Just read this on another forum & thought there's be enough Muncie owners here to warrant a repeat! I can't confirm or deny any truth, maybe some-one with more knowledge will add?? If it's a non issue or bogus issue please delete.

From Chevelle forum...
I was not aware the GL5 & Hypoid additives that contains sulphur & is very slick was harmfull to the syncros in our muncie's that are rated for GL4 80/90 LUBE ONLY. I was unknowingly running GL5 lube in my muncie for 4+ yrs and it has been shifting harder even though clutch is adj correctly. Now i know why after reading the info from the Redline Oil Site which i have LISTED BELOW FOR YOU ALL TO READ TO AVOID DAMAGE TO YOUR MUNCIE'S.

Also,i checked approx 9 auto parts stores in my area and not one of them sells or stocks any 80/90 std trans lube that not rated for GL5/Hypoid,they are all rated for GL5/hypoid use . None of the 9 stores i checked stock the lower rated GL4 80/90 lube thats rated for our older muncie std trans so beware of this as i am sure many of you are running the wrong GL5 rated lube that will eventually tear up your syncro's.

 

have read about some oils attacking the brass

 

Thanks for the heads up..

 

Yes there appears to be truth in this claim. I like to hear answers from the manufacturers instead of other forums, so I contacted Mobil Oil this morning and they state:

"Mobil gear lubricants are API GL-5 rated and they can corrode yellow parts (brass and Bronze) under high heat and load it is not recommended. Gear oils that are GL-4 rated are still available however, Mobil does not have the appropriate product. You may want to check with other petroleum manufactururer's or your local dealer."

The following are 3 manufacturers of GL-4 oil:
CITGO CITGEAR Standard XD is a multipurpose API GL-4 gear lubricant which uses a sulfurphosphorus additive system. The additives impart some extreme pressure properties but to a lesser degree than CITGO Premium Gear Oils (MP). The additives also impart antiweld, antiscuff and antiwear properties. API Service Category GL-4.


Royal-Purple Max-Gear® exceeds Eaton’s stringent GL-5 / MIL-L-2105D
Gear Oil Specs. Max-Gear® also is safe for GL-4 applications
or bronze synchro gears.

AMSOIL Manual Transmission & Transaxle Gear Lube
SAE 75W-90 API GL-4
New AMSOIL Synthetic Manual Transmission and Transaxle Gear Lube (MTG) meets and exceeds the gear, bearing, synchromesh and seal demands found in automobiles and light trucks. This NEW product by AMSOIL costs less than 1/2 of the Chrysler and GM OEM counterparts where the competitor oil is currently only available. Use this where the manufacturer requires a GL-4 only gear lube.

 

Would this affect a ST-10?

 

I have Mobil 1 in there now (GL-5). Before that had Valvoline, nonsynthetic (also GL-5)... I am effed...

wonder if that's why it is so hard to put into gear sometimes.... I don't think so, still shifts ok.

 

does the same go for Saginaw's? also how can you tell if your car has a Muncie or Saginaw? Part #'s?

 

According to Mobil and other oil company website FAQ's any transmission with brass or bronze parts such as synchronizers and bushings could be affected. This would be all manual transmision manufacturers. There is no evidence as to how much usage, mileage, or time it takes to effect the parts. I've run the newer oil in both toys with Muncie's for several years with no noticeable problems, but I think I'll change the oil since it's easy to do and additional peace of mind.

 

As mentioned, AMSOIL recently came out with a synthetic fluid specifically designed for this application:
AMSOIL Synthetic Manual Transmission and Transaxle Gear Lube 75w90 API GL-4

MTG is formulated with extreme pressure (EP) additives and advanced synchromesh qualities that provide smooth shifts while protecting gears, bearings and seals. It is not corrosive to yellow metals, such as copper, that are used in some synchromesh systems. MTG provides the maximum transmission and transaxle internal component protection.

 

Great topic and few of know of this issue.

I purchased two AutoGear Muncies in the last two years,..both for 69 Camaros. Though the same set up (clutch, etc.) was used, one shifted like silk,..the other was balky, especially on higher RPM down-shifts.

I called George, the chief engineer at Autogear, and told him of my problem. He said, "get the synthetic out of the one that shifts poorly" I said, "how did you know I was running synthetic in that one?". He said, I could tell by your explanation of the problem"..."Are you running a syn in the tranny that shifts well?" "No",..I said, and my lesson was learned.

He stated that the synchros in Muncies will not perform well with a syn and recommended most any conventional/mineral 80-90 lube with a sub-spec of MT-1. Valvoline 80-90 meets his requirement. MT-1 is the additive that protects the yellow parts. GL rating was not mentioned.

Syns can actually prevent synchros from slowing enough to engage according to George.

I changed to the Valvoline, and now I have two Muncies that shift like silk.

Call George,

www.autogear.net

...a wealth of info.

 

A HUGE thanks to all for this info
The days when I used to buy used used Muncies for $75 are long gone

Thanks again!

*EDIT*
Just went out to the garage and looked at what oil I used a month ago or so when I drained and changed it.....Valvoline GL-5 .. I cant get that oil out of there fast enough!!!!
First I need to find a local dealer or Trans shop that has the GL-4

Thanks again.....Muncies aint cheap anymore.

 

I have been using Mobil 1 in my Muncie for about 3 years now. No problems whatsoever and it shifts as smooth as silk. I would suggest you check your shift linkage and clutch adjustments as the cause of "hard to put in gear sometimes".

 

have GL-5 rated oils changed since 1973? i'm looking in the FSM for 1973 and it says to use SAE 80 or SAE 90 GL-5 oil in the transmission.

GM from 1973 says to use GL-5, but this thread says to use GL-4.

can somebody clear up my confusion here, please?

 

I believe stock car trans builder Tex Powell (Tex racing) recommends NON synthetic gear lube in his trannys that use synchros....something about the synthetic fluid being TOO slippery and not clinging to the synchros....
...redvetracr

 

well that rules out the Royal Purple and Amsoil products listed above.

that leaves Citgo and i found one by Penzoil. ofcourse nobody seem so have either of these in a GL-4.

but i'm still confused. have GL-5 rated oils changed since 1973? the FSM says to use a GL-5 oil.