Changing Rear Diff. Fluid

[lmholmes11]

Hey guys,

Ive read some posts on the forum about changing the differential fluid in my 01' 2500DH. Being as i'm just getting started taking care of my truck myself, i was wondering if anyone has a step by step procedure showing how to do so? Or even a link would work. Thanks guys!

[DmaxMaverick]

Rear end hot to warm. Park on level surface. Place suitable drain pan beneath diff. Remove drain plug. Wait until drips stop, or become 1 in about 30 seconds. Clean and replace drain plug. Fill to 1/2" to 3/4" below fill hole (first pinky knuckle). Clean and replace fill plug. Drive. Check for leaks, periodically. Fill is about 3-1/2 to 4 qts.

Same for the front, except:
Remove skid plate, if it has one.
Fill up to fill hole.
Fill is about 2 qts.

Recommended (required) fluid is synthetic 75-90 for normal use in moderate climate. Synthetic 75-140 for very heavy use, in hot climates. You can use 75-140 synthetic in the front diff., but you may have issues with synthetic if the wrong vent plug is installed. I've been using Amsoil synthetic in my front with the original plug, and no problems. OEM front recommendation is 85W-90 GL-5 lube for lower 48 climates. Synthetic is recommended for extreme cold climates, and GM has been covering the vent plug replacement and synthetic service under warranty if they determine your climate is cold enough. I doubt it is still covered for 2001 models, though. I recommend synthetic lube in the front, in any case.

[lmholmes11]

ok thanks DMAX,

One question though, I heard that my truck may or may not have the drain plug at the bottom, and that I might have to take off the pan. Also, is the filler hole easy to spot on top?

[DmaxMaverick]

If it doesn't have a drain plug, you're under the wrong truck (don't change your neighbor's lube on accident). The fill plug is in the cover, above center to the right (passenger side). They couldn't have made it any more simple. The worse case is you may have to remove the spare tire, if you have issues with access. If you have a pump (like a Sta-Lube pump and jug), it's easy. If you have to "pour" it in, it's easier with the spare out of the way. The pumps will work with just about any jug, water, coolant, 4 qt. oil, etc. Autozone, etc. used to have the lube pumps for less than $5. Well worth it. I use an old Sta-Lube GL-5 gallon jug, and just pour what I need into it and pump away. Don't forget the front diff, if you have one.

[lmholmes11]

Ok i looked under the truck after i asked you that, and i did see a drain plug on the bottom with a square in it, thanks for the help. I talked to the dealer about flushing the tranny also, pretty expensive. How often should it be flushed out, and can you tell if it needs it or not by simply seeing the quality on the transmission dip stick?

Thanks again for the help

[DmaxMaverick]

The tranny should be flushed a few times over its lifetime (about every 100K or so miles). When depends on how it's used and serviced. You can do it yourself in your driveway very easily for the cost of the fluid, and some time (about an hour the first time). Try a search of this forum for the flush procedure, it's been repeated many times. I do a drain/fill service about every 25K miles, and a flush at about every 100K. You should do a flush if you change fluid types, regardless of mileage (such as dino to synthetic). DO NOT allow a flushing machine to be used for a flush. This will damage the tranny. Some "machines" are OK, but they are passive, allowing the tranny to do the pumping. The same method is used for the DIY flush.

If you drain/fill/filter service it regularly, you shouldn't flush it often. It should be regularly serviced at about 50K miles for normal use (daily driving, light to moderate towing), and 25K miles for very heavy use (mostly heavy towing or commercial use). That's an aggressive schedule, GM recommends about double those miles. GM does not recommend a flush under normal conditions. The service intervals can be extended with using synthetic fluid (Amsoil, M-1, Transynd), which I recommend. I use Amsoil Torque-Drive ATF, which carries the same TES-295 spec as Transynd (Allison's recommended fluid for commercial use).

The Control-Main filter (external spin on) should be changed often. Many folks, including me, change it about every other engine oil change. GM recommends a filter change at the service interval. Don't forget to clean and reuse the magnet located on top of the filter (even some dealers still toss them with the old filters). The internal filter needs replacement only at overhaul (recommended by Allison). The pan has a drain plug, so no need to drop the pan.