This weekend my truck is going to be down since i am replacing a u-joint. i figured that while im down there, i might as well change the fluid in the rear diff. 155000 miles, and i have no idea if its ever been done. I have i believe the 8.8 rear end with LS. I am planning on pumping out the fluid and refilling with diesel to work gunk loose and then remove the back cover. Is diesel ok or should i try something else? Brake cleaner maybe? then, what gear oil should i use? i want to run synthetic so i was thinking like a royal purple. i have heard that with royal purple, friction modifier isnt needed. is this true? if not, is 4 ounces of fm enough? i really like my LS and i dont want to loose its functionality. Thanks for any help!

 

bump cause i wanna do it to.

 

This is fine, just be sure to jack up the rear wheels to get the load off them if you do suck all of the old oil out. Fill the axle with diesel then spin it in first and reverse a little.

If you have never done the oil change in that many miles then this is a good idea because you could have condensation and all sorts of other gunk in there. After you've worked it around sufficiently pop the cover and remove it. Use a towel to sop the leftover crap out of the bottom. Check your pinion seal to see if it leaks, this is a good time to change it if it dribbles. Also check your vent line.
You can reseal it like factory with the adhesive sealant but if possible go to your local hose and gasket supply and buy a sheet of gasket material and make a gasket for the cover. This is so much better in my opinion and if you rtv one side to the cover and apply a little oil to the other surface before assembly you can reuse it over and over. I use the original synthetic oil in mine with a little Lucas treatment. I only have LS on my 02 but use the factory juice along with a little Lucas as well.

While your under the back end you may also want to consider purging your brake system at each wheel. At 155,000 miles you will have considerable gunk buildup in your brake lines if you use your truck on your farm like I do. I have drums on my 6cyl and disks on my 8cyl but I use the 6 the most out in the pasture and around pulling a 5th wheel and it sees allot of moisture so I have to really pay attention to maintenance on that one. You'd be suprised how much crap will work its way into your brake lines. :-/

 

Sounds good. Is there something i should do to get the diesel residue out of the rear end? Or should i just let it evaporate as much as possible? And thanks for the idea about purging the brakes, that hadnt even occured to me since i havent had to work on mine since i got the truck back in August.

 

While you're at the parts house, ask if there is a gasket available. I was able to find a premade Felpro to fit my rear diff. And while you've got the filler plug out, clean it up really good. It should have a magnet in it that will have picked up a bunch of junk. Mine is a 9.75" and I used 8oz of friction modifier (1 I lost a little while trying to fill it up, and 2 my clutches were binding up) and a good synthetic fluid. Worked wonders.

Definitely purge the brake system. I sucked all the old fluid out of the master cylinder and refilled with synthetic brake fluid and pumped until it ran clean. What came out was really dirty.....

 

I can look at my master cylinder and tell that its gonna be bad.... i dont think they have ever been flushed.... Ill look into the gasket, but i dont want to spend 30 bucks when i could use the rtv sealant (that is the correct term right?) for much less.lol. But i do realize this is not the project to skimp out on. A thought just occured to me.. Should i work on my front diff while im at it? And would it be the same as working on the rear?

 

Also, i was just over on Autozone's website, and lucas oil is 18 bucks for 1 quart. everything else is between 5 and 7 bucks for 1 quart. i dont have access too my owners manual and wont till friday, so is 1 quart enough? (i dont think so, just thought id ask) and is royal purple worth the extra ten bucks a bottle?

 

I don't know about Royal Purple, only what I've heard on TV. I'd just get a good name brand and go with it. 1 quart is definitely not enough. Gonna take probably 3, and that's assuming you don't lose any in the process of trying to fill it up. Make sure you put your friction modifier in first. The gasket I bought was $12 I think from a mom & pop parts house in town, so you shouldn't be hurting on cost there.

I haven't done my front diff yet, but I can't see where it would be much different. I know that it doesn't have to work nearly as hard as the rear all things considered. Definitely check your fluid level, though......

 

well i will definately check the fluid level, but i think ill leave the fluid change for another day. thanks for all the help!

 

this is great! ill be doing this when the snows gone. ill think i do the front to, but ill just drop it out.

 

espically since the PO didnt do anything but the maintance to keep it running. 258k and all original everything(except plugs and engine oil)

 

WOW! lol im glad i got to mine before it had that many miles with virtually no maintanance lol

 

Yep, before you pop the cover and drain it you want to drop the rear back down so it's sitting on it's tires. If the ground is level this gives the housig a little tilt towards the back. Whatever doesn't come out just sop it out with a rag and let air dry. A little residue wont hurt, it's oil too. Button it all back up and refill till it comes out of the hole.

$30 for a gasket is ridiculous. I made mine for about $1.25 each.
Buy a sheet of gasket material, the stuff that's close to 1/16" thick. It's super cheap at a hose and gasket store. If you dont have one (I doubt cause pretty much every decent sized town has one) then you can buy sheet single thickness material at autozone. Don't buy the square assortment pack, they will have rolls of the gray/black material of variouis thickness in the back. Ask for it, it might be $3 (but realize you will get three times as much for that much at a hose gasket supply and if you are anything like me, you can always find places to use gasket material on your farm) but it will definitley not be something they shelve out on the floor.

Clean the diff cover, smear a coat of oil or grease around the sealing surface, then lay on top of the material. Theres your outline to cut out...slick as snot.

 

hahaha i realize 30 bucks is outrageous for a gasket. its just been my experience with stuff like that, that prices are generally outrageous. but if i can get the gasket/material that cheap i will deffinatly do it as the rtv sealant is 10-13 bucks. and your right about needing gasket material around the farm ... come to think of it we have some but it is about 2 inches wide and a quarter inch thick. lol

 

Yeah you need to do this and soon. It really affects your braking performance and will eat the insides ouf your wheel cylinders/calipers out.
If you can afford it purge the whole system and refill with DOT-5 synthetic. I have DOT-3 in my 02 but next purge I will swap out with DOT-5. I already swapped out to DOT5 on my 00. I use DOT-5 on my military vehicles so this is why I stock it. The M35A2 uses an air over hydraulic system and the hydraulic side is filled with DOT-5 because of its superior moisture resistance. DOT-5 just plain keeps so much longer that DOT-3 and you will get 0 condensation in your lines with it.