Well my gears are going to go in on October the 11th, and I just need to know what everyone's opinion is on gear oils. The tops brands that I know of is Motorcraft, Amsoil, RP, and Redline. My local performance shop recommended 75w90 oil, but the tag on the limited slip said only 75w140. Any opinions on this?

 

As far as weight, Ford used to recommend 75w90 and changed it to 75w140. I am sure they had a reason to do so. I would use the 75w140.

 

Yep.

And you probably already know this - don't fergit the 4oz of LS monkygoop if it's a Ford LS gearset.

http://www.fcsdchemicalsandlubricant...ransaxle Fluid

Or use whatever additive the specific LS gearset manufacturer specifies fer the clutchpacks...

MGD

 

Yep, I'm just going to buy a bottle of it at the performance shop. So any opinions on actual brands? Should I buy some cheap 75w140 oil for the break-in, then go with some RP/Amsoil?

 

When I installed my new Yukon gears I went with Quaker-State 75w140 syntech with the 4oz bottle of FM from Motorcraft.

Haven't had one single problem with this ''Setup''.

 

Use the type and grade oil (and additives) recommended by the gear manufacturer, not Ford, when you regear. Same goes for whatever LS/locker you put in.

 

Well the LS that's going in is a Ford Trac-Lok that came out of an 02 Exploder (same spline count and axle). The tag that came with it says "75w140 SYNTH OIL ONLY", so I guess that answers which weight to go with. I think I'm just going to be safe and buy 6 quarts of either Amsoil or Royal Purple, depending on which one I can get cheaper.

 

Why not buy regular oil for the breakin. Then use the synthetic after. I don't see the point in buying synthetic for only 500 miles.

 

You can also use Mobil, Royal Purple, or Lucas. Most quality synthetics come with the friction modifier additive for your limited slip. However, be sure to double check. Red Line sells two different types of oil, one with friction modifier and one without. While you're re-gearing, change the differential cover. Get one that at least has drain and fill plugs to make for easier service. Ideally, your new cover will allow for more fluid capacity and have cooling fins. I like Mag Hytec. But shop around. There are a lot of options.

 

Yeah, I'm not going to buy an aftermarket cover just for a fill plug and some cooling fins. Since I'm going to lower my truck shortly after the gears go in, I wouldn't even be able to admire it.

I'm just going to bite the bullet and go for Amsoil. No point in risking a $800 investment just because I didn't want to pay for the good stuff.

 

Ah, but with the aftermarket covers, you can check the dipstick to monitor the condition of your fluid, and drain & fill w/out having to take the cover off.

 

Yeah, but I'm only going to pull the cover twice. Once for all the new parts to go in, and once after the break in to make sure everything is still lined up properly.

Oh yeah, I ended up buying 6 quarts of Amsoil for like $108.

 

Then that fluid will last forever? You don't want to check on it?

 

Not permanent, should be changed about every 100k. Unlike engine oil, you do not lose any through combustion. Only way to lose gear oil is a leak. Other reasons to change it would be if driven through high water where it could get water into the breather tube.

 

Which I'm not going to be doing. My truck is still in the single digits on dirt roads.