HOW TO: Change your front/rear diff oils

[theroofable]

As tjkj2002 explains in one of his posts on this thread the diffs are not pressurized systems and therefore the lubricant isn't forced into all areas of the differential - it is a "splash" system. The synthetic oils don't stay on the gears throughout the rotation as well as thicker 'dino' oils do - so going with a synth really isn't as good for your system as an 85W-140 dino oil.

You're spending money on a synthetic oil that doesn't do as good a job as a dino oil. Think of it this way: If it makes you feel better you could buy a gallon of 85W-140 for half the cost of a quart of full synth, change your diff oils twice as often and still save money! arty52:

Bob

Just verifying that I can use the 85w-140 in the front and the rear? If so Im off to buy 1 gal of it on tuesday, and hopefully get it changed before the weekend!

 

[67Customs]

As tjkj2002 explains in one of his posts on this thread the diffs are not pressurized systems and therefore the lubricant isn't forced into all areas of the differential - it is a "splash" system. The synthetic oils don't stay on the gears throughout the rotation as well as thicker 'dino' oils do - so going with a synth really isn't as good for your system as an 85W-140 dino oil.

You're spending money on a synthetic oil that doesn't do as good a job as a dino oil. Think of it this way: If it makes you feel better you could buy a gallon of 85W-140 for half the cost of a quart of full synth, change your diff oils twice as often and still save money! arty52:

Bob

I've read that a few times and I've done a lot of research on it.

However, that still doesn't explain to me why in my owners manual they specifically say to use 75W-140 in the front. They apparently thought it to be better at the time of that publication but thought 80W-90 to be good when writing the FSM.

Will my Dana 30a blow up because I use 85W-140? Probably not. I just want to know why they can't get it straight and if 75W-140 is better for my Dana 30a.

In all honesty, I'm most likely going to run Valvoline DuraBlend 85W-140 during my next change. Split the difference. But, she has already ran 60K miles on a couple of changes of Mobil 1 75W-140 front and back with zero problems.

 

[TwoBobsKJ]

I've read that a few times and I've done a lot of research on it.

However, that still doesn't explain to me why in my owners manual they specifically say to use 75W-140 in the front. They apparently thought it to be better at the time of that publication but thought 80W-90 to be good when writing the FSM.

Will my Dana 30a blow up because I use 85W-140? Probably not. I just want to know why they can't get it straight and if 75W-140 is better for my Dana 30a.

In all honesty, I'm most likely going to run Valvoline DuraBlend 85W-140 during my next change. Split the difference. But, she has already ran 60K miles on a couple of changes of Mobil 1 75W-140 front and back with zero problems.

In my opinion the Owner's Manual is as much marketing as information - and that's verified by the fact that the fluids referenced are always "Mopar-brand" so-and-so. With the 75W-140 Chrysler is pushing the more expensive product. But the FSM is for the mechanics who actually work on the vehicle and they are advised to use the stuff that will work well. In this case it is dino oil vs synth.

I think your choice is a good one (DuraBlend.) Gives you peace of mind and will do a good job in your diffs. :happy107:

Bob

 

[Moon]

I got the diff oil changed in the hooptie last friday. The only tip that I would mention (besides the ones already posted), is: DO NOT let the old gear-oil get into your car. It smells like so much nasty-ass, and doesn't seem to want to go away on its own. I had a rag with a little bit of the old oil on it. I threw it out the window while driving down the road, but the awful smell remains.

:cheers:

 

[tjkj2002]

I got the diff oil changed in the hooptie last friday. The only tip that I would mention (besides the ones already posted), is: DO NOT let the old gear-oil get into your car. It smells like so much nasty-ass, and doesn't seem to want to go away on its own. I had a rag with a little bit of the old oil on it. I threw it out the window while driving down the road, but the awful smell remains.

:cheers:

Try doing the front diff in a Cat 621B,55 gallons of 80w-90,that's one big drain pan.

 

[first&lastKJ]

I have an 02 and 07 KJ does anyone know what gear lube came in them from the factory.

 

[TwoBobsKJ]

I have an 02 and 07 KJ does anyone know what gear lube came in them from the factory.

Do they have the towing package? Do they have TracLok?

That determines what was in the rear diff from the factory...

Bob

 

[first&lastKJ]

Do they have the towing package? Do they have TracLok?

That determines what was in the rear diff from the factory...

Bob

No, and No.

 

[TwoBobsKJ]

No, and No.

They most likely used the 75W-90 synth. But you can put in 85W-140 dino in both front and rear diffs.

Bob

 

[first&lastKJ]

Thanks. I think i'll go with the 75w-140 synthetic front and rear in both of our KJ's.

 

[sevenhelmet]

I'm now using 80W-90 front and rear and I've put over 100 miles on it since the change with no problems.

 

[mdmaroon]

ahhh yes, been meaning to do a write up on this for a while now.

The rear has been pretty much covered. The only difference is I let the RTV cure on my cover for about 30 minutes and its held up great.

As for the front, this is really simple. There are two plugs, unlike the back. You have a drain plug, and a fill pulg. All you have to do is:

Unblot the drain plug.
let old oil drain out.
Put drain plug back on.
Unbolt fill plug.
Fill with new oil.
Put fill plug back on.

YOU'RE DONE!!! This is of course, if you DO NOT have any skid plates up front. I would imagine that skids up front would have to be taken off.

One thing: Take the fill plug out FIRST. If you take out the drain plug, and then for some reason can't get the fill plug out, then you aren't going anywhere until you do get it out, one way or another. Maybe you'll need a tow truck to take you to a shop...

I know it's not too likely that this will happen, but at least if you take the fill plug out first, you know you'll be able to get fluid in, assuming everything is okay with the drain plug. If you can't drain it, then you just put the fill plug back and you can still drive.

 

[Squeeto]

...
Someone was asking where to put the jack stands. Here is where I put them. I dont know if it is correct or not, but seems alright to me.

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I like this way as well. But it causes the diff to point up not hang down. If the oil level needs to be 1cm below the fill hole we aren't accomplishing this by filling until the oil drips out.

I figure that some fluid can be sucked out but how important is this oil level? It looks like the bottom of the axle (thus seals) is below the proper oil level anyway.

________

So I must jack the front to get under the truck for the front diff. If I let the axle hang it actually points down even if the front of the truck is elevated?


Sorry for being so cautious about this. This is the first vehicle I have owned that requires the level to be below the fill.

 

[Squeeto]

Okay, I tried this on the rear axle and it does work:

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String to diff cover:
level = 1 13/16 inch
hanging = 1 15/16 inch

I don't think that this trick works on the front though.

 

[theroofable]

I like this way as well. But it causes the diff to point up not hang down. If the oil level needs to be 1cm below the fill hole we aren't accomplishing this by filling until the oil drips out.

I figure that some fluid can be sucked out but how important is this oil level? It looks like the bottom of the axle (thus seals) is below the proper oil level anyway.

________

So I must jack the front to get under the truck for the front diff. If I let the axle hang it actually points down even if the front of the truck is elevated?


Sorry for being so cautious about this. This is the first vehicle I have owned that requires the level to be below the fill.

Im pretty sure its meant to be 1cm below the top of the fill hole. Therefore, it needs to be jacked up so that when it oozes out, but when level again, it would be above the fill plug.
When i did it, I used a giant syringe, and pumped the required amount of fluid into each diff. This is one way to ensure the proper level.

 

[sevenhelmet]

I used a gallon fluid pump for mine and had no problems. Just watch out for the little plastic "wingtip" on the fill nozzle of some of them. The little plastic tips can break off inside a gearbox if you aren't careful.

x2 on carefully taking out the fill plug first. One stripped head or torn piece of plastic can ruin your whole day.

 

[Squeeto]

I use this:

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It's slow but mess free.

 

[tjkj2002]

Sorry for being so cautious about this. This is the first vehicle I have owned that requires the level to be below the fill.

Just fill till the bottom of the fill hole,no issues will result.

Want a fun diff to fill try a RockJock60 as the cover is laid out at 60 degrees.If I fill to the fill hole I'll blow every seal,I have to add exactly 2.75qts.

 

[Squeeto]

Just fill till the bottom of the fill hole,no issues will result.

This is the 3rd gear oil change that I have done on this truck. Each time I stuck a finger in to try and guess the depth down a cm. Next time I will do as you all say.

Thanks.

I suppose the minds at Jeep don't want the seals to sit in gear oil 24/7 and the extra 1cm was for those of us who park on hills, curbs, the neighbors bike, etc.

 

[tjkj2002]

This is the 3rd gear oil change that I have done on this truck. Each time I stuck a finger in to try and guess the depth down a cm. Next time I will do as you all say.

Thanks.

I suppose the minds at Jeep don't want the seals to sit in gear oil 24/7 and the extra 1cm was for those of us who park on hills, curbs, the neighbors bike, etc.

The reason is the back fill plug is rubber,just pops in/out.If filled to the bottom of the fill hole it may or maynot weep a little gear oil.

The seals are there to seal,does not matter if they are in constant contact with the oil.No oil touching the seals means no oil in the bearings.