Bet your rear axle is over full now

[radar doctor]

Thanks JOE

Many Thanks, Keep up the posts Joe, Bill

 

[Joseph Donnelly]

Thanks, guys.



I was trying to emphasize that getting the rear gears set right is important, and secondly, I may not agree with the factory fill, at least with what I know at this point. In general, 75-90 tends to be very thin (you'll find out when you remove the cover). Synthetics are pretty stable, but I have seen a black crust on the Mag Hytec dipstick on another truck that should not have had moisture in there to degrade (hydrolyze) the lube. That was a reputable 75-140, which may not be the best for miles per gallon on an empty truck, but years of use has led us to the rule-of-thumb that 75-140 is usually better than 75-90 under heavy loads, and a premium 90 weight like LE607 is pretty hard to beat regarding degradation, lubricity, and load capacity in the ambient temperature range for which it is appropriate. 607 has a pour point of -11 deg. and a channel point of -60 deg. That means the point where it won't refill the channel cut by the ring gear is -60 deg. F. Steel is more brittle at low temps, so you will be driving easy until the diff warms up anyway. I have found that Kevin Dinwiddie is very up front and fair in his appraisals and recommendations. He is the first oil person who told me not to buy his product for an application! He told me to use Castrol in the NV4500. I am using 607 in my 97's diffs and at 770 hp it can use all the quality I can buy in lubricants. Especially under load, thin lubes and lower quality lubes can be squeezed out and the gears will scuff. If that happens, they will howl for the rest of their lives, even if you replace the lube with something better. Many of us can buy synthetics for significantly less than we pay for LE607. 607 is much better at keeping seals from leaking than are most synthetics.



The factory warranties the diffs for 3 yr/36,000 miles. The way I drive, they will last that long on most any lube. I am more concerned with how the gears and seals will perform over a longer term, so I am doing what I feel is best. If a catastrophic failure should occur, I will discuss it with the dealer and then deal with the results. When I checked my diff, it was HOT and that told me right away the backlash was probably too tight, since I had just been driving around in town, unloaded, and taking it easy. To me, proper clearances are more important than which bottle of lube I choose, and whether the fill is 1/2 inch above or below factory recommendation. I am experienced with setting up gears, and i realize that many of us Rammers aren't. I'm not suggesting everyone get a dial indicator and set the backlash, or even check it. I am suggesting that it is too easy to get very concerned about one thing we see, and not notice other things that may be important.



Overall I am quite favorably impressed with the American Axles. The Dana's were not perfect. Carrier preload was insufficient to marginal in many cases, the ring gear was narrower (comparing the Dana 80 to the AA 11. 5), etc. I fixed the preload in my 1997's Dana 80. It took hours. It took a couple minutes to fix the backlash on the AA 11. 5 in my '04.