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Discussion Starter #1
Hi, I spoke to some people and they swear the differentials should always be lubricated with standard "mineral" oil, but at 15k (as I wheel my FJ quite a bit) I replaced everything with mobil1 or royal purple synthetic (this is front diff, transfer case, rear diff, on a manual transmission).

I am at 30k now and I was wondering what I should do, back to standard or...?
 

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Discussion Starter #2 (Edited)
I did some more research on the forum and it seems one should use different fluids in different parts of the transmission; this is an attempt to create a full list:

It seems the correct spec for the oil is 75W85; the 6MT oil must not be too slippery otherwise the synchros won't work well so it should be different from those used for hypoid gears.

Quantities:
Front Diff: ~1.5 quarts
Read Diff: ~3+ quarts
Transfer Case: ~1.5 quarts
Total "Gear Oil": ~6+ quarts

6MT: ~2 quarts
Total "Manual Transmission" Oil: ~2 quarts


Oils available on the market (please let me know of inaccuracies or additions to this list):

Redline:
Apparently Redline is the only company that provides 75W85 grade:
Mobil(1):
Royal Purple:
Amsoil:
Castrol:
Pennzoil:
Lucas:
  • Front/Rear Diff, Transfer case: SAE 75W-90 Synthetic Gear Oil
  • 6MT: I was not able to find an oil specifically suited for MT in the Lucas product range.

Gasket Washers:
  • Rear diff, drain & fill; Front diff, fill (Total 3): Toyota PN 12157-10010
  • Front diff, drain (Total 1): Toyota PN 90430-24003
  • TC/6MT drain & fill (Total 4): Toyota PN 90430-18008
All the above gaskets can be found at a local dealership (even if somebody mentioned the Front Diff ones are "special orders") or online for example at Toyota Part Sales (TRD4U, Toyota of Dallas) or at Toyota Parts Zone (California). In both sites you will have to do a part number search.

Torque specs:
  • All TC and 6MT, fill & drain: 27 ft*lbs torque 24mm Socket
  • Front diff, fill: 29 ft*lbs torque 10mm Hex Socket (Allen)
  • Front diff, drain: 48 ft*lbs torque 10mm Hex Socket (Allen)
  • Rear diff, fill & drain: 36 ft*lbs torque 24mm Socket
Hints on the procedure:
  • Drive around a bit to warm up the oil for faster draining
  • Always remove the fill plug first, to avoid the case when you begin to drain and then you realize the fill plug is stuck
Links of interest:
 

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I have noticed nobody mentions the central differential (torsen) found only in MT models. Shouldn't it be serviced too?
It's part of the transfer case.

Most members on this forum that change their own differential lubes use synthetic gear lubes, and for good reason. Synthetics are by far better than dino in this type of application, no question. They measurably reduce temps in the rear diff, and handle the high load stresses with ease. IIRC the FJ even comes from the factory with synthetic gear lube in the rear diff.

If someone is telling you that 'only' dino lubes should be used in differentials, they I would be very wary of their advice.

DEWFPO
 

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Discussion Starter #6
It's part of the transfer case.
Yeah, that is what I found out.

If someone is telling you that 'only' dino lubes should be used in differentials, they I would be very wary of their advice.
Ok but at least it seems that some fluids might interfere with the synchronizers in the transmission and some others are not suitable to be used with hypoid gears etc

I will read again and again and find out what is recommended and prepare a list in the second post. Feel free to contribute with your preferences ;)
 

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Discussion Starter #7
I have updated the second post with some more info and links. What do you guys think? According to what I've read the 6MT box needs a different oil to not interfere with the synchros; for all the differentials, there is some debate on the need for 75W-85 as specified by Toyota over the more common 75W-90.
 

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I use Amsoil Severe Gear 75W90 in my Diffs, with no issue.
I'll probably change to the same in my transfer case soon too.
I've read here somewhere that people have been happy with the GL4 Amsoil Transmission Oil in the MT6.
 

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Seems like thats a pretty comprehensive list of all the "common" fluids used on the FJ.

From what Ive gathered, the 75w85 for the diff+tc isnt a very strict requirement (as is the use of any LS modifiers since the 4x4 FJ doesnt use them... dunno about the 4x2?). Some members even claim their service department uses "off the shelf" bulk fluid which usually comes in 75w90... mine does unless I insist on the genuine Toyota 75w85 for ~+$180. Seems 75w90, especially synthetics, is fine with the important factor being the quality/cleanliness of the fluid at the time of change.

For synchos (bronze?) on the trannies, Ive been hearing OEM and/or redline for best performance.
 

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I use Amsoil Severe Gear 75W90 in my Diffs, with no issue.
I'll probably change to the same in my transfer case soon too.
I've read here somewhere that people have been happy with the GL4 Amsoil Transmission Oil in the MT6.
This is what I use in my diff's and Xfer case with no problems. I have an AT and I also use the AMSOIL (ws version) of the tranny fluid in it. :bigthumb:
 

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I've seen people on the forum mention Mobile Delvac 75W-90, may want to add it to your list.

From what I've found most of the GL-5 synthetic oils (Mobile 1, etc) have some kind of LSD additives in them. The Delvac is made for heavy-duty applications (18 wheelers and the like) and thus has no LSD-type additives at all. The Mobile 1 won't hurt anything (from what I've read) but the auto FJ doesn't have an LSD, so the Delvac may be better for it. I think it's on the 30k mile maintenance thread that someone talks specifically about Delvac.
 

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Yes I've found it, I will update the chart above!
Maybe also with a place to get it. I already have 2+ qts of Mobile 1 for my tcase and front diff, but I was looking around for the Delvac and found it one place online for ~$45/gal, but that was it and it was difficult to find (ended up finding the link on a Porsche forum).
 

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Good looking list Manoweb. :bigthumb:

I run Amsoil Severe Gear as well in the rear diff.
 

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Good looking list Manoweb. :bigthumb:

I run Amsoil Severe Gear as well in the rear diff.
X2, in my '07 I just changed the rear diff with RP 75W-90 synthetic @ 15,000 and glad I did (came out black)! Pushing 50K now and need to change the front diff & tranfer case with auto trans. I'm guessing Manoweb has a later model FJ with 75W-80 spec. Any thoughts about using Lucas Oil products? Lucas SAE 75W-90 Synthetic Gear Oil : Lucas Oil - Lucas SAE 75W-90 Synthetic Gear Oil
 
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