Gear Oil Question: Grassroots Motorsports forum: Grassroots Motorsports Magazine

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Dec. 7, 2011 1:23 p.m. Woody SuperDork

It's time to change the gear oil in my 2005 Tacoma 4x4's front and rear differentials and the transfer case.

When I went to buy 75W-90 oil, I noticed that all of the synthetics were labelled "Limited Slip". I knew that this was what I needed for the LSD rear, but I was wondering if this would be right for the front and the t-case. I know that you used to just add friction modifier for LSD use and I guess that you no longer need to. But, is this stuff too slippery for non-LSD applications?

Or, am I just over thinking this...
Dec. 7, 2011 3:51 p.m. Brett_Murphy Dork

Wouldn't it be less slippery for LSD applications (at least clutch type). Too little friction and the LSD won't work.

Buy whatever grade and weight your service manual states and you should be fine.
Dec. 7, 2011 3:59 p.m. Streetwiseguy Dork

Most synthetic gear oils are rated for LSD, but I have found its not always adequate, so I add the LSD additive. The friction modifier does make the clutch plates slip easier when not under load, to avoid chattering around corners.
Dec. 7, 2011 4:37 p.m. itsarebuild HalfDork

Brett, that's what thought..... but i have been reading up on this all day for my e30 LSD swap and this is what i have found.

the friction modifier is not for making the clutches grip. rather it seems to be to make them slip. both the mobil 1 and redline sites indicate that the friction modifier should be added to non-ls based gear lubes in LS differential applications at 4% and then in 1 oz. increments until the differential stops chattering. in other words, more friction modifier = more consistent slip of the clutches.

i have no idea if this is good for a transmission or transfer case, but the sites id's non LS type gear oils for these applications so i guess it does make a difference and it seems like they are available without the modifiers so think i'd go that way.
Dec. 7, 2011 7:38 p.m. Brett_Murphy Dork

Well, heck. Learn something new all the time.
Dec. 8, 2011 6:52 a.m. mthomson22 New Reader

I just went through a similar fluid change in my 03 Safari AWD, but more out of necessity than maintenance. Turns out GM speced sub par fluid in the transfer case causing the clutches to slip then engage with a 'bang'. I researched a little and found that GM issued a TSB to have the oe fluid drained, refilled with a different oe fluid, driven for a few miles and drain refill. Questioning whether I wanted to trust GM to get it right again I started looking for alternatives.

Turns out Royal Purple has a whole line of gear/atf fluids and some with friction modifiers. I ended up using Max ATF in the transfer case and Max Gear 75/90 for the front and rear diffs.

I've never tried any RP stuff before, but I will now. It completely cured the slip bang issues on my Safari, and I don't get any bind/release in the limited slip rear diff either.

just my $.02

mark
Dec. 8, 2011 11:09 a.m. pres589 Dork

I've also had a positive experience with Royal Purple diff fluid; 1995 Mustang GT would chatter and moan around corners, especially after some driving, fixed with a fluid change from whatever was there before to RP & a small bottle of LSD additive from the corner parts store. I've been very happy with Royal Purple stuffs so far.
Dec. 8, 2011 11:30 a.m. rotard Reader

I had phenomenal results with Redline products in the transmission and differential on my RX-8. It was definitely worth the price. It was definitely a somewhat messy job and I would recommend nitrile gloves to anyone doing it. It's hard to get that smell off.
Dec. 8, 2011 11:44 a.m. z31maniac SuperDork

This is one of the times I'd go to the dealer and say, "Sell me the right stuff for X" and not worry about it.
Dec. 8, 2011 12:28 p.m. mthomson22 New Reader

z31maniac wrote:

This is one of the times I'd go to the dealer and say, "Sell me the right stuff for X" and not worry about it.

I hope I never have to have one of those times.
Dec. 8, 2011 12:47 p.m. z31maniac SuperDork

mthomson22 wrote:

z31maniac wrote:

This is one of the times I'd go to the dealer and say, "Sell me the right stuff for X" and not worry about it.

I hope I never have to have one of those times.

Why is that? You buy their stuff that was designed with that application in mind.

I went through two different sets of trans fluid before going back to stock in my 350Z, the aftermarket synthetic stuff wouldn't let the trans shift into 2nd until the box was warmed up.

My Speed 3 diff started groaning like crazy when the "correct" aftermarket syn was put it, took it back to the dealer for the stock stuff, everything was good.
Dec. 8, 2011 5:50 p.m. iceracer SuperDork

I did the whole change on my Liberty with Amsoil. Couldn't be happier. Actually gained 1.5-2.0 mpg. Even with the synthetic, I had to add Slip Lock to the rear Trac-Loc differential.. Many transfer case use ATF.
Dec. 8, 2011 5:57 p.m. RexSeven SuperDork

The Motul 75W-90 fluid in my MS3 has been superb so far. The shifting is smooth and it warms up quickly unlike the factory or Ford Motorcraft fills I've tried, esp. in cold temperatures. I'm not experiencing any of the LSD groaning z31maniac mentioned.
Dec. 8, 2011 6:23 p.m. Woody SuperDork

Update:

I got tired of thinking about this and just put Mobil 1 in everything. It was surprisingly affordable at about $10 per quart.

I'm done.
Dec. 8, 2011 6:44 p.m. Dr. Hess SuperDork

I use Mobil SHC630 in anything without clutches (LSD) or syncros, and Redline MTL in things with syncros and the Redline stuff for LSD aps in those.
Dec. 8, 2011 7:11 p.m. Woody SuperDork

Red Line was my first choice, but I couldn't find it locally.