The dealer wants $75/diff to change the fluid...pretty steep! Is there anything special about the fluid? I have a standard Dana 60F in front and a limited slip Dana 80 in the rear. <br><br>Please help me save some money here.<br><br>John

 

John, the diffs are easy to do, even for this amateur wrench turner. You'll need a thin putty knife to tap into the cover joint to break the seal, and a tube of blue RTV gasket maker. Go for it!

 

Thanks C. So you say there is no real gasket just a silicon seal??

 

I have an '02 and there was no fiber gasket, just lots of silicone. Use a single edge razor to clean the surfaces, and protect the gears with newspaper or a rag while you're scraping the old stuff off. Might want to use some acetone or brake cleaner to degrease the mating surfaces before applying the RTV.

 

The first time I did it, I didn't even remove the cover. I just used a suction gun to pull it out. The second time, I had to remove the cover because it got hit by a brake drum traveling at about 60 MPH (I was doing about the same speed, do the math)

Anyway, the parts guy recommended some Permatex Hypalon (or something like that), which DOES NOT WORK. It stays in a jelly-like consistency. Good for gasket dressing I suppose, but not good for &quot;gasket-making&quot;. The stuff that was originally on there was gray silicone, and heavier than usual. I believe I found what they use, and it is &quot;Permatex Ultra Gray&quot; it is much thicker in consistency than the usual RTV, and it worked great even with my dinged up cover.

I don't want to start an &quot;oil war&quot;, I am not passionate about one brand over the other. I used Valvoline Dura-Blend 85W-140 and that is some pretty amazing stuff, judging by the spot in the driveway that remained shiny and wet after detergent, simple green, pressure washing, and even cat litter and paint thinner and even lacquer thinner. I finally got it up using naptha and cat litter twice. In my experience with gear oil (a lot), I've never seen anything so tenacious. Not that pouring oil on concrete is anything like scientific testing

 

Oh yeah, also what Commatoze said, anytime you're using RTV, the mating surfaces must be completely clean and oil-free to get decent adhesion.<br>

 

Good point about leaving the cover on for one change. I found a big magnet mounted to my cover that was really doing its job. It probably wouldn't hurt to suck out the old lube instead of breaking the cover off.

 

But if you are going to take the covers off, you may want to change to synthetics. Go 75W-140 for towing. Regular driving, go with the 75W-90. I switched to Valvoline Synthetic. No friction modifier required and the LSD works great.

 

That sounds impressive! Good tip. I always use Permatex #2 on anything that holds gear oil with a gasket. That stuff will seal oily surfaces well, too.<br>

 

[quote author=Smoke Dog link=board=5;threadid=17433;start=0#163149 date=1058974385]<br>But if you are going to take the covers off, you may want to change to synthetics. Go 75W-140 for towing. Regular driving, go with the 75W-90. I switched to Valvoline Synthetic. No friction modifier required and the LSD works great.<br>[/quote]<br><br><br>What about Friction modifiers for Limited Slip?? Is it necessary or does synthetic gear oil not require it ???

 

I also need to change the oil in my diffs... anyone know how much I'm going to need for both front and back?<br><br>Thanks for your help,<br>g

 

And your truck is a....

 

Sorry... I forgot that part.<br><br>Truck is a 99 Cummins 4x4 with a Dana 60 in front and an 80 in back.<br><br>Thanks...