Just wondering at what interval the front and rear diff fliuds need to be changed? Have 4200 miles on the truck and can't find any change intervals in the manual. Thanks for the help

Well, I changed my diff the first time at 560 miles. I'm a big believer in "break-in" lube changes, especially in the rear end where the gears actually "wear in" during the break-in period and produce a lot of heat and metallic debris. But, that having passed for you is a moot point. I changed again at 23,000 miles and I just changed again at 99,800 miles. I was a bit tardy on the last change, with 76,600 miles racked up on that lube, but it was Amsoil synthetic and the fluid and the rear end looked great when I replaced my cover with a Mag-Hytec yesterday.

It should be in the manual, I remember seeing it there. I know if you use synthetic lube, you can go longer intervals.

You will not believe the crud that comes out the first change - easy to see that not doing it could result in way premature wearout of the rear end. Synthetic lube is called for in the rear end because of heat related breakdown of the lube. Since I tow heavy a lot, I change mine at 25k intervals (last change looked like I just put it in, so I might go longer).

Thanks for the replies guys. I called the dealer today and they told me that it is synthetic in the rear diff and that it is a 100,000 mile fluid. Also asked if it should be changed after break in and they said no. They said if I towed heavy I could change it at 50,000 miles otherwise don't worry about it until 100,000 miles. What to do???????????????????????????????????????????????? ????

I'm a little surprised that the dealer didn't jump on an early change, because they sell the GM specified "grape juice" at a huge markup and can charge you $300 for a 20 minute rear diff change! I agree that the synthetic lube is a 50 to 100,000 mile lube - but Eaton, the manufacturer of our differentials, is specific on breakin lube change. I had slivers and small chunks of metal on my drain magnet after the breakin change - and there's other assembly grit and casting sand in there when brand new.

I had a Corporation 14 bolt full floater that had never had the lube changed (I too thought it "Lifetime"). TRASHED the thrust side carrier bearing, and had I not caught it, would have trashed the ring and pinon. Lube changes are cheap insurance - I use Amsoil , but there are other good ones as well.

I use the Valvoline equalelant(sp) and change mine annually. Get yourself the bottle pump sold at WallyWorld for pumping lube into the lower unit on an outboard boat motor. Screws onto a standard bottle of gear oil and you can put it in yourself in no time. You may have to add a bit of tubing to the suction to make it reach the bottom of the bottle to get it all out. Just my $.02. Works for me.

BB

The manual says to change the rear diff oil after the first 500 mile of towing. I don't remember what the interval is after that. I have done mine anually which I'm sure is probably overkill and use mobil 1 syn.....

I replaced the front and rear gear oil with Amsoil severe service 75-90. I drove to Alaska to see my son towing a 24' enclosed car trailer with 4 Harleys 2 440 race sleds and 1/2 of an aircraft. After returning I took a look at the fluid--looked like knew!! Just the other day, It was in for an oil filter change--we took a look at all fluids--65000 on the gear oil now--looked like it was put in yesterday!!

Greg Carter Vermont

I replaced the front and rear gear oil with Amsoil severe service 75-90. I drove to Alaska to see my son towing a 24' enclosed car trailer with 4 Harleys 2 440 race sleds and 1/2 of an aircraft.
Greg Carter VermontWow, that must have been a trip and a half, from vermont to alaska and back....Yikes, how long did it take ya?h
As for the topic at hand, i swapped out both front/rear diff 4k miles after i bought. Truck then had 28k on it, i dont think fluid had ever been changed, but didnt notice anymore than some small filings. But was glad i changed. I used Gm grape juice, cause i got it for a good price, and peace of mind...Might as well do your front diff to, just make sure you get the approriate vent cap(need white, stock is black)

Hi--We spent a week each way on the road--I only drove during the day--2 weeks in Alaska playing with my son--riding the bikes-dragstrip time in Palmer Alaska-my kid ran the staging lanes on weekends. The last fronter-GREAT PLACE!!!!!!!! By the way, I wasn't driving one of those GREAT Duramax's--We did this trip with our 1997 6.5 td suburban 2500. The truck has Amsoil in it from stem to stearn--runs like a dream--4-10 gear-worst mileage was through the Canadian rockys--10-12.--best little over 20-remember-4-10 gear and what I was pulling --I ran most of time on cruise 75!!

Greg Carter Vermont