I just recently had my M21 rebuilt by a very reputable guy and it developed a leak in front. Pulled the tranny and he said it was the countershaft sleeve. He pulled it apart and I re-installed it. I thought it was coming from the front cover that the throw out bearing rides on but he's the expert. Well just got finished intalling and it leaks worse. I still think its the front cover. Is that a fluid seal? He said there should just be a little oil that lubes the throw out bearing there. It's the cover that slides over the spindle and has 4 bolts. I did notice that one of the bolts does not tighten up real well.

In the area you're describing, it's either leaking at the input shaft or the counter-shaft plug in the front of the tranny. Also, the TO bearing is not lubricated by tranny fluid (tell your tranny man).

You may have a tranny that's over-filled (can happen if the car isn't flat when adding gear oil),..it will leak in the area you describe if this is the case. Might even run it 1/4 inch lower than the fill hole.

If you're running a synthetic lube, many with this problem solved it by using a conventional gear oil.

Lastly,..the gear oil will typically make it's way to the bottom of the bellhousing. If the "front cover" you're describing is the semi-circular shaped piece of tin on the front of the bellhousing, that has nothing to do with the leak.

It is a 70 M21 so it has the 2 plugs in the case. I filled it with car level to 2nd plug just coming out and yes this is the 1st time I used Redline synthetic fluid. It is leaking straight back onto the tranny from the front. Never got inside the bellhousing. Do you think the front bearing cover (input shaft cover) with a semistripped bolt will leak from there? It grabs but not very good.

It is a 70 M21 so it has the 2 plugs in the case. I filled it with car level to 2nd plug just coming out and yes this is the 1st time I used Redline synthetic fluid. It is leaking straight back onto the tranny from the front. Never got inside the bellhousing. Do you think the front bearing cover (input shaft cover) with a semistripped bolt will leak from there? It grabs but not very good.

No oil in the bell housing rules out the front bearing retainer leaking.

I suspect the counter shaft is leaking, hole to large. Trying one of the home brewed repairs may or may not work, the only real fix is the bush the case, weld and redrill the case or the best idea is a new Super Case.

I'd still try dropping the level a lil. Muncies do not have any type of front seal, and will drip if they are too full. Mine was happiest with just enough oil that I could reach it with my pinky, if it was even to the fill hole, it would leak out the front.

Well I drained the Redline synthetic and installed regular 80-90 gear oil. Drove it around for about 1/2hr and it got alot better. Tranny was wet but not dripping. I hope this was residue from the Redline. I did the pinky fill and will see if that helps. Really don't want to pull again, although practice makes perfect.

Max, I'm having the same problem. I pulled the tranny and changed input shaft cover. They're still available from GM. I installed new gaskets twice and it stll leaks. I'm only 275 miles from the "Run to the Rockies" but I'm afraid that the M21 will run out of lube and burn up. Maybe a good time for a TKO500!

I was told to fill the countershaft hole with silicone and let it set up before bolting it to the bell housing. Mine does not leak.

Ya know what sucks is it didn't leak before the rebuild. I drove it around some more tonight and I had my puddle back. Thought I would have some preventative maintenance done on it and looked what it got me. Then tonight I had a brand new battery crap out on me. It's a good thing I love this car. My builder put some Gorilla goup on the countershaft the 2nd time and he said he never had one leak after using that. Looks like mine is a 1st.

My builder put some Gorilla goup on the countershaft the 2nd time and he said he never had one leak after using that. Looks like mine is a 1st.
But did he clean the area with either lacquer thinner or BraKleen to remove all traces of oil? If oil film isn't removed by other means other than wiping clean, the sealant will not have a good "grip" with the surface to seal.

Ya know what sucks is it didn't leak before the rebuild. I drove it around some more tonight and I had my puddle back. Thought I would have some preventative maintenance done on it and looked what it got me. Then tonight I had a brand new battery crap out on me. It's a good thing I love this car. My builder put some Gorilla goup on the countershaft the 2nd time and he said he never had one leak after using that. Looks like mine is a 1st.

"Gorilla Goup", thats a new one:)
Once the shaft hole is to big there is little you can do with silly puddy or any number to home brewed fixes.

The front bearing retainer has a drain back hole for oil that is thrown on the bearing to drain back. Under normal driving conditions the oil in a muncie is pushed up on the side of the case, very little in in the bottom. The counter gear acts like a big mixer slinging the oil up the sides.

You can drive the car, very little will leak out while in use. Muncies do not create internal pressure so for the most part they don't force oil out.

When the car sets you will get a puddle.

Thats exactly whats happening. He described the same thing. It's dry when I get home but then leaks when turned off. I hate leaks. I was checking on the Muncie Super Case as you suggested (Muncieman). Is this a direct replacment and can I use my tail shaft and all internals. I see it comes with a larger front bearing but that is included with the case. I would like to have gone with a 5 or 6 speed but this is an original 69 Z28 but had a 70 M21 in it. It has the correct 302DZ and 4:10 still in it.
Muncieman - I sent you a private message if you get a chance to check it out, I would appreciate it.

The Muncie oil system works well when there are no air leaks. Think of putting a straw in a glass of soda and removing the straw with your thumb over the top. Release your thumb and the soda drains out.

The reason the Autogear SuperCase was developed is because the majority of these 30 or 40 year old Muncies have worn cases. A new SuperCase works.

I've seen "professional rebuilders" install the gland nuts backwards and the Chinese nuts that everyone is using are junk and not correct. With a good nut and good bearing retainer you will have no leaks from the input. Speaking of retainers I DO NOT Recommend GM retainers. GM makes a crap retainer that most of the time is counterbored wrong.

You CANNOT USE SYNTHETICS, especially the well hyped Red Line and Amsoil in these boxes. These oils flow too easy and will dump out of the front. Standard Valvoline is fine.

Take Care,

Paul
http://www.5speeds.com

I have the new Supercase on order. Thanks....