kennyS

Truck is a 97 f150 4.6 4x4 offroad edition with 8.8 front and rear axles.

-----sorry if this has been brought up before but my phone doesnt let me search the forums very well.

Anyway, times finally come to regear my axles. This weekend my truck goes up on 37s from 35s, gets a 3" body lift on top of the 6" fabtech suspension I already have, and axles are going from 3.55ls to 4.88ls.

Anyways my question is what oil should I run with brand new gears? I've heard of people using "break in" oils before they flush it and use the regular (I believe its 80w-90 with Ls additive).

I'm not positive if this is something that really should be done, but if so what oil should I run and for how long. And also is 80w-90 correct? I've already rebuilt the rear end once but I can't really remember what oil I bought. Its a 8.8 with the stock LSD carrier.

techrep

iTrader: (1)

would ask the people installing your gears... they are smart...

kennyS

Your telling me to ask myself.

techrep

iTrader: (1)

I guess so..my 3:73LS used 75W-140W ...I went with Mobil 1 and 4oz. friction modifier.
I doubt you want to dump $60 of gear oil after break-in though.

kennyS

What's friction modifier? I've never used that I always put the oil with the limited slip add and that's it

techrep

iTrader: (1)

same thing...Ford calls it Friction Modifier

twoskinsoneman

I just rebuilt mine. FWIW I put in 75-140 of the cheapest autozone (or whatever) brand and friction modifier for the 500 mile break in. When I change it and inspect I'll be filling with the mobile 1 75-140w with no need to add modifier.

BFP F150

check out royal purple for any fluid or gear oil one of the best companies on the market

kennyS

Is this what I should do aswell? I've never messed with new gears I rebuilt my last axle with another used axles guts and I'm pretty sure I used 80-90 but Idk much about the purpose of different weights of oil

twoskinsoneman

From what I researched Ford now recommends the 75-140. That's the route I would go. I used the cheaper stuff for the break in because it is getting dumped at 500 miles. I'm going to use mobile1 because I like the brand and IMO it's a high quality product like several others also it's synthetic which is recommended by my ring and pinion manufacturer. Royal purple is also a top quality brand from what I've read.

Most importantly follow your manufacturers instructions.. especially the break in instructions. Don't blow them off.