C5 Rear Differential
Thread Starter
Melting Slicks
Joined: Mar 2001
Posts: 3,251
Likes: 48
From: Parkland Florida
Corvette Challenge Champ-01
Dragster Challenge Champ-06
C5 Rear Differential
Put a 3 rib C5 rear diff with C6 3:42 ring and pinion in my ‘03 Corvette coupe. Everything went well with install. Drove car after install. Did not register speed on speedo cluster until 20 mph. Checked registered speed while driving with GPS. Speedo was dead on accurate. No check engine lights At that point I changed out the speed sensor, same results. BTW, C5 and C6 rear differentials use the same exact speed sensor part number from GM. I have run out of ideas. The one rib rear different original to the car had a 2:73 gear set. Any help would be much appreciated. ;
Last edited by Turbo Bob; May 29, 2023 at 03:38 PM.
Instructor
Joined: Aug 2022
Posts: 243
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From: Ashburn, VA
Put a 3 rib C5 rear diff with C6 3:42 ring and pinion in my ‘03 Corvette coupe. Everything went well with install. Drove car after install. Did not register speed on speedo cluster until 20 mph. Checked registered speed while driving with GPS. Speedo was dead on accurate. No check engine lights At that point I changed out the speed sensor, same results. BTW, C5 and C6 rear differentials use the same exact speed sensor part number from GM. I have run out of ideas. The one rib rear different original to the car had a 2:73 gear set. Any help would be much appreciated. ;
Think about it this way...on 70's muscle cars when we did gear changes...the speedo would be fucked going from dog leg 2.32 gears to 4:10's lol Would have to change the gears in the tranny to speedo cable to get the speedo to read right. Or if you were cheap and lazy (me)...just know that when it says you going 50...its really 30 mph
Thread Starter
Melting Slicks
Joined: Mar 2001
Posts: 3,251
Likes: 48
From: Parkland Florida
Corvette Challenge Champ-01
Dragster Challenge Champ-06
Well the story gets better. It seems when the rear differential was rebuilt the ring gear was not positioned properly. Also the PCM was reprogrammed for the gear change from 2:73 to 3:42 gear set. So with the ring gear not being positioned properly the speed sensor was not picking up the signal 100 percent. Lesson learned. Coming apart soon to reposition the ring gear.
Last edited by Turbo Bob; May 30, 2023 at 06:46 PM. Reason: Add Signature
Melting Slicks
Joined: Jan 2004
Posts: 3,247
Likes: 210
From: Detroit MI
Ran into this with a 3.90 gear that was in my car when I bought it. Speed sensor was off position relative to the ring gear teeth and didn't register anything until 15-20 mph. I can't remember if it was due to the housing (may have been from an automatic) or ring gear thickness. In your case however I'm not sure how you "reposition the ring gear".
Thread Starter
Melting Slicks
Joined: Mar 2001
Posts: 3,251
Likes: 48
From: Parkland Florida
Corvette Challenge Champ-01
Dragster Challenge Champ-06
Ran into this with a 3.90 gear that was in my car when I bought it. Speed sensor was off position relative to the ring gear teeth and didn't register anything until 15-20 mph. I can't remember if it was due to the housing (may have been from an automatic) or ring gear thickness. In your case however I'm not sure how you "reposition the ring gear".
Last edited by Turbo Bob; Jun 2, 2023 at 08:56 AM. Reason: Signature
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I know you need a reprogram for the trans shifts, etc. But I was told years back that the A4 C5s need no correction on the speedo to read correctly! However, the 6 speed C5s do. I don't know why 1 would be different from the other. I think the OPs issue is more with the speed sensor not getting a proper, consistent signal.....
Le Mans Master
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From: Florida
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I know you need a reprogram for the trans shifts, etc. But I was told years back that the A4 C5s need no correction on the speedo to read correctly! However, the 6 speed C5s do. I don't know why 1 would be different from the other. I think the OPs issue is more with the speed sensor not getting a proper, consistent signal.....
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Drifting
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From: De Pere, WI
You do NOT need to reprogram for a gear ratio change for speedometer calibration. Have been down that road before. You simply don't need to do it. You only need to adjust anything if you have an auto trans car for shift points.
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Put a 3 rib C5 rear diff with C6 3:42 ring and pinion in my ‘03 Corvette coupe. Everything went well with install. Drove car after install. Did not register speed on speedo cluster until 20 mph. Checked registered speed while driving with GPS. Speedo was dead on accurate. No check engine lights At that point I changed out the speed sensor, same results. BTW, C5 and C6 rear differentials use the same exact speed sensor part number from GM. I have run out of ideas. The one rib rear different original to the car had a 2:73 gear set. Any help would be much appreciated. ;
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