C2: M20 bearing rattle?

[Dan Pepper]

I have been expertincing a chatter/rattle when engaging the clutch from a dead stop going into fwd or rev. Last summer I replaced the clutch and release bearing, also installed a roller pilot bearing in the process. The flywheel was a little blue in a few spots, and was resurface. Figured that'd cure the chatter. All of this to no avial.

The trans does leak a small amount of fluid from the front seal - drips a little from the bell housing. Didn't catch it before as I thought it was the leaky (now replaced) rear main seal. Thinking the problem could be the input shaft bearing (and leakly seal) in the trans. What's the best way to diagnose? Hate to take the trans out again - it was a real PITA "turtling" around on the garage floor with an M20 on my chest...

[Tom P.]

Re: C2: M20 bearing rattle?

Muncies DO NOT have a front seal.
If oil is leaking from the front of your Muncie, it USUALLY can come from only 2 places: the bolt holes for the front bearing retainer, or, the hole in the front of the case for the counter gear shaft. The second being the MOST probable source. If this is the source, it requires a complete teardown of the tranny to repair the hole. The hole in the front of the case for the counter gear shaft is tapered and the front of the shaft is tapered. As the shaft is installed, the taper fit creats an oil seal. In time, with wear and abuse, this hole becomes enlarged and allows oil to leak. It is impossible to count the number of Muncies that I've rebuilt in the last 35yrs that have needed this hole repaired.

[Joe L.]

Re: C2: M20 bearing rattle?

Tom-----

Yes, there certainly is no front seal on a Muncie, contrary to "popular opinion". However, I didn't think that the forward end of the cluster shaft or the hole for it in the forward end of the case were tapered. I always thought that these were just a tight interference fit and that, over time and with multiple shaft removals, the interference fit was reduced and leaks ensue.

Have you ever measured the shaft or the hole to confirm a taper? I have the parts here to check it myself, but if you've already done it, I won't bother.

[Barry Chappell]

Re: C2: M20 bearing rattle?

I had a leak from the front shaft area. I pulled the trans back, cleaned the area (shaft/case) and applied a generous amount of RTV, then bolted the trans back up before the RTV set.
It has never leaked again.
That was about 25 years ago.

Barry

[Terry F.]

Re: C2: M20 bearing rattle?

Just wondering how you repair the counter shaft hole? That does not sound like fun at all. I was told that it is not that hard to stretch the case on a muncie. Is that true? I was told that if you break a counter shaft gear, it often results in a elongated case hole for the counter shaft. Any comments on this? Are there any good sources for replacement gears on muncie 4 speeds? I have a muncie that needs an input gear and I would like to find one that matches the condion of the rest of the transmission which is excellent. I believe it is a wide ratio, 21 tooth input. I pulled it from my first car in about 1973. Terry

[Jim T.]

Re: C2: M20 bearing rattle?

One place to check for Muncie gears is www.5speeds.com/muncie.htm.

[Joe C.]

Re: C2: M20 bearing rattle?

Terry:

The correct and permanent repair is to ream the hole for the countershaft. An insert is then pressed in, and reamed for an interference fit with the countershaft. This is an ideal opportunity to replace a 64-65 7/8" countershaft with the later 1" type. This does, however involve complete replacement of the cluster gearset. Another trick is to rebore the countershaft to move the C/L closer to the mainshaft.

Joe

[Terry F.]

Re: C2: M20 bearing rattle?

Wow, I didn't realize people would go so far to get a transmission back together. What did you mean by reboring the C/L closer to the main gear. Are you saying you can tighten up slack in the gears between the counter gear and the cluster shaft? Or, are you saying the case gets stretched and the oportunity allows you to bring it back to factory clearances?

Anyone know anything about the counter shaft gears that had that stamped steel plate rivited to the front of the counter gear? What was it for? Was it an oil slinger or some sort of dampener?

Also, what about the use of automatic transmission fluid in a muncie? Does that work under hard driving. Any opinions? Thanks, Terry

[Clem Z.]

Re: C2: M20 bearing rattle?

we always used auto trans fluid in 4 speeds we drag raced for beter and smother shifting BUT you will get "gear rattle" at idle

[Joe C.]

Re: C2: M20 bearing rattle?

Terry:

The C/L of the cluster shaft can safely be moved closer to the mainshaft by a few thousanths. This is closer than factory specs, and provides slightly better gear mesh because contact is moved closer to the root diameters of the gears.
I had a stretched case in my 65 Muncie (with 7/8" pin). The case was machined for the 1" pin and cluster gear, and the C/L was moved closer by, I think .004". It shifts very smoothly, and is super quiet.
I can say that GM specified ATF in manual transmissions. I owned an 86 Trans Am with 5 speed which specified ATF.

Joe

[Terry F.]

Re: C2: M20 bearing rattle?

I can see where it would do well in cold weather but I was wondering how it would do under stress. I only took one transmission apart with it in it and thought for sure someone had made a mistake. That was about 30 years ago. I later learned that it was used routinely starting somewhere in the 70's or so. Thanks for the responce. Terry

[frank mccracken]

Re: C2: M20 bearing rattle?

I have seen many people try to seal the front counter shaft pin with just sealant, myself included. It never seems to work tho. What DOES work is, and many people give me a "bubba" till they try it, is I make a gasket that matches the front surface of the trans including the ears with a hole for the bearing support, add some black permatex at the pin for good measure and bolt 'er all together. You bell housing covers the pin hole nicely with the gasket in between. You must make a full gasket tho because trans alignment is critical. My current '65 has a weepy pin and this "system" is in place right now and doing the job. I have done this many times before and consider it to be a permanent repair. Saves a TON of money in machineing and labour.