Changing the diff fluid front and rear on a 1999 Dodge Ram 4x4 diesel. But apparently I need to know which Dana I have to accurately buy the correct fluid. Stuff is expensive so don't want to blow my wallet up anymore then I need too.

So how do I know which rear and front end I have and if its limited slip or not?
I can get the fluid amounts here http://dodgeram.info/tech/BRSpecs/fluids/specs.html once I know.

Additionally there apparently is some debate on whether amsoil with limited slip modifier already added is enough or if more needs to be added. Should I not add any more modifier and just watch performance or just add it anyways because it can't hurt.

Thanks guys!

 

Well after some internet searches found a guide that said to pull the BOM number off the tag affixed to the rear end and consult a chart, I have the Dana 70.

So only issue remaining is if it is a limited slip or not.

 

I use Mobile 1 75-90 LS on my limited slip rear diff, but its a 11.5 AAM, they say with the LS you dont need and modifier, and I find it way cheaper than amsoil, and gets changed out every 30k miles. I switched from amsoil after reading up on it, good luck

 

I used Royal Purple with the friction modifier already in it. No problems from it.

 

Ummmmmmm - As far as I know, and have been doing, if you drop the diff lube on an LSD then you have to add back the proper amount of friction modifier. I have a Dana 70 as well and the service manual calls for the addition of friction modifier when servicing the diff. I was using the Dodge product, sold in 4oz bottles X 2 to get the required 8oz. Way expensive stuff from the ******* so I found a product at DASH (NAPA) that comes in an 8oz tube and is a friction modifier for 1/3 of the price at the dealer.

Cheers!

Mike

 

You've all been most helpful thank you.

 

If you have an auto then you have the Dana 70. If you have a manual then you have the Dana 80. If you're not sure if you have a limited slip carrier or not then, if you're going to change the lube, just pull the cover and make sure which one you have. As for needing friction modifier or not, that will depend on if you even have a LS or not, what lube type/weight you use, and how the truck is driven. Most synthetic lubes will already contain a friction modifier so you wont have to add more. Regular gear lube will need friction modifier but I'd always start with one bottle and see how your LS reacts before adding anymore. Add to much friction modifier and you will eliminate all function of the LS, which can be minimal to begin with in an OEM limited slip carrier. A limited slip with lots of miles will also not need much friction modifier but one in newer good shape will need more. If you live where its hot and you choose a lighter weight lube then you may need two bottles but live where the climate is cool and you use a medium weight lube then you may not need any.....etc. So you can see my point.