C2andyP

My 1966 C2 has a noisy box.....but how noisy is a M20 box in good condition? Should it be silent? Or do most have some bearing/gear noise?

Kerrmudgeon

Mine was pretty quiet in forward gears, only a gear whine in reverse. BUT....if yours is noisy like an M22 somebody may have put 22 clusters in a 20/21 box. You never know. If it's noisy in all gears, and your gear oil is correct and full, that's what I would suspect.

Avispa

Bearing noise more than gear noise. There will be some gear whine, but there's more noise from the cluster gear (rotates on needle bearings) and under no load (neutral and 4th gear) has lost of backlash noise, the main drive gear and the main shaft, both of which rotate on ball bearings. Depending on how well aligned your bellhousing opening is with the crankshaft, the mainshaft and tailshaft can rattle around and buzz a bit as well, especially at high vehicle speed.

Dan Hampton

In all gears (except reverse)? How about your insulation under the transmission tunnel? They really should be quiet unless someone, as Kerrmudgeon indicated, tossed in some 20 degree helix gears. I would suspect the input bearing, first, and the output shaft bearing, second, if it is a bearing noise. Pretty easy and painless fix once the trans is out of the car (input).

C2andyP

The box has a grumble in neutral and whines mainly in 1 2 3, the whine gets higher pitched as speed increases, I can hear the whine in 4th but never go that fast to see if 4th gets worse at speed.

DZAUTO

Unless the internals of your Muncie are in fact M22 gears, then it SHOULD BE quiet, even when idling in neutral. But even an M22 in good condition is quiet. SOOOOOOOOOOOO, it would be my suspicion that there is a problem.
Also, to convert an M20 or 21 to an M22, you do not just install an M22 cluster-----------------THE ENTIRE GEAR SET HAS TO BE REPLACED: Input gear, 1st gear, 2nd gear, 3rd gear, cluster gear and front reverse idler gear.

GTOguy

Been driving Muncie transmissions since my first car many moons ago. A noisy M-20 or M-21 usually means worn out bearings. Does it get quiet when you push the clutch in at idle? If so, new bearings are in order.

Dan Hampton

Well....if it doesn't whine as bad in 4th as it does in 1-2-3, it would indicate the front input bearing, imho. The reason being is that in 4th, all the side loading of the other gears is gone and you are now in direct drive through the main shaft. Simply think of it as a cocking action on the input when forced to spin through the cluster to the three other gears. In fourth, that action doesn't exist. I doubt you have an issue with the needle bearings in the input since that is a double row of bearings and you would have to have created some real havoc to destroy those. Bad bellhousing alignment will chew through the input bearing rather quickly, too, if you are looking for a potential cause. How many miles on the transmission and what is the level of fluid in the case?

Kerrmudgeon

Sorry, I used the wrong terminology. By cluster I meant the all the guts of the trans. I'm going straight to hell I know.