What is the best fluid I should use for my muncie 4spd trans?
When I first rebuilt it I was told to use Lucas differential fluid but a trans guy I know said that differential fluid is very thick and I should consider mixing a royal purple or other specific manual trans fluid as that would have less viscosity and penetrate the nooks and crannies of the gears better.

Any thoughts?

I don't want to use manual trans fluid for the new cars, any recommendations for my muncie 4spd?

Thanks,
-Brett

 

Years ago when I had my Muncie, I switched to 30 wt synthetic engine oil.....the shifting improved a LOT, smooth as silk,

I made the switch when finding out that new stick shift trannies were using ATF in them,

if not for the posi additive thing, I am thinking same for the diffy also, something I keep forgetting about...

 

These transmissions were not designed for synthetic lubricants. 80/90 gear weight oil is all they require. It's worked for me for 38 years

 

I recently had a m20 muncie rebuilt and they said to run 20w/50w/ engine oil but I did not like the idea of that as the factory recommends 80w/90w/ gear oil so put in straight 80w/gear oil and shifts great no problems I would not run the lucas oil with the 80w/90w/ gear oil as this is to thick and you will have problems shifting when cold.

 

There is nothing in a 4-speed box that would prevent you from using synthetic lube. The transmission was 'designed' to have some kind of a lubricating fluid of a specific viscosity and adequate lubricating characteristics. Synthetic lube will extend the life of the internal 'working' components and may even reduce the friction losses through the tranny. If I had one, I would definitiely put synthetic in it. [Use same viscosity rating as your Corvette Owner's Manual specifies.]

 

Use GL-4. GL-5 is for differentials; it has additives that can damage yellow metals.

 

I just bought a fresh M-20 from a guy who specializes in rebuilding Muncie and B-W trannies.

His recommendation was 75/90 syn gear oil - I just filled it last week with Valvoline

good luck, Ed

 

 

I dunno guys, WTF is the diff between one that does use 30 weight and these old Muncies?? Mine ran fine for 3 years daily driven, fairly quickly too, up/down shift, to Florida/back twice while house hunting....cruise 75+ freeways....went automatic overdrive down here....tranny was inspected by Darryl of 4 speed fame here when he bought it, pronounced it healthy.....

I never did a thing to the tranny except change the oil....never had the side plate off, the improvement of shifting was fantastic....

methinks guys doing work on them are more CYA mode than anything else due to warranty....

 

I had the same problem when I first got m 74 4sp. corvette, I even posted a thread asking if I should use royal purple. I was thinking about using royal purple on the tranny, but found out that synthetic oils will damage the synchros and decided to go with castrol High performance 80w/90. It's expensive to rebuild these trannies and I don't want to damage mine, so I just played it safe and went with no synthetic fluids for my tranny.Good luck deciding.

 

Plain Jane 80W90 Castrol in my M-20. That's all that was ever intended to go in it, so that's what is in it. Don't over think it.

 

Only 38 years? You consider that proof?

 

Actually there is something in an old muncie trans that gets damaged by synthetic oil.. can't remember exactly what the problem is but I do recall it being discussed ad nauseum in previous threads. It would be good for my feeble memory to review exactly what the problem is with using synthetic oil in an old muncie 4 spd. I used synthetic 80/90 for a while and it didn't seem to hurt anything but switched back to regular dino gear oil. Was it copper parts in there? can't recall...

 

~3 years of vastly improved smooth shifting, like a modern lightweight tranny, not a truck box.....

you all's choice....

 

No parts in a Muncie will be damaged or have reduced function or life if you choose synthetic lube over organic products. Your metal parts will, of course, last longer, however....

 

This is from Redline:

These differences are mainly distinguished by the level of active additives employed in the product. Different applications require different additive levels and different component materials can be affected by the levels of additives present in the lubricant.

Having said that GL-4 and GL-5 gear oils are not compatible and manufacturer's recommendations should be adhered to. They cannot meet the same specifications and the product performance and tests are different.

Typically, a GL-5 gear oil will have about 2 times the active additive level of a GL-4 product. This additional additive can cause problems with yellow metals like brass or bronze.

Here is Amsoil:

AMSOIL Transmission fluid recommendations for Cars and Light Duty Trucks
Product Description
AMSOIL Synthetic Synchromesh Transmission Fluid (MTF) is a premium-quality synthetic lubricant designed to surpass the most demanding lubrication requirements of manual transmissions and transaxles where non-extremepressure fluids are used.
AMSOIL Synthetic Synchromesh Transmission Fluid protects gears and bearings in extreme temperatures. It outperforms conventional oils and delivers outstanding performance from -40°F to 300°F. AMSOIL MTF maximizes energy efficiency and resists the effects of heat, oxidation, sludge and varnish deposits.
Unlike its mineral oil counterparts, AMSOIL Synthetic Manual Synchromesh Transmission Fluid prevents the thinning effects of mechanical shear for stable viscosity, superior film strength and excellent anti-wear performance. It protects against rust, keeps seals soft for long life, and is compatible with brass synchros for smooth synchromesh shift quality.
Ideal for Many General Motors, Chrysler, Honda and Other Vehicles
AMSOIL Manual Synchromesh Transmission Fluid is a higher quality, lower cost replacement for multiple vehicle manufacturer-branded products. This premium synthetic formulation provides enhanced anti-wear protection and lasts longer in service. AMSOIL Manual Synchromesh Transmission Fluid exceeds the performance requirements of both manual transmissions and transaxles.
Excellent for Service Centers
AMSOIL Manual Synchromesh Transmission Fluid is a versatile transmission lubricant. It reduces inventory needs, is readily available and is cost-effective compared to vehicle manufacturer-branded products.
Performance FeaturesAPPLICATIONS
Recommended for automotive and light-truck applications that require synchromesh transmission fluid. Applications include manual transmissions and transaxles such as New Venture NV T350, NV 1500, NV 2550, NV 3500, NV 3550, NV 5600, and Tremec T4, T5, T18, T56, T176, TKO500, TKO600, TR 3450 and TR 3550. Replaces MTF-94 fluid for Land Rover, MG, and Mini Cooper. Replaces Honda Genuine MTF fluid for manual transaxles and Texaco MTX fluid. Not for use in engines, hypoid rear axles, limited-slip or wet clutch applications.

 

Mike, it may only prove I'm getting a little older but hopefully wiser as well

 

I was making a joke by comparing your statement of 38 years proven experience vs. someone saying 'I've used brand X product for almost 3 months and my car hasn't done blowed up, so that proves that brand X is some good stuff.'

 

That is exactly how I took your comment . I think we are on on the same page on this one

 

That's right guys. These 'new fangeled' things could be a pig-in-a-poke. I mean, microwave ovens, cell phones...they could give you cancer, right? My gosh, using synthetic oils is like playing with fire . Of course, about every manufacturer of a well-made vehicle puts synthetic oils in now. The others would too [because they know they are that much better], but they're savin' money. Well, stick with your 38 year-old experience and the rest of us will live in the 21st century.