I replaced my tranny fluid about 2500 miles ago with GL5 gear oil. I guess I didn't do my homework prior to switching the fluids, since I'm just barely learning now that GL5 can be problematic to the tranny. So I'll be switching over to either Redline MT-90 or Royal Purple Sychromax soon.

My question is: Have I done significant damage to the tranny? Is there anything, besides switching over to a GL4 oil, that I should do now?

 

ask your self this.

if the GL or API rating is to determine the grade of the product then why would running a better/higher grade hurt your transmission?

also, why would running synthetic fluide's have any better results then what was recomended for the vehical.

 

I'll admit that I'm not very knowledgable on this subject matter, so please correct me if I'm wrong. But I don't think the GL rating determines the degree of "better/higher". The GL rating is a description of additives within the fluid (1 being nothing, and 5 having the most). From what I've read on other threads, these additives can lead to damage of the tranny synchro's. What I'm asking is how long it takes for this damage to occur, assuming it truly does happen.

I am thinking of switching to synthetics in the tranny simply because the only GL4 oils I have found happen to be synthetic. We don't need to turn this into a dino vs synthetic debate, since we have plenty of those

 

First off, I can't even find GL4 Gear oil anymore. It's all GL5 and I run it in mine. And have for quite a few years.

And I can't comment on if its a rating or a rating of additives.. No idea. Just know my tranny works fine and has 207K HARD miles on it and shifts perfectly. =/

I do know that when the Haynes manual I have came out, GL5 wasn't around.

If I had to guess, I'd say it's some kind of quality rating, not a variant of some kind of gear oil. Like a API rating.

 

So I got curious and did some searching around... yea its not a quality rating, its a rating of the additives in the oil.

But, unless you can find GL-4 Gear oil here, you're stuck special ordering from somewhere (dunno where? heh).. but like I said I've been using GL5 for years.. I'm sorry Im not special ordering oil for my 22 yr old pile. Tranny has been fine.

 

I found this comment on a Unimog forum,

"I talked to a tech at Valvoline about their dual rated GL-4/ GL-5 gear oil. He said there are different additives that can be used to make the oil Extreme Pressure rated ( GL-5) . He said the additives that Valvoline uses in their GL-4/GL-5 will not harm yellow metals ."

and from my searching I found that yellow metals are brass, bronze, copper.... Which bushings are typically made of (like in our spindles).. but I dont know whats all inside our transmissions, thats the only part of my truck I've never cracked open.

I used Mobil1 Synthetic in my transmission and Valvoline dino oil in my difs

 

thanks for the info Drew. Well it's reassuring to know that my truck isn't going to blow up tomorrow! I may switch over to GL4 sometime, but I won't make it an urgent matter.

 

GL4 is available from a variety of sources.

And, most dealerships have been using 75w90 GL5/6 since the trucks were brand new. Don't worry, your truck probably had GL5 in it for 20 years before you got it.

That said, I like the shifting performance of Redline MT90 the best of all the oils I've used, which are a LOT of them.

 

so simple awnser is,these fluide are backwards compatible with an GL5, over gl4. and API ratings.

also certian atf is backwards compatible,
like mercron, ii,iii,iv.

or dextron and atf.

if i remeber correctly.

 

I'm not sure exactly what you meant but just to clarify for others

GL5 is NOT necessarily backwards compatible with GL4 although some brands MIGHT be.

 

So GL5 isn't something new?

But why can I no longer find GL4 in any of the parts stores in my area, and just in the past few years they've all switched over to GL5? And when I could get GL4, I couldn't find GL5?

 

No, GL-5 is not new. The driver's manual for the 94 pickup says to use either GL-4 or GL-5 in the manual transmission. I think there's a good chance that the transmissions had GL-5 put in them at the factory. If any transmission oil has been added or replaced over the years, chances are it's GL-5.