# Gear oil for a 4 speed muncie



## 1968 Q8 (Jun 9, 2011)

Simply put... what do I use (brand?/viscosity?/weight?) I've heard to stay away from GL5??? :confused


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## geeteeohguy (Feb 2, 2008)

Non-synthetic GL3 or GL4 75w-90 or 85w-90. Specified is straight 90 weight, but I haven't seen it in years, literally. They say the GL5 is corrosive, but I don't believe it. Still, run the dino based GL3/GL4 stuff and you'll be fine. No synthetic oil in a Muncie, though.


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## 1968 Q8 (Jun 9, 2011)

Awesome. That's the info I was looking for. Any specific brand? or just go with something reputable...


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## geeteeohguy (Feb 2, 2008)

I've used Valvoline, Kendall, and even Staylube over the years. All are of a high grade. Valvoline is the one found at Kragen's or Napa, usually.


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## 68greengoat (Sep 15, 2005)

geeteeohguy said:


> Non-synthetic GL3 or GL4 75w-90 or 85w-90. Specified is straight 90 weight, but I haven't seen it in years, literally. They say the GL5 is corrosive, but I don't believe it. Still, run the dino based GL3/GL4 stuff and you'll be fine. No synthetic oil in a Muncie, though.


I'm running 75w-90 Amsoil synthetic in my Saginaw. Just out of curiosity, Jeff, what is it about Muncie that you can't run synthetic?


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## MITYGTO (Jun 10, 2011)

*Gear Oil in a 4 speed Muncie*



68greengoat said:


> I'm running 75w-90 Amsoil synthetic in my Saginaw. Just out of curiosity, Jeff, what is it about Muncie that you can't run synthetic?


I am also curious why you would not suggest running synthetic in a Muncie?


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## 1968 Q8 (Jun 9, 2011)

*apparently* there's an mineral additive of some sort that is abbrasive/corrosive to the brass synchros....apparently. I'm not about to find the hard way, lol.


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## MITYGTO (Jun 10, 2011)

*Gear Oil for a Muncie 4 speed*



1968 Q8 said:


> *apparently* there's an mineral additive of some sort that is abbrasive/corrosive to the brass synchros....apparently. I'm not about to find the hard way, lol.


I have a local Amsoil rep with a retail store. I can ask him the next time I am in there and advise. He is a pretty knowledgeable guy. I will also post to a Corvette forum I belong to and ask the question.

I can't comment on what you have heard but I am totally sold on synthetics and have used them for years. Oils, Trans and differentials, oil filters, water wetter you name it.


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## MITYGTO (Jun 10, 2011)

*Gear oil for a 4 speed Muncie*

Received some input on the Corvette Forum from Hib Halverson, technical writer. Hib is well known in the automotive community and is a reliable source of information. He advises that if you use a synthetic lube that meets the GL4 standard (90wt or 75W90) it will work fine in a Muncie,Redline MT90 would be one example. Hib ran the Red Line product successfully in his 71 big block Corvette. Synthtics are far and away a superior product. Hope this helps......


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## geeteeohguy (Feb 2, 2008)

I got my information on other forums...the HAMB was one, but also from Muncie parts suppliers. Also a Corvette forum. And from driving Muncies for over 30 years. I know synthetic is "better" , and I know it flows much better, and because of this, it can leak better, too. Especially if your case has a worn countershaft bushing, which 95% of them do, if original. Also, there was some disussion that it was TOO slick for the synchro rings to grab properly, resulting in grinding shifts. Google it, and you'll find that the serious "Muncie Guys" only use dino oil in their gearboxes.


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## Jeff's Classics (Feb 24, 2010)

I've been running RedLine MT-90 synthetic in my Super T-10 (basically a later Muncie) in my '74 Corvette for 13 years with no problems...engine is a 450 hp 383 stroker.


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