I am new to the forum, I have lurked a long time and appreciate the knowledge and experience of the members. I truly am not mechanically inclined. I have a consumer/owner question. I have a 2002 Chev. 2500HD, 8.1, 2wd, Allison, crew cab. I am the original owner, it has 23000 miles on it. I recently took it to a Firestone store for an oil change. In the process with the usual "we suggest you do this" pitch, it was suggested I change the differential fluid. The cost is $89.50. I declined as I was going to take it to my dealer for some warranty work and I wanted to make sure thiis is something that should be done. At the dealership I was told this is something that they suggest as a preventive measure. Their cost is $345.00. When I asked why it is so expensive I was told the fluid they use is $45.00/unit and it takes four or five units ( I have forgotten how many he said or what the unit is, probably quarts). The dealership describes this as a differential flush, Firestone described it as a change. Does this make sense?

I trust the dealer and realize they must follow GM protocol, but the prices are not even close.

Just so you know I bought the truck for retirement and to pull my 32' Holiday Rambler TT to the Rockies and points west. It is now paid for and I am about ready to go. Needless to say the truck has spent more time resting than working.

Sorry for the book, but thanks for your opinions.

Durell

The diff oil from GM is quite expensive. You'd be better off getting some Mobil 1 and changing it yourself or taking it to the oil change place for $90.00. Changing it is just fine, however, I've never heard of a flush.

It takes 3.75 quarts. I used Mobil 1 75w-90 synthetic at about $8/qt. The job is very simple to do. The differential has both a fill and drain plug. I lowered my spare tire to move it out of the way for the refill. Good idea to lower the spare once in a while anyway.

At the dealership I was told this is something that they suggest as a preventive measure. Their cost is $345.00.

Yikes! :eek: I am in the wrong business. I should be offering differential fluid changes.

Thanks for the responses. I do not mind being taken for a ride, but I want a good looking chauffer. (don't tell my wife I said that).
Durell

If you have a limited slip you will also need the limited slip additive. But just go with Royal Purple as it already has the additive mixed in.

I have the G80 locker does that need special additive like the limited slip?

any of the full synthetic gear lubes will work, no additive is needed..

Amsoil sever gear 75W 110 would be a good choice if you will be towing your trailer full time. It works good in cold weather also. Price should be in the 12 dollar range per quart.

a "flush" is just draining the old lube and putting new lube in it. i would look in my owners manual under the maintnance section. it will have a chart of when things need changed or looked at. see what they recomend in the manual before changing it. however it wont hurt to change it now it just might not be necessary.

Thanks again, guys. I have the locking rear end. I will also regap my plugs at .045. I understand this will give me VW mileage.:-) Economical is not a work used to describe this truck, but it sure tows well. I don't think I can overload it, but I am sure my bride of 43 years will try.

sorry guys, that should be "word" not "work". I try to not use the "w" word.

I use Mobil 1 syn rear gear lube for mine as well. It is easy to find at Autozone, and it is very good oil. I have had no issues with it.

do i need to add additive on a 2001 2500 LB7?...i am gonna use Mobil 1 75w-90

If you have a limited slip you will also need the limited slip additive. But just go with Royal Purple as it already has the additive mixed in.

Only the 03+ Cummins Dodges with the American axle 11.5 axle need the additive,as GM does not use limited slips. I would just change the oil using Mobil 1 as suggested.The only reason Id change it with just 23K miles is to get out the moisture that builds up over time,and any get the silverish color original oil out if it hasnt ever been changed.

how often should u change it?

check your owner's manual. I changed my front and rear diff fluid at 100k and will probably do so again at 140k when I flush the trans again. (or just rebuild the f'n thing...)