tfvesquire

I just changed the old gear oil in my Muncie and forgot how nasty gear oil smells. No odd color and no shavings of pieces of anything came out so good new on that end. I must have a later model Muncie case because to my pleasant surprise, it has a drain plug!! After letting it drip out for about 20 mins I was ready to put the new fluid back in.

I read a lot about guys and gals running Muncie's and looking for a safe synthetic that wouldn't effect the brass parts inside, especially the synchros and decided on Redline MT-90. I picked up a fluid pump from NAPA, but found out the pump part was too large to fit inside most quart bottles. After rummaging thru my empty containers the only one I could find that would work was a milk carton. Seriously?

I got the new fluid in the milk carton, but the pump's screw threads did not line up so I had to hold the top of the pump and the carton just to get it to work. You can probably guess what happened the first time I primed the fill hose and then went to pump the first of the fluid into the case. POW! the hose flew off the pump and splattered gear oil all on my face, arms and the exhaust. WTF. I was on my back and wedged under the car so I had to keep going. Was able to hold the fill hose on the pump while trying to keep the milk carton from collapsing as the fluid level went down. Had some choice words along the way.

Got it to the point where the fluid just started to run out of the fill hole and buttoned it up. Out of two quarts, I put in about 1 1/2 to 1 3/4 depending on how much flew out on the first try. With some gear oil left I decided to pump it back into one of the quart bottles. Once again, I forgot about the friggin hose flying off and on the third pump it flew off and sprayed gear oil on my pant leg and shoe. Once again, WTF?

I let the car idle a few minutes and then took it out for a light driver around the block, letting the gear oil coat everything. No apparent change in shifting which was a good thing. When I took it on the highway, I felt the shifts were smoother and at higher speeds the car felt like it had an overdrive compared to before. Maybe placebo effect, but I'm convinced synthetic is the way to go.

After shutting it down and parking it over night, looked under the car this morning and no leaks. Sweet. Now, I'm wondering if I should change the rear end fluid with synthetic before I go on my cross country trip in July. Anyone running synthetic in the differential with posi? Let me know your thoughts good and bad.

Thanks,

Ted

ghostrider20

I would stick with standard rear diff oil and two bottles of GM position lube.

GTOguy

You are correct on the Placebo effect. Synthetic fluid is not recommended in the industry for the Muncie or T-10, and can lead to synchronizer over-riding and damage. In addition, gear oil does not damage brass....never did and never will. Total myth that has no bearing in reality.

SWCDuke

There is some evidence that the EP additive in GL-5 (what gives it the pungent odor) can "corrode yellow metal", but it's only an issue at well over 250 deg. F, which is well above the operating temperature range.

The industry recommended this formulation for manual transmissions designed from the 30s to 50s well into the seventies. It was only beginning with newer designs in the seventies that the gear oil spec was changed from Mil-L-2105/GL-5 to GL-4

Has anyone ever disassembled a vintage transmission and found synchronizer corrosion (corrosion, not wear)? I haven't, nor have I seen any bonafide evidence of such from any other source.

These myths are promulgated and kept alive by millions of dollars in advertising with nary a shred of evidence ever presented.

I also recommend conventional 80W-90 GL-5 for vintage manual transmissions that originally speced Mil-L-2105 or the modern GL-5 equivalent.

Duke

SI67

I did not know that the General had branched out into lifestyle products.

tuxnharley

wmf62

I beg to differ on 'not damaging brass parts'. somewhere here in the archives is a discussion of that topic.

we contacted many of the major oil providers and many said their fluid should not be using with brass parts.



Bill

tfvesquire

**************************************** *
Well, placebo effect aside, I definitely feel an overall smoother shifting both in town and especially on the highway running it hard thru the gears. I have used synthetics in most of my cars and I swear by them. I was just concerned about swapping the Muncie gear oil for a synthetic that would not affect the synchros. I don't have any concerns about corrosion, but there was plenty of postings on various sites about certain synthetics causing the synchros to "float" for lack of a better term and cause premature wear.

IMHO, synthetics were created in response to people who want to get the most performance and efficiency out of their vehicles. I've used synthetic fluids in the rest of my vehicles with no issues. Like I said in my OP, I have no experience on running synthetic fluids in the differential, especially when you need to add posi fluid. If the consensus says keep what I have and don't mess with it then that is good enough for me.

Thanks to all who posted suggestions. Except for those of you with minds in the gutter......

GTOguy

If your car shifts smoothly, no worries. The thing with synthetic is, it is so slick, that the synchronizer cones can't get a grip in some transmissions and stop the gear rotation as fast as they need to to prevent grinding. If not grinding, ok. I don't know it all, but I am a master auto tech, and have been for decades, so I go by experience and what works and what doesn't. I will not be running any synthetic gear oils in my old American muscle cars. My choice. Whatever works for you, your choice. In 40 years of tearing down transmissions and gearboxes with brass components, I have NEVER seen deteriorated brass or bronze due to gear oil. Some of these transmissions were over 100 years old. Most were over 40 years old. So, how many centuries does it take for gear oil to dissolve or even corrode brass? I've been trying to verify this myth for the past ten years, and have gotten zero actual facts or proof. Therefore, I call absolute BS on it. Show me some proof.

wmf62

here's the link

https://www.corvetteforum.com/forums...ion-fluid.html

apparently we will continue to disagree, I did my homework but i'll still drink beer with you...



Bill

pop23235

So does the General.

DansYellow66

I ran synthetic in my Muncie for quite a few years after rebuilding. No issues with performance. The only thing I noticed that was odd was that the case took on an oily sheen like it was permeated with oil. But leaks other than the usual countershaft hole were nothing unusual.

Anyway I pulled it out last year and put in GL4 instead.

Can't tell a bit of difference either way.

Wish I had had a drain plug however.

wmf62

just because 'someone' says it's a 'myth' doesn't make it so..., and vice versa...
Bill

GTOguy

Bill, I'd hoist one with you as well, any time! I read the link, and found what I've found for the past ten years: somebody claiming that the oil eats brass. I have yet to see any real life lab tests posted with results, or any forensic evidence. The brass in all the 50+ year old Muncies and T-10's, New Process, Warner Gear, Brown-Lippe, etc. transmissions I have seen has never been eaten away by corrosion....only wear and tear from abuse. Some of these brass parts had been immersed in this 'toxic' oil for over 75 years at the time of my inspection. Until I see an unbiased scientific test, with photos and documentation, I'm calling this BS. I have the same issue going on on the Pontiac forums with the same result: No living human that I know of has actually come across this phenomenon. I am always willing to be proven wrong: learning is part of life! Cheers!

GCD1962

Autogear says not to use synthetic oil in their new Muncies. They advise to use GL5-M

pop23235

Bring forth any evidence, please.

wmf62

the only evidence I have is stated in the link I posted in #10 above
Bill

pop23235

Sorry, but that link is to another discussion. I'd have to see parts with corrosion.

wmf62

that 'link' is definitely 'on-subject'...; damage to yellow parts...

as to corroded parts, I have no clue and have never seen any myself; however I was not about to risk a $4,000 transmission...


Bill