[Hurst65]

Hey Guys,

I pulled the M20 out of my car today because it sounds like it has rocks in it and I had a horrible vibration. The vibration would start at around 50 mph. The shifter handle would rattle so bad it would numb your hand if you tried to hold it steady. I was expecting to find a bad front bearing but, now I'm not sure what to think. To me, all the gears look good. I don't see any chipped teeth. There was no metal in the oil and there was hardly anything on the magnet.

When I turn the transmission by hand I can hear and feel something but, I'm not sure where it's coming from. I hear/feel it most when I have it in 4th gear. It kind feels like 4th gear wants to catch on something but, it doesn't. When I ran the car on jack stands, it sounded bad!

I'm not a transmission guru and I've never really had one apart on my own. If I post some pictures, can some of you guys take a look and see what you think? Now that I've got it out, I'm thinking I'll go ahead and rebuild it. I may need some help with that too. I figured I'd ask first.
Thanks!
Eric

[Hurst65]

Here's a couple pictures..
Any help would be great!

[Sun Tuned]

Driveshaft/ u joint(s) will do that around 50 too.

Not saying it's your only issue but I had one do it so bad on my 65 once when I was in high school, it dang near broke the console before it let go.

[Hurst65]

That was my first thought, too.
When I put the car up on stands and ran it, the drive shaft looked great. Very smooth. The drive shaft and the rearend are both new. I installed a new Currie 12 bolt crate rearend and a new drive shaft a couple years ago. Both seem like they are doing excellent.
The transmission sounded like it had rocks in it.

[helmerrock]

Could be countershaft needle bearings or rear bearing.

[Lemans64]

Also would suspect U joint issue. Blown u joint would cause the shifter to rattle real bad. If u had a bad bearing in the trans u would hear more so in 1-3 gears and not so much in 4th.

[mechanickeith]

Originally Posted by Lemans64

Also would suspect U joint issue. Blown u joint would cause the shifter to rattle real bad. If u had a bad bearing in the trans u would hear more so in 1-3 gears and not so much in 4th.

Totally agree with this. 1-3 goes through the countershaft. 4th is straight trough the main shaft. Check the front U joint.

[Hurst65]

Hummm... I'll check the front U joint, thoroughly, tomorrow..
The rearend and the drive shaft probably have less than 2k miles on them. They are like new. It's a new 3" shaft with 1350 joints. I didn't notice anything obvious today.

Let me back up a little and say that this noise and vibration have been gradually getting worse for some time. I drove it on the hwy, for the first time since last fall, this past week. It's basically been in the garage all winter. Now, it's really bad!

The transmission is noisy in all gears but, it's especially bad in 4th. Anything over 50 mph is a rattle fest! Lol

If I turn the transmission by hand, with the cover off, I can hear and feel something. If I push the slider into 4th and turn it, it gets worse. I just can't tell what's going on. It feels notchy... almost like a gear wants to catch on something but, it doesn't.

How do my gears look? How bad are the brass rings?

The counter shaft pin is a 1" pin and I don't see any leakage around it.

How bad is my reverse gear? (see pic below)

Also, what about my speedo gear? I thought they were pressed on. This one is a plastic gear with a metal clip.

[squidtone]

Hurst65,
How does your pilot bearing look in the back of the crankshaft? It this is worn excessively, it would definitely allow huge vibrations, even grinding/clashing.
How much does the input shaft wiggle around when you grasp the front? A little wiggle-arity is okay, but not excessive.
How does the rear bushing (inside the tailshaft housing) look? If it's worn, the yoke could occasionally flop around and or resonate creating a rattle-fest.
How much can you move the countergear back and forth inside the case? If it's over 0.020"-0.025" I think there can be excessive noise.

Is there a sheet metal gear on the front of the countergear? This is for taking up gear lash...it's meant to keep noise down in idle/neutral situations. The sheet metal gear is spring loaded and held on with rivets. These have been known to start to let go and create noise for a while, then BOOM. Instant metal bits. If your trans is original stock, it might still have this gear. Check that too. I'm not sure how easy it is to check it with the trans still together. (Repro countergears don't come with that gear lash takeup gear.)

Good luck and post back!
Dave

[Hurst65]

Dave,
I'll check the pilot bearing tomorrow. I didn't take the bell housing and clutch off yet. I did look in there to have a peep. The pilot bearing is there and in one piece. ...nothing obvious... I'll know tomorrow.

The input wiggles around some. I'm not sure what is considered excessive.

This transmission had M21 gears in it when I first got the car about 8 or 9 years ago. I talked my dad into helping me change it over to an M20. My dad was a diesel mechanic and specialized in Allison automatics. I bought a new M20 input and counter gear to do the conversion and mostly just helped him do the change over. We did the change, put a new tail shaft bushing in and put it back together. That was the first time either one of us had been into a Muncie. It's been pretty good until recently...

The counter shaft thrust feels okay, I guess... I haven't measured it but, I doubt it's more that .025".

[geeteeohguy]

I agree with what these gents have said. My experience with these trannies: Start it and let it idle in neutral. Listen. And push the clutch in. Listen. Is it quieter with the clutch pushed in? If so, your bearings are worn. With my Muncie's, I've always found that replacing even 'good' bearings made a big difference in noise. I never seem to have gear problems. Just bearing and synchro wear over time. That, and countershaft hole wear in the front of the case, which will cause an oil seep. My VIBRATION experience has been caused by a missing pilot bushing in one car, a defective pilot bushing (I like bearings here myself, per factory), and, more commonly, a worn driveshaft yoke/rear transmission bushing/bent driveshaft. The FIRST thing I would check is the driveshaft yoke and trueness. I had a bend shaft in my '65 for years until I went and sent it in to be checked 'just because'. Car went from a buzzer to smooth as glass. For $125. Good luck, let us know what you find.

[Hurst65]

Yes, the transmission is much quieter with the clutch pushed in.

I got the bell and clutch off today. Clutch and flywheel look good. The pilot bearing is in one piece but, it feels dry.

I checked the U-joints. They feel really good. Still like new...

The tail shaft bushing does have a little wear. I slid the tail housing on over the yoke. There is a tiny amount of play but, I'm not sure if that's enough to cause a huge problem.

More pictures -

[Hurst65]

Currently, there's two things that I see/feel may be bad.
1. The rear bearing feels a little rough.

2. The 3-4 slider looks like it's worn, to me. What do you guys think?

Pics -

[Sun Tuned]

Before you buy bearings do some research....

Most have 8 balls, some have 12 and if you look you can find the max load bearings that have 11 balls but those 11 are the same size as the 8 so the load capacity is greater thus a better bearing. I'd source them seperately so you can get the good ones.

And by all means spin them in your hand before you lay down your long green...
If they aren't glass smooth at the counter they ain't gonna get no better when you leave and put em in the trans.

Food for thought.

[John Milner]

Sliders definitely look worn. If it were mine and since it is tore down this far I would replace the cluster needles and thrust washers, front and rear bearings, 3-4 slider for sure and possibly the other if it looks like this one, and shifting keys. Synchronizers are pretty cheap as well. I've actually seen a lot worse reverse gears work just fine as well. You might just dress the worn spots on it a little with a file. I'm guessing that it is either the front or rear bearing making the noise though.

[Hurst65]

Originally Posted by Sun Tuned

Before you buy bearings do some research....

Most have 8 balls, some have 12 and if you look you can find the max load bearings that have 11 balls but those 11 are the same size as the 8 so the load capacity is greater thus a better bearing. I'd source them seperately so you can get the good ones.

And by all means spin them in your hand before you lay down your long green...
If they aren't glass smooth at the counter they ain't gonna get no better when you leave and put em in the trans.

Food for thought.

Thanks for the heads up on the bearings!

[Hurst65]

Originally Posted by John Milner

Sliders definitely look worn. If it were mine and since it is tore down this far I would replace the cluster needles and thrust washers, front and rear bearings, 3-4 slider for sure and possibly the other if it looks like this one, and shifting keys. Synchronizers are pretty cheap as well. I've actually seen a lot worse reverse gears work just fine as well. You might just dress the worn spots on it a little with a file. I'm guessing that it is either the front or rear bearing making the noise though.

Thanks for looking. I'll get a complete rebuild kit on the way. ...and some new sliders.
Yeah, I think I'll just clean the reverse gear up a little.
I'm also going to finally take the time and get the correct speedo gears. My speedo has been off for waaaay too long!

What do you guys think about an iron mid plate? Is it worth it on something like this? Just curious.

[Hurst65]

Well,... I got the transmission back in the car last night.
The transmission seems like it's doing good. It's quiet and shifts really nice. Best of all -- the shifter doesn't rattle anymore! Yea!

I still have a weird vibration between 55 and 65.. ugh.. I guess I'll be chasing that down.. I'm not sure what it is.

All parts came from Paul Cangialosi at 5speeds.com. Paul was a great guy to deal with and his Muncie rebuild DVD was a big help.

I went with new Italian made "torque lock" sliders and hubs. I also took Paul's advice and changed the speedo drive gear to a new steel pressed on gear.

Here are some photos-

[Hurst65]

Here's the finished trany -

I also took some time to clean and repaint the bellhousing. I feel like I spent most of the time cleaning parts. I made two line-up studs and they worked great on the install. The transmission went right in on the first try.