75k and never changed diff fluid

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I have an 04 2500 4 x 4 dodge with 5.9 Cummins. I've never changed the fluid out of my diff as it's always been out of sight out if mind. I've learned this is something I should have done some time ago. Anyway, first off, have I killed my gears? I don't drive the truck hard and I only occasional tow a 5k trailer. Second, what weight gl-5 synthetic gear oil am I supposed to use? I'd look it up in the owners manual but I've never had one. Also, is it as simple as draining with a mityvac and refilling or do I need to make a mess and remove the covers? As always, thanks for the helpful replies.
 
Highly doubt you damaged it. There are TONS of people that go 200K and never change it. On the Trailblazer it never was changed till 110K. No damage. Although I would change it at this point VERY easy to do.
 
Your gears are fine, FWIW I did the mityvac method on my old 99 F359 and seapped it with Mobil 1 75w140 for the first time at over 200k
shocked.gif
when I got it, so 75k is not bad. What does the interwebs call for? I suspect it’s the same as my old truck, check Amsoil’s site for the exact specs for your truck.
 
Not a problem. Get on RAM.com or Dodge.com and you should be able to look up your owners manual.

To be honest, most truck makers do not suggest you need to change the rear diff for the first 150,000 miles unless you have severe service like lots of towing or going off-road. It's only us gear heads who do. (Ever wonder why there is no drain plug on the rear diff?).

Take a look at your owners manual and feel free to bring up any issues.

One more thing. Your transfer case does need changes. For severe service (which I like to use), it is usually 50,000 miles or so. Most people think, front diff, transfer case and rear diff. It should be front diff, rear diff and 3 times more for the transfer case.

You need to make a mess and take off the rear cover. That way you can clean out any gear shavings.

SF
 
Originally Posted By: monster1
I have an 04 2500 4 x 4 dodge with 5.9 Cummins. I've never changed the fluid out of my diff as it's always been out of sight out if mind. I've learned this is something I should have done some time ago. Anyway, first off, have I killed my gears? I don't drive the truck hard and I only occasional tow a 5k trailer. Second, what weight gl-5 synthetic gear oil am I supposed to use? I'd look it up in the owners manual but I've never had one. Also, is it as simple as draining with a mityvac and refilling or do I need to make a mess and remove the covers? As always, thanks for the helpful replies.
The owners manual has the recommended viscosity .
 
Originally Posted By: monster1
I have an 04 2500 4 x 4 dodge with 5.9 Cummins. I've never changed the fluid out of my diff as it's always been out of sight out if mind. I've learned this is something I should have done some time ago. Anyway, first off, have I killed my gears? I don't drive the truck hard and I only occasional tow a 5k trailer. Second, what weight gl-5 synthetic gear oil am I supposed to use? I'd look it up in the owners manual but I've never had one. Also, is it as simple as draining with a mityvac and refilling or do I need to make a mess and remove the covers? As always, thanks for the helpful replies.


Unless the fluid got water in it, you've probably done zero harm. Heck, my 73 Satellite went close to 200k (with some trailer towing) on a lightweight 8.25 rear gear before the fluid ever got changed, and it proceeded to continue quite happily until over 240,000 miles (still going when I sold the car). Solid axle differentials are notoriously tough, with a few exceptions. None of those exceptions show up under a 3/4 ton Ram (unfortunately, half tone Rams do get the 9.25, which has a lot of reliability problems due to the tooling being so old.)
 
Originally Posted By: CT8
Originally Posted By: monster1
I have an 04 2500 4 x 4 dodge with 5.9 Cummins. I've never changed the fluid out of my diff as it's always been out of sight out if mind. I've learned this is something I should have done some time ago. Anyway, first off, have I killed my gears? I don't drive the truck hard and I only occasional tow a 5k trailer. Second, what weight gl-5 synthetic gear oil am I supposed to use? I'd look it up in the owners manual but I've never had one. Also, is it as simple as draining with a mityvac and refilling or do I need to make a mess and remove the covers? As always, thanks for the helpful replies.
The owners manual has the recommended viscosity .
75W90, I have RP full syn Severe Gear in mine, along with the oversize rear diff cover (Mag-Hytec).
 
I know plenty of people who sent their vehicles to the junkyard with the differential fluid that the vehicle rolled off the assembly line with. Many with hundreds of thousands of miles on them.
 
Originally Posted By: demarpaint
I know plenty of people who sent their vehicles to the junkyard with the differential fluid that the vehicle rolled off the assembly line with. Many with hundreds of thousands of miles on them.


^^^^^^^^^^^^^^^^^^^^^^^^
THIS-they don't seem to wear out under normal use.
 
Early 90's Dana 70 rears had some side carrier bearing problems, but it sounds like yours has had an EASY life so far!
 
I never change differential oil unless it has to be opened up for some reason. That only happened once in 38 years for an axle seal. I make sure the level is up and that's it. I doubt your diff. has been damaged and is the most durable component on your truck.
 
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I changed the factory fill diff fluid in my 99 Dakota at 90k just out of a combination of boredom and curiosity. One word of caution, differential oil smells terrible. I mean i can’t even describe it. FF looked fine to me. I cleaned the magnet and filled it back up with Mobil 1 and some slip lock? additive. I can’t remember the name exactly. It made noise with just the mobil 1 and no additive.

I’m guessing I won’t need to do it again with a good quality oil in there now.
 
I suspect that my '88 GMC has the factory fill in the rear end, but it doesn't make noise or have excessive play. I have a mini spool waiting to be installed, so it will be taken care of soon enough.
 
Originally Posted By: Lubener
I never change differential oil unless it has to be opened up for some reason. That only happened once in 38 years for an axle seal. I make sure the level is up and that's it. I doubt your diff. has been damaged and is the most durable component on your truck.


You're not alone. I know people who have never checked the level. They drive until something breaks or until they go for rear brakes and are informed they have a leak.
 
I didn't change the diff fluid in my 2002 Tacoma until about 140K miles. I have about 210K now. No problems--not would I expect any. I used Mobil 1 and really double I'll bother changing the diff oil again in that vehicle.

I couldn't get the diff drain plug on my daughter's 2002 Trailblazer off (even with a breaker bar), so I just let it be. I don't expect there to be any issues and I'm not concerned about it.
 
I have 170k on my Ford ranger and I just changed the rear factory fill. I haven't checked the front yet because it's too cold out. I would not worry at all about 75k
 
Thanks for the peace of mind guys. I'll get the transfer case changed right away. And worry a little later about the differential fluid. I definitely need to check the level in the rear though because when I was checking suspension components the other day, I looked back and saw fluid stains on the pumpkin. I have a leak somewhere.
 
Originally Posted By: monster1
Thanks for the peace of mind guys. I'll get the transfer case changed right away. And worry a little later about the differential fluid. I definitely need to check the level in the rear though because when I was checking suspension components the other day, I looked back and saw fluid stains on the pumpkin. I have a leak somewhere.
Just get a new gasket then when you do the change. Theres not many places it can leak. More than likely that gasket.
 
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