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90 weight has worked for 100+ years.Why would you want to change?
 

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I use regular gear oil in mine. I have seen comments where the lubricating properties of the synthetic allow the syncros to continue to turn too fast while shifting resulting in gear grinding between gears. I don't know this to be true. I've run synthetic in my Harley 5 speed tranny for 5 years with no problems but I am planning on going back to regular Dino oil to see if it will quiet the gear box down. I hear it will eliminate most of the notorious "Harley neutral to first gear clunk".

Don
 

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Gear oil

anyone running synthetic oil in there muncie.....

Or should I just put in 90 weight gear oil...Thanks.
Never, never run any oil in a Muncie or Super T-10 Borg Warner but the highest grade gear oil you can get 85-140 Pennzoil perferably

I was told this by the champion of standard shift transmissions Joe Liberty
Of Joe Liberty Gears. He told me that the greatest cause of gear failure in Muncie transmissions is the incorrect gear oil by guys looking for something better. There is nothing

Garys Gearbox gary
 

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Only GL4!!!

80w, 85w-90, 90w no real difference in any of my muncies. But make sure it's a GL4 lube. Anything GL5 or higher is not good for bronze metals in the muncie. I personally run 85w-90 GL4 in mine, but can only find it at the local napa.
 

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On Muncie OIL

anyone running synthetic oil in there muncie.....

Or should I just put in 90 weight gear oil...Thanks.
The muncie was designed in the early 1960's and the idea is to give protection, a layer of gear oil between the gears. Engineers at that time did testing and discovered heavy weight gear oil gave the best protection.

Now I'm not sure what synthetic is for but I am positive it is not for Muncie transmissions. If you doubt me, Call Liberty Gears and ask them. They will tell you what they told me years ago......The major cause of Muncie failure is folks running the wrong lubricant in them.

If you want your trans to shift better have someone put new sliders in it as well a all new FORGED BRASS SYNCHRO RINGS, don't use the cheap cast rings or you will be sorry
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Garys Gearbox
 

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IMO, Redline MT-90 makes the shifts noticeably smoother than 60s technology gear lube. It's not GL-5, so is safe for brass synchros.

Whatever you choose, make sure it's not GL-5. Sta-Lube still makes conventional 85W90 GL4. The P/N for a 1 gallon jug is SL24239.
 

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Gear Oil

anyone running synthetic oil in there muncie.....

Or should I just put in 90 weight gear oil...Thanks.
According to the engineers at General Motors, they only warranted the trans back then if you ran the 90 wt gear oil and according to legand Joe LIberty of Liberty Gears, he told me that he agrees
Garys Gearbox
 

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On Gear oil

For some it would be temp variance, I use LE syn. in all my gear boxes. Lubes better and turns more freely.:)
I have a standard shift Transmission shop. Sometime after the snythethics came out people were asking me about it and I could not give them a truthful answer. So one of the companies that I was doing business with was Joe Liberty Gears. He makes a variety of transmissions for the Nascar circut, drag racing, clutchless transmissions, air shifted transmissions and many others. One day when I was on the phone with him this is what he told me about lubricating the muncie trans. He said that of all the thousands of muncie transmissions that had come to his shop for repair, the bulk of them were broken because they had the wrong fluid in them. Further that only 90 wt gear oil offered protection against breakage and that while a lighter fluid might enable the trans to shift a slight bit easier that it was not worth the risk to steer away from 90 wt gear oil.
Garys Gearbox
 
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