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Greetings,
I have a 2004 Corvette with 25K miles and it is an A4 transmission. The current gears are stock 2.73. The only mod I have done is a cat back exhaust system. I have had several muscle cars where the mods never stopped, and the spending of money never stopped either. One mod always gave way to another. It was really fun, but that is not what I want to do with my Vette. I just want to maximize my stock engine and get a more responsive car with better acceleration. hence the 3.42 gears. Can you just swap out the gears and leave it at that? Do you need a tune? Does the computer need any changes? I am not interested in stall converters either. I really want this to be simple and not lead to more **** and more expense. I am not a mechanic and will need to find a shop to do the work.
Yes you will need a tune. Think of it like this. Now your engine is turning higher rpm for the speed you're moving, the computer will think the tranny is slipping.
You will love the gearing. I have the 3.15s and if I have an issue, will be going to 3.42s. I can't even imagine driving it with 2.73s as it would be such a dog. I have done a lot of reading on it and it seems for me that with the driving I do the 3.42s would be the sweet spot between performance and highway mileage. Your tuner will also be able to adjust your throttle progressivity tables (how fast the throttle opens compared to your foot) which will also put more pep into it for you.
One thing you need to look into - I do not believe the gears will go into that housing without modification. Some posts say it's easier/better just to get the new diff.
Close to six years ago a bearing in the 3.15 rear drive on my A4 began failing at Buttonwillow Raceway, lots of metal in the rear drive fluid. I had a 3.73 rear drive and a WaveTrac differential installed. I got by Mclaren and a Lamborghini last October at Arizona Motorsports Park with a stock engine.
I like the 3.73 for road course tracks. If you are only going to drive on street, the 3.42 would be a better choice.
Yes you will have to have the PCM reprogrammed by a knowledgeable shop or the shift points will be wrong. In my case, the PCM would not shift the transmission from 2nd to 3rd at full throttle, hitting rev limit first before the PCM was reprogrammed at A&A Corvette in Oxnard CA.
A gear ratio change requires a simple software tune adjustment for speeedometer accuracy. A shift kit and transmission software tune make a big improvement to the way the car drives, even with 2:73 gears; instead of shifting for EPA ratings it becomes more responsive and less sluggish especially for part throttle kick down.
A gear ratio change requires a simple software tune adjustment for speeedometer accuracy. A shift kit and transmission software tune make a big improvement to the way the car drives, even with 2:73 gears; instead of shifting for EPA ratings it becomes more responsive and less sluggish especially for part throttle kick down.
I believe the speed is measured at the axel, so the speedometer is unaffected by a gear change. Whereas, a change in tire size would affect the speed sensor.
With a gear change the trans shift points would need to be adjusted in the tune.
Close to six years ago a bearing in the 3.15 rear drive on my A4 began failing at Buttonwillow Raceway, lots of metal in the rear drive fluid. I had a 3.73 rear drive and a WaveTrac differential installed. I got by Mclaren and a Lamborghini last October at Arizona Motorsports Park with a stock engine.
I like the 3.73 for road course tracks. If you are only going to drive on street, the 3.42 would be a better choice.
Yes you will have to have the PCM reprogrammed by a knowledgeable shop or the shift points will be wrong. In my case, the PCM would not shift the transmission from 2nd to 3rd at full throttle, hitting rev limit first before the PCM was reprogrammed at A&A Corvette in Oxnard CA.
I have the 3.15 performance rear axle in my 2004 vert. I'm considering a LS6 CAM and updating to 3.73 rear gears. Curious why you feel the 3.42 is better for the street. I would like to improve my off-the-line performance knowing that I may sacrifice some top end speed. I'm also looking to do this without adding headers or a higher stall. I already have a Callaway Honker CAI, Corsa X-pipe w/axleback, and a prior A4 tune with low-temp stat. I know if I add the CAM and new rear gears, I will need another tune but just trying to better understand the pros/cons of the 3.42 vs. 3.73 rear gears.
I have the 3.15 performance rear axle in my 2004 vert. I'm considering a LS6 CAM and updating to 3.73 rear gears. Curious why you feel the 3.42 is better for the street. I would like to improve my off-the-line performance knowing that I may sacrifice some top end speed. I'm also looking to do this without adding headers or a higher stall. I already have a Callaway Honker CAI, Corsa X-pipe w/axleback, and a prior A4 tune with low-temp stat. I know if I add the CAM and new rear gears, I will need another tune but just trying to better understand the pros/cons of the 3.42 vs. 3.73 rear gears.
The 3.42 increases wheel torque by 10%. The 3.73 increases wheel torque by 20%.
Its not like we’re discussing 4.56’s or something crazy. 3.73 is a good street gear, and you have stated off line performance as you goal, even at the expense of top end speed. And as far as top end, there’s a couple hundred rpm difference.
Here's a chart just so you can see how that gear would affect rpm's with a auto, you would be buzzing 2300rpm at 70mph in overdrive
…vs 2100 rpm at 70 mph with 3.42’s. That hardly noticeable. What this chart fails to demonstrate is the acceleration benefit throughout the gears under acceleration, and that’s where the lower gears really help the otherwise stock engine take advantage of the power curve sooner.
Last edited by vette4fl; Feb 15, 2022 at 01:27 PM.
I don’t believe a 3.15 and larger gear ratio will fit in a 2.73 carrier. So, not just a gear swap.
You might talk this over with your shop first.
You are correct. You need a 3 series carrier. A 3.15 can be used for either the 3.42 or 3.73. I believe you could also go with a 3.90. Not sure on the 4.10. My car came with the 3.15, so I went from a 3.15 to a 3.42, and I really like it.
You are correct. You need a 3 series carrier. A 3.15 can be used for either the 3.42 or 3.73. I believe you could also go with a 3.90. Not sure on the 4.10. My car came with the 3.15, so I went from a 3.15 to a 3.42, and I really like it.
Did you add any other performance parts with your 3.42 gears? CAM, intake, exhaust, headers, etc.? If not, what the biggest difference you felt just switching from 3.15 to 3.42 rear gears?
"Curious why you feel the 3.42 is better for the street."
Drove it for an hour today to formulate my answer.
With A4 and 3.73 rear drive, stock engine and torque converter, first is pretty low, a tire shredder with stock size, 300 wear rating tires. My PCM is programmed to not allow an automatic 3rd to 1st downshift out of a turn - which with the 3.15 rear drive had me all over the track a couple of times.
Only manual downshifts on track for the last few years have kept me out of trouble.
On the other hand, the 3.73 is a circuit breaker, breaking tires loose before breaking something more expensive.
Would I go 3.73 with WaveTrac differential again- absolutely.
Keep in mind that I am a 77 year old with 12 years, 23 days on road course tracks with this car, not a drag racer. My car number is my age-
Yes you will need a tune. Think of it like this. Now your engine is turning higher rpm for the speed you're moving, the computer will think the tranny is slipping.
I just put a 3.42 diff in my auto 05 and I got a trans slip check engine. I’ve had the trans inspected cause it’s under warranty and they’ve told me everything looks good with the trans and torque tube will a tuner be able to tune that check engine?
Just need to adjust the PCM so it recognizes the gear ratio change. Find a shop that will do that. If the shop changed the diff didn't realize you needed that, find a shop that understands what needs to be done
Installing 3.42 Gears
