Never gave much thought to what oil to put in my Muncie 4 speed until reading about some of the new formulations being bad for the brass parts, GL-5, or causing the synchros to not work as well. I know I need oil meeting GL-4 specification. Has anybody had experience with any of the synthetics? I heard some synthetics are TOO slippery causing the synchros to slip. Impossible to remove without tearing the transmission down. Do I need straight 80W-90 gear lube, non synthetic? No local auto parts stores stock the older formulations.

What are people using today?

 

Redline makes a GL-4 oil called MT-90

 

GL-4 for brass synchro transmissions. You already know why.
They had non synthetic GL-4 at Autozone.

 

Sta Lube has the GL-4 you need. NAPA has it:

http://www.napaonline.com/Catalog/Ca...229_0006410049

 

I have used Mobil 1 GL-5 synthetic since 1990 (25 years!) in my tranny and it has never worked better-still has the GL-5. With that said, I did buy some GL-4 Redline synthetic recently and will change it over the winter to the redline synthetic. The synthetic works MUCH better than the conventional gear oil in my 4 speed. My 4 speed used to get much hotter with conventional versus synthetic gear oil and was very notchy and difficult to shift in very cold weather--not with the synthetic Mobil 1-so much for too slippery. I have also never heard of the brass synchros every going bad from using a GL-5 synthetic from a live person and I searched the internet extensively for someone-any make of car or year-reporting brass synchros going bad from using GL-5 synthetic....Nothing. This reminds me of the topic that synthetic gear oil will not allow the posi diff to work correctly along with Eaton does not recommend a synthetic in their rears and synthetic motor oil causes engine leaks. Just saying......

 

From here:

http://www.secondchancegarage.com/pu...-4-speed-3.cfm

...is this:

"According to West, synthetic oils shouldn't be used in Muncie four-speed transmissions, no matter what type of car they are in. He feels that synthetics are not "synchro friendly." They are so slippery they don't allow synchro rings to grab on to the cone of the gear and synchronize properly. This will lead to grinding the gears. Synthetics also have a different consistency then a natural fluid. The early Muncie cases, especially, tend to be more porous so they don't hold up well with a synthetic. The synthetics leak out of them more easily than natural gear lubes."

and,..

"A GL4 is West's gear lube of choice — a natural 85/90W gear oil. GL5 is supposed to be superceding GL4, but there's lots of talk about this in the car hobby. GL5 has not been around as long enough to know how it's going to unfold. So, West recommends being safe rather than sorry. He thinks GL5 has sulfur in it that is corrosive to brass. It also acts like synthetic and doesn't allow synchro rings to grab the cones of the gears. West suggests sticking to a GL4."

From here:

http://www.widman.biz/uploads/Transaxle_oil.pdf

...is this:

"When we use a GL-5 product in a transmission that requires GL-4, we normally find 2 to 4 times as much copper (brass) in the used oil as we would with a GL-4 product. Eventually the synchronizers wear to the point that they no longer make contact with the other other half of the cone, bottoming out before stopping the opposing gear."

and this:

"Here is a (photo in the link) synchronizer that has been worn by GL-5 oil. You will note that there are no longer any teeth on the
brass, completely worn or “peeled” away."

From here:

http://www.crankshaftcoalition.com/w...nsmission_lube

...is this:

"Muncie 4-speed,..A GL4 spec non synthetic gear oil is recommended.
The problem with using synthetic transmission lubricants is the 'threads' on the inside of the bronze synchro ring are there to 'cut through' the oil film, and the trans uses the lube as a sort of a friction brake. Really slippery lubricants can allow the synchro ring to skate across the film and the gearbox won't 'slow down' quickly enough, causing slower, noisier gear changes."

From here:

http://lucasoilsportsmancup.proboards.com/thread/75

...is this:

"Gear oil for Saginaw, Borg Warner or Muncie. GL-5 gears oils which are required in hypoid differentials are not to be used in most synchromesh transmissions because the chemicals used to provide the extreme pressure protection can be corrosive to synchronizers, which are commonly made of brass or bronze. Typically, the use of a GL-5 lubricant in a synchromesh transmission will shorten the synchronizer life by one half...in the end I would recommend using a GL-4 Transmission gear lube."

...and on and on.

If one is hell-bent (not me) on using a synthetic I'd use this from Red-Line, who recognized the problems stated above and has recently come up with a formulation they say will work with our Muncies. From here:

http://www.evasivemotorsports.com/mm..._Code=RL-58304

...is this:

"Helps to slow synchros"

and,..

"Improved copper corrosion protection to prolong synchro life"

and from here:

http://chemsailoils.co.za/index.php?...ory&path=66_69

"Since most GL-5 gear oils for differentials are too slippery for manual transmissions, Red Line offers these products,.."

 

I'm with Dark Blue, pretty much the same as I've been hearing for years.
IIRC, when GL-5 came out it was recommended for T10s and they showed premature brass synchro wear.
Besides, dyno GL-4 is going to be cheaper than synthetic GL-5.

 

Good points Dark Blue. Like I said I have 2 qts of Redline Synthetic GL-4 ready to go in my Super T-10 because I have heard but never seen anyone with an issue with Gl-5 and figure why tempt fate. My only concern is the GL-5 maybe effecting the brass/bronze rings but I have used Mobil1 for 25 years with no issues-that is a LONG time...My other comment is that my trans was notchy when cold with conventional gear oil and perfect with synthetic and I have never heard of any gear grinding using GL-5 in my trans. Still don't buy the theory that synthetic is too slippery either for a diff or a manual trans.

Lastly, comments about the amount of brass/copper than comes out of a tranny using synthetic in and by itself is limiting since we have no idea how that particular tranny was shifted and under what conditions. Would the same tranny show wear with conventional oil? Who knows? but without very controlled conditions using both fluids lots of speculation...Something to think about: There are lots of manual tranny's using GL-5 with brass/copper synchros today in many types and years of cars and if GL-5 was NOT compatible, there would be trashed manuals all over the place and clearly that is NOT the case.

 

just rebuild my Muncie last fall and that is what I put it. It was recommended by Jody @ Jody's transmissions. He posts a lot. On the Chevelle and Camaro boards.

 

Thanks everybody, very helpful.

 

The amsoil 75w 90 is very good stuff and is GL-4, another one to consider.

http://www.amsoil.com/shop/by-produc...r-lube-75w-90/

 

If you opt for this one, more than happy to get AMSOIL products for forum members at dealer wholesale pricing, about 25% below retail, via the AMSOIL Preferred Customer Program. Drop me a PM if interested.

 

The bottle shows synthetic . . isn't everyone saying don't use synthetic?

 

Royal Purple MaxGear 75W90.

 

I am surprised no one mentioned GM Synchromesh Fluid!! Says its part synthetic. What I used in my Muncie.

New GM part # 88900333

Old GM part # 12345349

 

What oil for T5 WC 1988 5 speed tranmission?

 

 

The AMSOIL Synthetic Manual Transmission and Gear Lube 75w90 is synthetic.

There some above that do use synthetics, but don't have a C3, so can't speak from experience on the Muncie syncros. I haven't looked at how the syncros on the Muncie work, but I do use synthetic in all of my own manual transmissions though none had synthetic as factory fill. It appears from the above, that most recommend to use a specific GL-4 fluid vice a GL-5. This AMSOIL MTG is a GL-4 fluid designed to protect the brass synchronizers.

If you are uncomfortable using a synthetic, I wouldn't.

P.S. The viscosity of the GM Synchromesh is ~40% lower than a GL-4 75w90.

 

Also, this is the oil that Tremec recommends for the TKO 5 speeds.

I have used it in the old Muncie and now with the TKO600.

The "Import" drivers speak highly of this oil on their forums.

 

I've recently been using the Brad Penn classic GL-4 gear oils on my Muncie builds, stuff works great and is reasonably priced.

Link: http://www.penngrade1.com/Products/G...SAE-80W90.aspx