# Muncie transmission



## Chris-Austria (Dec 23, 2010)

Hi!

I want to change the oil in my Muncie. Can you tell me which fluid and how much of it will be needed to do it?
And are there any things I should know for this job? I'll search it for a drain plug and if I can't find it I might have to use the fill plug to get it out and fill it up until the oil level reaches the fill plug again?!

Not sure if it's a M21 or M22.. does this make any difference regarding the fluid?

Chris


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## Chris-Austria (Dec 23, 2010)

Okay just checked the car.. I don't have a drain plug.. just the fill plug. This makes it hard to change at home. 
Either way.. I should know what fluid and how much? And should I have the oil sucked out, fill in some new, drive around 10 minutes and change it again to get rid of all the old fluid or is there another "trick"?


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## 68GTO4004Spd (Jun 19, 2008)

3 pints of 80/90 weight gear oil. To drain, take out the 4 bolts holding the trans to the bell housing and roll trans to drain it out of the fill hole. Bolt it back up, and fill until it just starts running out of the fill hole.


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## Chris-Austria (Dec 23, 2010)

Thanks. Syntetic oil?


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## the65gto (Oct 9, 2008)

68GTO4004Spd said:


> 3 pints of 80/90 weight gear oil. To drain, take out the 4 bolts holding the trans to the bell housing and roll trans to drain it out of the fill hole. Bolt it back up, and fill until it just starts running out of the fill hole.


ON mine, you would also have to unbolt the shifter and speedo cable. ?


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## Matthew (Feb 11, 2011)

I've never tried this, but it seems to me that method of rolling on to its side might require removing the cross member and supporting the back end of the engine. Like I said, have not tried it. I changed the fluid in mine by using a hand vacuum pump to remove the old oil. And no, I do not think the synthetic oil is recommended. Should be about 40 oz, but like the gentleman said earlier, it is full when it runs out the fill hole. Regards, Matt


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## Chris-Austria (Dec 23, 2010)

Good to know, thank you.
I don't like the idea of rolling the transmission, I'll search for a vacuum pump to remove the old oil. Maybe I'll do it twice (first the old oil, then the new oil after driving it some minutes).

I'll search the shop over here for oil's and see if I can find 80/90 (non synthetic). If I have no luck I'll tell you what I can get.


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## Matthew (Feb 11, 2011)

Chris, Lucas is a great brand of gear oil. Matt


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## geeteeohguy (Feb 2, 2008)

I just suck the old oil out with a suction gun. Easy as pie. Never needed to unbolt the trans, unbolt the shifter, unbolt the trans mount, disconnect the speedometer, etc. What a lot of work that would be! 80-90 mineral based gear oil, until it comes out of the filler hole. A bit less than 2 quarts. Never use synthetic in a Muncie....it will shift poorly. M22 is the only early Muncie with a drain plug. You probably have an M20 transmission.....M21's are pretty rare and only came with cars that had 3.90 gears and steeper.


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## Chris-Austria (Dec 23, 2010)

Is there a easy way to see if it's a M20 or M21? My 66 GTO has a 69 rear end (9795084)
so it's hard to say what was in there. I was told my rear end is also pretty rare.

I'll try it like you said, suck it out and fill it till it comes out again.

It will be 80/90 mineral based, maybe from Lucas if I can find it. What about 90 oil or I think somewhere in my garage is a bottle of 75/90...
No matter what, I won't use synthetic, thanks for that information. How often do you change transmission oil?


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## Matthew (Feb 11, 2011)

Chris, not that it is easy, but I believe the M21 input shaft has 26 teeth and the M20 input shaft has 21 teeth. Others please correct me if I'm mistaken. Matt


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## Chris-Austria (Dec 23, 2010)

I now was in the shop to see what I can get.
I have to chose between Castrol EP 80 or Castrol EP 80w90. Is the 80w90 better for me? Higher numbers are better for high temperatures I guess like with engine oil? The transmission will see the drag Strip twice a year and I don't have a fluid cooler for the transmission.

So what would you use? Price is the same... both mineral based.


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## 68Resto-mod (Nov 10, 2009)

I got my re-build kit from 5Speeds.com. They helped me identify my Muncie by counting input splines and number of groves around the spline (1 or 2). Problem is, you have to pull the trans to do this. Here is a link to one of there tech articles:

Muncie 4 Speed Transmissions

I put AMSOIL Severe Gear 75W-90 synthetic gear lube in both the trans and posi rear. Not sure if this was a mistake or not. There are many oil war forum threads out there and I don't want to start one here. I haven't driven the car yet but it will be running under its own power in a month or so. Some say the synthetics are too slippery and this is not good for proper syncro operation. Guess I will find out soon.

Good luck


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## Matthew (Feb 11, 2011)

Chris, I think your best option there is the 80W-90. Castrol is a good brand. You should change manual transmission fluid 30K-50K under normal driving. Matt


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## geeteeohguy (Feb 2, 2008)

Chris, what Matthew said. I run my manual gear oil for a long, time: 100k miles or so. If you change it at 50k, you will be more than safe. It never wears out, but can get contaminated or leak out over time. I haven't put 30k miles on my '65 in the past 25 years!!


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## Chris-Austria (Dec 23, 2010)

Thank you again, I'll get the 80w90. The transmission oil is the only fluid that isn't fresh anywhere in the car. That's why I want to change it because I'm not sure how many miles the old fluid has seen.


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## BearGFR (Aug 25, 2008)

Using the vacuum hand pump is definitely the way to go here. The problem with the unbolt and roll method (besides being harder) is that the entire weight of the transmission is left hanging on the input shaft, supported only by the clutch disk hub and pilot bearing/bushing, and that's awfully rough on all those parts.

Bear


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## Chris-Austria (Dec 23, 2010)

I won't unbolt the transmission because I'm afraid of doing it and I have the feeling it could make the oil change an unnecessary risk of doing damage to something.
I'll order the 80w90 and try to find a hand pump or electric pump to get the old oil out.

I thought it might be a good idea to raise the front of the car so that most oil is on the backside of the Transmission, that way I might be able to get it out better?! Then I'll fill it up, make the car stand even and fill in the rest until it comes out of the plug hole.

And since I have to order at least 4 litres I could make the change twice.. so the new oil will combine with the (remaining) old and I might get out more "dirt" than with only 1 change.

After that I'll run it for the next 5-6-7... years.. until I feel it has to be redone  I'm only driving about 2000miles every year. Maybe 3000 if gas is cheap and time isn't short.


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## leeklm (Mar 11, 2012)

Hey chris, I would do the suck method for now, but next time your trans is out it is easy to add a drain plug.

Sent from AutoGuide.com Free App


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## geeteeohguy (Feb 2, 2008)

And keep the car level. The trans dips at the bottom. Low spot is in the center. You'll get a better clean-out with the car not tilted.


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## 1969Judge (Mar 12, 2012)

Found out most new gear oils are GL-5 and not good for brass syncros. Get GL-4, Im using Redline 75/90 in my new rebuild.


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## Chris-Austria (Dec 23, 2010)

Castrol Manual EP 80W-90

The 80w90 that I can get is GL-4. I'll go and buy it tomorrow.


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## geeteeohguy (Feb 2, 2008)

The GL5 being hard on brass synchros and parts is pretty much an old wives tale. Nobody is able to substantiate it that I have found. In my experience, I've handled brass parts that were immersed in GL5 for decades and they looked like new. That said, the GL-4 is the stuff to use.


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## Chris-Austria (Dec 23, 2010)

I will get the GL-4 80w90 tomorrow, thanks.
But I have another question:

Is it possible to determine if I have a wide or close ratio Muncie by turning it and count the difference from input to output?
I think of a method similar to the method when I checked what rear end ratio I got? 10 turns of the tire are 35.5 turns on the driveshaft, so I have a 3.55.
Is there a way to perform such a test with the Muncie?!

If I knew the ratio I can be sure which Muncie I got.. if it's a wide ratio it must be a M20. If it's a close ratio it has to be a M21 and not the M22 because I don't have a drain plug.


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## geeteeohguy (Feb 2, 2008)

I think it would be pretty hard to tell by rotating it. The M-21 has a 2.20 first gear and the M-20 has a 2.52 first gear if it's a '66-up unit. Hopefully, with your 3.55 rear gear, you have an M-20.


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## Chris-Austria (Dec 23, 2010)

With the codes on the housings I found out it has to be a 63-65. But not if it's an M20 or M21. Is there a chart how many rpm are needed in first gear with my 3.55 rear for a certain reading on the speedometer with either a 2.20 or a 2.52 first gear?


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## 1969Judge (Mar 12, 2012)

Try this:
Gear Calculator


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## geeteeohguy (Feb 2, 2008)

If it's a '63-'65 M-20, it has a 2.56 first gear. They went to 2.52 in '66. My '65 M-20 is the original trans to the car, and is a 2.56 gear, as well. A little better 'out of the hole' than a 2.52 or a 2.20.


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## Chris-Austria (Dec 23, 2010)

I think it is the 2.56 first gear that I have, if it's a M20. I'm pretty sure (by the codes) that I have a 63-65 transmission, probably a 65 like yours.
What do say about strenght? My engine now produces something about 450hp.. the rear end will handle it I was told, but the M20 or M21? 
(I use Nitto 555r tires (275/50/15) for drag race)

I got a electic pump for the oil change by the way: PROXXON - AP 12


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## the65gto (Oct 9, 2008)

Chris-Austria said:


> I think it is the 2.56 first gear that I have, if it's a M20. I'm pretty sure (by the codes) that I have a 63-65 transmission, probably a 65 like yours.
> What do say about strenght? My engine now produces something about 450hp.. the rear end will handle it I was told, but the M20 or M21?
> (I use Nitto 555r tires (275/50/15) for drag race)
> 
> I got a electic pump for the oil change by the way: PROXXON - AP 12


It says for diesel and fuel oil, wonder how it will do with 80/90?


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## Chris-Austria (Dec 23, 2010)

The guy who owns it did a lot of Transmission, rear end and engine oil changes with it. He said it works well with 85w90 so I can try it with my 80w90. Hope he is right.

"Saugt problemlos Motoren-, Diesel- und Heizöl." This means it will handle without any problems engine oil, Diesel and light fuel oil (which is the same as Diesel just with a color additive). I didn't read the Homepage until now but on the pump is a sticker that says "not for use with water and gasoline".

If it doesn't work I'll go to a shop and let them do the work.


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## geeteeohguy (Feb 2, 2008)

Chris, drive the car before you drain the transmission, it'll thin the oil out and be much easier on the pump. Cold gear oil is like honey, literally. The '63-'65 M20 and M21's are not as strong as the '66-up units. The countershaft is smaller in diameter, as well. Mine has held up well, and was even behind a 428 that was once in my '65. I rebuilt it in 1983 and it's still going strong. It all depends on how you drive it. If you don't abuse it, it'll hold up. If you power shift, speed shift, or drag race the car a lot, you will break parts. I usually broke u-joints and I broke a rear end. I _did_ brake the front bearing retainer off of my Muncie before the rebuild power shifting at redline from 1st to 2nd gear getting around a VW Rabbit Diesel that was entering the freeway at 11 mph. The Rabbit went back around me and on its merry way as I coasted to the side of the road, dead in the water, leaving a trail of gear oil. It's all in how you drive the car.


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## Chris-Austria (Dec 23, 2010)

I never power shift and will race the car 2-3 times every year.
When you start with lets say 3000rpm will the rear end or the transmission be more abused?
And when you did the rebuild, did you use stronger parts to make it more durable? Where I live such a rebuild would be pretty expensive, almost as expensive as getting a new transmission. If It breaks sometime I must think of using a new transmission, either a stronger Muncie or something like the Tremec 5 speed... if it will fit into my car.

I'll drive it before I change the oil, okay! I'll also do this before I change engine oil. The pump says max. 40°C. I'll use the infrared thermometer because I want to damage the pump of my friend.


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## geeteeohguy (Feb 2, 2008)

Since a stick shift car has direct mechanical link-up to the rear tires, both the trans and the rear end take an equal amount of abuse when the hammer is dropped. I did not upgrade my trans when it was rebuilt because back then, steel mid-plates and other components were not available. Even syncros were hard to find. I used all USA made new old stock parts, because repro's were not being produced at the time. If I had your car, which is a '66 with a 428, I would sell or trade the '65 Muncie (they are sought after by restorers) and upgrade to a '66-'72 M-20 with the steel mid-plate. You might be money ahead to order a complete, rebuilt transmission from a USA vendor and simply have the whole thing shipped to you, ready to go.


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## geeteeohguy (Feb 2, 2008)

Chris, check out tbtrans.com (where I've gotten parts, good service) and Riverside Gear. Both providers have brand new Muncies, kits, mid-plates, and even brand new super cases for these units. Almost ALL old Muncie transmissions I've dealt with have a worn case where the countershaft rides, and they tend to seep oil there (at the front of the trans) A new case, or new super case, will eliminate that leak. With the power you have, it may be wise to upgrade to a Super case or even an M22 transmission. Some of the prices are pretty reasonable: $1100-up for a reman unit ready to go. Or, you could run your current transmission and very possibly be able to get many years and miles out of it.


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## Chris-Austria (Dec 23, 2010)

I didn't plan on rebuilding or getting a new one until it is not necessary. Until now it has no sign for me to be bad or worn out... also the rear end seems to be in good shape, I have no reason to think it isn't.
It's just that the labor time is that expensive that I don't want to do something twice. If my 65 Muncie breaks I thought it doesn't make much sense to rebuild it, better get a newer M20 or the M22 like you said.
I'm not sure if I would like a 5 speed because it isn't authentic.. but on the other hand it has some gears for great acceleration and also a 5th gear for cruise even with my 3.55:1 rear end I guess. (at the moment highways speeds are not that much fun if I drive a longer distance...).

But I'm pretty sure I won't find a good Muncie or 5 speed over here, so I might need to ship one to me. I'll check both websites, thank you!

I also don't know if my M20 was rebuild... or is it possible that the codes are not a solid indication for what is inside? If I'm lucky my Muncie will last longer than I thought.. but also like you said.. sometimes there is very little oil on the transmission housing, didn't find out where it comes from but it's really just a little.. it will make a spot once a month in the garage that you have to search for to see it. But I will check the front of my Muncie for a leak now.

I haven't been on the dyno until now, but I think my GTO will be able for a high 8 sec. time on the 1/8 mile. It's not a race car and it won't see much of this abuse.. I'll wait and see what happens next year and I'll use the time to learn more about transmissions... About one year ago I didn't know much about engines, so it never gets boring


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