Afternoon Ladies and Gents, Ive got a bit of a simple question that all of the googling I could muster was unable to answer.
So from the symptoms my car is displaying I have reason to believe that the clutch packs in the diff are failing, now of course I'm going to have it properly inspected to be sure of the problem, but I'm 99% sure thats what it is.
I have been referred to Unitrax Drivetrain Inc in Anaheim CA as the local vette/viper experts when it comes to trans and diff rebuilds (also open to suggestions if anyone else comes to mind), and when speaking with them about the costs of tearing it all down and replacing all failing parts I found out that it'll only be an extra $400 or so to re gear the old gal, which sounds mandatory.
I currently have the 3.15 performance axle, and have heard that the increase in SOP performance when swapped to 3.42's isn't a huge difference. So I'm strongly considering 3.73's for some good get up and go. However everywhere I read has people swapping torque converters whenever going above 3.42. This is my only car and everyday driver, and will likely never see any form of track.
My main question comes from a c4 thread I found where first gear in the auto was wayyy too low if swapped to certain lower gears without a converter, so no traction was possible ever. Is the same true for the C5's? Or are their any other detrimental effects of not installing one that I'm not thinking of?
I really want more zest out of her at lower speeds and off the line, but don't wanna sacrifice drivability.
Its a pure bolt on's car, full intake and shorty headers and back exhaust, and I'm unlikely to ever dip into the motor, so this would be about the peak of my mods for more power (not counting the final tune id be getting to tie it all together)
Thank you all for your time, I'm anxious to see what everyone says.
-Gabe

 

Also, before anyone says. Im not buying one of west coast corvettes complete rear diffs because the cost of one of those alone is how much or even slightly more than the labor and parts would be would be for clutches and ring/pinion, without labor. So while their units are probably amazing, its too rich for my blood, I'm a full time college student without the cash to blow on much excess,
-Gabe

 

ok so there is lots of google type info on the gear ratios of the 700r4 and our version of that trans combined with the different rear end ratios.

the swap up is one one of the least expensive power to the wheel upgrades...


so this is what i would do.....look at the engine RPM from your google search in OD at a set MPH with your new ratio rear end. ( i can help you with that if you need it.) then go for a drive and try and approximate that RPM level by shifting to a lower gear. see if you are comfortable with the noise level.....that will give you a good feeling for what it will be like driving at a normal cruising speed.

and go from there if the higher RPMs dont bother you can go as high as your want in the rear end ratio. the higher numerically you go the more wheel spin in first you are going to get. first gear is really LOW and adding a really low rear end (higher numeric ratio) will make first gear almost too steep. 2, 3 and OD not so much of an issue

so 3.43 is probably a really sweet spot due to the first gear steepness

on the Torque converter question.....yes a really loose torque converter will under certain conditons let the engine RPM spool way up while delivering less RPM to the rear wheels.....changing torque converters is probably a $1200 job and less lock up of the torque converter will make MPG go down

i did this on my C3 when I put in the 700r4 trans so i know all the things you are talking about. we need to see how the engine management system on the c5 communicates to the Torque converter for lock up. we need to make sure it isnt calling for lock up and cancelling out your high stall speed torque converter. the lock up is why we get so such good gas mileage

 

If you're not going to race your car, the high stall TC isn't needed. You'll enjoy almost instant response from the 3.73s and your car will feel much quicker. Go for it and don't worry about the rest. That one mod will be a ton of fun.

 

Thanks so much for the feedback you two, they've both actually helped. Still open to suggestions as well.
-Gabe

 

I changed from 3.15 to 3.73 on my A4 Coupe not quite two years ago. The car had developed a ring/ pinion whine after a track day and a check also revealed that one or both bellville springs were broken in the differential (very low torque to turn one rear wheel with the trans in park and car raised).

The new rear drive included a Wavetrac differential instead of clutch packs.

Keep in mind that the PCM will have to be reprogrammed and that since 3.73 is not a stock option for the C5 A4, a dealer does not have the appropriate program. Without the reprogram, the engine will hit rev limit before the transmission up shifts at WOT and general around town shift speeds and firmness will be inappropriate.

My car was very well reprogrammed by A&A Corvette in Oxnard, CA.

In my case, I had the programmer set the 3-1 (or 2-1) downshift speed slow enough that the transmission would not downshift to 1st coming out of the slowest turn on the tracks I run. An unexpected shift to 1st there would put the car sideways if I didn't react very quickly even with the 3.15 rear gears.

With a stock engine and torque converter and the active handling system in Competitive Driving mode, the 3.73 ratio provides enough torque in 1st to easily make smoke and also wheel spin on the 2-3 upshift at WOT. At WOT and with the active handling system in normal on mode, it will pull power at the 2-3 shift because of wheel spin, especially if there is any lateral G on the car.

My first reaction at Laguna Seca with new 3.73 gears was "The car goes!"

Around town, 1st is pretty low but workable with the reprogram.

Overall fuel mileage dropped by about 2 mpg going from 3.15 to 3.73 gears.