Rear diff. looked ok, front diff. looked bad! Why?

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countryboy9799

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I changed the differentials and 5 speed transmission on my 99 dodge cummins, it has 120K miles on it and never been changed.
The transmission and front diff. looked dark and dirty but the rear diff. still had a golden color to it but was dark. I thought since the rear does most of the work it would be the other way around, can anyone explain how come it was like this?
I added amsoil 75W-90 severe gear lube to the differentials and 75W-90 MTG to the transmission, do you guys think I should have gone with a thicker lube? Thanks
Scott
 
same happened on my chevy. IMO, it is because condensation occurs, and the diffs are not closed systems. If it has never been changed, you have at least 7 or 8 full temperature cycles, the rear diff moves enough power and has enough inefficiency to heat up to the point where water can come off. Unless youre in 4wd a lot, the front does not do the same.

Whether you should have gone with the thicker lube in the diff is really dependent upon how much you haul and tow. 90wt syn lubes are decent, you might think of upping it to a 110 if you haul a lot, but I wouldnt loose sleep...

JMH
 
Originally Posted By: JHZR2
same happened on my chevy. IMO, it is because condensation occurs, and the diffs are not closed systems. If it has never been changed, you have at least 7 or 8 full temperature cycles, the rear diff moves enough power and has enough inefficiency to heat up to the point where water can come off. Unless youre in 4wd a lot, the front does not do the same.

Whether you should have gone with the thicker lube in the diff is really dependent upon how much you haul and tow. 90wt syn lubes are decent, you might think of upping it to a 110 if you haul a lot, but I wouldnt loose sleep...

JMH


Correct. There is no heat when not using the front differential and moisture builds up. Some of the dark color you see is actually a little rust that forms. If nothing else engaging it in to 4WD every once in awhile helps, just to circulate the gear oil.
 
Thanks guys.
Does this mean I should change the front more often? I know I need to change them more often anyways, what do you recommend for change intervals? I dont pull a lot with it, mainly just the boat and a pickup camper a little. According to the manual it says it does not need to be changed unless under severe load. I do live in MN so that is part of why I went with the 90 for better mileage in the cold, the stuff it had in from the factory really created a drag while coasting when it was below zero.
I couldnt really tell any wear on the gear's so that is good.
 
If it came with a factory tow prep or a hitch it was probably 75-140 synthetic.
If you don't tow heavy your probably fine.
If the rear is Limited slip you should add some LSD additive.
Or does Amsoil gear lube already contain it?
 
I do my AAM axles at 40k intervals with SVG 75w90. Both come out clean and clear, but my front spins all the time unlike yours. I will probably step up to the 110 next time as well.

Amsoil SVG already has the lsd addative in it.
 
The manual calls for
transmission 75W-85
front diff. 80W-90
rear diff. sae 90

Is what I put in going to be similar to what the book calls for? Also what is the difference and advantage to going with 110? Is it just thicker?
I dont have the limited slip so I would be fine there, thanks.

The manual also says unless severe load the fluids don't need to be changes, what are your thoughts on this? I am sure the transmission and front diff. benefited from it.
 
The deal is the specification changed in 2006. When I get home I can post the link, but suffice to say the "new 90" is now only the lower half of the "old 90" spec range. The newly created SAE 110 is now the upper viscosity spec range of what the "old 90" used to be.
 
Up until recently the 110 was a thick 90 weight. SAE actually made a new viscosity spec. That's why you see 110 weights now.
Sure you can go without changing fluids, but that will cut the life of components at a much faster rate, especially with heavier loads/high speeds. If you ever paid to have an axle replaced or rebuilt, you realize it's much better to do preventative fluid changes.

If you tow often or heavy loads once in a while, I would use the 75W-110.
 
I think that what some of you might be seeing is that some of the front diffs use a mineral fluid and the rears use a synthetic.
 
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