Difference between GL4 and GL5 redline?
- Thread starter Seoirse
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Scramble
New member
I put Red Line MT90 in the trans & the RL 75-90 in the Diffs & T/C. I think you'd be OK but the 75-90 is cheaper than the MT90 so You'd be spending more money.
On amazon 4 quarts of the MT90 is almost $60. But it just says for transmissions, as opposed to other differentials. I kinda feel dumb asking as gears are gears are gears. So it would actually be cheaper for me to run MT90 all the way through.
phattyduck
Elite Member
You definitely need to use a GL5 in the transfer case and diffs. Hypoid gears and GL4 don't mix well.
If you *really* want to use a single fluid, a non-synthetic GL5 should work in everything. Make sure it is labelled as safe for synchros. You may lose shifting quality with a GL5 (not as many additives for synchros), but it won't hurt anything directly (there are many Subarus running around right now with GL5 fluid inside combined transmission/differential housings).
-Charlie
If you *really* want to use a single fluid, a non-synthetic GL5 should work in everything. Make sure it is labelled as safe for synchros. You may lose shifting quality with a GL5 (not as many additives for synchros), but it won't hurt anything directly (there are many Subarus running around right now with GL5 fluid inside combined transmission/differential housings).
-Charlie
Oh believe me it’s not about using a single fluid and more about saving money on fluid. I’m all for using the correct stuff and honestly ive spent way too much on this 5 speed swap to cheap out now
Scramble
New member
The RL gear oil is usually $2 cheaper per qt than the MT90. $17 vs $19 if I remember correctly.
JZiggy
Senior Member
Your diffs will not thank you unless they get GL-5. Note that GL-4 does NOT have the required extreme pressure wear additive level for hypoid gears.
Your tranny will be OK with GL-5, but will shift a lot better with GL-4. The tranny doesn't use hypoid gears, just helical gears, so it doesn't need the same level of wear protection.
Your tranny will be OK with GL-5, but will shift a lot better with GL-4. The tranny doesn't use hypoid gears, just helical gears, so it doesn't need the same level of wear protection.
Renegade_Medic
New member
This right here. I had to search high and low for GL4 for my old Jeep Manual transmission. It had brass gears. Had to have Napa special order a gallon of it.
Agree. 80w-90 valvoline gear oil in front diff, tcase and rear diff without issues. Pick up a gallon at autozone and that’s plenty. For my transmission I used redline. Have used 80w-90 valvoline also and when I switched to redline I feel no difference.
As far as the whole gl4 and gl5 and brass sunchros. I don’t know. Could be true could be not. FSM says either is ok. But people swear gl4. So **** it.
phattyduck
Elite Member
Almost all modern GL5 fluids will not chemically damage synchros. That's an issue that has long since past. I have a few hundred thousand miles under my belt with GL5 fluids on brass synchros (on Subaru and Toyota AWD manuals that share fluid between transmission and hypoid gears).
If you *can* use a GL4 fluid in a normal manual transmission (that is, most manuals), it will generally have a better formulation so the synchros *mechanically* work better, and thus give better shift feel.
-Charlie
Gonna jump in here and say the absolute best stuff I've used, and I've used MT-90 (it's very good), is the Amsoil GL5 75w110 Severe Gear lub in all my transfer cases and the manual tranny of the T4R. I will never use anything else period, just my personal experience and $0.02.
