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Off Topic GL4-GL5 gear oil

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tinman58

tinman58

Jedi Knight
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Please forgive me for this post. I can not find any thing to tell me that the Lucas 75w-90 GL-4 / GL-5 gear will work in my 98 dodge ram with the nv4500 manual trans. The book says to use GL-4 because of the synchro's . GL-4 is hard to find and I am in the middle of moving to Idaho and of course the tranny is leaking like a LBC.
I have made 6 trips pulling a 17 trailer and still have a few more to go. I don't want to get stuck in the middle of Nevada.
Thank you
 
Hi Dan,

If you have a Napa auto parts close you can cheque to see if the have Sta-Lube GL4 in stock for you..if not, they can order it for you...

Cheers
Tush
 
If a gear oil is cross listed as GL4/GL5, look to see if it meets MT1 (IIRC) which is a requirement to sell it to Uncle Sugar since he doesn't like his older equipment damaged unless it has been put into use as a drone/target of some kind. The extreme pressure (EP) additives in the MT1 (IIRC) blessed stuff are buffered to where they are yellow metal safe. The caveat is that a GL5 has a much higher loading of EP additives and sometimes friction modifiers that are there to protect differential components but play havoc with syncromesh operations in some transmissions. On (quickly dons flame resistant underwear) miata.net, this topic is flogged on a fairly regular basis with the general consensus being that the five speed boxes don't really seem to care what goes into them while shifting operations in the six speed boxes are adversely impacted by GL5. If for some reason you can't round up any GL4, get a MT1 (IIRC) rated GL5 and use it until you get a chance to slow down and repair the leak before going to the trouble of getting a proper GL4. After all, something in there is going to be better than nothing in there in the interim.

You might also want to go to bobistheoilguy.com and then search for GL4/GL5 information.
 
Synchromesh is over-rated anyway. Just learn how to drive without it, and then don't worry. Pretty much all of the semis are that way; just because synchros wear out and they want to go a million miles without an overhaul.

Ok, I'm kidding, but only a little bit. If you learn how to double-clutch, you can't be stranded by worn out synchro rings. And it's actually not impossible to drive without the clutch; I've limped home that way many times (used to own a GM car that liked to snap clutch cables).

Also, from your description and what I have personally seen of the problem; I don't believe you are likely to notice any problem with yellow metal erosion before you are finished moving. It is a very long term problem that takes years and years to develop.

However, there is another problem that can show up quicker : some modern synthetic oils are too slick to allow for good synchro operation. I don't know if the Lucas falls into that category or not.

But I do know that, as the rules are written, almost any oil that meets GL5 is also going to meet GL4! Kind of amazing when you hear the tales of how GL5 is bad and GL4 is good; but the fact is that the GL4 and GL5 specifications are purely performance based, neither places any limits on either base oil or additive package except in performance terms. And the yellow metal corrosion test for GL5 is actually more stringent than that for GL4! It is just more or less coincidence that, in order to meet the performance standards for GL5, manufacturers using that additive have to use a lot more of it to meet the GL5.

Used to be that most GL5 oils were advertised as GL5/GL4; but most manufacturers quit doing that to reduce confusion. Lucas apparently doesn't care about confusion.

Frankly, what I would do in your situation is pick up some Redline MT-90 instead. Order it from Amazon, they'll deliver anywhere in the US in just a few days. It's expensive, but is rated GL4 (only) and is specifically designed to improve performance in synchronized manual transmissions. Also contains none of the additive that can attack yellow metal.

It just makes sense to me to use an oil designed for the application, rather than using a general-purpose "hypoid" oil in a non-hypoid device.

There are other products similar to the MT-90; usually with names like synchromesh fluid, or manual transmission oil. Likely they would work well too; I've only tried the Redline.
 
Thank You,
I feel much better after reading the article. Now I just need to take apart the rear housing and the gear venders off to stop the leak. It looks like Amcco in Florida just used sealant and no gasket at the mating surface.
 
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