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Hi everyone. I cleaned up the undercarriage of my 66 over the winter and have put probably 100 or so miles on it. The transmission was greasy when I started and was far from perfect when I finished but it looks like it may be leaking more now toward the tail shaft. It does need a clutch but I was trying to hold off until next year. The car shifts fine. Should I be worried about having to rebuild the whole thing? I’m not even sure how to check the fluids in it. Thanks in advance.
Most likely leaking from the reverse shaft seal or pin. To replace the seal you have to remove the tail shaft housing which you do when trans is out of the car. If its leaking at the pin you might be able to seal it in place. Check that your tapered pin is properly installed from the top down, if someone hammered it in upside down the tail shaft housing is probably buggered. At any rate drive the pin up and out with a pin punch and clean where it goes in with brake cleaner. Then coat the pin with a generous amount of RTV, press some RTV into the hole as well. Reinstall pin (from the top down), tap in lightly but firmly. Wait at least 24 hours for RTV to setup and then drive and check for leakage after. If you remove the trans to do a clutch it may be a good time to go thru it and replace wear items like brass blocker rings, bearings, thrust washers, and all gaskets. Plenty of good guides on how to rebuild a muncie can be found online. Last helpful hint, if you do rebuild use caged roller bearings instead of the loose pin bearings on the countershaft, much easier for a novice to do.
Here is a photo showing the fluid fill plug on the passenger side of the trans. Some transmission cases also have a lower drain pug, but not all have it. Take out the plug and feel inside for oil with your finger. If you can’t feel oil at the level of the hole, you need to add some. Add the correct oil using this hole until it slowly starts to leak out, then just put the plug back in.
It could also be leaking at the side cover gasket/shaft seals and/or mid-plate gasket. It would be worth a few minutes when under the car and snug up all those bolts. But probably will not be that easy to dry it up totally.
I'm actually learning a lot about Muncie's. Correct me if I'm wrong...............
1) filling to overflow on a Muncie could be considered overfilled and cause a leak
2) input hole on the case if worn will cause a leak and require machining and a bushing.
3) speedo (Bullet) gear at the transmission can be a source for leaks if the plastic gear shaft is worn or the O-ring on the bullet is damaged.
4) if you tilt a perfectly good Muncie with full level of fluid it will leak at a good rate through the input shaft...
5) If lucky, transmission cover gasket could be the only problem......Not in my case!!!
The reason I am posting is because my 65 Coupe's M20 is leaking profusely.........This will be the first project that I will not perform (Too Fricking Old)....Tear down, locally, Friday or Monday.......
My clutch is slightly slipping in 4th gear, that I have just noticed.....I'm concerned that Stay-lube is getting into the Bell housing..........So it's time!
Not stealing the thread....I'm just a little anxious!!!
If I get results on seals, bushings, case damage........I'll report back.............
Just went through this in my 63. I was certain it was an easy fix, turned out to be the tail shaft bushing ( first time I've ever seen one this bad ). Everything else was fine but did a complete tear down to be sure and replaced all the seals and gaskets. One thing I've learned is if its leaking in one spot you have others not far behind.
I'm actually learning a lot about Muncie's. Correct me if I'm wrong...............
1) filling to overflow on a Muncie could be considered overfilled and cause a leak
2) input hole on the case if worn will cause a leak and require machining and a bushing.
3) speedo (Bullet) gear at the transmission can be a source for leaks if the plastic gear shaft is worn or the O-ring on the bullet is damaged.
4) if you tilt a perfectly good Muncie with full level of fluid it will leak at a good rate through the input shaft...
5) If lucky, transmission cover gasket could be the only problem......Not in my case!!!
The reason I am posting is because my 65 Coupe's M20 is leaking profusely.........This will be the first project that I will not perform (Too Fricking Old)....Tear down, locally, Friday or Monday.......
My clutch is slightly slipping in 4th gear, that I have just noticed.....I'm concerned that Stay-lube is getting into the Bell housing..........So it's time!
Not stealing the thread....I'm just a little anxious!!!
If I get results on seals, bushings, case damage........I'll report back.............
Have a great 4th!
Don't blow your fingers off!!!!!!!!!!
I think you mean the front countershaft hole in the case instead of input hole. Best to repair but there are supplemental ways to seal up. Filling to bottom of fill port should not cause leaking normally, but worn parts/seals could could result in leaks.
I think you mean the front countershaft hole in the case instead of input hole. Best to repair but there are supplemental ways to seal up. Filling to bottom of fill port should not cause leaking normally, but worn parts/seals could could result in leaks.
John Hinckley suggested that to fix a countershaft leak cut a gasket to seal around the countershaft opening at the front of the transmission. I fixed my leaking M20 this way.
Yes, or DZAuto posted a repair method recently that from memory involved peening the aluminum to shrink the bore down and finishing it to an interference fit again. If the countershaft to hole fit is pretty loose when you pull it out, you might contact him to see if he could help you with repair.
I'm actually learning a lot about Muncie's. Correct me if I'm wrong...............
1) filling to overflow on a Muncie could be considered overfilled and cause a leak
2) input hole on the case if worn will cause a leak and require machining and a bushing.
3) speedo (Bullet) gear at the transmission can be a source for leaks if the plastic gear shaft is worn or the O-ring on the bullet is damaged.
4) if you tilt a perfectly good Muncie with full level of fluid it will leak at a good rate through the input shaft...
5) If lucky, transmission cover gasket could be the only problem......Not in my case!!!
The reason I am posting is because my 65 Coupe's M20 is leaking profusely.........This will be the first project that I will not perform (Too Fricking Old)....Tear down, locally, Friday or Monday.......
My clutch is slightly slipping in 4th gear, that I have just noticed.....I'm concerned that Stay-lube is getting into the Bell housing..........So it's time!
Not stealing the thread....I'm just a little anxious!!!
If I get results on seals, bushings, case damage........I'll report back.............
Have a great 4th!
Don't blow your fingers off!!!!!!!!!!
Yes to both of these.
Reason is that Muncies vent to atmosphere thru the front main bearing.
There is a hole in the front bearing retainer That should be at the 12Oclock position when installed.
Tilting a full of fluid Muncie forward will cause the lube to run past the front roller bearing as its not sealed and out past the input splines.
Last edited by AzMotorhead; Jul 3, 2020 at 06:03 PM.
Hope you rectify your problem........This is a good post.......It will help me tremendously.......Of course, I will be dropping beers while the work is being done.......But I will have a better understanding of my potential issues with this M20.....
Hope you rectify your problem........This is a good post.......It will help me tremendously.......Of course, I will be dropping beers while the work is being done.......But I will have a better understanding of my potential issues with this M20.....
All the best, Members!!!
I appreciate all the advice and replies. I’ve definitely learned a lot going through them. I may try and tackle it this winter. It does seem like it may be a job above my pay grade though! Haha!
Spend a few minutes snugging all the bolts up and you might get lucky. Don’t tighten the side cover too much as they can strip out but make sure the tai housing bolts are good and tight. Probably won’t dry it up completely but if any are loose it might slow it down and doesn’t cost anything.
Addressing the Muncie front main case oil leak: A thick rubber O-ring was set in the depression the counter shaft rides in.
The remaining void was filled and lightly leveled with Ultra Black.
Spend a few minutes snugging all the bolts up and you might get lucky. Don’t tighten the side cover too much as they can strip out but make sure the tai housing bolts are good and tight. Probably won’t dry it up completely but if any are loose it might slow it down and doesn’t cost anything.
M20 leaking
