New 5.38 gears in diff - Break in ??

[sw99]

Just got the 5.38's installed. Axles are GM Dana 60F and a FF14 rear. The 14 bolt has a new detroit locker. I have some assembly lube that I have had for years. I was thinking of using it in the diffs for gear break in. My plan is do a proper break in and change out in 500 miles or so. I will be using plain ol' 80/90 GL5 since I don't need a friction modifier for the detroit. Perhaps after break in I will go synthetic but that is undecided. The vehicle is used 60% around town and 40% offroad trials with moderate off roading.

Will there be any benefit to using the assembly lube for the new gears, bearings and such? I'm talking a couple of squirts in the fill plug to mix with the 80/90. Will the additives help protect and break in the gears/bearings? Probably cant hurt thats for sure. I just hate not using stuff...

Thanks folks!

 

[901Memphis]

Try Mos2

https://bobistheoilguy.com/forums/threads/mos2-in-differential.129367/

 

[sw99]

Here is some info I found for it - NAPA Engine & Bearing Assembly Grease:

Engine and bearing assembly grease is a proven per- lubricant for all gasoline and Diesel engines. The base oils are highly refined, thicken with lithium 12-hydroxy stearate and treated with carefully selected rust and high temperature oxidization inhibitors.
Engine and bearing assembly grease is fortified with zinc and dialkyldithiophosphate plus other unique proprietary extreme pressure (ep) additives. These additives enhances and sustain anti-suffing, galling and wear-in properties of the zinc compound.

 

[oldhp]

Won't hurt it. Might help some. With that steep of gear I wouldn't go over 500 miles for sure , maybe less on first oil change.

 

[artificialist]

Joe Gibbs just created a break in oil for gears recently:
http://www.drivenracingoil.com/dro/break-in-gear-oilhtml/

 

[Zaedock]

I have never used a break in oil for any gears I have installed.

I see no advantage to using assembly lube. Easy driving and early first change are more important than any additive. I recommend a simple 80W90 for break in.

 

[LargeCarManX2]

I would have used Amsoil 250w gear oil and changed out once then run the 110w.

 

[dnewton3]

Assembly lube is important in an engine because many parts that see high-load/high-rpm are far away from that first blush of pressurized lube. True metal-on-metal contact with no tribochemical barrier present can be hazardous. Additionally an engine goes from no rpm to perhaps 1500 rpm upon at cold start; there is no moderate "ramp up" as it's nearly immediate.


A diff is a different story, though. The lower part of the ring gear sits bathed in the lube when at rest, and the whole diff gearset/bearings will have a very short period of time until they are fully covered with lube, relative to the loading. Also, no one typically hammers a diff so quickly that it cannot get wet before it's at high loads and high rpm; i.e. you most likely back up and pull out slowly. Therefore the ring gear and pinion get several revolutions to coat themselves in lube before you ever turn it at speed. And it's often very progressive in the escalation of the rpm, not immediate.

The VAST majority of wear in a diff happens in the first 500 miles or so. Having such steep gears might bring this down to 350 miles, give or take a bit. As you said, you don't need LS additive, so any GL-5 will do well. However, I would recommend considering using a lube that is also SAE J2360 certified. There are many dino lubes that meet this certification. You get a decent dino for break in that also has excellent performance properties. In would recommend this for use after break in as well, but perhaps in syn. That would depend upon your specific use and anticipated OCI duration.


Will assembly lube hurt? Probably not. Will it help? I doubt it.

 

[sw99]

Thanks for all the replies, I appreciate the feedback for sure. I went ahead and added some gitts and shiggles today when I filled her up. The 14 bolt sure hold a lot of oil, almost a gallon... Used plain ST 80/90 GL5. I'll change out around 300 miles just to be safe.