bigdogbr

I am having the rear changed in my 98 vette. It's automatic and i'm going to 3:42.
Is there a speed sensor that needs changing or will it have to be re-programmed afterwards? Any chance the computer will just figure it out?

SaberD

it needs a tune.

https://www.corvetteforum.com/forums...to-3-42-a.html

NukeC5

Just tuning is needed. You will like the gear change, really wakes the car up. But the car won't know how to shift at WOT until you get it tuned, it will just red line until you let off the peddle. (Ask me how I know). Also as you are aware of, the spedo will be off.

Are you installing a used take out diff or a new aftermarket? And is it single or three rib? I suggest the RPM stage II. Outstanding diff for the price. I push around 600whp on nitrous through mine with full racing slicks. It uses C6 output shafts which are good for around 900whp if I recal.

I had the bad luck of purchasing a used 3-rib and paid for the instal. Worked fine but I discovered why it was removed. Had gear whine from hell. After living with if for months, I ordered the RPM unit and used the three rib I got used as a core. Good for a lot of power and nice and quiet. Make sure you know what you are buying. Because odds are, a used diff was removed for a reason.

tommyo4

I was just looking into this and didn't realize how expensive just the parts are. I was hoping to be all in at around 1500 but was told a rebuilt rpm runs about 1800 for parts alone plus install.....tell me if I'm wrong.

NukeC5

Looks like the price has increased. But your existing diff can be worth some as a core. My three rib was worth $700. A basic 2.73 single rib is probably good for $300. Still, it's quite pricey. I also opted to do a t-tube rebuild kit, the high strength converter drive plate, and poly 6 shooter bushings. Made for a big expensive job, but it was a good time to do it along with my 3200 stall converter. Now wishing I had done 3600-3800. It's not a cheap modification to get into.

tommyo4

Unfortunately no, the 1800 is the price with your core included!

bigdogbr

Thank you for the replies. The rear is in and working well. BUt yes, i'm hitting the rev limiter and it needs reprogramming. I know I am going to be happy with this change.
Thanks for the info.

john8642

I believe the 2:73 case has the speed sensor in a different position than the 3:15 and 3:42. If you started with the 2:73 case, your speedometer won't work. I was researching replacing the shafts in my 03Z with C6 Z06 shafts and they discussed the case difference on page 3 of this thread:

https://www.corvetteforum.com/forums...-z06-guts.html

NukeC5

That's interesting, I started with 2.73's and have had two 3.42 diffs work fine in my 99.

tblu92

When changing gears on a C5--You do NOT have to make a speedo correction in your tune---However on an auto trans you do have to make a "shift point correction" for all the P/T tables as well as the WOT tables---Both upshift and downshift----

If you car had 2.73's it is a -25% change
If your car had 3.15's it is a -9% change

C5 Pete

What he's talking about is the physical location of the speed sensor in the diff. The 2.73 has it in a slightly different location compared to the 3.15/3.42 diff. The sensor will still plug into the diff, but you cannot install a different gearset into the 2.73 diff without a spacer, while the 3.15/3.42 diff will accept any aftermarket gear ratio.

v98roadie

You can read my thread on it. Cost me a bundle because I tried to save a few bucks. The 2.73 three rib case has the shift speed sensor in a slightly different location than the 3.15 / 3.42 three rib case. Though the gears fit it won't work with an A4 without some modification. I love my A4 with 3.73 gears in it. Huge difference!

tblu92

Ok he didn't say if he replaced the dif with a complete different unit like out of a Z06 or changed gears in his own dif------both scenarios require different fixes---