Diff oil - 75W or 80W, any difference?

[brucecooner]

I need to change the diff oil in both ends.

The original manuals call for 80W-140 in the rear for heavy duty or towing applications.

Sure, I figure I'll go with that, or something close in the rear (Dana44). I might tow something, someday.

Was going to stick with 90 in the front.

 

Thing is, it's easy to find 75W-140.

As far as cold weather performance, we don't have cold weather here in Phoenix.

Does the difference between 75W or 80W have any other impact?

Some posts say all 75 is synthetic, synthetics will cause your seals to leak blah blah blah...

 

Will either diff even notice or care if it gets one versus the other?

 

I know mine has limited slip, I guess I'll just roll with whatever friction modifiers they put in there.

Won't make much difference since mine's not leaving the driveway anytime soon anyway.

 

[gogmorgo]

The second number is the important one, the first is just when cold. 75 vs 80 shouldn’t be an issue. 

If you off-road it, climbing rocks or even just steep hills in low range, you’re also putting a fair bit of stress on the axle, so likely just as well off with the 140 anyhow. 
In my mind if switching to synthetic does anything to your seals, your seals needed changed anyway. 

[TurboedMJ]

I am putting this in my diffs and using lubelocker style gaskets. Make sure the gasket surfaces are clean 

https://www.amazon.com/gp/aw/d/B000IG5QPK?ref=ppx_pt2_mob_b_prod_image

[brucecooner]

On 5/18/2023 at 11:37 AM, TurboedMJ said:

I am putting this in my diffs and using lubelocker style gaskets. Make sure the gasket surfaces are clean 

https://www.amazon.com/gp/aw/d/B000IG5QPK?ref=ppx_pt2_mob_b_prod_image

 

I went with lube locker gaskets too.  Whoever changed the rear oil last time really believed more RTV is better, but it wasn't too difficult to remove.

The old oil was dark but not thick.  I had been worried they'd been allowed to leak out and run low, but both diff covers indicated they were still full to the plugs.

 

I got the Valvoline synthetic at a decent price, the squeeze packs took delicate handling but got the job done.

I found docs online saying the Dana 44 wanted like, 30+ ft lbs on the cover bolts, but I went with 25. Lowered that to 20 on the fronts. Probably overkill, I looked the cover bolt torque up in a service manual after I was done and I think the service manual said 14. Oh well, they don't leak.

 

What's weirder is that my service docs said the 44 would take over 2 quarts of oil, but it started flowing out of the plug at a bit under 2.

Same in the front (Dana 30), took a bit less than the rear, still under 2 quarts.  Maybe I missed draining some, but both were flowing out of the plugs when I put it back in, so off we go.

 

I was most curious about what look like scratch marks on the rear... carrier(?), er, that cage thing that rotates with the big gear and has the little gears inside it.

 

It didn't look like there was anything for this to scrape against.

I jacked up both rear wheels so I could spin them (LSD), and I did hear a sort of grinding sound as this thing rotated, but I don't think it was actually coming from inside the diff.

 

I dunno, it's never made funny noises from the rear axle, and it drives normally so I guess these are just there from the factory or something.

 

 

[pizzaman09]

On 6/9/2023 at 2:28 AM, brucecooner said:

 

I went with lube locker gaskets too.  Whoever changed the rear oil last time really believed more RTV is better, but it wasn't too difficult to remove.

The old oil was dark but not thick.  I had been worried they'd been allowed to leak out and run low, but both diff covers indicated they were still full to the plugs.

 

I got the Valvoline synthetic at a decent price, the squeeze packs took delicate handling but got the job done.

I found docs online saying the Dana 44 wanted like, 30+ ft lbs on the cover bolts, but I went with 25. Lowered that to 20 on the fronts. Probably overkill, I looked the cover bolt torque up in a service manual after I was done and I think the service manual said 14. Oh well, they don't leak.

 

What's weirder is that my service docs said the 44 would take over 2 quarts of oil, but it started flowing out of the plug at a bit under 2.

Same in the front (Dana 30), took a bit less than the rear, still under 2 quarts.  Maybe I missed draining some, but both were flowing out of the plugs when I put it back in, so off we go.

 

I was most curious about what look like scratch marks on the rear... carrier(?), er, that cage thing that rotates with the big gear and has the little gears inside it.

 

It didn't look like there was anything for this to scrape against.

I jacked up both rear wheels so I could spin them (LSD), and I did hear a sort of grinding sound as this thing rotated, but I don't think it was actually coming from inside the diff.

 

I dunno, it's never made funny noises from the rear axle, and it drives normally so I guess these are just there from the factory or something.

 

 

I'd hazzard a guess that those scratch marks are machining marks from cleaning up the casting flash.

[cruiser54]

Ooooh, it's a limited slip!!