C4 Tech/Performance L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

C4 RPO Clarification

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Old Oct 8, 2025 | 07:38 PM
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Default C4 RPO Clarification

I'm getting ready to rebuild the factory rear end, which will include a new ring pinion.

Found my build code sheet. If I understand this correctly, my car has the 3.07 and the Z51 performance package? I boxed the two codes below:


Last edited by JL_L98; Oct 9, 2025 at 01:00 PM.
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Old Oct 8, 2025 | 09:02 PM
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Old Oct 8, 2025 | 09:11 PM
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The build sheet posted is NOT the larger D44 gear but a D36 for an AT/MD8 that the SPID confirms. Why do you feel you need new Ring & Pinion gear set?
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Old Oct 9, 2025 | 07:23 AM
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I threw the codes in Copilot - I somewhat trust what I get from there, but like to verify.

Correct on the D36 - my car has the 700R4

As for the ring and pinion update, the fluid inside my case looked and smelled like septic water. I'm starting fresh for piece of mind.

Thx for the replies.

Last edited by JL_L98; Oct 9, 2025 at 07:33 AM.
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Old Oct 9, 2025 | 07:49 AM
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Take a whiff of any mineral gear oil and that's what it smells like. If it was burned, you wouldn't be able to breathe within 10 feet.
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Old Oct 9, 2025 | 12:55 PM
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Originally Posted by JL_L98
I threw the codes in Copilot - I somewhat trust what I get from there, but like to verify.

Correct on the D36 - my car has the 700R4

As for the ring and pinion update, the fluid inside my case looked and smelled like septic water. I'm starting fresh for piece of mind.

Thx for the replies.
How many miles? I doubt you need gears and likely no bearings etc either. Your first move should be a service with appropriate fluids and using GM/ACD Additive for the LSD. Are there noises or other differential related issues that lead you to believe you need a rebuild? Save your $$$ for another project.
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Old Oct 9, 2025 | 01:05 PM
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Originally Posted by WVZR-1
How many miles? I doubt you need gears and likely no bearings etc either. Your first move should be a service with appropriate fluids and using GM/ACD Additive for the LSD. Are there noises or other differential related issues that lead you to believe you need a rebuild? Save your $$$ for another project.

Appreciate all the feedback. The rear has 180k - probably more.

I've already been through the motor, trans, steering system, suspension, HVAC, electrical /sensors and exhaust systems on the car. This is last thing to go through.

Just trying to confirm I've read the codes correctly so I know what to buy.

Last edited by JL_L98; Oct 9, 2025 at 01:23 PM.
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Old Oct 9, 2025 | 02:01 PM
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Originally Posted by JL_L98
Appreciate all the feedback. The rear has 180k - probably more.

I've already been through the motor, trans, steering system, suspension, HVAC, electrical /sensors and exhaust systems on the car. This is last thing to go through.

Just trying to confirm I've read the codes correctly so I know what to buy.
So long as you buy for D36 you're good. I imagine that a new D36 3.07 ring/pinion might be a difficult find and that's actually why I mentioned the first move be a service of what you have. If you're actually doing a rebuild aside from what you would normally consider I believe it wise to also replace the pinion differential thrust washers. Dana/Spicer part # for reference should be 40266 and you need 2. They were also used in the Jeep D35. Most critical first check I would think to be the fit of the differential pinion shaft to the case.
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Old Oct 9, 2025 | 02:20 PM
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Originally Posted by WVZR-1
So long as you buy for D36 you're good. I imagine that a new D36 3.07 ring/pinion might be a difficult find and that's actually why I mentioned the first move be a service of what you have. If you're actually doing a rebuild aside from what you would normally consider I believe it wise to also replace the pinion differential thrust washers. Dana/Spicer part # for reference should be 40266 and you need 2. They were also used in the Jeep D35. Most critical first check I would think to be the fit of the differential pinion shaft to the case.
All excellent advice and in scope for the rebuild.

My intent here is to fully understand what I have before disassembling it. Also to identify part availability & cost - much to your point about being hard to find.... this full restoration has brought me many challenges in that department.

I've read that the 3.07 and up gear ratio is a different thickness than the lower ratio, and alternative options vary based on that detail. Confirming my factory ratio allows me to consider the potential options I may have to select from as I approach the project.

Thanks for the communication.

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