I'll be getting a new 9" for my '77 F-150 in a week or two. I was wondering which gear oil to use and was hoping someone with a little more knowledge about lube could help me out with this decision.

My current thoughts are to put in $2/qt Advanced Auto Special for the first 500 mile break in - then put in a "real" lube for the remainder of its life. Does this make sense? Should I splurge on expensive lube even for the break in -- would it make a difference? After the break in period is there really a difference between the $2/qt and $9/qt lubes? Are any brands generally agreed as being superior to the average lube?

Thanks in advance!

 

well it all depends is yours a open diff? pretty much any lube that meets or exceeds the GL-5 spec is a pretty good oil and will serve you well. i would use either 85w90 or 75w140 depending on how the axle was built i would use the 75w140 if it has a locker of the axle was built with "play" in it. the break in period on a diff is about 3 to 5 k before everything really gets seated right. i would use a gl-5 in the above mentioned weights in a synthetic or a dino oil. something like rp does well in these it is 9.00 a qaurt tho. but i was looking around and found that the walmart supertech gear oil meets the Mack gear lube specs. i am running the supertech gear lube right now. it is 7.00 a gallon

 

It's a Detroit Truetrac w/ Precision Gear 3.50.

You would recommend going 3-5k before draining & refilling rather than 500 miles because between 500-3k there will still be junk that hasn't worked itself loose into the oil?

I'm looking to make this the only time I have to deal w/ the rear unless I decide to change the gearing at somepoint in the future, so if RP/Redline/some-other-ridiculously-expensive lube will make a difference I'm more than willing to pay an extra $15-20 now to prevent future headaches.

However, I'm not looking to throw money away (heck, there are a lot of other things my truck could use the money on!!!), so if "lube is lube is lube (GL5)" I'm perfectly fine putting walmart el cheapo lube in my truck if it's basically the same as any other lube.

Basically I'm wondering:

Are the more expensive lubes worth the money?

If so, which ones are worth the money?

& now your post has me wondering:

What grade of lube? (I was thinking 85-140, but I have nothing to back that up - I'm in TX, so lots of heat, not much cold)

What break in period?

Thanks for your reply!

 

well i would use the 75 or 85w140 in the locker as they are loud by nature and built very loose most will have about 2'' of play at the wheels. i am using the cheap stuff in mine. it works well and meets all the specs i change it every 50k or when i submerge it in water. actually there has never been one single bad thing ever said abou the walmart oils and gear lubes. so WPP must be doing something right.

 

Who did you buy the locker from an what do ther recommend? I would follow their advise. My rearend builder told me to run dino for break in, should be 35-50 mile trip with complete cool down first 3-4 runs, then app.500 mile change to whatever you want, he likes the 85-90.

I have a drag only car an 35 mile trips would kill gas budget and land in jail here in Pa. I just warmed up on jack stands numerous times with cool down made some passes on it an changed to synthetic. I like the uniform consistency