Have a 1998 CTD 12V 4x4 with the Dana rear end (limited slip). Wanted to change the fluids, front and rear. Went to dealer to get the fluids, additive and gear oil. Additive was reasonable enought, about $9, but they wanted $40.96 per quart for the gear oil which was a synthetic.

Question is, do I have to use a synthetic? What fluid have you guys used? How many quarts rear, how many quarts front? Does it use a gasket or RVT?

Thanks

Sorry but posted this by mistake in the 24V area, reposted in 12V, but don't know how to delete from here

 

Synthetic is recommend if you tow heavy, but they can goof up some LSD.

I run good old fashioned dino, changed often and some L.S. additive.

RTV works fine on the cover. In fact, you'll have to search to find a paper gasket. I like the RTV Ultra Black. I apply, attach loosely for 10 minutes and then tighten to spec. make sure the cover is flat around the holes and you won't have any issues.

May be a good time for an aftermarket cover if that interests you.

Dave

 

In 1998 the diff came with dino from Dodge. The only reason to use synthetic is when towing as Fishing2Deep4U says.

 

In the manual for my 2002, it says to use 75w140 synthetic for towing. I changed mine over to this when I serviced it. You can get 75w140 synthetic at an auto patrs store for about $15 a quart, not $40 like at the dealer. Get the limited slip additive from the dealer though.

 

Most synthetics are already have friction modifiers in them. This makes additional additive not needed.

I ran 2 different synthetics with my Powr-Lok and in both cases the synthetic turned the diff into a peg leg. So, I just run dino and Ford Motorsports LS additive. I found it is far better than the Dodge stuff and provides predictable engagement.

Dave

 

That's what it says on the bottle, but misleading. At least it was for me. I had my Dana 70 rear diff rebuilt. They put dino in it. After 500 miles, I sucked the dino out with a pump and put in Royal Purple 75W90. Then, for the next2 months the diff would go grump-grump on turns when cold in the mornings. After it warmed up a bit it would go away. I called Fort Worth Gear & Axle and their tech told me that the synthetic oil is compatible with the friction modifier additive, but doesn't have it. (The bottle says it does?) So, on his recommendation, I went to the local Ford dealer and bought 4 ounces of their friction modifier. I sucked out a little of the oil from the diff and poured it in. (hold your nose, it stinks!) After 3 days, no more grump-grump in the morning.

 

4 ounces??

I use 1-1/4 ounces with a Mag Hytech. So a bit higher capacity over stock. Are you sure your LSD is working with that much additive??

Dave

 

In Dana 80 w/anti-slip, use Lucas 75W90 synthetic gear oil...at $10 and change per quart in gallon container... + 4 oz of Chrysler friction improver at $4.82/bottle. Rear axle was chattering when reverse on hard turns. After the lubricant change completely eliminated noise and seems to roll easier. After approx. 3000 mi. still working good. Sealed rear cover with black RTV silicone...no leaks.

 

Napa has the gaskets in stock.. I paid 29.00 for two gaskets and a thermostat.

 

I used Amsoil 80w-90 AGL in the front and rear 2001 axles, and I have always used Permatex Ultra Black on diff covers. Never any leaks. With the LSD additive you want to use the least amount possible. When refilling the diff, leave the additive out. Then drive it a couple of miles and make some tight figure 8 turns. This will get the new fluid worked into the clutch pack really good. If the rear chatters too much for your taste add a small amount of the additive. Make some more tight turns to work the additive in. Repeat until you are comfortable with the LSD operation. Remember that you can always add more, but you cannot take any out.

 

I've made money making sure grips work again after "home tech" changed the fluid. I agree with all the posters who said "use the MOPAR friction modifier"....and while you are there pick up a tube of the MOPAR gray gear lube rtv. Seals up like no other. Don't mess with the gasket.

 

I've got the Royal purple 75W90 in mine. It seems to be a little to loose for my rear end as the limited slip doesn't want to lock up once I break a tire loose. The RP supposedly has modifier in it but I haven't added any. If I do will it give my lsd more bite or less?

 

What is a good mileage to change the diff fluid at? Also, what is the best fluid for a 2001 3500 5 speed?

 

Mine had the stock fluid in it at 65K miles. I'd change every 50K minimum, synthetic, no towing.

 

Towing (and often in 115+ heat) I change the rear every 20k with 75/140 mopar fluid. Front gets changed about twice that since it's just along for the ride.

Severe duty interval calls for every 15K.
Normal duty interval calls for.......never.

I guess somewhere between there will be just fine.