Rear fluids, dino or synthetic
 

I tow pretty heavy for these ole trucks. GCVW is about 23500. I have always used dyno in the rears but am thinkin about synthetic this time. I'm synthetic in the trans now. I'm thinkin about synthetic in the transfer case and rears. The question is is this smart in these ole rears or should I continue to change it out every year? This is a 4x4 with a limited slip rear in the rear. Watcha think?

I have no personal experience w/ this, but the guy I got my truck from said he ruined a few rears on his previous diesels by running dino. He was pulling ~12k trailers. He switched to synthetic and ran it so far w/ no problems. I'm running w/ mobil 75w90 LS synthetic with my 8600# trailer and so far no problems. I'd definitely trust synthetic over dino pulling what you're pulling.

Rear Diff
 

I converted all of the fluids over to Amsoil synthetics but when I had to get some service work done on the rear diff the repair shop wouldn't replace the rear diff fluid with synthetic. They recommended I stick with dino oil!!!!!!

So, who knows for sure, just my experience.

Yep here in lies the problem. I really can't complain about the dino. The ole Dodge has about 180K on it with no rear problems. (yet) I was just wondering if it would be a better idea to go syn. Anyway I guess if it ain't broke don't fix it. I thought maybe it would run a bit cooler with syn. Idono I'll stayed tuned and keep listening.

I don't think there's much point in synthetic in the transfer case and front diff. You aren't in 4wd when you are hauling the fiver down the highway, so all that stuff is just coasting along and not getting hot.

Definitely a good idea out in the rear diff and in the trans, the synthetic handles the heat much better.

Thanks Dave Hey what brand and weight would you suggest for my situation?

I'd run an 85W-140 out back. I'm sure you get it plenty hot and that rear probably has a good bit of wear so you want a thick lube.

Mobil1, Royal Purple, Redline, Amsoil, they are all good.

Thanks Dave
Yeah I think that's what's in it now but dino. I'm gonna change out the rear to syn and just change the front and transfer with dino.

make sure you get one with the LS additive (I know Mobil 1 makes it) already in it, or make sure to add some seperate. Some friction modifier for the clutches I think.

I have Mobil1 in the rear of my dually and just dino in the front.

BTW, use silicone EVEN if you get new gaskets!!! mine looked perfect, and were perfectly clean. New gasket and they LEAK! I torque the bolts a little more and they STILL LEAK. A thin bead of oil grade silicone on the gasket (or no gasket and more silicone) will help. If you do no gasket, only barely tighten the bolts at first so as not to smoosh out all the silicone. Let it cure for several hours (overnight) then tighten them.

i run ams in mine all around except for the motor

Thanks guys

Yeah I used Valvoline dyno that had the LS stuff in it but added anyway and will probably do so again if it's compatable with synthetic. I don't use a gasket just silicone. Seems to work better for me. LOL

Hey DZL DAMON, I use aviation gasket maker on them. Works more like a gasket sealer but thicker. Never once had a problem with it, and holds them in place. Good stuff and no waiting period. Just my 2 cents.....

GARY!! havent talked to you in a while...gonna have to give you a call this week if your around for a meet and coffee before its to cold

When I had my D70 rebuilt back in June the repair shop told me the exact same thing. They also said that the dino runs best in them and that running synthetic is bad for them. That's the extent of their explanation. This was from a reputable repair ship in coon-***-ville Louisiana so take it for what it's worth. That said, I will be swapping to AmsOil when it comes due and I also run AmsOil in the engine. Since I don't drive it all the time now, but when I do drive it it's run pretty hard, I wanted the extra protection of a synthetic.

Hi Nick

Yeah sounds good. Should be here for a little while anyway. Would like to get away in a week or so but ya never know. I see ya saw Wana for the pin job. Talk to ya later