Technical Muncie M20 for dummies

Why would anyone use bronze , you need a hard material that mimics the countershaft , i.e steel, you'd wallow out a bronze bushing in record time . You bore the case at least .250 oversize , you make the bushing a light press fit into the case , then the bushing is sized so the counter shaft is a light press fit . The last case my machinist friend & I did , bushing was .400 oversize. Also be sure that the bushing is installed flush with the internal thrust washer surface .

 

ANY transmission can be broken if you apply yourself; I know a couple guys who could break an anvil in half without knowing how they did it.

 

Bronze/oillite bushings are harder material than the aluminum main case and mid plate. The counter gear shaft does not spin in the bushing so the bushing does not have to be the same hardness as the shaft. All the bushing does is make the hole in the case and mid plate round again? The main shaft SPINS in a bronze bushing in the tail shaft housing, does that bushing need to be the same material as the main shaft?

 

No . Since the yoke spins in the tale stock bronze bushing thus needing lubricity, bronze ( alloy) is used .
The countershaft does not spin , it does have a tremendous amount of lateral pressure acting on it . It needs to be a press fit , what possible benefit could warrant the use of bronze or oilite bronze ?

 

You just answered both of your own questions.
Cast bronze and oillite bronze bushings are stronger than cast aluminum. Cast aluminum in what the muncie 4speed cases are made from. If you machine the countergear shaft hole in the case and mid plate for a bushing, and it is done properly, you will have to press the countergear shaft back in on reassembly. I know of several transmission shops that have done it this way. I'm pretty sure they know what they're doing because they don't want the transmission coming back on their dime. FWIW, do you know that a lot of machinery in industrial, agriculture and automotive use bronze bushings?
The gear oil in the transmission lubes the yoke and the main shaft, the tailshaft bushing doesn't lube anything. The yoke spins in the bronze tailshaft bushing. The seal pressed in the tailshaft housing keeps the gear oil in the transmission once the yoke is installed. Thanks.

 

No authority, but having assembled a few transmissions the time spent to get or make a dummy counter shaft will save hours of grief and f ing around pushing needle bearings out the other end.

 

I just realized there's zero need for this discussion, sorry for taking up bandwidth on a useless exercise .

 

For a 1" shaft a appropriate length of 3/4 " PVC plastic pipe works great for a dummy shaft

 

The easiest way is to hunt down an early M20 / M21 case for the 7/8" countershaft pin and bore it to the later 1" size

On my Road Race [made from unobtanium] M22 there was a complete teardrop shaped insert installed with an interference fit.
This prevented the main gears and countershaft from "growing apart" when being fed 650 ft/lbs

Here is the only photo I have of this


A common mistake made with Muncie's is swapping the front main 8 roller bearing for a H/Duty 12 roller bearing.

The 8 roller bearing has deeper grooves for thrust loads from 45° helix gearsets, whereas the 12 roller has shallower grooves designed for high radial loads on gearsets with low helix or square-cut gearsets

 

Sorry ETH727 for hijacking the thread to answer my question! But it’s still on topic lol. Appreciate the conversation gents.

 

Nothing to add, just wanted to show off my M-20.

 

Countershaft bore wear is a common issue.

Its getting harder an harder to find a used OE case that is not worn out as more years go by ,and if you do find one that's good, its pricey.

The case front and rear bores get machined for sleeves, not the mid plate.

There are some mid plates available that are made to bolt in the countershaft, so the 1/2 flat in the countershaft, can't spin out the flat in the midplate, not sure if a OE case can be used with that setup or not.

Riverside Gear in Michigan will sleeve a case, its close to $400.00 though.
I used to have a machinist in Chicagoland that was setup to do them, it was costing me about $250.00 per case, but he is no longer.

You may be able to find a machinist willing to do it for less?
Will he do it right???

Bill

 

Guess the standard 12 pack my friend used to charge me was a good deal ? 1967 to 2017 we never had a failure , guess we were doing it OK ,

 

Okay let’s keep it simple . You’re at a swap meet and you see a Muncie for sale. You ask the guy what’s the deal this tranny. He doesn’t know it since he got from grandpa that passed away. How can you tell it’s good or bad?

 

Pull the side cover and see how bad it is. Assume it needs synchros, bearings and bushings at a minimum.

 

It's best to assume that a swap meet trans, with unknown history, will need a complete overhaul, so pay accordingly.

 

Always!

 

I have offered $250 for decent looking Muncies before. Of course the sellers were expecting a huge payday and said no.

I did pick up a pair of M21 units real cheap around 1975.

 

In the late 60's , early 70's we had 6 local scrap yards , some of the proprietors new the difference between m-20,21 & 22's & would price accordingly , others , a 4-speed was a 4-speed , $100 everyday , we didnt let on there was a difference , got some great deals !

 

I paid $300 for my M20 but that was about 4 years ago. I spent years trying to find one reasonably priced.

Larry

 

Does it matter what brand clutch to use with a Muncie? Or is that more of an engine question?

 

Pick your torque ,pick your clutch , bell housing & flywheel dictate size , street or race ?

 

I like diaphragm pressure plates but that’s JMO. You need a clutch disc that matches the splines on your transmission, the early ones were 10 spline, later are 26. And a 10 1/2” clutch will be fine, the 10 1/2” fits the 12 3/4”, 153 tooth flywheel. If you go to an 11” clutch you will need the 14”, 168 tooth flywheel. Also consider your starter, if it has mounting holes straight across and you do not want to change it get the 153 tooth ‘wheel. If your starter has staggered bolt holes then you will need the 168 tooth flywheel.

 

Replace the pilot bushing.

 

It’s all stock just a cruiser. No plans on racing unless the cops are after me.

 

So I removed the cover to see the gears . They are in good condition. I wasn’t able to get the shift forks installed because of the shift linkages. Do the linkages need to be removed to engage the forks and close the cover?

 

It makes it easier.

 

I run an 11" Zoom clutch with a 168T flywheel. Application is a C30 Chevy truck. I use a truck style bellhousing and starter.

 

The gear teeth can be perfect and normally are, it's the engagement teeth for the syncro's that need to be examined thoroughly, that's where all the action is. It sure would be nice if the rest of us could see inside this thing...

 

The larger clutch pressure plate & flywheel requires the use of the larger bell housing , the 11 or 12" PP won't fit in a bell housing for 10 1/2" PP & as mentioned there are starter fitment issues .