Differentials and transmission fluids changed

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jyi786

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On Friday evening, I changed both differential and the transmission fluid for the truck.

I started with the rear differential. To my surprise, it was quite clean. The front differential was a different story; the fluid that came out of it looked like mud. The transmission fluid was also very dirty, but didn't smell burnt or anything. I got all the old fluid pumped out (via the trans line); took about 16 quarts of fluid to get it looking cherry red.

Drove 100+ miles today. Truck feels much smoother now, and is a little faster on the uptake now. Also, more importantly, the drivetrain feels like a single unit instead of different components; they're not trying to fight each other and instead now feel like they work completely in tandem. Worth it for me and the peace of mind!

If anyone has any questions about the process, I'm happy to answer.
 
vollosso

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Does the front and rear cover have a drain and fill plug? What fluids did you use? How much did they take?
 
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jyi786

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The front differential has a drain plug and a fill plug. The rear only has a fill plug. To drain it, you have to crack it open.

I bought 5 quarts of Mobil 1 gear oil.
https://www.amazon.com/Mobil-104361-75W-90-Synthetic-Gear/dp/B000ONZXPK

I forget exactly how much I used, but when it was all said and done, I have half a quart left. I want to say the rear differential used 2.5 qts, and the front used 2 qts. All I did was fill both the rear and front until it reached the bottom of the fill plug hole.
 
swathdiver

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The front differential takes 80W-90 and the rear 75W-90 Synthetic. Like the OOP, many folks put the same fluid in both.

I just did mine as well and used the OEM fluids from ebay and amazon which were great deals. Same feeling, before the truck felt like it was trying to go in two directions, like a bucking trailer, now it's quite seamless but still have to do the transmission.
 
vollosso

vollosso

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Is there a replacement cover for the rear with a drain plug? Or does it seal up well when it gets cracked?


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you really want to open it to not only get the bad fluid out but clean as much as possible. You'll be surprised how dirty that back cover is. The right gasket and sealant will prevent leaks. I never had a leak issue on any of my diffs/tranny. This is one area you just want to buy right. I have heard horror stories with leaks on tranny, not so much diff but you never know. Get the right gasket. Not worth the headache for $10-15 dollar saving every 60k+ miles.
 
swathdiver

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The rear cover has been in use for over thirty years, so yes, there are covers with drain plugs and many are finned as well. I had them on my Buicks back then.

I reused my rear differential gasket and did not sealer either. No leaks.
 
kbuskill

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jyi786 said:
On Friday evening, I changed both differential and the transmission fluid for the truck.

I started with the rear differential. To my surprise, it was quite clean. The front differential was a different story; the fluid that came out of it looked like mud. The transmission fluid was also very dirty, but didn't smell burnt or anything. I got all the old fluid pumped out (via the trans line); took about 16 quarts of fluid to get it looking cherry red.

Drove 100+ miles today. Truck feels much smoother now, and is a little faster on the uptake now. Also, more importantly, the drivetrain feels like a single unit instead of different components; they're not trying to fight each other and instead now feel like they work completely in tandem. Worth it for me and the peace of mind!

If anyone has any questions about the process, I'm happy to answer.
Click to expand...

Just curious how many miles are on your truck?
 
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Warriorpluto

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swathdiver said:
The front differential takes 80W-90 and the rear 75W-90 Synthetic. Like the OOP, many folks put the same fluid in both.

I just did mine as well and used the OEM fluids from ebay and amazon which were great deals. Same feeling, before the truck felt like it was trying to go in two directions, like a bucking trailer, now it's quite seamless but still have to do the transmission.
Click to expand...

have a link? part number
 
vollosso

vollosso

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Doing this today. Is the 373 rearend open or slip? Aka do i need slip additive?


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