I have a few questions on rear and front differential oils for a 1991 Toyota Corolla Alltrac AWD DXL, 5sp transmission with the 4A-FE engine. My owners manual doesn't specify if I use GL-4 or GL-5 oil. It only mentions oil weights that can be used, which are 75w-90, 80w-90 or 90? I have an open rear differential, so with that is it ok to use oils with a limited slip modifier already in the oil? Because that's all I can find in any of the stores in my area. Do the transmission and rear diff oil weights need to match? Lastly. my rear diff has chalk mark on it with a 75 right above the fill plug. I assume that was the oil used. Any feedback would be great. Thank you.
What Gear Oil do I Use?
- Thread starter Kiyarsa
- Start date
Help Support alltrac.net:
hedgeclipper
New member
Sorry to bump a dead thread, but I'd like to continue this debate here.
I also have an AE95 and I'm worried I've used the wrong oil. I did some research about brass synchros and came to the conclusion that GL-5 oils were bad for our (manual) transmissions, so I bit the bullet and spent a lot of money on 6 L of MT-90, as it was the only pure GL-4 75W90 I could find. Then, I found this, which recommends only 75W90 GL-5 for AE95s, however I did read about others using GL-4 oils in AE95s for the same reason as me.
I also made a thread about this on BITOG, in which people are saying to use the GL-5. However, I've heard lots of anecdotes about people running MT-90 in 80s/90s all-tracs. If it's working for others, then I'm happy to stick with the oil I put in mine. The wiki says that GL-4 oils are acceptable for hypoid gears operated under "moderate speeds and loads." Maybe our all-tracs with 100-220 hp or so fall under that category?\
@Tippo how long have you been running MT-90 in your SR185? Do ST185s also share the same gear oil for the (manual) transmission and the transfer case?
I run redline 75w90ns. its a gl5 but does not have the friction modifier that damages the syncros. And yes st185 (and all other gens) transfer and trans share oil, this is why the gl5 is required. I have been running this for many years after destroying a trans with standard gl5.
https://www.redlineoil.com/75w90-ns-gl-5-gear-oil
https://www.redlineoil.com/75w90-ns-gl-5-gear-oil
hedgeclipper
New member
thanks. That makes perfect sense. Now that I read their site, that oil is clearly ideal for this exact scenario.
Unfortunately, I already have MT-90 in there. How bad do you think it would be if I keep running the GL-4 for a while?
yyonline
Well-known member
Redline 75W90NS or the OE Toyota fluid. Personally, I use the Toyota fluid. You need a GL5 fluid designed for manual transmissions. Most GL5 is designed for differentials and doesn't work well with synchros.
Any 75W90 GL5 is fine for the rear diff. You don't need friction modifier for an open diff or Torsen diff, but it won't hurt anything. Friction modifier is only needed for a clutch-type LSD.
Any 75W90 GL5 is fine for the rear diff. You don't need friction modifier for an open diff or Torsen diff, but it won't hurt anything. Friction modifier is only needed for a clutch-type LSD.
My understanding is that gl4 will shear and lose viscosity due to the hypoid gears in the diff. It will likely be ok for a bit, not sure for how long. Oil is less expensive than a transmission is.
