New gears, what oil post break in?

Just got yukon 4.88s installed front and rear and I am still in the break in stage. The axles are a hp dana 30 and a chrysler 8.25, I know the shop put in synthetic gear oil but not sure on the brand (probly doesn't matter). I'm assuming synthetic was used because they feel it can handle the heat better during break in, I have done some highway driving to heat them up and plenty of town driving too.

So is there any reccomendations on what oil I should now use post break in? I doubt the gears will continue to run hot after some miles are put on them but I would like to know what you guys that HAVE regeared are using, not what your brothers, friends, dads, uncle said to use. I checked yukons site and searched around but can't find reccomendations from yukon, I will double check with them soon and give them a call but let me know your choice of gear oil with new gears is!

I always thought that like an engine, it's best to do a break in with dino oil.
I'm not sure, and I'm by no means an expert!

However, post break in, I've had the best results just running standard gear oil, and changing it often.

Our axles aren't picky (granted you don't have special lockers), however dirty oil, or even worse... water in your axles, will kill bearing and gears.

I agree on regular oil. Its better to spend money on multiple chages then expensive sythetic and try to run it longer. \

Also, I would look into getting alloy axle shaft seals, they work well to keep out water from getting into the diff. ~70 bucks is well worth it when you have $$$ in the diff in gears.

The shop is very experienced in gear installs so I let them decide on what went in there. I do change the oil often enough id say every 12-18 months? I'm willing to change it more often if I noticed I was in water/mud more then normal. Wheeling wise, i tend to stay mostly in rocks, no water crossings really, only mud I encounter is going to the next section of rocks!

I personally always used regular dino oil in my diffs, just figured maybe the new gears would run at higher temps or would benefit from synthetic oil since everything in there is fresh and new. I run an aussie up front but it doesn't care whats in there oil wise. I guess I'm thinking like engines, if you get a new car and run synthetic from the start it is better then running dino and going to synthetic. I know oil discussions will last forever but I'm just looking for opinions from guys who wheel with new gears. I'm sure yukon will also be able to validate anything gear guys know.

I run Coastal 80W90. Just bought another 5 gallon drum at Advance yesterday and the price is up to $54. I use it in all my diffs from my rear D60 W/ARB in my XJ to my 1951 chevy pickup. Also great in any manual trans.

There is no reason to spend 10 bucks a quart an gear oil, especially if your just using in a differential!

austinaubinoe said:

I run Coastal 80W90.

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Exactly what I use! cheapest stuff advanced has to offer

Well you paid for oil that will/should be drained in 500 miles. How did they tell you to break them in. They need to go through heat then cold cycles to break in right. Go bout 15 miles then stop and let them get completely cool then do it again a few more times or so. That is what I have been told and found most gear manufacturers recommend.

My self. I followed the above routin and have had no issues. I also am on the boat that feel synthetic really isn't nessaccery and I use 85-140 but most of my weather here is hot so that's what they recconend

austinaubinoe said:

I run Coastal 80W90. Just bought another 5 gallon drum at Advance yesterday and the price is up to $54. I use it in all my diffs from my rear D60 W/ARB in my XJ to my 1951 chevy pickup. Also great in any manual trans.

There is no reason to spend 10 bucks a quart an gear oil, especially if your just using in a differential!

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Winner, Winner, Chicken Dinner!

The most expensive oil I've ever used is Valvoline Durablend.

I've been running cheap masterpro oil, probably the same as coastal.

I change it every other oil change.

Yes I have done the heating and cooling cycles, guess if you guys think dino oil is fine then thats what I'll go for.

Srmitchell- every other oil change! wow I thought once a year was often lol

Magimerlin- I was told to follow yukons instructions, heat them up let them cool a bunch of times, take it easy for 500 miles, no towing, no abuse ect.

I'm loving the 4.88s and 33s so far best combo I've driven, plus I'm getting around 20mpg maybe slightly less but its wayyy better then 3.55s and 33s! All the old gear threads on here helped me decide so thanks guys!

XGarfX said:

Yes I have done the heating and cooling cycles, guess if you guys think dino oil is fine then thats what I'll go for.

Srmitchell- every other oil change! wow I thought once a year was often lol

Magimerlin- I was told to follow yukons instructions, heat them up let them cool a bunch of times, take it easy for 500 miles, no towing, no abuse ect.

I'm loving the 4.88s and 33s so far best combo I've driven, plus I'm getting around 20mpg maybe slightly less but its wayyy better then 3.55s and 33s! All the old gear threads on here helped me decide so thanks guys!

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Have you corrected the speedo gear yet?

RCP Phx said:

Have you corrected the speedo gear yet?

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Yes I have, 41 tooth gear set me just about right. My speedo was wayyyyy off at first but its all good now. Now I just want some new covers to replace my skids, this project never seems to end...

I "break in" with the cheap stuff then run Lucas from there out. I set up my own gears and have for many years with no issues.

Lucas is conventional or synthetic? Haven't really looked at Lucas diff fluid in a while.

Well i guess its good to know I don't have to spend big bucks on synthetic, that cash could go towards my next wheeling trip comin up where I really get to test out these 4.88s!

Waste of money putting quality gear oil in the diffs unless you're towing or subjecting them to extreme heat.

I use synthetic in my CTD which is probably even overkill for that application.

Just IMO.

I suggest you use any full synthetic that's available and put a super strong magnet on the inside of the diff cover to capture wear material.