hey guys,
i was wondering what weight oil these rear ends take? its a 4:10 limited slip on a F-350 dually.
i just replaced the VSS on the diff and some little pices of metal fell inside so i wanna change it ASAP.
so what brand are all of you guys running and what weight? ohh and how much does it hold?
thank you very much
Mitch

 

Since it's limited slip, don't forget to add friction modifier!

RP
Zach

 

it holds about 4 qts.
just clean up the cover really well and the diff and use rtv to seal er up.

the book calls for premium 80w-90.

i run royal purple max gear synthetic. 75w-90. already has the friction modifier in it. although i have an open diff.

dont forget to take a rag and wipe out on each side of the ring gear. it has some pockets on each side of it that hold a little fluid in there.

 

One more thing worth mentioning... The fill plug in the side is magnetic, so pull it out & clean it before you button everything up & get ready to refill.

 

I second 1997F-350, Royal Purple Max Synthetic 75W-90 with the friction modifier already added. I have a 4.10 L/S and it works great. I also run Royal Purple in my 5 spd tranny.

 

should i flush it out first? since i live on a farm i have gear 80w-90 that i could use for a flush. should i drain the old stuff, but the 80w-90 in there and then i was thinking of putting RP synthetic 75w-90 or the amsoil. i am a fan of amsoil so im leaning tward that. but im gunna go shop around a bit to see prices and such. so what do you guys think about the flush? and also what is this friction modifier???
thank you for the help guys!
Mitch

 

Frictrion modifier is the stuff that makes the gear oil more slippery. If you use too much the limited slip will become a limitless slip. I run Amsoil 75w-140 in mine without modifier.

I wouldn't bother with a flush. Pull the cover while the oil is hot and the majority will drain on it's own. Then use a rag to wipe out the crap in the bottom of the pumpkin.

Servicing the rear diff is much easier if you remove the VSS and pour the lube in from the top. The fill plug on the side is at a funny angle for a bottle, unless you use a pump.

 

Pardon me for butting in but what is the VSS? I need to do rear diff. fluid change also. jcab

 

vehicle speed sensor. its on top of the differential and has wires coming out of it.

 

What 1997F-350 said.

Pull the sensor from the top of the housing and the fill plug from from the side, then just pour in from the top until it runs out the side.

 

No problem, VSS stands for vehicle speed sensor. its a little plug-in on the top of your rear DIFF. it tells you how fast you are going and tells the computer or somthing when to shift. so if that goes bad, you have no speedo and your tranny shifts really really really weird or not at all.
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Frictrion modifier is the stuff that makes the gear oil more slippery. If you use too much the limited slip will become a limitless slip. I run Amsoil 75w-140 in mine without modifier.

I wouldn't bother with a flush. Pull the cover while the oil is hot and the majority will drain on it's own. Then use a rag to wipe out the crap in the bottom of the pumpkin.

Servicing the rear diff is much easier if you remove the VSS and pour the lube in from the top. The fill plug on the side is at a funny angle for a bottle, unless you use a pump
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i went to Bumper to bumper and bought amsoil 80w-90 and then he gave me a little tube of that limited slip oil. its pretty small and told me to dump in the whole thing. i bought a gallon of that 80w-90 and he told me to dump in like 3.5 quart. is there any way to tell when to stop??? and he told me to pull off the rear diff and spray brake cleaner in there to get anything chunky out of there.
thanks
Mitch

 

First, be very careful if you use brake cleaner, you do not want to shoot it down the axle shaft and it will degrease everything that it touches, ring gear, spider gear, bearings, etc. I don't use it in a rear diff. I just remove the rear cover, be sure and clean the outside good before you pull it off or you will get dirt in the diff. Have a large drain pain under the diff to catch the fluid, then use paper towels and long needle nose pliers or a screw driver to wipe out the diff. This will remove all of the "chunky stuff".

After cleaning the inside of the diff. reinstall the cover using RTV. Remove the fill plug (halfway up the diff.) remove the VSS (top front of the diff.). Pour fluid in through the VSS hole until it comes out the fill hole. Replace fill plug, replace VSS. Your done.

Friction modifier is used to make the limited slip "slip". with out it you could have full time positive traction, which is very hard on very thing in a turn.

 

posi track any one not add this? what would happen if i did not add this. would it do any damage besides to the tires? muahahah i like, i think.
thanks guys!!!! your a big help!!! saved me so much time and i appreciate it!
Mitch

 

I know poeple who have not added it and had no problems, I also poeple that have not added it and had to rebuild the rear end due to worn parts. It does not cost much, so why not just add it and be safe?

 

The vast majority of lubes on the shelf today say they are safe for use with limited slips without additional friction modifier.

If you are getting tire scuff on low speed turns or any type of chattery noises from the rear then I would recommend adding the modifier in 1-2oz. increments, using only the minimum amount necessary to quiet it down. Dumping the "recommended" amount of modifier will make your L/S act like an open diff.... It will be useless.