Greetings,this question may sound dumb to some but are there any thing special procedures I need to be aware of in changing the lube in my rear differential on my 01 3500 CTD.<br> Going to switch to synthetic. Thanks in advance for any and all help! .........Mike

 

Not really. When I changed mine and went to synthetic I did a couple of things.<br><br>First, get the cover off. Try not to wear too much of the fluid by popping it off. Get a putty knife in the bottom edge and let it drain before getting the cover all the way off.<br><br>Then, jack up one side at a time to drain the axle housings all you can. Make sure you use a lint free cloth (got mine at NAPA) to wipe out the inside of the differential.<br><br>Have some steel wool to help get the sealer off the inside of the cover and the differential housing. Use brake cleaner to help cut the factory sealer and prepare surface for the new sealant.<br><br>I used the Copper Plus sealant after the black stuff recommended by the parts store didn't hold up to the synthetic lube. Can't remember who makes it but that's the name of it.<br><br>Put a thin bead of sealer around the cover. Make sure to circle the holes. Let it set for about five minutes before you install it on the differential. Wipe off the excess immediately.<br><br>I waited the required time before putting in the new lube to make sure I didn't spring a leak. Seems like it was 30 minutes or an hour. Can't remember. <br><br>Fill her up. Make sure you allow plenty of time for the axle housings to take the lube so that you are sure you have enough in. Don't overfill or you can cause a seep at the pinion seal.<br><br>Be patient scraping the old sealant off. It's tough stuff.<br><br>

 

I put the sealer on as stated above and installed the cover with the bolts finger tight. Came back the next morning and very lightly tightened them and filled it up. No leaks at all. I used the red Hi-temp RTV. The sealing surfaces have got to be clean and free of oil film or it will leak. You may want to consider the Mag Hi-Tech cover. It is sealed with an o-ring and adds to the capacity of the housing. Money well spent in my opinion.

 

Don't forget the friction modifier if you have the anti-spin differential option.

 

I used Valvoline synthetic and left the friction modifier out until I tried it. LSD works great with the modifier out and the synthetic in mine. If you are going to synthetic, you may want to try it without the modifier first. Since the change, I've had no &quot;shudder&quot; on turns at all and both wheels hook up good.

 

All due respect Smoke Dog, but steel wool is the last thing I would want near any precision machined parts.A good old fashion gasket scrapper is all you should probably use on the engine, trans, or axle components.I have a suggestion,Cummins 1, while you have the rear apart, change the axle seals, if they haven't already been done. My truck just seems to eat them and it doesn't seem to matter who changes them.

 

Point taken on the steel wool. What I did was cover the ring gear with a couple of lint free wipes and watched for any stray wool on the wipe. The only exposure was the face of the differential. At the time it's all I had and the scraper wan't getting the sealer off. Since then, I've found some of the green scrubbers and the work as good or better. Also, when cleaned out the lower part of the differential, I really cleaned it.

 

If you use the big &quot;A&quot; synthetic, you don't need the modifier. Don't know about the rest of them.

 

Ditto here, no friction modifier needed with big &quot;A&quot; and LSD works fine. I just scraped the old gasket off, used the red high temp RTV, let it set for about an hour, replaced fluid, and drove it about two hours after and don't have any leaks.

 

Where did you get the info that no friction modifier is needed with synthetic? There is an article in this months Trailer Life about a guy towing with a Cherokee with LS dif who went to a dealer, bought Mopar synthetic and installed it himself. When the diff failed he was refused warranty because he hadn't used a modifier. Be carefull.

 

Some synthetics already include the modifier, or at least say that they include it. I've heard of several cases where people still needed to add it even when the synthetic specifically said it wasn't required--probably just boils down to differences in LSDs. I know the factory fill is not synthetic, but the LSD on my truck needed some modifier added right off the dealer lot--either the factory forgot it, or the clutches were a bit more prone to chatter than some.

 

Not all synthetics are the same or equal!<br><br>From Amsoil's website: &quot;AMSOIL Series 2000 synthetic gear lube provides limited slip performance.&quot;<br><br>From Royal Purple in reference to their MAX-GEAR lube: &quot;No extra additives or friction modifiers required for use in limited slip differentials.&quot;

 

Yep, I'm sure that's what their respective websites say, but I've heard of situations where both those brands and others that say no additive is needed have needed the additive. It's not that they're lying to us, just that the individual units differ.

 

[quote author=Wilber1 link=board=4;threadid=8768;start=0#85019 date=1040931359]<br>Where did you get the info that no friction modifier is needed with synthetic? There is an article in this months Trailer Life about a guy towing with a Cherokee with LS dif who went to a dealer, bought Mopar synthetic and installed it himself. When the diff failed he was refused warranty because he hadn't used a modifier. Be carefull.<br>[/quote]<br><br>I'm guessing he didn't read the lube container to see that the additive was needed even though he used the MOPAR oil. Been there, went through that before.<br><br>Quote right from the AMSOIL brochure, &quot;The Series 2000 Gear Lubes supply limited slip performance without aftermarket limited slip additives&quot;.<br><br>Mine has been in for over three years in this truck with no chatter or other problems or additives. I pull up to 26000 pounds with mine.

 

Just another thing to add, most manufacturer's recommend driving 8 to 10 tight figure of 8 patterns after changing the differential fluid to get the new stuff worked in. Good luck!