97 4R70W (code U) 2WD
I need to replace the rear differential case oil. According to Haynes manual I need to add friction modifier to 75W140 synthetic oil. According to the posts I read in this forum friction modifier is needed for LS. Is mine LS or not? Thanks.

EDIT: I realized LS goes with rear differential, not transmission. I read the differential tag. It says 3 55 88 7 (and what appears to be a serial number). I suppose 88 means 8.8 ring gear? And only 10.25 is LS? Thanks.

 

You are a little confused. The differential(axle code), not the transmission(code), is the telling factor for limited slip or non ls.

Look at the codes below for determining which you have.

Axle Codes (should be on a label in the driver's side door jam)

non-limited slip

X27 – 3:31
X19 – 3:55
X26 – 3:73
X25 – 4:10

limited slip

H9 – 3:55
B6 – 3:73
B5 – 4:10


You're correct in that if you have a ls differential you'll need the friction modifier. Some fluids come with it mixed in, others don't. Look closely or ask when you buy. Use full synthetic of your choice.

Joey

 

If you go with Royal Purple 75W140 full synthetic fluid, you don't need to worry about adding the friction modifier.

I just found a place online that sells RP for $10/qt + shipping. I received my order last night... going to do the deed this weekend. If you want the business info, PM me.

KC :-)

 

Why not just post the website to share with everybody?

 

Because if they get flooded with orders, they might increase the price for all future purchases. Besides, it doesn't take a rocket surgeon to do a google search for fluid and compare prices.

 

You know what.... you're right. Sorry for being a bit ****ish... not enough coffee this morning.

Here's the site...

http://www.hrpworld.com/index.cfm

 

I dont care what Royal Purple says, the manufacturer calls for friction modifier, it needs to be in there. My roomate fried his rear end in his dodge b.c he put straight Royal Purple in it. But go ahead do as you please