GL4/GL5 transmission fluid

I read my manual and it states gl4 or gl5 for my manual transmission. 75w90. I picked up 3 quarts of Lucas 75w90 synthetic gear oil and it has both gl4 and gl5 ratings.

I have been reading a lot on here, and apparently the gl5 rated gear oil can harm the brass synchro' in the manual tranny? Is this the case? Should I use the 3 quarts I have for the t-case, front/rear diff's and buy a gl4 only for my manual transmission?

I've read a lot of oil threads in my day, from snowmobile to atv to truck forums and some people can be alarmists.

 

My manual says GL5 for the tranny. If you go to the dealer, they put in GL5. I trust Toyota. I've used GL5 for 16 years on this truck. I believe that's a half-truth under certain circumstances for other /older vehicles that eventually spread and became gospel... however wrong.

 

That's what I was thinking, but it's nice to hear from someone with real experience (16 years) trying to find a gl-4 only gear oil is like finding a unicorn here in Canada. Amazon has that redline mt90 stuff but it's $21 a quart and $23 to ship it!

 

Yes the gl-5 is the one you want.

I had my 94 truck in for a warrantee repair and the dealer did a curtsy oil change. The clown filled the rear end , tcase, trany, front end all from the same barrel of gl-4/gl-5. I told them Nooooooo but the dealer insisted it was per spec and all was fine. I had to double clutch to shift. It was crap.
I changed trany oil back to my mix of 2 qrt mtl90 and 1 castrol dino oil. ( all mtl90 seems to run hot in the summer) been good combo for toyota since 96.

 

Update

Just changed my fluids. When I went back to the auto parts store to get more gear oil, as I cleaned them out of Lucas 75W90 GL-4/GL-5, they were still out of the Lucas, but for $5 more a quart they had this Pennzoil 75W90 GL-4 only gear oil. I bought this for the transmission.

On a side note the front diff is a real PITA to change compared to the T-case, Trans, and rear diff. 2 skid plates (bolt threads basically stripped on way out), years of crude falling on your face (from skid plates) and Allen headed bolts. Do I EVER HATE Allen head bolts. loosened the fill plug first, it was tight. Then onto the drain plug, Hercules himself must have tightened it. The bolt started to strip, but I hit it back in square with a hammer and finally it snapped free.

Anyway its a good feeling to have all fresh synthetic fluids in my drive-train (put Pennzoil Platinum motor oil in last week with Synthetic filter)

 

My understanding is that difference between GL4 and GL5 rated gear oils is their extreme pressure and wear ratings - GL5 having a higher rating than GL4. In many cases the improved rating of GL5 is achieved through a greater amount of additives (such as sulfur) which can cause issues with synchros on some manual transmissions. This is why some gear oils will only be GL4 rated, some will only be GL5 rated, and others will be both GL4 and GL5 rated. It depends on the individual formulation of the particular gear oil and what it contains for additives.

If the manufacturer (e.g. Toyota) specifies GL4 or GL5 for the particular transmission, it means that either one can be used and the transmission does not contain parts which would be affected by using GL5 instead of GL4 gear oil. Differentials usually spec GL5 as a minimum whereas manual transmissions usually spec GL4 as a minimum because differentials experience more extreme pressure and wear than a manual transmission.

 

Yes the pressure ratting is different in the different spec oils , but the effect on the syncros is just the opposet . Some oils grades are to slippery and the syncros don't work right. They don't slow down and sync with each other that's why it's hard the shift.

Heat is the other killer. More so in a transaxle because you have gears and a diff gear all making heat. That's were the gl-? Becomes more noticeable when wrong. Throw a had on the trAnsmission next time you come off a hour run down the freeway. Surprising how hot it gets.

Anyway party on.

 

My 04 owners manual says gl-4 or gl-5
Did they change the spec at a certain year?
I used gl-5 75/90 synthetic and shifts good

 

Read what buckoma said. I can't see gl-5 hurting anything.

 

I am sure stuff like Redline MT-90 might work better in some situations, but GL5 certainly won't hurt the tranny.

A lot of people fret over being blown to bits by a terrorist attack while ignoring the 1001 risks they take every day that are 1001 times more likely to happen. I see this trans oil debate as similar.

 

I'll say the same thing I say about engine oil and grease - brand doesn't matter as long as you use the correct type specified in the manual and change it at the proper interval.

 

My first car was a cavalier z24 and I changed the oil with anything from Walmart brand to Mobil 1, at 8000+ KM intervals and it had 350,000km when I sold it and it purred like a kitten!
I agree with the above.

 

I put gl 5 in a manual transmission (Mazda) and got synchro clashing (book called for gl 4), put up with it for a while then read abt Redline mt90. Changed to the mt 90 & completely stopped the clashing.

 

And this is the basic reason I believe most people say put GL4 in the first gen manual Tacoma. Other vehicles may have issues with GL5 and that general thought gets carried over to the Tacoma. I will continue to say that you may (or may not) get better results with the GL4/MT90, but the GL5 won't hurt the Tacoma.

 

I know this is an old post, and I don't know how many people will read it.

I am switching from Redline MT-90 in my 2002 Tacoma manual because I have been unsatisfied with the year round performance for the price. Given how much cheaper it is, I am just going to run the Lucas GL-5 75W90 in my tranmission this go around. I do not understand why people fuss so much about the MT-90. It was not that bad, but definitely not that good either, in Montana year-round temperatures for me. I had trouble in 1st, mainly, but overall MT-90 didn't shift as well when colder. Why spend more for something that just doesn't show a clear benefit?