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Discussion Starter #1
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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Discussion Starter #2
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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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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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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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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Discussion Starter #7
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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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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Discussion Starter #10
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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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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Discussion Starter #12
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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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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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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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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Discussion Starter #16
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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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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Discussion Starter #18
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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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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