Rebuilt my M-20 muncie and would really like to run Amsoil in it. I've read posts where most are using Amsoil 75-90w gear lube. After visiting Amsoil's website I see they make a Manual Transmission Gear Oil Gl-4. Its recommended for older muscle cars. Has anyone used it? I'm also going to use Series 2000 in the rear-end.

The manual transmission oil is new and I haven't tried it yet. It is for older transmissions with brass blocker rings. I have the old Amsoil 75W90 in my Muncie.

I've got one of three Muncies on Amsoil 80-90 and of the three, it's the only one that leaks,..out the front,..probably the front plug or slinger nut.

Any others notice leaks using Amsoil or other syns?...or is it my dumb luck.

BTW...I believe they've dropped the "2000" lingo.

Your right on the series 2000, its been replaced with Severe Gear. I have a quart of 2000 and am trying to find some more locally. There's been alot of posts on the pros and cons of synthetic gear oil and one of the cons is the leaking problem. It seems Muncies have a problem leaking even with dino oil too. I'm hoping with the fresh rebuild with the AutoGear case I'll get lucky. Everyone has their own opinion on dino oils and synthetic and I respect that, would love to hear some input from those who have used both. I plan on using either Amsoil or Mobil 1 in the 327. I've never used synthetics before. I'm starting to get pumped, dropped the motor and tranny in Tuesday! What started out six years ago as a front end rebuild and engine overhaul turned into a ground up restoration. Just want to thank everyone on this site for all the great info, could have never done it without you!

the T10 in my Nova always leaked a little out the front of the trans somewhere- i think it was that little plug where the countershaft or whatever runs.
so i had to put 1/4 of a quart of Amsoil in it every year- no biggie.
as for whether the stuff works- when i put it in the rear end of the Nova, it made it run a lot cooler compared to the dino junk that was in there. i could even feel the difference from the driver's seat.
when i put synthetic engine oil in every car i've ever put it in, the idle speed has increased and smoothed out from jsut changing the oil.
hell, my current winter beater AWD Astro van with 216,000 miles on it ran better after i drained out the Valvoline and put 10w-30 mobil 1 in it. 3000 miles later, no leaks, and the oil still looks new... and it runs soooo much better than it did when i got it.

I had my super T-10 rebuilt and used valvoline synth in it and it leaked real bad. I went back to reg oil and it barely leaks. Kind of mad about that, because I really like the amsoil, but I don't want a mess under my tranny. I use it in 12 bolt in the 69 and the 10 bolt in my 96 both with posi's and it works great.

If you're running Eation Posi out back, Eaton specifically instructs to NOT use syns. The cutches weren't designed for it and could cause premature wear, separation, and chatter. Go to their site for more info.

Just to clarify, Eaton has chosen not to test its posi units with all the syns avaiable on the market and instead just says to use dino oil. It really has nothing to do with their clutches being designed for dino or syn. However, Amsoil among other syn companies, have tested their oils and are recommended for use in the eaton posi with the oil being warrented too. Ive used Amsoil in my Eaton for years with great results and our resident tranny guru "big gear head" also uses Amsoil in the units he sells and installs.
Here are the facts from Amsoil tech:

Amsoil Syns are ok in EatonPosi (http://www.brainerd.net/~knudsen/69RS/Eaton%20LSD.doc)

I've been using syn oils for over ten years in all my work trucks and personal cars, I would highly recommend it to anybody.. I had the same thing happen the first time I used it in my work truck, my engine idle went up by a couple hundred rpm's...

Thanks guys, found some Amsoil Severe Gear for the rearend, don't have an Eaton so no problems there. Just got done filling it, a hair under 2 1/2 quarts. Ended up just buying some Valvoline 80w90 for tranny, had a hard time deciding between that and the syn. Will run either Amsoil or Mobil 1 in the motor after break-in.

Do you have an Amsoil dealer close to you?

hi there, I have been using straight valvoline 50 weight racing motor oil in our muncies for over 20 years it works very well,as compared to conventional 80-90 weight gear lube, it allows the box to run cooler and also improves the shifting at higher rpm. I have not personally used any of the newer synthetic lubes so im not at liberty to say how well they work. i do know that some synthetic lubes may not work correctly,the reason being they are to slick and during a shift,as the slider and sync ring are coming towards the syncro cone of the gear, it will not stop the gear from spinning so the slider can lock over the engaging teeth on the gear. instead you may get a grind going into gear.good luck regards tom T&B Trans

On the Eaton lubricant recommendation for their posi's...

When a posi fails under warranty it's returned to Eaton for diagnosis. I'm sure Eaton has logged a higher failure rate on units which used synthetic lubricants. That's enough of a "test" for me, and enough for Eaton to recommend conventional oils exclusively for their posi.

Trust me,..if the reverse were true, they'd recommend a synthetic to reduce warranty claims.

Engineers are pretty smart to begin with and I'll bet the engineers at Eaton are tops.

I'm sure Eaton has logged a higher failure rate on units which used synthetic lubricants. That's enough of a "test" for me, and enough for Eaton to recommend conventional oils exclusively for their posi.



I am running amsoil in my eaton posi rear. No problems. I think you are assuming alot with what you said above. Where are the facts that amsoil or synthetics is causing these to fail??

The point of the Eaton lube issue is that at least Amsoil WARRANTS their lube in the Eaton posi. Other syn makers maybe have not gone to that extent. So to lump all of them into a 'danger' group is certainly not logical when Amsoil warrants their oil in the Eaton.
Eaton has a good history with low failure rate with their posi units or they wouldnt continue to sell them. Its just that engineers and lab tests have PROVED that Amsoil and maybe some other lube do work great as proven by many folks on this site as well as others.
The homework that lowrida is doing is good caution and he got good 'confirmed' information, not speculation.
If there was a posi failure with Amsoil in it, just holding a sample of the gearlube for analysis would confirm that the lube will still be in specs for continued use. Then its an installation problem that might cause failure. Posi's are extremely touchy in their setup and Im betting most failures are due to improper alignment during the install, hardly the lube's fault Im sure you'd agree.

just a quick note on syn oil for your engine. once you put syn oil in your engine you should not switch back to conv oil as the seals will fail. im sure there are people that will argue with this.and there is proably people who have switched with no problems. but this is the recommendation of all dealers i have worked for.

another thing i have found not to do is proform a trans pwr flush if the transmission is high mileage like 160k. i guess the junk was the only thing holding that customer trans together. even though im sure he was experncing problem before and thats why he wanted a trans flush.

Here's a fact.

On the back of the newer Amsoil 80-90 quarts, is this: "Compatible with synthetic and petroleum gear oils and MOST limited slip differentials".

So obviously, Amsoil is learning what Eaton already knew.

It goes on to explain that IF chatter occurs, they recommend we purchase their additive. (There is no recommendation for continued chatter...which somebody above says to return the posi to Amsoil for a full refund. Of course, Amsoil will be very slow to blame their lubricant so I'm guessing you'll be SOL, but I don't have any knowledge of the program).

Again, if Eaton thought syns were better for their posi units, they'd recommned them to reduce warranty expenses. Instead, Eaton spends time and money to expicitly recommend to NOT use synthetics.

And I'm sure the marketers of Amsoil, Red-Line, Royal Purple, Mobil-1, etc,..all believe their syn somehow doesn't apply to Eaton's recommendation. If you wish to experiment, knock yourself out.

But you're taking the word of lubricant marketers over that of engineers at Eaton.

And since the engineers and chemists (not marketers) at Amsoil know far more about lubricants than Eaton engineers, and since Amsoil warrants their lubes in the Eaton posi, Id take their word and refer back to the letter.
Note also, Eaton says not to use syns (since they DIDNT research them in their units, per the letter shown). They only require certain GL grading such as GL5, then add the tag not to use syns, (since they dont test every lube in their unit). Its a catch 22 or rock and hard place when people want the better lube quality of a syn and get conflicting information. Thats why Amsoil put out that letter. Nobody has to experiment with any lube, if the lube manufacturer specifically warrants it. Id take the lube company warranty and run cooler temps in the posi any day of the week.
Nobody has to use any brand of lube they dont want to use. But I will defend the syn products and the sometimes conflicting information, with facts from the lube maker.
If someone wants to live in the dark ages when it comes to modern age lubes, thats ok. With over 30 years of using them with excellent results, Im a firm believer in them. Others can choose not to believe the facts and keep throwing away money on early oil changes and inferior performance and protection compared to syns, that is their right and the dino oil companies love them for it.
Its obvious you wont use a syn in your car and thats ok. Gentlemen can disagree. I will let the facts continue to guide my support of syns. :beers:

All new GM trucks produced sence 1998 have had synthetic oil in the rear end. They also use the Eaton Governor Lock in them with the carbon fiber lined clutche plates. Guess what, no failures of the clutch materials. I don't understand why Eaton says not to use synthetic oils, but I guess they forgot to tell GM.

Don't know about the newer locker units with different clutch linings, but we're talking about two different technologies.

This is straight from the Eaton site,..the FAQ section regarding the Limited Slip defferentials:

"What type of lubricant and limited slip additive should I use with my newly purchased Eaton Limited Slip Differential?

Eaton strongly recommends utilizing an API-GL5 approved Mineral-Based 80W-90 Axle Lubricant and one 4-oz bottle of Limited Slip Additive (GM or Ford)."

Here's the site:
http://www.traction.eaton.com/prod6.htm

More info:
http://www.traction.eaton.com/prod3.htm

And info about their lockers:
http://www.traction.eaton.com/prod2.htm

Here's another concern after some research on the Vette site,..a few over there have experienced reduced effectiveness of the Eaton posi with synthetics. The thinking is that the slippery synthetic can actually cause slippage.

Also, do you not agree Eaton (who's been around for 100 years) studies and logs the causes of failed posi units? Or do you believe Eaton simply tosses them aside and hopes the next one works?

Lastly,..since 1961 (Eaton's first posi), how many billions of trouble-free miles have been logged on how many million Eaton posi's that almost always out-lasted the cars they were used on, primarily with the use of petro gear oil?

The use of synthetic oild in the rear end isn't to make the posi last longer, but to make the ring & pinion gears and bearings last longer and run cooler. The posi doesn't get that much wear on it, so that isn't a concern. Any posi that is used for drag racing should not have any additive in it because the additive makes the clutches slip easier. Drag racers should use a synthetic oil without the additive to make the clutches lock up better.

Two of the links that you provided are for the Governor Lock, which is used in GM trucks. As I said before, ALL of the GM trucks produced from '98 and up have SYNTHETIC oil in in the rear end, and they have a tag on the rear end that says to use synthetic oil.

There is something missing here, if Eaton logs its unit failures, I wonder how they know if the lube had anything to do with it since most people wouldnt think to send in a sample of the fluid. The shop would drain the fluid to find out whats going on inside the pumpkin. That fluid is now mixed with all the other fluids in the big tank for recycling. If a sample of fluid was taken, then of course it could be tested. If the owner said he was using 'some syn' oil, and cant remember what he put in, that shouldnt black eye another good lube.
I stand by the manufacturers of the lubes to know what they are building and selling and WARRANTYING.
If you dont want to use a syn cuz that card in the box scares you, thats cool, dont use it. However, with documented success and warranty of a syn, let others make an informed decision themselves. I dont know about Mobile or Purple or the others but its been shown here that at least Amsoil puts their money where their mouth is and backs up their recommendations in writing.
Let the facts lead folks to their own conclusions.

This is what engineers do for a living.

A drop of lubricant could be quickly analyzed with a $50 kit purchased by you or I to determine if it's mineral or chemical based.

Eaton is an $11 billion company (they did $11.1B in 2005) with 59,000 employees,..they have labs, testing facilities, and mayby a couple of hundred engineers on staff dedicated solely to differentials.

Needles to say, the engineers at Eaton have very sophisticated methods to determine the composition of all their materials and lubricants for most everything they produce and sell.

Eaton has absolutely no vested interest in recommending a lube type, other than to reduce warranty claims and unhappy customers. If anyone has a better theory, what would it be?

On the other hand, Amsoil has a bias. And again,..they now acknowledge their lube won't work in all posi units as I noted above.

This verbiage is from their web-site and is also on each new quart of gear oil:
"AMSOIL 80W-90 SYNTHETIC GEAR LUBE is compatible with most limited slip differentials".

Note the word "most". Here's the link for the above...go about two-thirds of the way down:

https://www.amsoil.com/StoreFront/agl.aspx

Here is their 'very-Amsoil-friendly' warranty:

https://www.amsoil.com/warranty.aspx

I'd hate to file a warranty claim with Amsoil,..lots of gotchas.

Straight-line 69, I'm not going to argue the synthetic oil subject anymore because it seems to be going nowhere, but I am impressed by your knowledge of Eaton. I was wondering where your information comes from. You seem to have access to information that most people wouldn't have. Do you have some contacts inside Eaton?

www.eaton.com

Time to lock this one down, the constructive info. has turned to vendor bashing. to bad too.