Advice on Rear Differential Leak for 1980 C10

Hey everyone,

I’m in the process of getting my 1980 Chevy C10 back on the road after it sat in storage for about 15 years. The truck was my grandfather’s, and I’m aiming to keep it as original as possible. While I was under it recently, I noticed what looks like a small leak around the rear differential. The fluid level isn’t dangerously low yet, but I think it might be time to check or change it and make sure everything is sealed up.

A few questions for you all:

1. What’s the best way to confirm if it’s a small leak or something bigger? Anything I should look for specifically?
2. What’s involved in changing or topping off the rear diff fluid on these trucks? Do I just need to pull the cover to drain it fully?
3. Any parts or supplies you’d recommend? I’m guessing I need fresh gear oil and maybe a new gasket if I pull the cover, but let me know if there’s anything else that would help.

Thanks for any advice you can share, especially if you've been through a similar job on a C10. I appreciate the help!

Wash off all the crud, dirt, oil. Check the oil level. Look for leaks after the differential is cleaned

Thanks JD. Would you recommend proactively cracking it open to change all the fluid?

AlabamaDan said:

Thanks JD. Would you recommend proactively cracking it open to change all the fluid?

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Yes. Don't pry on the cover to break it loose. Use a thin putty knife and tap it between the differential and cover in various spots. Clean the inside with break clean, and note any oddities or lack thereof in the gear oil.

Then fill it with fresh 80w or 80w90 gl5.

Leave one bolt at the top of the cover installed loose, then when you break the seal of the cover, it stays put, let’s you drain it, then remove the bolt and pull cover after drained.

Then you don’t have the cover fly off and make a big splash.

Make sure you can remove the fill plug first before pulling the cover.

Good advice from all. Love it!