New Guy & Rear Diff. Question

[Big Jon]

If knowledge is power, this is one powerful site! I've already gained a lot of valuable knowledge from you guys and I hope I'll be able to contribute some of that back. I've had my new truck for about five weeks now and I love it! I've already got one of ICEMAN's tailgate graphics ordered.



Now on the rear differential: I will be taking the truck on it's first tow this weekend (nothing big: 5000 #'s total) and was gong to have the rear differential fluid changed out in favor of the 75-140W synthetic that the owner's manual recommends for towing. I have a mechanic friend who says 90W petroleum based is the only way to go, and that I'll shorten the life of the rear end with synthetic. He figures Chrysler puts the recommendation in only to get us to by the Mopar synthetic at about $20 a quart.



Is this guy sniffing carb cleaner, or does he have a point? If he's wrong, what is the benefit of running the synthetic in the rear differential?



Thanks,



Jon

 

[klenger]

I think that the manual recomends synthetic for towing, but states either 75-90 or 75-140 for more heavy duity towing applications. Either one is an improvement over conventional gear lube.



Does anyone know what weight Dodge puts in at the factory?



kl



Edit: It appears that I didn't know what I was talking about. The owner's manual does state to use 75W-140 Synthetic for towing. The trucks are delivered with straight 90 weight non-synthetic.

I have ordered a Mag-Hytec cover and plan to change to synthetic gear lube for towing our 5er. I'm trying to decide what is the best product for this. Here are the options I've found:

Amsoil 75W-90 GL-5

Amsoil 80W-90 GL-5

Amsoil 85W-140 GL-5

AmsOil 2000 75W-90 GL-5

Mobil 1 75W-90 GL-5



85W-140 seems to be heavier than necessary for my application. Mobil 1 is about $1. 00 / qt cheaper and I can get it at Autozone. I'm leaning towards Amsoil 2000 75W-90. Feedback please.

 

[Big Jon]

Thanks Ken. I am still curious though - why the synthetic lube recommendation... . I mean, what does it do for the differential when towing that good old dino-lube doesn't?



Jon

 

[klenger]

Less friction, less wear, better protection in cold and hot weather, better milage. Check out http://www.amsoil.com. They have some info. on synthetics. By the way, I am not a dealer, but I was about 15 years ago.

 

[Phil Stuart]

Gear Lube Question

Big Jon,



I replaced the original cover with a Mag Hytec about 2 months ago and the install was easy. I myself went with the Amsoil Series 2000 75w 140 synthetic gear lube. I did not have to add any friction modifier after test driving in a series of figure eight turns for about 8 times. No clutch chatter. You will need 8 quarts of lube when going to the Mag Hytec cover. Well worth the money spent on the cover and the synthetic lube. Good piece of mind.



Phil Stuart

 

[JeffreyHahn]

Dana delivers axles with synthetic premixed with friction modifier.

There have been problems with using the heavy duty with modifier. Seems modifier has been eating seals. This only seems to be a problem with Jeep/Dodge axles. If you can use a synthetic (ie Amsoil) without the modifier you would probably get

more mileage out of your seals.

 

[Big Jon]

Thanks guys,



I've been thinking about the Mag Hytek cover, what with the larger lube capacity and that convenient drain plug, it does seem like the smart way to go. I guess I'd better add that to my to-do list .



I had no idea the friction modifier was a seal eater. I had enough troubles with rear mains with my old '85 Ford 6. 9L..... I really don't want to experience rear wheel lock-up again.



Jon

 

[tlippy]

I can't believe this post got this far without all the site's experts chiming in!!!!!!!!! A call to MagHytek will give you their opinion-and it ain't Amsoil! I live in a climate where it's 20 degrees and lower at night for 6 months of the year and couldn't make up my mind which synthetic to use - 90 or 140. I did finally end up putting in Redline 140 w/o the emulsifier - per conversation with Redline. Still had some trepidation. Finally some of the guys who had installed a temp gauge in their Mag's reported readings of 190 after just a short drive. That kinda eased my mind - knowing that the oil got that hot. I think you will be amaxed at how funky to OE oil is - phew. Just remember to stick your finger down in the sump and sloop out the OE stuff. I let my truck sit overnight with the cover off just so I could get the last bit of drain.

 

[Big Jon]

Hmmmmm... ... ... . well, it's all clear as dirty lube oil to me now.



I did a search, looking back at the past year, and found a couple of threads on the rear differential and who's got what lube in it. If I remember correctly, the Mag Hytek cover was popular as was the Valvoline version of synthetic. It seemed like it was pretty close to tied on who was using 75-140W vs. 75-90W.



I still don't understand if running synthetic is going to HARM my rear end, rather than HELP it. I've got a local mechanic saying synthetic will eat up a differential in 15,000 miles (of course, he likes the Duramax too, so maybe I ought to take his advice real lightly). I've got the Service Manager at the Chrysler dealer saying he doesn't know why the Owners Manual recommends synthetic for towing/HD applications - he says stick with the factory fill (90W), and I've got what seems like the majority of the membership running Valvoline synthetic.



I dunno, maybe I otta start a new thread. Maybe title it pre vs. post turbo for a pyro. That otta get some attention



Jon

 

[Extreme1]

Originally posted by Big Jon

I've got a local mechanic saying synthetic will eat up a differential in 15,000 miles...

He would probably argue that Ford owns Cummins too.



Synthetic lube is the only way to go. Follow the owners manual on this.



Do a little research and choose the brand YOU feel most comfortable with. You know the value of opinions. These diffs do run hot, don't skimp! Repairs on these parts ain't cheap!



And be sure to clean the little sump out in the bottom after you pull the cover...

 

[EMDDIESEL]

I am getting the prybar out and ordering a Mag Hytec Diff cover tommorow morning from Geno's (Since my stock one is leaking). So in the meantime, i want to get the gear lube now. I have an 01' Auto 4x4 short bed with 3. 54 gears and a limited slip.

I dont tow or haul anything and i live in the Northeast. What weight gear oil should i get? and how much do i need?