Changing Front/Rear Differential Fluids for First Time; Newbie Questions

[jbcrane]

My Wrangler turns 1 Year old today and I'm getting ready to change Dif fluids for the first time (after a recent re-gear) and have some newbie questions:
M186/open/front and M220/anti-spin/rear. The gear oil stated in the user manual is the proper gear oil for the stock 3.45 gear configuration. But I just switched my gears from 3:45 to 4:88 (and love it). Does this change the weight of the gear oil required? Hope not - just spent a fortune on it.

Purchased:
3 quarts of 75W85 Gear Oil (part number: 68378949AA)
Also picked up the Friction Modifier (part number: 4318060AD)

Questions are:
1) how much friction modifier to add? The bottle says "apply 2-5% by gear lubricant weight..." Not sure how much the rear Dif takes - each bottle is 32 oz. so 5% of 32 oz. is 1.6 oz. I've read some posts saying the rear takes about 1.6qts, or about 51-52 oz, which means about 2.5 oz of friction modifier...? Am I over thinking this? Measure? Don't want to just dump the whole 4oz bottle in and call it good...

2) Silly question, but thinking I'll mix the Friction Modifier in the gear oil bottle and pump it all in together... rather than first the gear oil then FM on top. Prob doesn't matter - it'll all get mixed together, but want to make sure to get the right ratio.

3) Leading to question 3: anyone have a good link for a pump? the Mopar oil doesn't have any kind of spout - just the 'old style' conventional plastic bottle neck shape which will make it difficult to pour into that small hole. Thinking a pump is a good idea...

I've read through several threads but honestly haven't read every single post - some are TL:DR and get off in the weeds... Hoping for a little succinct help here.

Thanks, JBC

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[JEEP4U]

Depends on your builder...............I use Lucas non-synthetic 85W-140 in my Dana 60s.

Check what is recommended in the new 4.88 manual 6 speed Jeep JL. 75W-85 seems a bit light, in my experience.

 

[jbcrane]

Dana Spicer OE 4.88's front and rear (30/44).

 

[word302]

First of all, never waste your money on gear oil from Mopar again. Next time get squeeze bottles from almost any quality oil manufacturer (I use Amsoil severe gear). I highly recommend getting some heavier weight oil in that rear axle (Dana recommends 75-140 in both axles by the way). You should be able to get a pump from almost any auto parts store.

 

[jbcrane]

First of all, never waste your money on gear oil from Mopar again. Next time get squeeze bottles from almost any quality oil manufacturer (I use Amsoil severe gear). I highly recommend getting some heavier weight oil in that rear axle (Dana recommends 75-140 in both axles by the way). You should be able to get a pump from almost any auto parts store.

Thanks. Only question about the heavier oil is the anti-spin engaging. Thoughts?

 

[jbcrane]

Dana recommends 75-140 in both axles by the way

Can you provide the source for this? I have looked and can't find it. Thanks.

 

[bjm00se]

If you've already purchased the oil, just use it.

Put the whole 4oz bottle in and call it good - that's why it comes in 4oz bottles.

Here's a pump (assuming you're filling, not draining)
https://www.amazon.com/Slippery-Pete-Fluid-Quart-Bottles/dp/B07CX4XKFH/ref=sr_1_7?keywords=gear+oil+pump&qid=1650554951&sr=8-7&th=1

But as mentioned above, any auto parts store will have one.

Word to the wise:

Be aware that gear oil has, um, a *POWERFUL AND VERY DISTINCTIVE* aroma. It is the literal opposite of "new car smell" - "junkyard smell." If you spill any, your garage will smell like a junkyard for months. If you get some on the ground, then get some on your back, then sit in the car and transfer it to your driver seat, well, it won't smell like a one-year-old jeep anymore.

 

[jbcrane]

Thanks Bullwinkle... I'll make sure to keep the stinky contained. I'll use what I've just purchased in the rear because it has been ~600 miles since the gear change. But I'll continue to research this and am pretty sure I'll be one of those guys who changes gear oil more frequently than recommended. Just seems like a smart thing to do; getting in there and making sure everything's cool. Gear oil seems to be a pretty hot-button topic - and I understand why. It's important. Thanks again.

 

[jbcrane]

But as mentioned above, any auto parts store will have one.

FWIW, I went to local O'Reilly's and they had no idea what I was talking about. Came home and ordered the exact one you sent link for. It'll be here tomorrow. Thanks again.

 

[Steph1]

Haven't seen this mentioned, but my gear installer that will also be doing my first post re-gear oil change told me that he pulls the covers to perform the first oil change to inspect the rings and pinions and clean everything up well and make sure that any metal particles are removed.

 

[bjm00se]

@jbcrane My bad, I forgot you're not putting any in the front, just the back. So use HALF the bottle and call it good.

 

[bjm00se]

FWIW, I went to local O'Reilly's and they had no idea what I was talking about. Came home and ordered the exact one you sent link for. It'll be here tomorrow. Thanks again.

I'm sure they have it, but the guy at the counter has never changed diff oil, so he doesn't know what you're talking about, and where to find it.

 

[jbcrane]

@jbcrane My bad, I forgot you're not putting any in the front, just the back. So use HALF the bottle and call it good.

No worries... I'm a measuring kinda guy so it'll be correct. And I'm holding off doing the front for now. Only put it in 4WD twice since the gear change and no point in throwing away good oil. I have a new front Dif cover coming though so I'll be ready to do it sooner rather than later.

 

[Jim1964]

I always change to LubeLocker reusable gaskets the first time I open a diff. I hate paper and RTV.

https://www.lubelocker.com/

Bought my last ones from Amazon.

 

[bjm00se]

There are two "shapes" of quart bottles for diff oil, but the pump I linked should work for both.

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