new gears. Take care
Bruce
(and tell Kelly we're saving her a paint brush :lol: )

 

:confused: :withstupid: :D