Rear diff swap
Thread Starter
Intermediate
Joined: Jul 2023
Posts: 25
Likes: 0
Rear diff swap
Hello everyone, I'm swapping out my 2.73 rear in my '99 C5 auto, for a 3.15. Does anyone know if the transmission needs to be reprogrammed after the swap? If so, what program, or device should I use? Thanks Very much for your help!
Racer
Joined: Oct 2021
Posts: 324
Likes: 157
From: Maine
I had a local tuning shop reprogram mine, I did the same swap to 3.15s they need to program a MINUS 15% change in the shift tables, I was told they did not touch the part throttle 1-2 and adjusted part throttle for 2-3 shifts and 3-4 and all the wide open throttle. They found all the information on the HP tuners forum, they sue HP-Tuners for all their programing.
Burning Brakes
Joined: Dec 2022
Posts: 1,007
Likes: 865
From: Nappytown MD
And don't be fooled by buying a handheld Tuner to do the re-programming, you need/want this done right and you need a real tool like HPTuners or other like tools to re-program the trans correctly. Better to pay someone once and get it right the first time.
Last edited by Missileboy; Feb 16, 2024 at 01:33 PM.
Drifting
Joined: Sep 2022
Posts: 1,784
Likes: 2,028
From: In the woods
2024 C5of the Year Finalist - Unmodified
^^ I second that. If you're going to go through the trouble of changing the diff go with 3.42. I currently have 3.15 in my 2K Coupe, it will have 3.42 soon.
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Race Director
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I had the 3.15 gear as OEM (G92 option). The 3.15 will help you, but not as much as the 3.42. But as posted, if you don't already have it, go 3.42. Some guys even go with a 3.73, which was never available from GM. One thing to keep in mind that you seldom see. That would be that the lower ratio (higher numerically) diff you go with makes it easier for the 4L60E trans to turn the axles. A small point, maybe. But the 4L60E isnt known for maximum durability, so any help you can offer it can't hurt any.....
